occt/src/OpenGl/OpenGl_View.cxx

// Created on: 2011-09-20
// Created by: Sergey ZERCHANINOV
// Copyright (c) 2011-2014 OPEN CASCADE SAS
//
// This file is part of Open CASCADE Technology software library.
//
// This library is free software; you can redistribute it and/or modify it under
// the terms of the GNU Lesser General Public License version 2.1 as published
// by the Free Software Foundation, with special exception defined in the file
// OCCT_LGPL_EXCEPTION.txt. Consult the file LICENSE_LGPL_21.txt included in OCCT
// distribution for complete text of the license and disclaimer of any warranty.
//
// Alternatively, this file may be used under the terms of Open CASCADE
// commercial license or contractual agreement.

#include <OpenGl_View.hxx>

#include <Aspect_NeutralWindow.hxx>
#include <Aspect_RenderingContext.hxx>
#include <Aspect_XRSession.hxx>
#include <Graphic3d_AspectFillArea3d.hxx>
#include <Graphic3d_Texture2Dmanual.hxx>
#include <Graphic3d_TextureEnv.hxx>
#include <Image_AlienPixMap.hxx>
#include <OpenGl_ArbFBO.hxx>
#include <OpenGl_BackgroundArray.hxx>
#include <OpenGl_Context.hxx>
#include <OpenGl_DepthPeeling.hxx>
#include <OpenGl_FrameBuffer.hxx>
#include <OpenGl_GlCore11.hxx>
#include <OpenGl_GraduatedTrihedron.hxx>
#include <OpenGl_GraphicDriver.hxx>
#include <OpenGl_RenderFilter.hxx>
#include <OpenGl_ShaderManager.hxx>
#include <OpenGl_ShadowMap.hxx>
#include <OpenGl_Texture.hxx>
#include <OpenGl_Window.hxx>
#include <OpenGl_Workspace.hxx>
#include <OSD_Parallel.hxx>
#include <Standard_CLocaleSentry.hxx>

#include "../Textures/Textures_EnvLUT.pxx"

namespace
{
  //! Format Frame Buffer format for logging messages.
  static TCollection_AsciiString printFboFormat (const Handle(OpenGl_FrameBuffer)& theFbo)
  {
    return TCollection_AsciiString() + theFbo->GetInitVPSizeX() + "x" + theFbo->GetInitVPSizeY() + "@" + theFbo->NbSamples();
  }

  //! Return TRUE if Frame Buffer initialized has failed with the same parameters.
  static bool checkWasFailedFbo (const Handle(OpenGl_FrameBuffer)& theFboToCheck,
                                 Standard_Integer theSizeX,
                                 Standard_Integer theSizeY,
                                 Standard_Integer theNbSamples)
  {
    return !theFboToCheck->IsValid()
        &&  theFboToCheck->GetInitVPSizeX() == theSizeX
        &&  theFboToCheck->GetInitVPSizeY() == theSizeY
        &&  theFboToCheck->NbSamples()      == theNbSamples;
  }

  //! Return TRUE if Frame Buffer initialized has failed with the same parameters.
  static bool checkWasFailedFbo (const Handle(OpenGl_FrameBuffer)& theFboToCheck,
                                 const Handle(OpenGl_FrameBuffer)& theFboRef)
  {
    return checkWasFailedFbo (theFboToCheck, theFboRef->GetVPSizeX(), theFboRef->GetVPSizeY(), theFboRef->NbSamples());
  }

  //! Chooses compatible internal color format for OIT frame buffer.
  static bool chooseOitColorConfiguration (const Handle(OpenGl_Context)& theGlContext,
                                           const Standard_Integer theConfigIndex,
                                           OpenGl_ColorFormats& theFormats)
  {
    theFormats.Clear();
    switch (theConfigIndex)
    {
      case 0: // choose best applicable color format combination
      {
        theFormats.Append (theGlContext->hasHalfFloatBuffer != OpenGl_FeatureNotAvailable ? GL_RGBA16F : GL_RGBA32F);
        theFormats.Append (theGlContext->hasHalfFloatBuffer != OpenGl_FeatureNotAvailable ? GL_R16F    : GL_R32F);
        return true;
      }
      case 1: // choose non-optimal applicable color format combination
      {
        theFormats.Append (theGlContext->hasHalfFloatBuffer != OpenGl_FeatureNotAvailable ? GL_RGBA16F : GL_RGBA32F);
        theFormats.Append (theGlContext->hasHalfFloatBuffer != OpenGl_FeatureNotAvailable ? GL_RGBA16F : GL_RGBA32F);
        return true;
      }
    }
    return false; // color combination does not exist
  }
}

IMPLEMENT_STANDARD_RTTIEXT(OpenGl_View,Graphic3d_CView)

// =======================================================================
// function : Constructor
// purpose  :
// =======================================================================
OpenGl_View::OpenGl_View (const Handle(Graphic3d_StructureManager)& theMgr,
                          const Handle(OpenGl_GraphicDriver)& theDriver,
                          const Handle(OpenGl_Caps)& theCaps,
                          OpenGl_StateCounter* theCounter)
: Graphic3d_CView  (theMgr),
  myDriver         (theDriver.operator->()),
  myCaps           (theCaps),
  myWasRedrawnGL   (Standard_False),
  myToShowGradTrihedron  (false),
  myStateCounter         (theCounter),
  myCurrLightSourceState (theCounter->Increment()),
  myLightsRevision       (0),
  myLastLightSourceState (0, 0),
  mySRgbState            (-1),
  myFboColorFormat       (GL_SRGB8_ALPHA8), // note that GL_SRGB8 is not required to be renderable, unlike GL_RGB8, GL_RGBA8, GL_SRGB8_ALPHA8
  myFboDepthFormat       (GL_DEPTH24_STENCIL8),
  myToFlipOutput         (Standard_False),
  //
  myFrameCounter         (0),
  myHasFboBlit           (Standard_True),
  myToDisableOIT         (Standard_False),
  myToDisableOITMSAA     (Standard_False),
  myToDisableMSAA        (Standard_False),
  myTransientDrawToFront (Standard_True),
  myBackBufferRestored   (Standard_False),
  myIsImmediateDrawn     (Standard_False),
  myTextureParams     (new OpenGl_Aspects()),
  myCubeMapParams     (new OpenGl_Aspects()),
  myColoredQuadParams (new OpenGl_Aspects()),
  myPBREnvState       (OpenGl_PBREnvState_NONEXISTENT),
  myPBREnvRequest     (Standard_False),
  // ray-tracing fields initialization
  myRaytraceInitStatus     (OpenGl_RT_NONE),
  myIsRaytraceDataValid    (Standard_False),
  myIsRaytraceWarnTextures (Standard_False),
  myRaytraceBVHBuilder (new BVH_BinnedBuilder<Standard_ShortReal, 3, BVH_Constants_NbBinsBest> (BVH_Constants_LeafNodeSizeAverage,
                                                                                                BVH_Constants_MaxTreeDepth,
                                                                                                Standard_False,
                                                                                                OSD_Parallel::NbLogicalProcessors() + 1)),
  myRaytraceSceneRadius  (0.0f),
  myRaytraceSceneEpsilon (1.0e-6f),
  myToUpdateEnvironmentMap (Standard_False),
  myRaytraceLayerListState (0),
  myPrevCameraApertureRadius(0.f),
  myPrevCameraFocalPlaneDist(0.f)
{
  for (int i = 0; i < Graphic3d_TypeOfBackground_NB; ++i)
  {
    myBackgrounds[i] = new OpenGl_BackgroundArray(Graphic3d_TypeOfBackground(i));
  }

  myWorkspace = new OpenGl_Workspace (this, NULL);

  Handle(Graphic3d_CLight) aLight = new Graphic3d_CLight (Graphic3d_TypeOfLightSource_Ambient);
  aLight->SetColor (Quantity_NOC_WHITE);
  myLights = new Graphic3d_LightSet();
  myNoShadingLight = new Graphic3d_LightSet();
  myNoShadingLight->Add (aLight);

  myMainSceneFbos[0]         = new OpenGl_FrameBuffer ("fbo0_main");
  myMainSceneFbos[1]         = new OpenGl_FrameBuffer ("fbo1_main");
  myMainSceneFbosOit[0]      = new OpenGl_FrameBuffer ("fbo0_main_oit");
  myMainSceneFbosOit[1]      = new OpenGl_FrameBuffer ("fbo1_main_oit");
  myImmediateSceneFbos[0]    = new OpenGl_FrameBuffer ("fbo0_imm");
  myImmediateSceneFbos[1]    = new OpenGl_FrameBuffer ("fbo1_imm");
  myImmediateSceneFbosOit[0] = new OpenGl_FrameBuffer ("fbo0_imm_oit");
  myImmediateSceneFbosOit[1] = new OpenGl_FrameBuffer ("fbo1_imm_oit");
  myXrSceneFbo               = new OpenGl_FrameBuffer ("fbo_xr");
  myOpenGlFBO                = new OpenGl_FrameBuffer ("fbo_gl");
  myOpenGlFBO2               = new OpenGl_FrameBuffer ("fbo_gl2");
  myRaytraceFBO1[0]          = new OpenGl_FrameBuffer ("fbo0_raytrace1");
  myRaytraceFBO1[1]          = new OpenGl_FrameBuffer ("fbo1_raytrace1");
  myRaytraceFBO2[0]          = new OpenGl_FrameBuffer ("fbo0_raytrace2");
  myRaytraceFBO2[1]          = new OpenGl_FrameBuffer ("fbo1_raytrace2");
  myDepthPeelingFbos = new OpenGl_DepthPeeling();
  myShadowMaps = new OpenGl_ShadowMapArray();

  myXrSceneFbo->ColorTexture()->Sampler()->Parameters()->SetFilter (Graphic3d_TOTF_BILINEAR);
}

// =======================================================================
// function : Destructor
// purpose  :
// =======================================================================
OpenGl_View::~OpenGl_View()
{
  ReleaseGlResources (NULL); // ensure ReleaseGlResources() was called within valid context
  for (int i = 0; i < Graphic3d_TypeOfBackground_NB; ++i)
  {
    OpenGl_Element::Destroy(NULL, myBackgrounds[i]);
  }

  OpenGl_Element::Destroy (NULL, myTextureParams);
  OpenGl_Element::Destroy (NULL, myCubeMapParams);
  OpenGl_Element::Destroy (NULL, myColoredQuadParams);
}

// =======================================================================
// function : releaseSrgbResources
// purpose  :
// =======================================================================
void OpenGl_View::releaseSrgbResources (const Handle(OpenGl_Context)& theCtx)
{
  myRenderParams.RebuildRayTracingShaders = true;

  if (!myTextureEnv.IsNull())
  {
    if (!theCtx.IsNull())
    {
      for (OpenGl_TextureSet::Iterator aTextureIter (myTextureEnv); aTextureIter.More(); aTextureIter.Next())
      {
        theCtx->DelayedRelease (aTextureIter.ChangeValue());
        aTextureIter.ChangeValue().Nullify();
      }
    }
    myTextureEnv.Nullify();
  }

  if (myTextureParams != NULL)
  {
    myTextureParams->Release (theCtx.get());
  }

  if (myCubeMapParams != NULL)
  {
    myCubeMapParams->Release (theCtx.get());
  }

  for (int i = 0; i < Graphic3d_TypeOfBackground_NB; ++i)
  {
    if (myBackgrounds[i] != NULL)
    {
      myBackgrounds[i]->Release (theCtx.get());
    }
  }

  myMainSceneFbos[0]        ->Release (theCtx.get());
  myMainSceneFbos[1]        ->Release (theCtx.get());
  myMainSceneFbosOit[0]     ->Release (theCtx.get());
  myMainSceneFbosOit[1]     ->Release (theCtx.get());
  myImmediateSceneFbos[0]   ->Release (theCtx.get());
  myImmediateSceneFbos[1]   ->Release (theCtx.get());
  myImmediateSceneFbosOit[0]->Release (theCtx.get());
  myImmediateSceneFbosOit[1]->Release (theCtx.get());
  myXrSceneFbo              ->Release (theCtx.get());
  myDepthPeelingFbos        ->Release (theCtx.get());
  myOpenGlFBO               ->Release (theCtx.get());
  myOpenGlFBO2              ->Release (theCtx.get());
  myFullScreenQuad           .Release (theCtx.get());
  myFullScreenQuadFlip       .Release (theCtx.get());
  myShadowMaps->Release (theCtx.get());

  // Technically we should also re-initialize all sRGB/RGB8 color textures.
  // But for now consider this sRGB disabling/enabling to be done at application start-up
  // and re-create dynamically only frame buffers.
}

// =======================================================================
// function : ReleaseGlResources
// purpose  :
// =======================================================================
void OpenGl_View::ReleaseGlResources (const Handle(OpenGl_Context)& theCtx)
{
  myGraduatedTrihedron.Release (theCtx.get());
  myFrameStatsPrs.Release (theCtx.get());

  releaseSrgbResources (theCtx);

  releaseRaytraceResources (theCtx);

  if (!myPBREnvironment.IsNull())
  {
    myPBREnvironment->Release (theCtx.get());
  }
  ReleaseXR();
}

// =======================================================================
// function : Remove
// purpose  :
// =======================================================================
void OpenGl_View::Remove()
{
  if (IsRemoved())
  {
    return;
  }

  myDriver->RemoveView (this);
  myWindow.Nullify();

  Graphic3d_CView::Remove();
}

// =======================================================================
// function : SetLocalOrigin
// purpose  :
// =======================================================================
void OpenGl_View::SetLocalOrigin (const gp_XYZ& theOrigin)
{
  myLocalOrigin = theOrigin;
  const Handle(OpenGl_Context)& aCtx = myWorkspace->GetGlContext();
  if (!aCtx.IsNull())
  {
    aCtx->ShaderManager()->SetLocalOrigin (theOrigin);
  }
}

// =======================================================================
// function : SetTextureEnv
// purpose  :
// =======================================================================
void OpenGl_View::SetTextureEnv (const Handle(Graphic3d_TextureEnv)& theTextureEnv)
{
  Handle(OpenGl_Context) aCtx = myWorkspace->GetGlContext();
  if (!aCtx.IsNull() && !myTextureEnv.IsNull())
  {
    for (OpenGl_TextureSet::Iterator aTextureIter (myTextureEnv); aTextureIter.More(); aTextureIter.Next())
    {
      aCtx->DelayedRelease (aTextureIter.ChangeValue());
      aTextureIter.ChangeValue().Nullify();
    }
  }

  myToUpdateEnvironmentMap = Standard_True;
  myTextureEnvData = theTextureEnv;
  myTextureEnv.Nullify();
  initTextureEnv (aCtx);
}

// =======================================================================
// function : initTextureEnv
// purpose  :
// =======================================================================
void OpenGl_View::initTextureEnv (const Handle(OpenGl_Context)& theContext)
{
  if (myTextureEnvData.IsNull()
    ||  theContext.IsNull()
    || !theContext->MakeCurrent())
  {
    return;
  }

  Handle(OpenGl_Texture) aTextureEnv = new OpenGl_Texture (myTextureEnvData->GetId(), myTextureEnvData->GetParams());
  aTextureEnv->Init (theContext, myTextureEnvData);

  myTextureEnv = new OpenGl_TextureSet (aTextureEnv);
  myTextureEnv->ChangeTextureSetBits() = Graphic3d_TextureSetBits_BaseColor;
}

// =======================================================================
// function : SetImmediateModeDrawToFront
// purpose  :
// =======================================================================
Standard_Boolean OpenGl_View::SetImmediateModeDrawToFront (const Standard_Boolean theDrawToFrontBuffer)
{
  const Standard_Boolean aPrevMode = myTransientDrawToFront;
  myTransientDrawToFront = theDrawToFrontBuffer;
  return aPrevMode;
}

// =======================================================================
// function : Window
// purpose  :
// =======================================================================
Handle(Aspect_Window) OpenGl_View::Window() const
{
  return myWindow->SizeWindow();
}

// =======================================================================
// function : SetWindow
// purpose  :
// =======================================================================
void OpenGl_View::SetWindow (const Handle(Graphic3d_CView)& theParentVIew,
                             const Handle(Aspect_Window)& theWindow,
                             const Aspect_RenderingContext theContext)
{
  if (theContext != nullptr
  && !theParentVIew.IsNull())
  {
    throw Standard_ProgramError ("OpenGl_View::SetWindow(), internal error");
  }

  if (myParentView != nullptr)
  {
    myParentView->RemoveSubview (this);
    myParentView = nullptr;
  }

  OpenGl_View* aParentView = dynamic_cast<OpenGl_View*> (theParentVIew.get());
  if (!theParentVIew.IsNull())
  {
    if (aParentView == nullptr
     || aParentView->GlWindow().IsNull()
     || aParentView->GlWindow()->GetGlContext().IsNull())
    {
      throw Standard_ProgramError ("OpenGl_View::SetWindow(), internal error");
    }

    myParentView = aParentView;
    myParentView->AddSubview (this);

    Handle(Aspect_NeutralWindow) aSubWindow = Handle(Aspect_NeutralWindow)::DownCast(theWindow);
    SubviewResized (aSubWindow);

    const Handle(OpenGl_Window)& aParentGlWindow = aParentView->GlWindow();
    Aspect_RenderingContext aRendCtx = aParentGlWindow->GetGlContext()->RenderingContext();
    myWindow = myDriver->CreateRenderWindow (aParentGlWindow->PlatformWindow(), theWindow, aRendCtx);
  }
  else
  {
    myWindow = myDriver->CreateRenderWindow (theWindow, theWindow, theContext);
  }
  if (myWindow.IsNull())
  {
    throw Standard_ProgramError ("OpenGl_View::SetWindow, Failed to create OpenGl window");
  }

  myWorkspace = new OpenGl_Workspace (this, myWindow);
  myWorldViewProjState.Reset();
  myToUpdateEnvironmentMap = Standard_True;
  myHasFboBlit = Standard_True;
  Invalidate();

  // choose preferred FBO format
  const Handle(OpenGl_Context)& aCtx = myWorkspace->GetGlContext();
  if (aCtx->IsWindowDeepColor()
   && aCtx->IsGlGreaterEqual (3, 0))
  {
    myFboColorFormat = GL_RGB10_A2;
  }
  else if (aCtx->HasSRGB())
  {
    // note that GL_SRGB8 is not required to be renderable, unlike GL_RGB8, GL_RGBA8, GL_SRGB8_ALPHA8
    myFboColorFormat = GL_SRGB8_ALPHA8;
  }
  else
  {
    myFboColorFormat = GL_RGBA8;
  }

  // Environment texture resource does not support lazy initialization.
  initTextureEnv (aCtx);
}

// =======================================================================
// function : Resized
// purpose  :
// =======================================================================
void OpenGl_View::Resized()
{
  base_type::Resized();
  if (!myWindow.IsNull())
  {
    myWindow->Resize();
  }
}

// =======================================================================
// function : SetMinMaxValuesCallback
// purpose  :
// =======================================================================
static void SetMinMaxValuesCallback (Graphic3d_CView* theView)
{
  OpenGl_View* aView = dynamic_cast<OpenGl_View*>(theView);
  if (aView == NULL)
    return;

  Bnd_Box aBox = theView->MinMaxValues();
  if (!aBox.IsVoid())
  {
    gp_Pnt aMin = aBox.CornerMin();
    gp_Pnt aMax = aBox.CornerMax();

    Graphic3d_Vec3 aMinVec ((Standard_ShortReal )aMin.X(), (Standard_ShortReal )aMin.Y(), (Standard_ShortReal )aMin.Z());
    Graphic3d_Vec3 aMaxVec ((Standard_ShortReal )aMax.X(), (Standard_ShortReal )aMax.Y(), (Standard_ShortReal )aMax.Z());
    aView->GraduatedTrihedronMinMaxValues (aMinVec, aMaxVec);
  }
}

// =======================================================================
// function : GraduatedTrihedronDisplay
// purpose  :
// =======================================================================
void OpenGl_View::GraduatedTrihedronDisplay (const Graphic3d_GraduatedTrihedron& theTrihedronData)
{
  myGTrihedronData = theTrihedronData;
  myGTrihedronData.SetCubicAxesCallback (SetMinMaxValuesCallback);
  myGraduatedTrihedron.SetValues (myGTrihedronData);
  myToShowGradTrihedron = true;
}

// =======================================================================
// function : GraduatedTrihedronErase
// purpose  :
// =======================================================================
void OpenGl_View::GraduatedTrihedronErase()
{
  myGraduatedTrihedron.Release (myWorkspace->GetGlContext().operator->());
  myToShowGradTrihedron = false;
}

// =======================================================================
// function : GraduatedTrihedronMinMaxValues
// purpose  :
// =======================================================================
void OpenGl_View::GraduatedTrihedronMinMaxValues (const Graphic3d_Vec3 theMin, const Graphic3d_Vec3 theMax)
{
  myGraduatedTrihedron.SetMinMax (theMin, theMax);
}

// =======================================================================
// function : BufferDump
// purpose  :
// =======================================================================
Standard_Boolean OpenGl_View::BufferDump (Image_PixMap& theImage, const Graphic3d_BufferType& theBufferType)
{
  const Handle(OpenGl_Context)& aCtx = myWorkspace->GetGlContext();
  if (theBufferType != Graphic3d_BT_RGB_RayTraceHdrLeft)
  {
    return myWorkspace->BufferDump(myFBO, theImage, theBufferType);
  }

  if (!myRaytraceParameters.AdaptiveScreenSampling)
  {
    return myWorkspace->BufferDump(myAccumFrames % 2 ? myRaytraceFBO2[0] : myRaytraceFBO1[0], theImage, theBufferType);
  }

  if (aCtx->GraphicsLibrary() == Aspect_GraphicsLibrary_OpenGLES)
  {
    return false;
  }
  if (theImage.Format() != Image_Format_RGBF)
  {
    return false;
  }

  const GLuint aW = myRaytraceOutputTexture[0]->SizeX();
  const GLuint aH = myRaytraceOutputTexture[0]->SizeY();
  if (aW / 3 != theImage.SizeX() || aH / 2 != theImage.SizeY())
  {
    return false;
  }

  std::vector<GLfloat> aValues;
  try
  {
    aValues.resize (aW * aH);
  }
  catch (const std::bad_alloc&)
  {
    return false;
  }

  aCtx->core11fwd->glBindTexture (GL_TEXTURE_RECTANGLE, myRaytraceOutputTexture[0]->TextureId());
  aCtx->core11fwd->glGetTexImage (GL_TEXTURE_RECTANGLE, 0, OpenGl_TextureFormat::Create<GLfloat, 1>().Format(), GL_FLOAT, &aValues[0]);
  aCtx->core11fwd->glBindTexture (GL_TEXTURE_RECTANGLE, 0);
  for (unsigned int aRow = 0; aRow < aH; aRow += 2)
  {
    for (unsigned int aCol = 0; aCol < aW; aCol += 3)
    {
      float* anImageValue = theImage.ChangeValue<float[3]> ((aH - aRow) / 2 - 1, aCol / 3);
      float aInvNbSamples = 1.f / aValues[aRow * aW + aCol + aW];
      anImageValue[0] = aValues[aRow * aW + aCol] * aInvNbSamples;
      anImageValue[1] = aValues[aRow * aW + aCol + 1] * aInvNbSamples;
      anImageValue[2] = aValues[aRow * aW + aCol + 1 + aW] * aInvNbSamples;
    }
  }

  return true;
}

// =======================================================================
// function : GradientBackground
// purpose  :
// =======================================================================
Aspect_GradientBackground OpenGl_View::GradientBackground() const
{
  Quantity_Color aColor1, aColor2;
  aColor1.SetValues (myBackgrounds[Graphic3d_TOB_GRADIENT]->GradientColor (0).r(),
                     myBackgrounds[Graphic3d_TOB_GRADIENT]->GradientColor (0).g(),
                     myBackgrounds[Graphic3d_TOB_GRADIENT]->GradientColor (0).b(), Quantity_TOC_RGB);
  aColor2.SetValues (myBackgrounds[Graphic3d_TOB_GRADIENT]->GradientColor (1).r(),
                     myBackgrounds[Graphic3d_TOB_GRADIENT]->GradientColor (1).g(),
                     myBackgrounds[Graphic3d_TOB_GRADIENT]->GradientColor (1).b(), Quantity_TOC_RGB);
  return Aspect_GradientBackground (aColor1, aColor2, myBackgrounds[Graphic3d_TOB_GRADIENT]->GradientFillMethod());
}

// =======================================================================
// function : SetGradientBackground
// purpose  :
// =======================================================================
void OpenGl_View::SetGradientBackground (const Aspect_GradientBackground& theBackground)
{
  Quantity_Color aColor1, aColor2;
  theBackground.Colors (aColor1, aColor2);
  myBackgrounds[Graphic3d_TOB_GRADIENT]->SetGradientParameters (aColor1, aColor2, theBackground.BgGradientFillMethod());
  if (theBackground.BgGradientFillMethod() >= Aspect_GradientFillMethod_Corner1
   && theBackground.BgGradientFillMethod() <= Aspect_GradientFillMethod_Corner4)
  {
    if (const Handle(OpenGl_Context)& aCtx = myWorkspace->GetGlContext())
    {
      myColoredQuadParams->Aspect()->SetShaderProgram(aCtx->ShaderManager()->GetColoredQuadProgram());
      myColoredQuadParams->Aspect()->ShaderProgram()->PushVariableVec3 ("uColor1", aColor1.Rgb());
      myColoredQuadParams->Aspect()->ShaderProgram()->PushVariableVec3 ("uColor2", aColor2.Rgb());
    }
  }
  myBackgroundType = Graphic3d_TOB_GRADIENT;
}

// =======================================================================
// function : SetBackgroundImage
// purpose  :
// =======================================================================
void OpenGl_View::SetBackgroundImage (const Handle(Graphic3d_TextureMap)& theTextureMap,
                                      Standard_Boolean theToUpdatePBREnv)
{
  Handle(Graphic3d_TextureMap) aNewMap = theTextureMap;
  if (theTextureMap.IsNull()
  || !theTextureMap->IsDone())
  {
    if (!theTextureMap.IsNull())
    {
      Message::SendFail ("Error: unable to set image background");
    }
    aNewMap.Nullify();
  }

  Handle(Graphic3d_CubeMap) aCubeMap = Handle(Graphic3d_CubeMap)::DownCast (aNewMap);
  if (theToUpdatePBREnv)
  {
    // update PBR environment
    const TCollection_AsciiString anIdOld = !myCubeMapIBL.IsNull()
                                           ? myCubeMapIBL->GetId()
                                           : TCollection_AsciiString();
    const TCollection_AsciiString anIdNew = !aCubeMap.IsNull()
                                           ? aCubeMap->GetId()
                                           : TCollection_AsciiString();
    if (anIdNew != anIdOld)
    {
      myPBREnvRequest = true;
    }
    myCubeMapIBL = aCubeMap;
  }

  if (aNewMap.IsNull())
  {
    if (myBackgroundType == Graphic3d_TOB_TEXTURE
     || myBackgroundType == Graphic3d_TOB_CUBEMAP)
    {
      myBackgroundType = Graphic3d_TOB_NONE;
    }
    return;
  }

  Handle(Graphic3d_AspectFillArea3d) anAspect = new Graphic3d_AspectFillArea3d();
  Handle(Graphic3d_TextureSet) aTextureSet = new Graphic3d_TextureSet (aNewMap);
  anAspect->SetInteriorStyle (Aspect_IS_SOLID);
  anAspect->SetFaceCulling (Graphic3d_TypeOfBackfacingModel_DoubleSided);
  anAspect->SetShadingModel (Graphic3d_TypeOfShadingModel_Unlit);
  anAspect->SetTextureSet (aTextureSet);
  anAspect->SetTextureMapOn (true);

  if (Handle(Graphic3d_Texture2D) aTextureMap = Handle(Graphic3d_Texture2D)::DownCast (aNewMap))
  {
    myTextureParams->SetAspect (anAspect);
    myBackgroundType  = Graphic3d_TOB_TEXTURE;
    myBackgroundImage = aTextureMap;
    return;
  }

  if (!aCubeMap.IsNull())
  {
    aCubeMap->SetMipmapsGeneration (Standard_True);
    if (const Handle(OpenGl_Context)& aCtx = myWorkspace->GetGlContext())
    {
      anAspect->SetShaderProgram (aCtx->ShaderManager()->GetBgCubeMapProgram());
    }

    myCubeMapParams->SetAspect (anAspect);

    const OpenGl_Aspects* anAspectsBackup = myWorkspace->SetAspects (myCubeMapParams);
    myWorkspace->ApplyAspects();
    myWorkspace->SetAspects (anAspectsBackup);
    myWorkspace->ApplyAspects();

    myBackgroundType = Graphic3d_TOB_CUBEMAP;
    myCubeMapBackground = aCubeMap;
    return;
  }

  throw Standard_ProgramError ("OpenGl_View::SetBackgroundImage() - invalid texture map set for background");
}

// =======================================================================
// function : SetImageBasedLighting
// purpose  :
// =======================================================================
void OpenGl_View::SetImageBasedLighting (Standard_Boolean theToEnableIBL)
{
  if (!theToEnableIBL
    || myBackgroundType != Graphic3d_TOB_CUBEMAP)
  {
    if (!myCubeMapIBL.IsNull())
    {
      myPBREnvRequest = true;
      myCubeMapIBL.Nullify();
    }
    return;
  }

  const TCollection_AsciiString anIdOld = !myCubeMapIBL.IsNull()
                                         ? myCubeMapIBL->GetId()
                                         : TCollection_AsciiString();
  const TCollection_AsciiString anIdNew = !myCubeMapBackground.IsNull()
                                         ? myCubeMapBackground->GetId()
                                         : TCollection_AsciiString();
  if (anIdNew != anIdOld)
  {
    myPBREnvRequest = true;
  }
  myCubeMapIBL = myCubeMapBackground;
}

// =======================================================================
// function : BackgroundImageStyle
// purpose  :
// =======================================================================
Aspect_FillMethod OpenGl_View::BackgroundImageStyle() const
{
  return myBackgrounds[Graphic3d_TOB_TEXTURE]->TextureFillMethod();
}

// =======================================================================
// function : SetBackgroundImageStyle
// purpose  :
// =======================================================================
void OpenGl_View::SetBackgroundImageStyle (const Aspect_FillMethod theFillStyle)
{
  myBackgrounds[Graphic3d_TOB_TEXTURE]->SetTextureFillMethod (theFillStyle);
}

// =======================================================================
// function : SpecIBLMapLevels
// purpose  :
// =======================================================================
unsigned int OpenGl_View::SpecIBLMapLevels() const
{
  return myPBREnvironment.IsNull() ? 0 : myPBREnvironment->SpecMapLevelsNumber();
}

//=======================================================================
//function : InsertLayerBefore
//purpose  :
//=======================================================================
void OpenGl_View::InsertLayerBefore (const Graphic3d_ZLayerId theLayerId,
  const Graphic3d_ZLayerSettings& theSettings,
  const Graphic3d_ZLayerId theLayerAfter)
{
  myZLayers.InsertLayerBefore (theLayerId, theSettings, theLayerAfter);
}

//=======================================================================
//function : InsertLayerAfter
//purpose  :
//=======================================================================
void OpenGl_View::InsertLayerAfter (const Graphic3d_ZLayerId theLayerId,
  const Graphic3d_ZLayerSettings& theSettings,
  const Graphic3d_ZLayerId theLayerBefore)
{
  myZLayers.InsertLayerAfter (theLayerId, theSettings, theLayerBefore);
}

//=======================================================================
//function : RemoveZLayer
//purpose  :
//=======================================================================
void OpenGl_View::RemoveZLayer (const Graphic3d_ZLayerId theLayerId)
{
  myZLayers.RemoveLayer (theLayerId);
}

//=======================================================================
//function : SetZLayerSettings
//purpose  :
//=======================================================================
void OpenGl_View::SetZLayerSettings (const Graphic3d_ZLayerId        theLayerId,
                                     const Graphic3d_ZLayerSettings& theSettings)
{
  myZLayers.SetLayerSettings (theLayerId, theSettings);
}

//=======================================================================
//function : ZLayerMax
//purpose  :
//=======================================================================
Standard_Integer OpenGl_View::ZLayerMax() const
{
  Standard_Integer aLayerMax = Graphic3d_ZLayerId_Default;
  for (NCollection_List<Handle(Graphic3d_Layer)>::Iterator aLayerIter (myZLayers.Layers()); aLayerIter.More(); aLayerIter.Next())
  {
    aLayerMax = Max (aLayerMax, aLayerIter.Value()->LayerId());
  }
  return aLayerMax;
}

//=======================================================================
//function : Layers
//purpose  :
//=======================================================================
const NCollection_List<Handle(Graphic3d_Layer)>& OpenGl_View::Layers() const
{
  return myZLayers.Layers();
}

//=======================================================================
//function : Layer
//purpose  :
//=======================================================================
Handle(Graphic3d_Layer) OpenGl_View::Layer (const Graphic3d_ZLayerId theLayerId) const
{
  Handle(Graphic3d_Layer) aLayer;
  if (theLayerId != Graphic3d_ZLayerId_UNKNOWN)
  {
    myZLayers.LayerIDs().Find (theLayerId, aLayer);
  }
  return aLayer;
}

//=======================================================================
//function : MinMaxValues
//purpose  :
//=======================================================================
Bnd_Box OpenGl_View::MinMaxValues (const Standard_Boolean theToIncludeAuxiliary) const
{
  if (!IsDefined())
  {
    return Bnd_Box();
  }

  Bnd_Box aBox = base_type::MinMaxValues (theToIncludeAuxiliary);

  // make sure that stats overlay isn't clamped on hardware with unavailable depth clamping
  if (theToIncludeAuxiliary
  &&  myRenderParams.ToShowStats
  && !myWorkspace->GetGlContext()->arbDepthClamp)
  {
    Bnd_Box aStatsBox (gp_Pnt (float(myWindow->Width() / 2.0), float(myWindow->Height() / 2.0), 0.0),
                       gp_Pnt (float(myWindow->Width() / 2.0), float(myWindow->Height() / 2.0), 0.0));
    myRenderParams.StatsPosition->Apply (myCamera, myCamera->ProjectionMatrix(), myCamera->OrientationMatrix(),
                                         myWindow->Width(), myWindow->Height(), aStatsBox);
    aBox.Add (aStatsBox);
  }
  return aBox;
}

//=======================================================================
//function : FBO
//purpose  :
//=======================================================================
Handle(Standard_Transient) OpenGl_View::FBO() const
{
  return Handle(Standard_Transient)(myFBO);
}

//=======================================================================
//function : SetFBO
//purpose  :
//=======================================================================
void OpenGl_View::SetFBO (const Handle(Standard_Transient)& theFbo)
{
  myFBO = Handle(OpenGl_FrameBuffer)::DownCast (theFbo);
}

//=======================================================================
//function : FBOCreate
//purpose  :
//=======================================================================
Handle(Standard_Transient) OpenGl_View::FBOCreate (const Standard_Integer theWidth,
                                                   const Standard_Integer theHeight)
{
  return myWorkspace->FBOCreate (theWidth, theHeight);
}

//=======================================================================
//function : FBORelease
//purpose  :
//=======================================================================
void OpenGl_View::FBORelease (Handle(Standard_Transient)& theFbo)
{
  Handle(OpenGl_FrameBuffer) aFrameBuffer = Handle(OpenGl_FrameBuffer)::DownCast (theFbo);
  if (aFrameBuffer.IsNull())
  {
    return;
  }

  myWorkspace->FBORelease (aFrameBuffer);
  theFbo.Nullify();
}

//=======================================================================
//function : FBOGetDimensions
//purpose  :
//=======================================================================
void OpenGl_View::FBOGetDimensions (const Handle(Standard_Transient)& theFbo,
                                    Standard_Integer& theWidth,
                                    Standard_Integer& theHeight,
                                    Standard_Integer& theWidthMax,
                                    Standard_Integer& theHeightMax)
{
  const Handle(OpenGl_FrameBuffer) aFrameBuffer = Handle(OpenGl_FrameBuffer)::DownCast (theFbo);
  if (aFrameBuffer.IsNull())
  {
    return;
  }

  theWidth     = aFrameBuffer->GetVPSizeX(); // current viewport size
  theHeight    = aFrameBuffer->GetVPSizeY();
  theWidthMax  = aFrameBuffer->GetSizeX(); // texture size
  theHeightMax = aFrameBuffer->GetSizeY();
}

//=======================================================================
//function : FBOChangeViewport
//purpose  :
//=======================================================================
void OpenGl_View::FBOChangeViewport (const Handle(Standard_Transient)& theFbo,
                                     const Standard_Integer theWidth,
                                     const Standard_Integer theHeight)
{
  const Handle(OpenGl_FrameBuffer) aFrameBuffer = Handle(OpenGl_FrameBuffer)::DownCast (theFbo);
  if (aFrameBuffer.IsNull())
  {
    return;
  }

  aFrameBuffer->ChangeViewport (theWidth, theHeight);
}

//=======================================================================
//function : displayStructure
//purpose  :
//=======================================================================
void OpenGl_View::displayStructure (const Handle(Graphic3d_CStructure)& theStructure,
                                    const Graphic3d_DisplayPriority thePriority)
{
  const OpenGl_Structure*  aStruct = static_cast<const OpenGl_Structure*> (theStructure.get());
  const Graphic3d_ZLayerId aZLayer = aStruct->ZLayer();
  myZLayers.AddStructure (aStruct, aZLayer, thePriority);
}

//=======================================================================
//function : eraseStructure
//purpose  :
//=======================================================================
void OpenGl_View::eraseStructure (const Handle(Graphic3d_CStructure)& theStructure)
{
  const OpenGl_Structure* aStruct = static_cast<const OpenGl_Structure*> (theStructure.get());
  myZLayers.RemoveStructure (aStruct);
}

//=======================================================================
//function : changeZLayer
//purpose  :
//=======================================================================
void OpenGl_View::changeZLayer (const Handle(Graphic3d_CStructure)& theStructure,
                                const Graphic3d_ZLayerId theNewLayerId)
{
  const Graphic3d_ZLayerId anOldLayer = theStructure->ZLayer();
  const OpenGl_Structure* aStruct = static_cast<const OpenGl_Structure*> (theStructure.get());
  myZLayers.ChangeLayer (aStruct, anOldLayer, theNewLayerId);
  Update (anOldLayer);
  Update (theNewLayerId);
}

//=======================================================================
//function : changePriority
//purpose  :
//=======================================================================
void OpenGl_View::changePriority (const Handle(Graphic3d_CStructure)& theStructure,
                                  const Graphic3d_DisplayPriority theNewPriority)
{
  const Graphic3d_ZLayerId aLayerId = theStructure->ZLayer();
  const OpenGl_Structure* aStruct = static_cast<const OpenGl_Structure*> (theStructure.get());
  myZLayers.ChangePriority (aStruct, aLayerId, theNewPriority);
}

//=======================================================================
//function : DiagnosticInformation
//purpose  :
//=======================================================================
void OpenGl_View::DiagnosticInformation (TColStd_IndexedDataMapOfStringString& theDict,
                                         Graphic3d_DiagnosticInfo theFlags) const
{
  base_type::DiagnosticInformation (theDict, theFlags);
  Handle(OpenGl_Context) aCtx = myWorkspace->GetGlContext();
  if (!myWorkspace->Activate()
   || aCtx.IsNull())
  {
    return;
  }

  aCtx->DiagnosticInformation (theDict, theFlags);
  if ((theFlags & Graphic3d_DiagnosticInfo_FrameBuffer) != 0)
  {
    TCollection_AsciiString aResRatio (myRenderParams.ResolutionRatio());
    theDict.ChangeFromIndex (theDict.Add ("ResolutionRatio", aResRatio)) = aResRatio;
    if (myMainSceneFbos[0]->IsValid())
    {
      TCollection_AsciiString anFboInfo;
      if (const Handle(OpenGl_Texture)& aColorTex = myMainSceneFbos[0]->ColorTexture())
      {
        anFboInfo += OpenGl_TextureFormat::FormatFormat (aColorTex->SizedFormat());
      }
      if (const Handle(OpenGl_Texture)& aDepthTex = myMainSceneFbos[0]->DepthStencilTexture())
      {
        anFboInfo = anFboInfo + " " + OpenGl_TextureFormat::FormatFormat (aDepthTex->SizedFormat());
      }
      theDict.ChangeFromIndex (theDict.Add ("FBO buffer", anFboInfo)) = anFboInfo;
    }
  }
}

//=======================================================================
//function : StatisticInformation
//purpose  :
//=======================================================================
void OpenGl_View::StatisticInformation (TColStd_IndexedDataMapOfStringString& theDict) const
{
  if (const Handle(OpenGl_Context)& aCtx = myWorkspace->GetGlContext())
  {
    const Handle(OpenGl_FrameStats)& aStats = aCtx->FrameStats();
    const Graphic3d_RenderingParams& aRendParams = myWorkspace->View()->RenderingParams();
    aStats->FormatStats (theDict, aRendParams.CollectedStats);
  }
}

//=======================================================================
//function : StatisticInformation
//purpose  :
//=======================================================================
TCollection_AsciiString OpenGl_View::StatisticInformation() const
{
  if (const Handle(OpenGl_Context)& aCtx = myWorkspace->GetGlContext())
  {
    const Handle(OpenGl_FrameStats)& aStats = aCtx->FrameStats();
    const Graphic3d_RenderingParams& aRendParams = myWorkspace->View()->RenderingParams();
    return aStats->FormatStats (aRendParams.CollectedStats);
  }
  return TCollection_AsciiString();
}

//=======================================================================
//function : drawBackground
//purpose  :
//=======================================================================
void OpenGl_View::drawBackground (const Handle(OpenGl_Workspace)& theWorkspace,
                                  Graphic3d_Camera::Projection theProjection)
{
  const Handle(OpenGl_Context)& aCtx = theWorkspace->GetGlContext();
  const bool wasUsedZBuffer = theWorkspace->SetUseZBuffer (false);
  if (wasUsedZBuffer)
  {
    aCtx->core11fwd->glDisable (GL_DEPTH_TEST);
  }

#ifdef GL_DEPTH_CLAMP
  const bool wasDepthClamped = aCtx->arbDepthClamp && aCtx->core11fwd->glIsEnabled (GL_DEPTH_CLAMP);
  if (aCtx->arbDepthClamp && !wasDepthClamped)
  {
    // make sure background is always drawn (workaround skybox rendering on some hardware)
    aCtx->core11fwd->glEnable (GL_DEPTH_CLAMP);
  }
#endif

  if (myBackgroundType == Graphic3d_TOB_CUBEMAP)
  {
    updateSkydomeBg (aCtx);
    if (!myCubeMapParams->Aspect()->ShaderProgram().IsNull())
    {
      myCubeMapParams->Aspect()->ShaderProgram()->PushVariableInt ("uZCoeff", myCubeMapBackground->ZIsInverted() ? -1 : 1);
      myCubeMapParams->Aspect()->ShaderProgram()->PushVariableInt ("uYCoeff", myCubeMapBackground->IsTopDown() ? 1 : -1);
      const OpenGl_Aspects* anOldAspectFace = theWorkspace->SetAspects (myCubeMapParams);

      myBackgrounds[Graphic3d_TOB_CUBEMAP]->Render (theWorkspace, theProjection);

      theWorkspace->SetAspects (anOldAspectFace);
    }
  }
  else if (myBackgroundType == Graphic3d_TOB_GRADIENT
        || myBackgroundType == Graphic3d_TOB_TEXTURE)
  {
    // Drawing background gradient if:
    // - gradient fill type is not Aspect_GradientFillMethod_None and
    // - either background texture is no specified or it is drawn in Aspect_FM_CENTERED mode
    if (myBackgrounds[Graphic3d_TOB_GRADIENT]->IsDefined()
      && (!myTextureParams->Aspect()->ToMapTexture()
        || myBackgrounds[Graphic3d_TOB_TEXTURE]->TextureFillMethod() == Aspect_FM_CENTERED
        || myBackgrounds[Graphic3d_TOB_TEXTURE]->TextureFillMethod() == Aspect_FM_NONE))
    {
      if (myBackgrounds[Graphic3d_TOB_GRADIENT]->GradientFillMethod() >= Aspect_GradientFillMethod_Corner1
       && myBackgrounds[Graphic3d_TOB_GRADIENT]->GradientFillMethod() <= Aspect_GradientFillMethod_Corner4)
      {
        // Set colored quad shader program
        Quantity_Color aColor1, aColor2;
        GradientBackground().Colors(aColor1, aColor2);
        myColoredQuadParams->Aspect()->SetShaderProgram(aCtx->ShaderManager()->GetColoredQuadProgram());
        myColoredQuadParams->Aspect()->ShaderProgram()->PushVariableVec3 ("uColor1", aColor1.Rgb());
        myColoredQuadParams->Aspect()->ShaderProgram()->PushVariableVec3 ("uColor2", aColor2.Rgb());
       
        const OpenGl_Aspects* anOldAspectFace = theWorkspace->SetAspects (myColoredQuadParams);

        myBackgrounds[Graphic3d_TOB_GRADIENT]->Render (theWorkspace, theProjection);

        theWorkspace->SetAspects (anOldAspectFace);
      }
      else
      {
        myBackgrounds[Graphic3d_TOB_GRADIENT]->Render (theWorkspace, theProjection);
      }
    }

    // Drawing background image if it is defined
    // (texture is defined and fill type is not Aspect_FM_NONE)
    if (myBackgrounds[Graphic3d_TOB_TEXTURE]->IsDefined()
      && myTextureParams->Aspect()->ToMapTexture())
    {
      aCtx->core11fwd->glDisable (GL_BLEND);

      const OpenGl_Aspects* anOldAspectFace = theWorkspace->SetAspects (myTextureParams);
      myBackgrounds[Graphic3d_TOB_TEXTURE]->Render (theWorkspace, theProjection);
      theWorkspace->SetAspects (anOldAspectFace);
    }
  }

  if (wasUsedZBuffer)
  {
    theWorkspace->SetUseZBuffer (Standard_True);
    aCtx->core11fwd->glEnable (GL_DEPTH_TEST);
  }
#ifdef GL_DEPTH_CLAMP
  if (aCtx->arbDepthClamp && !wasDepthClamped)
  {
    aCtx->core11fwd->glDisable (GL_DEPTH_CLAMP);
  }
#endif
}

//=======================================================================
//function : prepareFrameBuffers
//purpose  :
//=======================================================================
bool OpenGl_View::prepareFrameBuffers (Graphic3d_Camera::Projection& theProj)
{
  theProj = myCamera->ProjectionType();
  const Handle(OpenGl_Context)& aCtx = myWorkspace->GetGlContext();

  Standard_Integer aSizeX = 0, aSizeY = 0;
  OpenGl_FrameBuffer* aFrameBuffer = myFBO.get();
  if (aFrameBuffer != NULL)
  {
    aSizeX = aFrameBuffer->GetVPSizeX();
    aSizeY = aFrameBuffer->GetVPSizeY();
  }
  else if (IsActiveXR())
  {
    aSizeX = myXRSession->RecommendedViewport().x();
    aSizeY = myXRSession->RecommendedViewport().y();
  }
  else
  {
    aSizeX = myWindow->Width();
    aSizeY = myWindow->Height();
  }

  const Graphic3d_Vec2i aRendSize (Standard_Integer(myRenderParams.RenderResolutionScale * aSizeX + 0.5f),
                                   Standard_Integer(myRenderParams.RenderResolutionScale * aSizeY + 0.5f));
  if (aSizeX < 1
   || aSizeY < 1
   || aRendSize.x() < 1
   || aRendSize.y() < 1)
  {
    myBackBufferRestored = Standard_False;
    myIsImmediateDrawn   = Standard_False;
    return false;
  }

  // determine multisampling parameters
  Standard_Integer aNbSamples = !myToDisableMSAA && aSizeX == aRendSize.x()
                              ? Max (Min (myRenderParams.NbMsaaSamples, aCtx->MaxMsaaSamples()), 0)
                              : 0;
  if (aNbSamples != 0)
  {
    aNbSamples = OpenGl_Context::GetPowerOfTwo (aNbSamples, aCtx->MaxMsaaSamples());
  }
  // Only MSAA textures can be blit into MSAA target,
  // while render buffers could be resolved only into non-MSAA targets.
  // As result, within obsolete OpenGL ES 3.0 context, we may create only one MSAA render buffer for main scene content
  // and blit it into non-MSAA immediate FBO.
  const bool hasTextureMsaa = aCtx->HasTextureMultisampling();

  bool toUseOit = myRenderParams.TransparencyMethod != Graphic3d_RTM_BLEND_UNORDERED
               && !myIsSubviewComposer
               && checkOitCompatibility (aCtx, aNbSamples > 0);

  const bool toInitImmediateFbo = myTransientDrawToFront && !myIsSubviewComposer
                               && (!aCtx->caps->useSystemBuffer || (toUseOit && HasImmediateStructures()));

  if ( aFrameBuffer == NULL
   && !aCtx->DefaultFrameBuffer().IsNull()
   &&  aCtx->DefaultFrameBuffer()->IsValid())
  {
    aFrameBuffer = aCtx->DefaultFrameBuffer().operator->();
  }

  if (myHasFboBlit
   && (myTransientDrawToFront
    || theProj == Graphic3d_Camera::Projection_Stereo
    || aNbSamples != 0
    || toUseOit
    || aSizeX != aRendSize.x()))
  {
    if (myMainSceneFbos[0]->GetVPSize() != aRendSize
     || myMainSceneFbos[0]->NbSamples() != aNbSamples)
    {
      if (!myTransientDrawToFront)
      {
        myImmediateSceneFbos[0]->Release (aCtx.operator->());
        myImmediateSceneFbos[1]->Release (aCtx.operator->());
        myImmediateSceneFbos[0]->ChangeViewport (0, 0);
        myImmediateSceneFbos[1]->ChangeViewport (0, 0);
      }

      // prepare FBOs containing main scene
      // for further blitting and rendering immediate presentations on top
      if (aCtx->core20fwd != NULL)
      {
        const bool wasFailedMain0 = checkWasFailedFbo (myMainSceneFbos[0], aRendSize.x(), aRendSize.y(), aNbSamples);
        if (!myMainSceneFbos[0]->Init (aCtx, aRendSize, myFboColorFormat, myFboDepthFormat, aNbSamples)
         && !wasFailedMain0)
        {
          TCollection_ExtendedString aMsg = TCollection_ExtendedString() + "Error! Main FBO "
                                          + printFboFormat (myMainSceneFbos[0]) + " initialization has failed";
          aCtx->PushMessage (GL_DEBUG_SOURCE_APPLICATION, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH, aMsg);
        }
      }
    }

    if (myMainSceneFbos[0]->IsValid() && (toInitImmediateFbo || myImmediateSceneFbos[0]->IsValid()))
    {
      const bool wasFailedImm0 = checkWasFailedFbo (myImmediateSceneFbos[0], myMainSceneFbos[0]);
      if (!myImmediateSceneFbos[0]->InitLazy (aCtx, *myMainSceneFbos[0], hasTextureMsaa)
       && !wasFailedImm0)
      {
        TCollection_ExtendedString aMsg = TCollection_ExtendedString() + "Error! Immediate FBO "
                                        + printFboFormat (myImmediateSceneFbos[0]) + " initialization has failed";
        aCtx->PushMessage (GL_DEBUG_SOURCE_APPLICATION, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH, aMsg);
      }
    }
  }
  else
  {
    myMainSceneFbos     [0]->Release (aCtx.operator->());
    myMainSceneFbos     [1]->Release (aCtx.operator->());
    myImmediateSceneFbos[0]->Release (aCtx.operator->());
    myImmediateSceneFbos[1]->Release (aCtx.operator->());
    myXrSceneFbo           ->Release (aCtx.operator->());
    myMainSceneFbos     [0]->ChangeViewport (0, 0);
    myMainSceneFbos     [1]->ChangeViewport (0, 0);
    myImmediateSceneFbos[0]->ChangeViewport (0, 0);
    myImmediateSceneFbos[1]->ChangeViewport (0, 0);
    myXrSceneFbo           ->ChangeViewport (0, 0);
  }

  bool hasXRBlitFbo = false;
  if (theProj == Graphic3d_Camera::Projection_Stereo
   && IsActiveXR()
   && myMainSceneFbos[0]->IsValid())
  {
    if (aNbSamples != 0
     || aSizeX != aRendSize.x())
    {
      hasXRBlitFbo = myXrSceneFbo->InitLazy (aCtx, Graphic3d_Vec2i (aSizeX, aSizeY), myFboColorFormat, myFboDepthFormat, 0);
      if (!hasXRBlitFbo)
      {
        TCollection_ExtendedString aMsg = TCollection_ExtendedString() + "Error! VR FBO "
                                        + printFboFormat (myXrSceneFbo) + " initialization has failed";
        aCtx->PushMessage (GL_DEBUG_SOURCE_APPLICATION, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH, aMsg);
      }
    }
  }
  else if (theProj == Graphic3d_Camera::Projection_Stereo
        && myMainSceneFbos[0]->IsValid())
  {
    const bool wasFailedMain1 = checkWasFailedFbo (myMainSceneFbos[1], myMainSceneFbos[0]);
    if (!myMainSceneFbos[1]->InitLazy (aCtx, *myMainSceneFbos[0], true)
     && !wasFailedMain1)
    {
      TCollection_ExtendedString aMsg = TCollection_ExtendedString() + "Error! Main FBO (second) "
                                      + printFboFormat (myMainSceneFbos[1]) + " initialization has failed";
      aCtx->PushMessage (GL_DEBUG_SOURCE_APPLICATION, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH, aMsg);
    }
    if (!myMainSceneFbos[1]->IsValid())
    {
      // no enough memory?
      theProj = Graphic3d_Camera::Projection_Perspective;
    }
    else if (!myTransientDrawToFront)
    {
      //
    }
    else if (!aCtx->HasStereoBuffers()
           || myRenderParams.StereoMode != Graphic3d_StereoMode_QuadBuffer)
    {
      const bool wasFailedImm0 = checkWasFailedFbo (myImmediateSceneFbos[0], myMainSceneFbos[0]);
      const bool wasFailedImm1 = checkWasFailedFbo (myImmediateSceneFbos[1], myMainSceneFbos[0]);
      if (!myImmediateSceneFbos[0]->InitLazy (aCtx, *myMainSceneFbos[0], hasTextureMsaa)
       && !wasFailedImm0)
      {
        TCollection_ExtendedString aMsg = TCollection_ExtendedString() + "Error! Immediate FBO (first) "
                                        + printFboFormat (myImmediateSceneFbos[0]) + " initialization has failed";
        aCtx->PushMessage (GL_DEBUG_SOURCE_APPLICATION, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH, aMsg);
      }
      if (!myImmediateSceneFbos[1]->InitLazy (aCtx, *myMainSceneFbos[0], hasTextureMsaa)
       && !wasFailedImm1)
      {
        TCollection_ExtendedString aMsg = TCollection_ExtendedString() + "Error! Immediate FBO (first) "
                                        + printFboFormat (myImmediateSceneFbos[1]) + " initialization has failed";
        aCtx->PushMessage (GL_DEBUG_SOURCE_APPLICATION, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH, aMsg);
      }
      if (!myImmediateSceneFbos[0]->IsValid()
       || !myImmediateSceneFbos[1]->IsValid())
      {
        theProj = Graphic3d_Camera::Projection_Perspective;
      }
    }
  }
  if (!hasXRBlitFbo)
  {
    myXrSceneFbo->Release (aCtx.get());
    myXrSceneFbo->ChangeViewport (0, 0);
  }

  // process PBR environment
  if (myRenderParams.ShadingModel == Graphic3d_TypeOfShadingModel_Pbr
   || myRenderParams.ShadingModel == Graphic3d_TypeOfShadingModel_PbrFacet)
  {
    if (!myPBREnvironment.IsNull()
      && myPBREnvironment->SizesAreDifferent (myRenderParams.PbrEnvPow2Size,
                                              myRenderParams.PbrEnvSpecMapNbLevels))
    {
      myPBREnvironment->Release (aCtx.get());
      myPBREnvironment.Nullify();
      myPBREnvState = OpenGl_PBREnvState_NONEXISTENT;
      myPBREnvRequest = true;
      ++myLightsRevision;
    }

    if (myPBREnvState == OpenGl_PBREnvState_NONEXISTENT
     && aCtx->HasPBR())
    {
      myPBREnvironment = OpenGl_PBREnvironment::Create (aCtx, myRenderParams.PbrEnvPow2Size, myRenderParams.PbrEnvSpecMapNbLevels);
      myPBREnvState = myPBREnvironment.IsNull() ? OpenGl_PBREnvState_UNAVAILABLE : OpenGl_PBREnvState_CREATED;
      if (myPBREnvState == OpenGl_PBREnvState_CREATED)
      {
        Handle(OpenGl_Texture) anEnvLUT;
        static const TCollection_AsciiString THE_SHARED_ENV_LUT_KEY("EnvLUT");
        if (!aCtx->GetResource (THE_SHARED_ENV_LUT_KEY, anEnvLUT))
        {
          bool toConvertHalfFloat = false;

          // GL_RG32F is not texture-filterable format in OpenGL ES without OES_texture_float_linear extension.
          // GL_RG16F is texture-filterable since OpenGL ES 3.0 or OpenGL ES 2.0 + OES_texture_half_float_linear.
          // OpenGL ES 3.0 allows initialization of GL_RG16F from 32-bit float data, but OpenGL ES 2.0 + OES_texture_half_float does not.
          // Note that it is expected that GL_RG16F has enough precision for this table, so that it can be used also on desktop OpenGL.
          const bool hasHalfFloat = aCtx->GraphicsLibrary() == Aspect_GraphicsLibrary_OpenGLES
                                && (aCtx->IsGlGreaterEqual (3, 0) || aCtx->CheckExtension ("GL_OES_texture_half_float_linear"));
          if (aCtx->GraphicsLibrary() == Aspect_GraphicsLibrary_OpenGLES)
          {
            toConvertHalfFloat = !aCtx->IsGlGreaterEqual (3, 0) && hasHalfFloat;
          }

          Image_Format anImgFormat = Image_Format_UNKNOWN;
          if (aCtx->arbTexRG)
          {
            anImgFormat = toConvertHalfFloat ? Image_Format_RGF_half : Image_Format_RGF;
          }
          else
          {
            anImgFormat = toConvertHalfFloat ? Image_Format_RGBAF_half : Image_Format_RGBAF;
          }

          Handle(Image_PixMap) aPixMap = new Image_PixMap();
          if (anImgFormat == Image_Format_RGF)
          {
            aPixMap->InitWrapper (Image_Format_RGF, (Standard_Byte*)Textures_EnvLUT, Textures_EnvLUTSize, Textures_EnvLUTSize);
          }
          else
          {
            aPixMap->InitZero (anImgFormat, Textures_EnvLUTSize, Textures_EnvLUTSize);
            Image_PixMap aPixMapRG;
            aPixMapRG.InitWrapper (Image_Format_RGF, (Standard_Byte*)Textures_EnvLUT, Textures_EnvLUTSize, Textures_EnvLUTSize);
            for (Standard_Size aRowIter = 0; aRowIter < aPixMapRG.SizeY(); ++aRowIter)
            {
              for (Standard_Size aColIter = 0; aColIter < aPixMapRG.SizeX(); ++aColIter)
              {
                const Image_ColorRGF& aPixelRG = aPixMapRG.Value<Image_ColorRGF> (aRowIter, aColIter);
                if (toConvertHalfFloat)
                {
                  NCollection_Vec2<uint16_t>& aPixelRGBA = aPixMap->ChangeValue<NCollection_Vec2<uint16_t>> (aRowIter, aColIter);
                  aPixelRGBA.x() = Image_PixMap::ConvertToHalfFloat (aPixelRG.r());
                  aPixelRGBA.y() = Image_PixMap::ConvertToHalfFloat (aPixelRG.g());
                }
                else
                {
                  Image_ColorRGBAF& aPixelRGBA = aPixMap->ChangeValue<Image_ColorRGBAF> (aRowIter, aColIter);
                  aPixelRGBA.r() = aPixelRG.r();
                  aPixelRGBA.g() = aPixelRG.g();
                }
              }
            }
          }

          OpenGl_TextureFormat aTexFormat = OpenGl_TextureFormat::FindFormat (aCtx, aPixMap->Format(), false);
          if (aCtx->GraphicsLibrary() == Aspect_GraphicsLibrary_OpenGLES
           && aTexFormat.IsValid()
           && hasHalfFloat)
          {
            aTexFormat.SetInternalFormat (aCtx->arbTexRG ? GL_RG16F : GL_RGBA16F);
          }

          Handle(Graphic3d_TextureParams) aParams = new Graphic3d_TextureParams();
          aParams->SetFilter (Graphic3d_TOTF_BILINEAR);
          aParams->SetRepeat (Standard_False);
          aParams->SetTextureUnit (aCtx->PBREnvLUTTexUnit());
          anEnvLUT = new OpenGl_Texture(THE_SHARED_ENV_LUT_KEY, aParams);
          if (!aTexFormat.IsValid()
           || !anEnvLUT->Init (aCtx, aTexFormat, Graphic3d_Vec2i((Standard_Integer)Textures_EnvLUTSize), Graphic3d_TypeOfTexture_2D, aPixMap.get()))
          {
            aCtx->PushMessage (GL_DEBUG_SOURCE_APPLICATION, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH, "Failed allocation of LUT for PBR");
            anEnvLUT.Nullify();
          }
          aCtx->ShareResource (THE_SHARED_ENV_LUT_KEY, anEnvLUT);
        }
        if (!anEnvLUT.IsNull())
        {
          anEnvLUT->Bind (aCtx);
        }
        myWorkspace->ApplyAspects();
      }
    }
    updatePBREnvironment (aCtx);
  }

  // create color and coverage accumulation buffers required for OIT algorithm
  if (toUseOit
   && myRenderParams.TransparencyMethod == Graphic3d_RTM_DEPTH_PEELING_OIT)
  {
    if (myDepthPeelingFbos->BlendBackFboOit()->GetSize() != aRendSize)
    {
      if (myDepthPeelingFbos->BlendBackFboOit()->Init (aCtx, aRendSize, GL_RGBA16F, 0))
      {
        for (int aPairIter = 0; aPairIter < 2; ++aPairIter)
        {
          OpenGl_ColorFormats aColorFormats;
          aColorFormats.Append (GL_RG32F);
          aColorFormats.Append (GL_RGBA16F);
          aColorFormats.Append (GL_RGBA16F);
          myDepthPeelingFbos->DepthPeelFbosOit()[aPairIter]->Init (aCtx, aRendSize, aColorFormats, 0);

          NCollection_Sequence<Handle(OpenGl_Texture)> anAttachments;
          anAttachments.Append (myDepthPeelingFbos->DepthPeelFbosOit()[aPairIter]->ColorTexture (1));
          anAttachments.Append (myDepthPeelingFbos->DepthPeelFbosOit()[aPairIter]->ColorTexture (2));
          myDepthPeelingFbos->FrontBackColorFbosOit()[aPairIter]->InitWrapper (aCtx, anAttachments);
        }
      }
      else
      {
        toUseOit = false;
        aCtx->PushMessage (GL_DEBUG_SOURCE_APPLICATION, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH,
                           "Initialization of float texture framebuffer for use with\n"
                           "  Depth-Peeling order-independent transparency rendering algorithm has failed.");
      }
    }
  }
  if (!toUseOit)
  {
    myDepthPeelingFbos->Release (aCtx.operator->());
  }

  if (toUseOit
   && myRenderParams.TransparencyMethod == Graphic3d_RTM_BLEND_OIT)
  {
    Standard_Integer anFboIt = 0;
    for (; anFboIt < 2; ++anFboIt)
    {
      Handle(OpenGl_FrameBuffer)& aMainSceneFbo          = myMainSceneFbos        [anFboIt];
      Handle(OpenGl_FrameBuffer)& aMainSceneFboOit       = myMainSceneFbosOit     [anFboIt];
      Handle(OpenGl_FrameBuffer)& anImmediateSceneFbo    = myImmediateSceneFbos   [anFboIt];
      Handle(OpenGl_FrameBuffer)& anImmediateSceneFboOit = myImmediateSceneFbosOit[anFboIt];
      if (aMainSceneFbo->IsValid()
       && (aMainSceneFboOit->GetVPSize() != aRendSize
        || aMainSceneFboOit->NbSamples() != aNbSamples))
      {
        Standard_Integer aColorConfig = 0;
        for (;;) // seemly responding to driver limitation (GL_FRAMEBUFFER_UNSUPPORTED)
        {
          if (myFboOitColorConfig.IsEmpty())
          {
            if (!chooseOitColorConfiguration (aCtx, aColorConfig++, myFboOitColorConfig))
            {
              break;
            }
          }
          if (aMainSceneFboOit->Init (aCtx, aRendSize, myFboOitColorConfig, aMainSceneFbo->DepthStencilTexture(), aNbSamples))
          {
            break;
          }
          myFboOitColorConfig.Clear();
        }
        if (!aMainSceneFboOit->IsValid())
        {
          break;
        }
      }
      else if (!aMainSceneFbo->IsValid())
      {
        aMainSceneFboOit->Release (aCtx.operator->());
        aMainSceneFboOit->ChangeViewport (0, 0);
      }

      if (anImmediateSceneFbo->IsValid()
       && (anImmediateSceneFboOit->GetVPSize() != aRendSize
        || anImmediateSceneFboOit->NbSamples() != aNbSamples))
      {
        if (!anImmediateSceneFboOit->Init (aCtx, aRendSize, myFboOitColorConfig,
                                           anImmediateSceneFbo->DepthStencilTexture(), aNbSamples))
        {
          break;
        }
      }
      else if (!anImmediateSceneFbo->IsValid())
      {
        anImmediateSceneFboOit->Release (aCtx.operator->());
        anImmediateSceneFboOit->ChangeViewport (0, 0);
      }
    }
    if (anFboIt == 0) // only the first OIT framebuffer is mandatory
    {
      aCtx->PushMessage (GL_DEBUG_SOURCE_APPLICATION, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH,
                         "Initialization of float texture framebuffer for use with\n"
                         "  blended order-independent transparency rendering algorithm has failed.\n"
                         "  Blended order-independent transparency will not be available.\n");
      if (aNbSamples > 0)
      {
        myToDisableOITMSAA = Standard_True;
      }
      else
      {
        myToDisableOIT     = Standard_True;
      }
      toUseOit = false;
    }
  }
  if (!toUseOit && myMainSceneFbosOit[0]->IsValid())
  {
    myDepthPeelingFbos->Release (aCtx.operator->());
    myMainSceneFbosOit     [0]->Release (aCtx.operator->());
    myMainSceneFbosOit     [1]->Release (aCtx.operator->());
    myImmediateSceneFbosOit[0]->Release (aCtx.operator->());
    myImmediateSceneFbosOit[1]->Release (aCtx.operator->());
    myMainSceneFbosOit     [0]->ChangeViewport (0, 0);
    myMainSceneFbosOit     [1]->ChangeViewport (0, 0);
    myImmediateSceneFbosOit[0]->ChangeViewport (0, 0);
    myImmediateSceneFbosOit[1]->ChangeViewport (0, 0);
  }

  // allocate shadow maps
  const Handle(Graphic3d_LightSet)& aLights = myRenderParams.ShadingModel == Graphic3d_TypeOfShadingModel_Unlit ? myNoShadingLight : myLights;
  if (!aLights.IsNull())
  {
    aLights->UpdateRevision();
  }
  bool toUseShadowMap = myRenderParams.IsShadowEnabled
                     && myRenderParams.ShadowMapResolution > 0
                     && !myLights.IsNull()
                     && myLights->NbCastShadows() > 0
                     && myRenderParams.Method != Graphic3d_RM_RAYTRACING;
  if (toUseShadowMap)
  {
    if (myShadowMaps->Size() != myLights->NbCastShadows())
    {
      myShadowMaps->Release (aCtx.get());
      myShadowMaps->Resize (0, myLights->NbCastShadows() - 1, true);
    }

    const GLint aSamplFrom = GLint(aCtx->ShadowMapTexUnit()) - myLights->NbCastShadows() + 1;
    for (Standard_Integer aShadowIter = 0; aShadowIter < myShadowMaps->Size(); ++aShadowIter)
    {
      Handle(OpenGl_ShadowMap)& aShadow = myShadowMaps->ChangeValue (aShadowIter);
      if (aShadow.IsNull())
      {
        aShadow = new OpenGl_ShadowMap();
      }
      aShadow->SetShadowMapBias (myRenderParams.ShadowMapBias);
      aShadow->Texture()->Sampler()->Parameters()->SetTextureUnit ((Graphic3d_TextureUnit )(aSamplFrom + aShadowIter));

      const Handle(OpenGl_FrameBuffer)& aShadowFbo = aShadow->FrameBuffer();
      if (aShadowFbo->GetVPSizeX() != myRenderParams.ShadowMapResolution
       && toUseShadowMap)
      {
        OpenGl_ColorFormats aDummy;
        if (!aShadowFbo->Init (aCtx, Graphic3d_Vec2i (myRenderParams.ShadowMapResolution), aDummy, myFboDepthFormat, 0))
        {
          toUseShadowMap = false;
        }
      }
    }
  }
  if (!toUseShadowMap && myShadowMaps->IsValid())
  {
    myShadowMaps->Release (aCtx.get());
  }

  return true;
}

//=======================================================================
//function : Redraw
//purpose  :
//=======================================================================
void OpenGl_View::Redraw()
{
  const Standard_Boolean wasDisabledMSAA = myToDisableMSAA;
  const Standard_Boolean hadFboBlit      = myHasFboBlit;
  if (myRenderParams.Method == Graphic3d_RM_RAYTRACING
  && !myCaps->vboDisable
  && !myCaps->keepArrayData)
  {
    // caps are shared across all views, thus we need to invalidate all of them
    // if (myWasRedrawnGL) { myStructureManager->SetDeviceLost(); }
    myDriver->setDeviceLost();
    myCaps->keepArrayData = Standard_True;
  }

  if (!myWorkspace->Activate())
  {
    return;
  }

  // implicitly disable VSync when using HMD composer (can be mirrored in window for debugging)
  myWindow->SetSwapInterval (IsActiveXR());

  ++myFrameCounter;
  const Handle(OpenGl_Context)& aCtx = myWorkspace->GetGlContext();
  aCtx->FrameStats()->FrameStart (myWorkspace->View(), false);
  aCtx->SetLineFeather (myRenderParams.LineFeather);

  const Standard_Integer anSRgbState = aCtx->ToRenderSRGB() ? 1 : 0;
  if (mySRgbState != -1
   && mySRgbState != anSRgbState)
  {
    releaseSrgbResources (aCtx);
    initTextureEnv (aCtx);
  }
  mySRgbState = anSRgbState;
  aCtx->ShaderManager()->UpdateSRgbState();

  // release pending GL resources
  aCtx->ReleaseDelayed();

  // fetch OpenGl context state
  aCtx->FetchState();

  const Graphic3d_StereoMode   aStereoMode  = myRenderParams.StereoMode;
  Graphic3d_Camera::Projection aProjectType = myCamera->ProjectionType();
  if (!prepareFrameBuffers (aProjectType))
  {
    myBackBufferRestored = Standard_False;
    myIsImmediateDrawn   = Standard_False;
    return;
  }

  // draw shadow maps
  if (myShadowMaps->IsValid())
  {
    Standard_Integer aShadowIndex = myShadowMaps->Lower();
    for (Graphic3d_LightSet::Iterator aLightIter (myLights, Graphic3d_LightSet::IterationFilter_ActiveShadowCasters);
         aLightIter.More(); aLightIter.Next())
    {
      const Handle(Graphic3d_CLight)& aLight = aLightIter.Value();
      if (aLight->ToCastShadows())
      {
        const Handle(OpenGl_ShadowMap)& aShadowMap = myShadowMaps->ChangeValue (aShadowIndex);
        aShadowMap->SetLightSource (aLight);
        renderShadowMap (aShadowMap);
        ++aShadowIndex;
      }
    }
    for (; aShadowIndex <= myShadowMaps->Upper(); ++aShadowIndex)
    {
      myShadowMaps->ChangeValue (aShadowIndex)->SetLightSource (Handle(Graphic3d_CLight)());
    }
  }

  OpenGl_FrameBuffer* aFrameBuffer = myFBO.get();
  bool toSwap = aCtx->IsRender()
            && !aCtx->caps->buffersNoSwap
            &&  aFrameBuffer == nullptr
            &&  (!IsActiveXR() || myRenderParams.ToMirrorComposer);
  if ( aFrameBuffer == NULL
   && !aCtx->DefaultFrameBuffer().IsNull()
   &&  aCtx->DefaultFrameBuffer()->IsValid())
  {
    aFrameBuffer = aCtx->DefaultFrameBuffer().operator->();
  }

  if (aProjectType == Graphic3d_Camera::Projection_Stereo)
  {
    OpenGl_FrameBuffer* aMainFbos[2] =
    {
      myMainSceneFbos[0]->IsValid() ? myMainSceneFbos[0].operator->() : NULL,
      myMainSceneFbos[1]->IsValid() ? myMainSceneFbos[1].operator->() : NULL
    };
    OpenGl_FrameBuffer* aMainFbosOit[2] =
    {
      myMainSceneFbosOit[0]->IsValid() ? myMainSceneFbosOit[0].operator->() : NULL,
      myMainSceneFbosOit[1]->IsValid() ? myMainSceneFbosOit[1].operator->() :
        myMainSceneFbosOit[0]->IsValid() ? myMainSceneFbosOit[0].operator->() : NULL
    };

    OpenGl_FrameBuffer* anImmFbos[2] =
    {
      myImmediateSceneFbos[0]->IsValid() ? myImmediateSceneFbos[0].operator->() : NULL,
      myImmediateSceneFbos[1]->IsValid() ? myImmediateSceneFbos[1].operator->() : NULL
    };
    OpenGl_FrameBuffer* anImmFbosOit[2] =
    {
      myImmediateSceneFbosOit[0]->IsValid() ? myImmediateSceneFbosOit[0].operator->() : NULL,
      myImmediateSceneFbosOit[1]->IsValid() ? myImmediateSceneFbosOit[1].operator->() :
        myImmediateSceneFbosOit[0]->IsValid() ? myImmediateSceneFbosOit[0].operator->() : NULL
    };

    if (IsActiveXR())
    {
      // use single frame for both views - caching main scene content makes no sense
      // when head position is expected to be updated each frame redraw with high accuracy
      aMainFbos[1]    = aMainFbos[0];
      aMainFbosOit[1] = aMainFbosOit[0];
      anImmFbos[0]    = aMainFbos[0];
      anImmFbos[1]    = aMainFbos[1];
      anImmFbosOit[0] = aMainFbosOit[0];
      anImmFbosOit[1] = aMainFbosOit[1];
    }
    else if (!myTransientDrawToFront)
    {
      anImmFbos   [0] = aMainFbos   [0];
      anImmFbos   [1] = aMainFbos   [1];
      anImmFbosOit[0] = aMainFbosOit[0];
      anImmFbosOit[1] = aMainFbosOit[1];
    }
    else if (aStereoMode == Graphic3d_StereoMode_SoftPageFlip
          || aStereoMode == Graphic3d_StereoMode_QuadBuffer)
    {
      anImmFbos   [0] = NULL;
      anImmFbos   [1] = NULL;
      anImmFbosOit[0] = NULL;
      anImmFbosOit[1] = NULL;
    }

    aCtx->SetReadDrawBuffer (aStereoMode == Graphic3d_StereoMode_QuadBuffer ? GL_BACK_LEFT : GL_BACK);
    aCtx->SetResolution (myRenderParams.Resolution, myRenderParams.ResolutionRatio(),
                         aMainFbos[0] != NULL ? myRenderParams.RenderResolutionScale : 1.0f);

    redraw (Graphic3d_Camera::Projection_MonoLeftEye, aMainFbos[0], aMainFbosOit[0]);
    myBackBufferRestored = Standard_True;
    myIsImmediateDrawn   = Standard_False;
    aCtx->SetReadDrawBuffer (aStereoMode == Graphic3d_StereoMode_QuadBuffer ? GL_BACK_LEFT : GL_BACK);
    aCtx->SetResolution (myRenderParams.Resolution, myRenderParams.ResolutionRatio(),
                         anImmFbos[0] != NULL ? myRenderParams.RenderResolutionScale : 1.0f);
    if (!redrawImmediate (Graphic3d_Camera::Projection_MonoLeftEye, aMainFbos[0], anImmFbos[0], anImmFbosOit[0]))
    {
      toSwap = false;
    }
    else if (aStereoMode == Graphic3d_StereoMode_SoftPageFlip
          && toSwap
          && myParentView == nullptr)
    {
      aCtx->SwapBuffers();
    }

    if (IsActiveXR())
    {
      // push Left frame to HMD display composer
      OpenGl_FrameBuffer* anXRFbo = myXrSceneFbo->IsValid() ? myXrSceneFbo.get() : aMainFbos[0];
      if (anXRFbo != aMainFbos[0])
      {
        blitBuffers (aMainFbos[0], anXRFbo); // resize or resolve MSAA samples
      }
      const Aspect_GraphicsLibrary aGraphicsLib = aCtx->GraphicsLibrary();
      myXRSession->SubmitEye ((void* )(size_t )anXRFbo->ColorTexture()->TextureId(),
                              aGraphicsLib, Aspect_ColorSpace_sRGB, Aspect_Eye_Left);
    }

    if (aCtx->GraphicsLibrary() != Aspect_GraphicsLibrary_OpenGLES)
    {
      aCtx->SetReadDrawBuffer (aStereoMode == Graphic3d_StereoMode_QuadBuffer ? GL_BACK_RIGHT : GL_BACK);
    }
    aCtx->SetResolution (myRenderParams.Resolution, myRenderParams.ResolutionRatio(),
                         aMainFbos[1] != NULL ? myRenderParams.RenderResolutionScale : 1.0f);

    redraw (Graphic3d_Camera::Projection_MonoRightEye, aMainFbos[1], aMainFbosOit[1]);
    myBackBufferRestored = Standard_True;
    myIsImmediateDrawn   = Standard_False;
    aCtx->SetResolution (myRenderParams.Resolution, myRenderParams.ResolutionRatio(),
                         anImmFbos[1] != NULL ? myRenderParams.RenderResolutionScale : 1.0f);
    if (!redrawImmediate (Graphic3d_Camera::Projection_MonoRightEye, aMainFbos[1], anImmFbos[1], anImmFbosOit[1]))
    {
      toSwap = false;
    }

    if (IsActiveXR())
    {
      // push Right frame to HMD display composer
      OpenGl_FrameBuffer* anXRFbo = myXrSceneFbo->IsValid() ? myXrSceneFbo.get() : aMainFbos[1];
      if (anXRFbo != aMainFbos[1])
      {
        blitBuffers (aMainFbos[1], anXRFbo); // resize or resolve MSAA samples
      }

      const Aspect_GraphicsLibrary aGraphicsLib = aCtx->GraphicsLibrary();
      myXRSession->SubmitEye ((void* )(size_t )anXRFbo->ColorTexture()->TextureId(),
                              aGraphicsLib, Aspect_ColorSpace_sRGB, Aspect_Eye_Right);
      aCtx->core11fwd->glFinish();

      if (myRenderParams.ToMirrorComposer)
      {
        blitBuffers (anXRFbo, aFrameBuffer, myToFlipOutput);
      }
    }
    else if (anImmFbos[0] != NULL)
    {
      aCtx->SetResolution (myRenderParams.Resolution, myRenderParams.ResolutionRatio(), 1.0f);
      drawStereoPair (aFrameBuffer);
    }
  }
  else
  {
    OpenGl_FrameBuffer* aMainFbo    = myMainSceneFbos[0]->IsValid() ? myMainSceneFbos[0].operator->() : aFrameBuffer;
    OpenGl_FrameBuffer* aMainFboOit = myMainSceneFbosOit[0]->IsValid() ? myMainSceneFbosOit[0].operator->() : NULL;
    OpenGl_FrameBuffer* anImmFbo    = aFrameBuffer;
    OpenGl_FrameBuffer* anImmFboOit = NULL;
    if (!myTransientDrawToFront)
    {
      anImmFbo    = aMainFbo;
      anImmFboOit = aMainFboOit;
    }
    else if (myImmediateSceneFbos[0]->IsValid())
    {
      anImmFbo    = myImmediateSceneFbos[0].operator->();
      anImmFboOit = myImmediateSceneFbosOit[0]->IsValid() ? myImmediateSceneFbosOit[0].operator->() : NULL;
    }

    if (aMainFbo == NULL)
    {
      aCtx->SetReadDrawBuffer (GL_BACK);
    }
    aCtx->SetResolution (myRenderParams.Resolution, myRenderParams.ResolutionRatio(),
                         aMainFbo != aFrameBuffer ? myRenderParams.RenderResolutionScale : 1.0f);

    redraw (aProjectType, aMainFbo, aMainFboOit);
    myBackBufferRestored = Standard_True;
    myIsImmediateDrawn   = Standard_False;
    aCtx->SetResolution (myRenderParams.Resolution, myRenderParams.ResolutionRatio(),
                         anImmFbo != aFrameBuffer ? myRenderParams.RenderResolutionScale : 1.0f);
    if (!redrawImmediate (aProjectType, aMainFbo, anImmFbo, anImmFboOit))
    {
      toSwap = false;
    }

    if (anImmFbo != NULL
     && anImmFbo != aFrameBuffer)
    {
      blitBuffers (anImmFbo, aFrameBuffer, myToFlipOutput);
    }
  }

  if (myRenderParams.Method == Graphic3d_RM_RAYTRACING
   && myRenderParams.IsGlobalIlluminationEnabled)
  {
    myAccumFrames++;
  }

  // bind default FBO
  bindDefaultFbo();

  if (wasDisabledMSAA != myToDisableMSAA
   || hadFboBlit      != myHasFboBlit)
  {
    // retry on error
    Redraw();
  }

  // reset state for safety
  aCtx->BindProgram (Handle(OpenGl_ShaderProgram)());
  if (aCtx->caps->ffpEnable)
  {
    aCtx->ShaderManager()->PushState (Handle(OpenGl_ShaderProgram)());
  }

  // Swap the buffers
  if (toSwap
   && myParentView == nullptr)
  {
    aCtx->SwapBuffers();
    if (!myMainSceneFbos[0]->IsValid())
    {
      myBackBufferRestored = Standard_False;
    }
  }
  else
  {
    aCtx->core11fwd->glFlush();
  }

  // reset render mode state
  aCtx->FetchState();
  aCtx->FrameStats()->FrameEnd (myWorkspace->View(), false);

  myWasRedrawnGL = Standard_True;
}

// =======================================================================
// function : RedrawImmediate
// purpose  :
// =======================================================================
void OpenGl_View::RedrawImmediate()
{
  if (!myWorkspace->Activate())
    return;

  // no special handling of HMD display, since it will force full Redraw() due to no frame caching (myBackBufferRestored)
  Handle(OpenGl_Context) aCtx = myWorkspace->GetGlContext();
  if (!myTransientDrawToFront
   || !myBackBufferRestored
   || (aCtx->caps->buffersNoSwap && !myMainSceneFbos[0]->IsValid()))
  {
    Redraw();
    return;
  }

  const Graphic3d_StereoMode   aStereoMode  = myRenderParams.StereoMode;
  Graphic3d_Camera::Projection aProjectType = myCamera->ProjectionType();
  OpenGl_FrameBuffer*          aFrameBuffer = myFBO.get();
  aCtx->FrameStats()->FrameStart (myWorkspace->View(), true);

  if ( aFrameBuffer == NULL
   && !aCtx->DefaultFrameBuffer().IsNull()
   &&  aCtx->DefaultFrameBuffer()->IsValid())
  {
    aFrameBuffer = aCtx->DefaultFrameBuffer().operator->();
  }

  if (aProjectType == Graphic3d_Camera::Projection_Stereo)
  {
    if (myMainSceneFbos[0]->IsValid()
    && !myMainSceneFbos[1]->IsValid())
    {
      aProjectType = Graphic3d_Camera::Projection_Perspective;
    }
  }

  bool toSwap = false;
  if (aProjectType == Graphic3d_Camera::Projection_Stereo)
  {
    OpenGl_FrameBuffer* aMainFbos[2] =
    {
      myMainSceneFbos[0]->IsValid() ? myMainSceneFbos[0].operator->() : NULL,
      myMainSceneFbos[1]->IsValid() ? myMainSceneFbos[1].operator->() : NULL
    };
    OpenGl_FrameBuffer* anImmFbos[2] =
    {
      myImmediateSceneFbos[0]->IsValid() ? myImmediateSceneFbos[0].operator->() : NULL,
      myImmediateSceneFbos[1]->IsValid() ? myImmediateSceneFbos[1].operator->() : NULL
    };
    OpenGl_FrameBuffer* anImmFbosOit[2] =
    {
      myImmediateSceneFbosOit[0]->IsValid() ? myImmediateSceneFbosOit[0].operator->() : NULL,
      myImmediateSceneFbosOit[1]->IsValid() ? myImmediateSceneFbosOit[1].operator->() :
        myImmediateSceneFbosOit[0]->IsValid() ? myImmediateSceneFbosOit[0].operator->() : NULL
    };
    if (aStereoMode == Graphic3d_StereoMode_SoftPageFlip
     || aStereoMode == Graphic3d_StereoMode_QuadBuffer)
    {
      anImmFbos[0]    = NULL;
      anImmFbos[1]    = NULL;
      anImmFbosOit[0] = NULL;
      anImmFbosOit[1] = NULL;
    }

    if (aCtx->arbFBO != NULL)
    {
      aCtx->arbFBO->glBindFramebuffer (GL_FRAMEBUFFER, OpenGl_FrameBuffer::NO_FRAMEBUFFER);
    }
    if (anImmFbos[0] == NULL)
    {
      aCtx->SetReadDrawBuffer (aStereoMode == Graphic3d_StereoMode_QuadBuffer ? GL_BACK_LEFT : GL_BACK);
    }

    aCtx->SetResolution (myRenderParams.Resolution, myRenderParams.ResolutionRatio(),
                         anImmFbos[0] != NULL ? myRenderParams.RenderResolutionScale : 1.0f);
    toSwap = redrawImmediate (Graphic3d_Camera::Projection_MonoLeftEye,
                              aMainFbos[0],
                              anImmFbos[0],
                              anImmFbosOit[0],
                              Standard_True) || toSwap;
    if (aStereoMode == Graphic3d_StereoMode_SoftPageFlip
    &&  toSwap
    &&  myFBO.get() == nullptr
    && !aCtx->caps->buffersNoSwap
    &&  myParentView == nullptr)
    {
      aCtx->SwapBuffers();
    }

    if (aCtx->arbFBO != NULL)
    {
      aCtx->arbFBO->glBindFramebuffer (GL_FRAMEBUFFER, OpenGl_FrameBuffer::NO_FRAMEBUFFER);
    }
    if (anImmFbos[1] == NULL)
    {
      aCtx->SetReadDrawBuffer (aStereoMode == Graphic3d_StereoMode_QuadBuffer ? GL_BACK_RIGHT : GL_BACK);
    }
    aCtx->SetResolution (myRenderParams.Resolution, myRenderParams.ResolutionRatio(),
                         anImmFbos[1] != NULL ? myRenderParams.RenderResolutionScale : 1.0f);
    toSwap = redrawImmediate (Graphic3d_Camera::Projection_MonoRightEye,
                              aMainFbos[1],
                              anImmFbos[1],
                              anImmFbosOit[1],
                              Standard_True) || toSwap;
    if (anImmFbos[0] != NULL)
    {
      drawStereoPair (aFrameBuffer);
    }
  }
  else
  {
    OpenGl_FrameBuffer* aMainFbo = myMainSceneFbos[0]->IsValid() ? myMainSceneFbos[0].operator->() : NULL;
    OpenGl_FrameBuffer* anImmFbo = aFrameBuffer;
    OpenGl_FrameBuffer* anImmFboOit = NULL;
    if (myImmediateSceneFbos[0]->IsValid())
    {
      anImmFbo    = myImmediateSceneFbos[0].operator->();
      anImmFboOit = myImmediateSceneFbosOit[0]->IsValid() ? myImmediateSceneFbosOit[0].operator->() : NULL;
    }
    if (aMainFbo == NULL)
    {
      aCtx->SetReadDrawBuffer (GL_BACK);
    }
    aCtx->SetResolution (myRenderParams.Resolution, myRenderParams.ResolutionRatio(),
                         anImmFbo != aFrameBuffer ? myRenderParams.RenderResolutionScale : 1.0f);
    toSwap = redrawImmediate (aProjectType,
                              aMainFbo,
                              anImmFbo,
                              anImmFboOit,
                              Standard_True) || toSwap;
    if (anImmFbo != NULL
     && anImmFbo != aFrameBuffer)
    {
      blitBuffers (anImmFbo, aFrameBuffer, myToFlipOutput);
    }
  }

  // bind default FBO
  bindDefaultFbo();

  // reset state for safety
  aCtx->BindProgram (Handle(OpenGl_ShaderProgram)());
  if (aCtx->caps->ffpEnable)
  {
    aCtx->ShaderManager()->PushState (Handle(OpenGl_ShaderProgram)());
  }

  if (toSwap
  &&  myFBO.get() == NULL
  && !aCtx->caps->buffersNoSwap
  &&  myParentView == nullptr)
  {
    aCtx->SwapBuffers();
  }
  else
  {
    aCtx->core11fwd->glFlush();
  }
  aCtx->FrameStats()->FrameEnd (myWorkspace->View(), true);

  myWasRedrawnGL = Standard_True;
}

// =======================================================================
// function : redraw
// purpose  :
// =======================================================================
void OpenGl_View::redraw (const Graphic3d_Camera::Projection theProjection,
                          OpenGl_FrameBuffer*                theReadDrawFbo,
                          OpenGl_FrameBuffer*                theOitAccumFbo)
{
  Handle(OpenGl_Context) aCtx = myWorkspace->GetGlContext();
  if (theReadDrawFbo != NULL)
  {
    theReadDrawFbo->BindBuffer    (aCtx);
    theReadDrawFbo->SetupViewport (aCtx);
  }
  else
  {
    const Standard_Integer aViewport[4] = { 0, 0, myWindow->Width(), myWindow->Height() };
    aCtx->ResizeViewport (aViewport);
  }

  // request reset of material
  aCtx->ShaderManager()->UpdateMaterialState();

  myWorkspace->UseZBuffer()    = Standard_True;
  myWorkspace->UseDepthWrite() = Standard_True;
  GLbitfield toClear = GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT;
  aCtx->core11fwd->glDepthFunc (GL_LEQUAL);
  aCtx->core11fwd->glDepthMask (GL_TRUE);
  aCtx->core11fwd->glEnable (GL_DEPTH_TEST);

  aCtx->core11fwd->glClearDepth (1.0);

  const OpenGl_Vec4 aBgColor = aCtx->Vec4FromQuantityColor (myBgColor);
  aCtx->SetColorMaskRGBA (NCollection_Vec4<bool> (true)); // force writes into all components, including alpha
  aCtx->core11fwd->glClearColor (aBgColor.r(), aBgColor.g(), aBgColor.b(), aCtx->caps->buffersOpaqueAlpha ? 1.0f : 0.0f);
  aCtx->core11fwd->glClear (toClear);
  aCtx->SetColorMask (true); // restore default alpha component write state

  render (theProjection, theReadDrawFbo, theOitAccumFbo, Standard_False);
}

// =======================================================================
// function : redrawImmediate
// purpose  :
// =======================================================================
bool OpenGl_View::redrawImmediate (const Graphic3d_Camera::Projection theProjection,
                                   OpenGl_FrameBuffer*                theReadFbo,
                                   OpenGl_FrameBuffer*                theDrawFbo,
                                   OpenGl_FrameBuffer*                theOitAccumFbo,
                                   const Standard_Boolean             theIsPartialUpdate)
{
  const Handle(OpenGl_Context)& aCtx = myWorkspace->GetGlContext();
  GLboolean toCopyBackToFront = GL_FALSE;
  if (theDrawFbo == theReadFbo
   && theDrawFbo != NULL
   && theDrawFbo->IsValid())
  {
    myBackBufferRestored = Standard_False;
    theDrawFbo->BindBuffer (aCtx);
  }
  else if (theReadFbo != NULL
        && theReadFbo->IsValid()
        && aCtx->IsRender())
  {
    if (!blitBuffers (theReadFbo, theDrawFbo))
    {
      return true;
    }
  }
  else if (theDrawFbo == NULL)
  {
    if (aCtx->GraphicsLibrary() != Aspect_GraphicsLibrary_OpenGLES)
    {
      aCtx->core11fwd->glGetBooleanv (GL_DOUBLEBUFFER, &toCopyBackToFront);
    }
    if (toCopyBackToFront
     && myTransientDrawToFront)
    {
      if (!HasImmediateStructures()
       && !theIsPartialUpdate)
      {
        // prefer Swap Buffers within Redraw in compatibility mode (without FBO)
        return true;
      }
      if (!copyBackToFront())
      {
        toCopyBackToFront    = GL_FALSE;
        myBackBufferRestored = Standard_False;
      }
    }
    else
    {
      toCopyBackToFront    = GL_FALSE;
      myBackBufferRestored = Standard_False;
    }
  }
  else
  {
    myBackBufferRestored = Standard_False;
  }
  myIsImmediateDrawn = Standard_True;

  myWorkspace->UseZBuffer()    = Standard_True;
  myWorkspace->UseDepthWrite() = Standard_True;
  aCtx->core11fwd->glDepthFunc (GL_LEQUAL);
  aCtx->core11fwd->glDepthMask (GL_TRUE);
  aCtx->core11fwd->glEnable (GL_DEPTH_TEST);
  aCtx->core11fwd->glClearDepth (1.0);

  render (theProjection, theDrawFbo, theOitAccumFbo, Standard_True);

  blitSubviews (theProjection, theDrawFbo);

  return !toCopyBackToFront;
}

// =======================================================================
// function : blitSubviews
// purpose  :
// =======================================================================
bool OpenGl_View::blitSubviews (const Graphic3d_Camera::Projection ,
                                OpenGl_FrameBuffer* theDrawFbo)
{
  const Handle(OpenGl_Context)& aCtx = myWorkspace->GetGlContext();
  if (aCtx->arbFBOBlit == nullptr)
  {
    return false;
  }

  bool isChanged = false;
  for (const Handle(Graphic3d_CView)& aChildIter : mySubviews)
  {
    OpenGl_View* aSubView = dynamic_cast<OpenGl_View*> (aChildIter.get());
    if (!aSubView->IsActive())
    {
      continue;
    }

    const Handle(OpenGl_FrameBuffer)& aChildFbo = !aSubView->myImmediateSceneFbos[0].IsNull()
                                                 ? aSubView->myImmediateSceneFbos[0]
                                                 : aSubView->myMainSceneFbos[0];
    if (aChildFbo.IsNull() || !aChildFbo->IsValid())
    {
      continue;
    }

    aChildFbo->BindReadBuffer (aCtx);
    if (theDrawFbo != NULL
     && theDrawFbo->IsValid())
    {
      theDrawFbo->BindDrawBuffer (aCtx);
    }
    else
    {
      aCtx->arbFBO->glBindFramebuffer (GL_DRAW_FRAMEBUFFER, OpenGl_FrameBuffer::NO_FRAMEBUFFER);
      aCtx->SetFrameBufferSRGB (false);
    }

    Graphic3d_Vec2i aWinSize (aCtx->Viewport()[2], aCtx->Viewport()[3]); //aSubView->GlWindow()->PlatformWindow()->Dimensions();
    Graphic3d_Vec2i aSubViewSize = aChildFbo->GetVPSize();
    Graphic3d_Vec2i aSubViewPos  = aSubView->SubviewTopLeft();
    Graphic3d_Vec2i aDestSize    = aSubViewSize;
    if (aSubView->RenderingParams().RenderResolutionScale != 1.0f)
    {
      aDestSize = Graphic3d_Vec2i (Graphic3d_Vec2d(aDestSize) / Graphic3d_Vec2d(aSubView->RenderingParams().RenderResolutionScale));
    }
    aSubViewPos.y() = aWinSize.y() - aDestSize.y() - aSubViewPos.y();

    const GLint aFilterGl = aDestSize == aSubViewSize ? GL_NEAREST : GL_LINEAR;
    aCtx->arbFBOBlit->glBlitFramebuffer (0, 0, aSubViewSize.x(), aSubViewSize.y(),
                                         aSubViewPos.x(), aSubViewPos.y(), aSubViewPos.x() + aDestSize.x(), aSubViewPos.y() + aDestSize.y(),
                                         GL_COLOR_BUFFER_BIT, aFilterGl);
    const int anErr = aCtx->core11fwd->glGetError();
    if (anErr != GL_NO_ERROR)
    {
      TCollection_ExtendedString aMsg = TCollection_ExtendedString() + "FBO blitting has failed [Error " + OpenGl_Context::FormatGlError (anErr) + "]\n"
                                      + "  Please check your graphics driver settings or try updating driver.";
      if (aChildFbo->NbSamples() != 0)
      {
        myToDisableMSAA = true;
        aMsg += "\n  MSAA settings should not be overridden by driver!";
      }
      aCtx->PushMessage (GL_DEBUG_SOURCE_APPLICATION, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH, aMsg);
    }

    if (theDrawFbo != NULL
     && theDrawFbo->IsValid())
    {
      theDrawFbo->BindBuffer (aCtx);
    }
    else
    {
      aCtx->arbFBO->glBindFramebuffer (GL_FRAMEBUFFER, OpenGl_FrameBuffer::NO_FRAMEBUFFER);
      aCtx->SetFrameBufferSRGB (false);
    }
    isChanged = true;
  }

  return isChanged;
}

//=======================================================================
//function : renderShadowMap
//purpose  :
//=======================================================================
void OpenGl_View::renderShadowMap (const Handle(OpenGl_ShadowMap)& theShadowMap)
{
  const Handle(OpenGl_Context)& aCtx = myWorkspace->GetGlContext();
  if (!theShadowMap->UpdateCamera (*this))
  {
    return;
  }

  myBVHSelector.SetViewVolume (theShadowMap->Camera());
  myBVHSelector.SetViewportSize (myWindow->Width(), myWindow->Height(), myRenderParams.ResolutionRatio());
  myBVHSelector.CacheClipPtsProjections();

  myLocalOrigin.SetCoord (0.0, 0.0, 0.0);
  aCtx->SetCamera (theShadowMap->Camera());
  aCtx->ProjectionState.SetCurrent (theShadowMap->Camera()->ProjectionMatrixF());
  aCtx->ApplyProjectionMatrix();

  aCtx->ShaderManager()->UpdateMaterialState();
  aCtx->ShaderManager()->UpdateModelWorldStateTo (OpenGl_Mat4());
  aCtx->ShaderManager()->SetShadingModel (Graphic3d_TypeOfShadingModel_Unlit);

  const Handle(OpenGl_FrameBuffer)& aShadowBuffer = theShadowMap->FrameBuffer();
  aShadowBuffer->BindBuffer    (aCtx);
  aShadowBuffer->SetupViewport (aCtx);

  aCtx->SetColorMask (false);
  aCtx->SetAllowSampleAlphaToCoverage (false);
  aCtx->SetSampleAlphaToCoverage (false);

  myWorkspace->UseZBuffer()    = true;
  myWorkspace->UseDepthWrite() = true;
  aCtx->core11fwd->glDepthFunc (GL_LEQUAL);
  aCtx->core11fwd->glDepthMask (GL_TRUE);
  aCtx->core11fwd->glEnable (GL_DEPTH_TEST);
  aCtx->core11fwd->glClearDepth (1.0);
  aCtx->core11fwd->glClear (GL_DEPTH_BUFFER_BIT);

  Graphic3d_Camera::Projection aProjection = theShadowMap->LightSource()->Type() == Graphic3d_TypeOfLightSource_Directional
                                           ? Graphic3d_Camera::Projection_Orthographic
                                           : Graphic3d_Camera::Projection_Perspective;
  myWorkspace->SetRenderFilter (myWorkspace->RenderFilter() | OpenGl_RenderFilter_SkipTrsfPersistence);
  renderScene (aProjection, aShadowBuffer.get(), NULL, false);
  myWorkspace->SetRenderFilter (myWorkspace->RenderFilter() & ~(Standard_Integer)OpenGl_RenderFilter_SkipTrsfPersistence);

  aCtx->SetColorMask (true);
  myWorkspace->ResetAppliedAspect();
  aCtx->BindProgram (Handle(OpenGl_ShaderProgram)());

//Image_AlienPixMap anImage; anImage.InitZero (Image_Format_Gray, aShadowBuffer->GetVPSizeX(), aShadowBuffer->GetVPSizeY());
//OpenGl_FrameBuffer::BufferDump (aCtx, aShadowBuffer, anImage, Graphic3d_BT_Depth);
//anImage.Save (TCollection_AsciiString ("shadow") + theShadowMap->Texture()->Sampler()->Parameters()->TextureUnit() + ".png");

  bindDefaultFbo();
}

//=======================================================================
//function : Render
//purpose  :
//=======================================================================
void OpenGl_View::render (Graphic3d_Camera::Projection theProjection,
                          OpenGl_FrameBuffer*          theOutputFBO,
                          OpenGl_FrameBuffer*          theOitAccumFbo,
                          const Standard_Boolean       theToDrawImmediate)
{
  // ==================================
  //      Step 1: Prepare for render
  // ==================================

  const Handle(OpenGl_Context)& aContext = myWorkspace->GetGlContext();
  aContext->SetAllowSampleAlphaToCoverage (myRenderParams.ToEnableAlphaToCoverage
                                        && theOutputFBO != NULL
                                        && theOutputFBO->NbSamples() != 0);

  // Disable current clipping planes
  if (aContext->core11ffp != NULL)
  {
    const Standard_Integer aMaxPlanes = aContext->MaxClipPlanes();
    for (Standard_Integer aClipPlaneId = GL_CLIP_PLANE0; aClipPlaneId < GL_CLIP_PLANE0 + aMaxPlanes; ++aClipPlaneId)
    {
      aContext->core11fwd->glDisable (aClipPlaneId);
    }
  }

  // update states of OpenGl_BVHTreeSelector (frustum culling algorithm);
  // note that we pass here window dimensions ignoring Graphic3d_RenderingParams::RenderResolutionScale
  myBVHSelector.SetViewVolume (myCamera);
  myBVHSelector.SetViewportSize (myWindow->Width(), myWindow->Height(), myRenderParams.ResolutionRatio());
  myBVHSelector.CacheClipPtsProjections();

  const Handle(OpenGl_ShaderManager)& aManager = aContext->ShaderManager();
  const Handle(Graphic3d_LightSet)&   aLights  = myRenderParams.ShadingModel == Graphic3d_TypeOfShadingModel_Unlit ? myNoShadingLight : myLights;
  Standard_Size aLightsRevision = 0;
  if (!aLights.IsNull())
  {
    aLightsRevision = aLights->UpdateRevision();
  }
  if (StateInfo (myCurrLightSourceState, aManager->LightSourceState().Index()) != myLastLightSourceState
   || aLightsRevision != myLightsRevision)
  {
    myLightsRevision = aLightsRevision;
    aManager->UpdateLightSourceStateTo (aLights, SpecIBLMapLevels(), myShadowMaps->IsValid() ? myShadowMaps : Handle(OpenGl_ShadowMapArray)());
    myLastLightSourceState = StateInfo (myCurrLightSourceState, aManager->LightSourceState().Index());
  }

  // Update matrices if camera has changed.
  Graphic3d_WorldViewProjState aWVPState = myCamera->WorldViewProjState();
  if (myWorldViewProjState != aWVPState)
  {
    myAccumFrames = 0;
    myWorldViewProjState = aWVPState;
  }

  myLocalOrigin.SetCoord (0.0, 0.0, 0.0);
  aContext->SetCamera (myCamera);
  if (aManager->ModelWorldState().Index() == 0)
  {
    aContext->ShaderManager()->UpdateModelWorldStateTo (OpenGl_Mat4());
  }

  // ====================================
  //      Step 2: Redraw background
  // ====================================

  // Render background
  if (!theToDrawImmediate)
  {
    drawBackground (myWorkspace, theProjection);
  }

  // Switch off lighting by default
  if (aContext->core11ffp != NULL
   && aContext->caps->ffpEnable)
  {
    aContext->core11fwd->glDisable (GL_LIGHTING);
  }

  // =================================
  //      Step 3: Redraw main plane
  // =================================

  // if the view is scaled normal vectors are scaled to unit
  // length for correct displaying of shaded objects
  const gp_Pnt anAxialScale = aContext->Camera()->AxialScale();
  if (anAxialScale.X() != 1.F ||
      anAxialScale.Y() != 1.F ||
      anAxialScale.Z() != 1.F)
  {
    aContext->SetGlNormalizeEnabled (Standard_True);
  }
  else
  {
    aContext->SetGlNormalizeEnabled (Standard_False);
  }

  aManager->SetShadingModel (OpenGl_ShaderManager::PBRShadingModelFallback (myRenderParams.ShadingModel, checkPBRAvailability()));

  // Redraw 3d scene
  if (theProjection == Graphic3d_Camera::Projection_MonoLeftEye)
  {
    aContext->ProjectionState.SetCurrent (aContext->Camera()->ProjectionStereoLeftF());
    aContext->ApplyProjectionMatrix();
  }
  else if (theProjection == Graphic3d_Camera::Projection_MonoRightEye)
  {
    aContext->ProjectionState.SetCurrent (aContext->Camera()->ProjectionStereoRightF());
    aContext->ApplyProjectionMatrix();
  }

  myWorkspace->SetEnvironmentTexture (myTextureEnv);

  const bool hasShadowMap = aContext->ShaderManager()->LightSourceState().HasShadowMaps();
  if (hasShadowMap)
  {
    for (Standard_Integer aShadowIter = myShadowMaps->Lower(); aShadowIter <= myShadowMaps->Upper(); ++aShadowIter)
    {
      const Handle(OpenGl_ShadowMap)& aShadow = myShadowMaps->Value (aShadowIter);
      aShadow->Texture()->Bind (aContext);
    }
  }

  renderScene (theProjection, theOutputFBO, theOitAccumFbo, theToDrawImmediate);

  if (hasShadowMap)
  {
    for (Standard_Integer aShadowIter = myShadowMaps->Lower(); aShadowIter <= myShadowMaps->Upper(); ++aShadowIter)
    {
      const Handle(OpenGl_ShadowMap)& aShadow = myShadowMaps->Value (aShadowIter);
      aShadow->Texture()->Unbind (aContext);
    }
    if (aContext->core15fwd != NULL)
    {
      aContext->core15fwd->glActiveTexture (GL_TEXTURE0);
    }
  }

  myWorkspace->SetEnvironmentTexture (Handle(OpenGl_TextureSet)());

  // ===============================
  //      Step 4: Trihedron
  // ===============================

  // Resetting GL parameters according to the default aspects
  // in order to synchronize GL state with the graphic driver state
  // before drawing auxiliary stuff (trihedrons, overlayer)
  myWorkspace->ResetAppliedAspect();

  // Render trihedron
  if (!theToDrawImmediate)
  {
    renderTrihedron (myWorkspace);
  }
  else
  {
    renderFrameStats();
  }

  myWorkspace->ResetAppliedAspect();
  aContext->SetAllowSampleAlphaToCoverage (false);
  aContext->SetSampleAlphaToCoverage (false);

  // reset FFP state for safety
  aContext->BindProgram (Handle(OpenGl_ShaderProgram)());
  if (aContext->caps->ffpEnable)
  {
    aContext->ShaderManager()->PushState (Handle(OpenGl_ShaderProgram)());
  }
}

// =======================================================================
// function : InvalidateBVHData
// purpose  :
// =======================================================================
void OpenGl_View::InvalidateBVHData (const Graphic3d_ZLayerId theLayerId)
{
  myZLayers.InvalidateBVHData (theLayerId);
}

//=======================================================================
//function : renderStructs
//purpose  :
//=======================================================================
void OpenGl_View::renderStructs (Graphic3d_Camera::Projection theProjection,
                                 OpenGl_FrameBuffer*          theReadDrawFbo,
                                 OpenGl_FrameBuffer*          theOitAccumFbo,
                                 const Standard_Boolean       theToDrawImmediate)
{
  if (myIsSubviewComposer)
  {
    return;
  }

  myZLayers.UpdateCulling (myWorkspace, theToDrawImmediate);
  if (myZLayers.NbStructures() <= 0)
  {
    return;
  }

  Handle(OpenGl_Context) aCtx = myWorkspace->GetGlContext();
  Standard_Boolean toRenderGL = theToDrawImmediate ||
    myRenderParams.Method != Graphic3d_RM_RAYTRACING ||
    myRaytraceInitStatus == OpenGl_RT_FAIL ||
    aCtx->IsFeedback();

  if (!toRenderGL)
  {
    const Graphic3d_Vec2i aSizeXY = theReadDrawFbo != NULL
                                  ? theReadDrawFbo->GetVPSize()
                                  : Graphic3d_Vec2i (myWindow->Width(), myWindow->Height());

    toRenderGL = !initRaytraceResources (aSizeXY.x(), aSizeXY.y(), aCtx)
              || !updateRaytraceGeometry (OpenGl_GUM_CHECK, myId, aCtx);

    toRenderGL |= !myIsRaytraceDataValid; // if no ray-trace data use OpenGL

    if (!toRenderGL)
    {
      myOpenGlFBO ->InitLazy (aCtx, aSizeXY, myFboColorFormat, myFboDepthFormat, 0);
      if (theReadDrawFbo != NULL)
      {
        theReadDrawFbo->UnbindBuffer (aCtx);
      }

      // Prepare preliminary OpenGL output
      if (aCtx->arbFBOBlit != NULL)
      {
        // Render bottom OSD layer
        myZLayers.Render (myWorkspace, theToDrawImmediate, OpenGl_LF_Bottom, theReadDrawFbo, theOitAccumFbo);

        const Standard_Integer aPrevFilter = myWorkspace->RenderFilter() & ~(Standard_Integer )(OpenGl_RenderFilter_NonRaytraceableOnly);
        myWorkspace->SetRenderFilter (aPrevFilter | OpenGl_RenderFilter_NonRaytraceableOnly);
        {
          if (theReadDrawFbo != NULL)
          {
            theReadDrawFbo->BindDrawBuffer (aCtx);
          }
          else
          {
            aCtx->arbFBO->glBindFramebuffer (GL_DRAW_FRAMEBUFFER, 0);
            aCtx->SetFrameBufferSRGB (false);
          }

          // Render non-polygonal elements in default layer
          myZLayers.Render (myWorkspace, theToDrawImmediate, OpenGl_LF_RayTracable, theReadDrawFbo, theOitAccumFbo);
        }
        myWorkspace->SetRenderFilter (aPrevFilter);
      }

      if (theReadDrawFbo != NULL)
      {
        theReadDrawFbo->BindBuffer (aCtx);
      }
      else
      {
        aCtx->arbFBO->glBindFramebuffer (GL_FRAMEBUFFER, 0);
        aCtx->SetFrameBufferSRGB (false);
      }

      // Reset OpenGl aspects state to default to avoid enabling of
      // backface culling which is not supported in ray-tracing.
      myWorkspace->ResetAppliedAspect();

      // Ray-tracing polygonal primitive arrays
      raytrace (aSizeXY.x(), aSizeXY.y(), theProjection, theReadDrawFbo, aCtx);

      // Render upper (top and topmost) OpenGL layers
      myZLayers.Render (myWorkspace, theToDrawImmediate, OpenGl_LF_Upper, theReadDrawFbo, theOitAccumFbo);
    }
  }

  // Redraw 3D scene using OpenGL in standard
  // mode or in case of ray-tracing failure
  if (toRenderGL)
  {
    myZLayers.Render (myWorkspace, theToDrawImmediate, OpenGl_LF_All, theReadDrawFbo, theOitAccumFbo);

    // Set flag that scene was redrawn by standard pipeline
    myWasRedrawnGL = Standard_True;
  }
}

//=======================================================================
//function : renderTrihedron
//purpose  :
//=======================================================================
void OpenGl_View::renderTrihedron (const Handle(OpenGl_Workspace) &theWorkspace)
{
  if (myToShowGradTrihedron)
  {
    myGraduatedTrihedron.Render (theWorkspace);
  }
}

//=======================================================================
//function : renderFrameStats
//purpose  :
//=======================================================================
void OpenGl_View::renderFrameStats()
{
  if (myRenderParams.ToShowStats
   && myRenderParams.CollectedStats != Graphic3d_RenderingParams::PerfCounters_NONE)
  {
    myFrameStatsPrs.Update (myWorkspace);
    myFrameStatsPrs.Render (myWorkspace);
  }
}

// =======================================================================
// function : Invalidate
// purpose  :
// =======================================================================
void OpenGl_View::Invalidate()
{
  myBackBufferRestored = Standard_False;
}

//=======================================================================
//function : renderScene
//purpose  :
//=======================================================================
void OpenGl_View::renderScene (Graphic3d_Camera::Projection theProjection,
                               OpenGl_FrameBuffer*          theReadDrawFbo,
                               OpenGl_FrameBuffer*          theOitAccumFbo,
                               const Standard_Boolean       theToDrawImmediate)
{
  const Handle(OpenGl_Context)& aContext = myWorkspace->GetGlContext();

  // Specify clipping planes in view transformation space
  aContext->ChangeClipping().Reset (myClipPlanes);
  if (!myClipPlanes.IsNull()
   && !myClipPlanes->IsEmpty())
  {
    aContext->ShaderManager()->UpdateClippingState();
  }

  renderStructs (theProjection, theReadDrawFbo, theOitAccumFbo, theToDrawImmediate);
  aContext->BindTextures (Handle(OpenGl_TextureSet)(), Handle(OpenGl_ShaderProgram)());

  // Apply restored view matrix.
  aContext->ApplyWorldViewMatrix();

  aContext->ChangeClipping().Reset (Handle(Graphic3d_SequenceOfHClipPlane)());
  if (!myClipPlanes.IsNull()
   && !myClipPlanes->IsEmpty())
  {
    aContext->ShaderManager()->RevertClippingState();
  }
}

// =======================================================================
// function : bindDefaultFbo
// purpose  :
// =======================================================================
void OpenGl_View::bindDefaultFbo (OpenGl_FrameBuffer* theCustomFbo)
{
  Handle(OpenGl_Context) aCtx = myWorkspace->GetGlContext();
  OpenGl_FrameBuffer* anFbo = (theCustomFbo != NULL && theCustomFbo->IsValid())
                            ?  theCustomFbo
                            : (!aCtx->DefaultFrameBuffer().IsNull()
                             && aCtx->DefaultFrameBuffer()->IsValid()
                              ? aCtx->DefaultFrameBuffer().operator->()
                              : NULL);
  if (anFbo != NULL)
  {
    anFbo->BindBuffer (aCtx);
    anFbo->SetupViewport (aCtx);
  }
  else
  {
    if (aCtx->GraphicsLibrary() != Aspect_GraphicsLibrary_OpenGLES)
    {
      aCtx->SetReadDrawBuffer (GL_BACK);
    }
    else if (aCtx->arbFBO != NULL)
    {
      aCtx->arbFBO->glBindFramebuffer (GL_FRAMEBUFFER, OpenGl_FrameBuffer::NO_FRAMEBUFFER);
    }

    const Standard_Integer aViewport[4] = { 0, 0, myWindow->Width(), myWindow->Height() };
    aCtx->ResizeViewport (aViewport);
  }
}

// =======================================================================
// function : initBlitQuad
// purpose  :
// =======================================================================
OpenGl_VertexBuffer* OpenGl_View::initBlitQuad (const Standard_Boolean theToFlip)
{
  OpenGl_VertexBuffer* aVerts = NULL;
  if (!theToFlip)
  {
    aVerts = &myFullScreenQuad;
    if (!aVerts->IsValid())
    {
      OpenGl_Vec4 aQuad[4] =
      {
        OpenGl_Vec4( 1.0f, -1.0f, 1.0f, 0.0f),
        OpenGl_Vec4( 1.0f,  1.0f, 1.0f, 1.0f),
        OpenGl_Vec4(-1.0f, -1.0f, 0.0f, 0.0f),
        OpenGl_Vec4(-1.0f,  1.0f, 0.0f, 1.0f)
      };
      aVerts->Init (myWorkspace->GetGlContext(), 4, 4, aQuad[0].GetData());
    }
  }
  else
  {
    aVerts = &myFullScreenQuadFlip;
    if (!aVerts->IsValid())
    {
      OpenGl_Vec4 aQuad[4] =
      {
        OpenGl_Vec4( 1.0f, -1.0f, 1.0f, 1.0f),
        OpenGl_Vec4( 1.0f,  1.0f, 1.0f, 0.0f),
        OpenGl_Vec4(-1.0f, -1.0f, 0.0f, 1.0f),
        OpenGl_Vec4(-1.0f,  1.0f, 0.0f, 0.0f)
      };
      aVerts->Init (myWorkspace->GetGlContext(), 4, 4, aQuad[0].GetData());
    }
  }
  return aVerts;
}

// =======================================================================
// function : blitBuffers
// purpose  :
// =======================================================================
bool OpenGl_View::blitBuffers (OpenGl_FrameBuffer*    theReadFbo,
                               OpenGl_FrameBuffer*    theDrawFbo,
                               const Standard_Boolean theToFlip)
{
  Handle(OpenGl_Context) aCtx = myWorkspace->GetGlContext();
  const Standard_Integer aReadSizeX = theReadFbo != NULL ? theReadFbo->GetVPSizeX() : myWindow->Width();
  const Standard_Integer aReadSizeY = theReadFbo != NULL ? theReadFbo->GetVPSizeY() : myWindow->Height();
  const Standard_Integer aDrawSizeX = theDrawFbo != NULL ? theDrawFbo->GetVPSizeX() : myWindow->Width();
  const Standard_Integer aDrawSizeY = theDrawFbo != NULL ? theDrawFbo->GetVPSizeY() : myWindow->Height();
  if (theReadFbo == NULL || aCtx->IsFeedback())
  {
    return false;
  }
  else if (theReadFbo == theDrawFbo)
  {
    return true;
  }

  // clear destination before blitting
  if (theDrawFbo != NULL
  &&  theDrawFbo->IsValid())
  {
    theDrawFbo->BindBuffer (aCtx);
  }
  else
  {
    aCtx->arbFBO->glBindFramebuffer (GL_FRAMEBUFFER, OpenGl_FrameBuffer::NO_FRAMEBUFFER);
    aCtx->SetFrameBufferSRGB (false);
  }
  const Standard_Integer aViewport[4] = { 0, 0, aDrawSizeX, aDrawSizeY };
  aCtx->ResizeViewport (aViewport);

  aCtx->SetColorMaskRGBA (NCollection_Vec4<bool> (true)); // force writes into all components, including alpha
  aCtx->core20fwd->glClearDepth (1.0);
  aCtx->core20fwd->glClearColor (0.0f, 0.0f, 0.0f, aCtx->caps->buffersOpaqueAlpha ? 1.0f : 0.0f);
  aCtx->core20fwd->glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
  aCtx->SetColorMask (true); // restore default alpha component write state

  const bool toApplyGamma = aCtx->ToRenderSRGB() != aCtx->IsFrameBufferSRGB();
  bool toDrawTexture = true;
  if (aCtx->arbFBOBlit != NULL)
  {
    if (!toApplyGamma
     &&  theReadFbo->NbSamples() != 0)
    {
      toDrawTexture = false;
    }
    if (theReadFbo->IsColorRenderBuffer())
    {
      // render buffers could be resolved only via glBlitFramebuffer()
      toDrawTexture = false;
    }
  }

  if (!toDrawTexture)
  {
    GLbitfield aCopyMask = 0;
    theReadFbo->BindReadBuffer (aCtx);
    if (theDrawFbo != NULL
     && theDrawFbo->IsValid())
    {
      theDrawFbo->BindDrawBuffer (aCtx);
      if (theDrawFbo->HasColor()
       && theReadFbo->HasColor())
      {
        aCopyMask |= GL_COLOR_BUFFER_BIT;
      }
      if (theDrawFbo->HasDepth()
       && theReadFbo->HasDepth())
      {
        aCopyMask |= GL_DEPTH_BUFFER_BIT;
      }
    }
    else
    {
      if (theReadFbo->HasColor())
      {
        aCopyMask |= GL_COLOR_BUFFER_BIT;
      }
      if (theReadFbo->HasDepth())
      {
        aCopyMask |= GL_DEPTH_BUFFER_BIT;
      }
      aCtx->arbFBO->glBindFramebuffer (GL_DRAW_FRAMEBUFFER, OpenGl_FrameBuffer::NO_FRAMEBUFFER);
      aCtx->SetFrameBufferSRGB (false);
    }

    // we don't copy stencil buffer here... does it matter for performance?
    aCtx->arbFBOBlit->glBlitFramebuffer (0, 0, aReadSizeX, aReadSizeY,
                                         0, 0, aDrawSizeX, aDrawSizeY,
                                         aCopyMask, GL_NEAREST);
    const int anErr = aCtx->core11fwd->glGetError();
    if (anErr != GL_NO_ERROR)
    {
      // glBlitFramebuffer() might fail in several cases:
      // - Both FBOs have MSAA and they are samples number does not match.
      //   OCCT checks that this does not happen,
      //   however some graphics drivers provide an option for overriding MSAA.
      //   In this case window MSAA might be non-zero (and application can not check it)
      //   and might not match MSAA of our offscreen FBOs.
      // - Pixel formats of FBOs do not match.
      //   This also might happen with window has pixel format,
      //   e.g. Mesa fails blitting RGBA8 -> RGB8 while other drivers support this conversion.
      TCollection_ExtendedString aMsg = TCollection_ExtendedString() + "FBO blitting has failed [Error " + OpenGl_Context::FormatGlError (anErr) + "]\n"
                                      + "  Please check your graphics driver settings or try updating driver.";
      if (theReadFbo->NbSamples() != 0)
      {
        myToDisableMSAA = true;
        aMsg += "\n  MSAA settings should not be overridden by driver!";
      }
      aCtx->PushMessage (GL_DEBUG_SOURCE_APPLICATION, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH, aMsg);
    }

    if (theDrawFbo != NULL
     && theDrawFbo->IsValid())
    {
      theDrawFbo->BindBuffer (aCtx);
    }
    else
    {
      aCtx->arbFBO->glBindFramebuffer (GL_FRAMEBUFFER, OpenGl_FrameBuffer::NO_FRAMEBUFFER);
      aCtx->SetFrameBufferSRGB (false);
    }
  }
  else
  {
    aCtx->core20fwd->glDepthFunc (GL_ALWAYS);
    aCtx->core20fwd->glDepthMask (GL_TRUE);
    aCtx->core20fwd->glEnable (GL_DEPTH_TEST);
    if (aCtx->GraphicsLibrary() == Aspect_GraphicsLibrary_OpenGLES
    && !aCtx->IsGlGreaterEqual (3, 0)
    && !aCtx->extFragDepth)
    {
      aCtx->core20fwd->glDisable (GL_DEPTH_TEST);
    }

    aCtx->BindTextures (Handle(OpenGl_TextureSet)(), Handle(OpenGl_ShaderProgram)());

    const Graphic3d_TypeOfTextureFilter aFilter = (aDrawSizeX == aReadSizeX && aDrawSizeY == aReadSizeY) ? Graphic3d_TOTF_NEAREST : Graphic3d_TOTF_BILINEAR;
    const GLint aFilterGl = aFilter == Graphic3d_TOTF_NEAREST ? GL_NEAREST : GL_LINEAR;

    OpenGl_VertexBuffer* aVerts = initBlitQuad (theToFlip);
    const Handle(OpenGl_ShaderManager)& aManager = aCtx->ShaderManager();
    if (aVerts->IsValid()
     && aManager->BindFboBlitProgram (theReadFbo != NULL ? theReadFbo->NbSamples() : 0, toApplyGamma))
    {
      aCtx->SetSampleAlphaToCoverage (false);
      theReadFbo->ColorTexture()->Bind (aCtx, Graphic3d_TextureUnit_0);
      if (theReadFbo->ColorTexture()->Sampler()->Parameters()->Filter() != aFilter)
      {
        theReadFbo->ColorTexture()->Sampler()->Parameters()->SetFilter (aFilter);
        aCtx->core20fwd->glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, aFilterGl);
        aCtx->core20fwd->glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, aFilterGl);
      }

      theReadFbo->DepthStencilTexture()->Bind (aCtx, Graphic3d_TextureUnit_1);
      if (theReadFbo->DepthStencilTexture()->Sampler()->Parameters()->Filter() != aFilter)
      {
        theReadFbo->DepthStencilTexture()->Sampler()->Parameters()->SetFilter (aFilter);
        aCtx->core20fwd->glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, aFilterGl);
        aCtx->core20fwd->glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, aFilterGl);
      }

      aVerts->BindVertexAttrib (aCtx, Graphic3d_TOA_POS);

      aCtx->core20fwd->glDrawArrays (GL_TRIANGLE_STRIP, 0, 4);

      aVerts->UnbindVertexAttrib (aCtx, Graphic3d_TOA_POS);
      theReadFbo->DepthStencilTexture()->Unbind (aCtx, Graphic3d_TextureUnit_1);
      theReadFbo->ColorTexture()       ->Unbind (aCtx, Graphic3d_TextureUnit_0);
      aCtx->BindProgram (NULL);
    }
    else
    {
      TCollection_ExtendedString aMsg = TCollection_ExtendedString()
        + "Error! FBO blitting has failed";
      aCtx->PushMessage (GL_DEBUG_SOURCE_APPLICATION,
                         GL_DEBUG_TYPE_ERROR,
                         0,
                         GL_DEBUG_SEVERITY_HIGH,
                         aMsg);
      myHasFboBlit = Standard_False;
      theReadFbo->Release (aCtx.operator->());
      return true;
    }
  }
  return true;
}

// =======================================================================
// function : drawStereoPair
// purpose  :
// =======================================================================
void OpenGl_View::drawStereoPair (OpenGl_FrameBuffer* theDrawFbo)
{
  const Handle(OpenGl_Context)& aCtx = myWorkspace->GetGlContext();
  bindDefaultFbo (theDrawFbo);
  OpenGl_FrameBuffer* aPair[2] =
  {
    myImmediateSceneFbos[0]->IsValid() ? myImmediateSceneFbos[0].operator->() : NULL,
    myImmediateSceneFbos[1]->IsValid() ? myImmediateSceneFbos[1].operator->() : NULL
  };
  if (aPair[0] == NULL
  ||  aPair[1] == NULL
  || !myTransientDrawToFront)
  {
    aPair[0] = myMainSceneFbos[0]->IsValid() ? myMainSceneFbos[0].operator->() : NULL;
    aPair[1] = myMainSceneFbos[1]->IsValid() ? myMainSceneFbos[1].operator->() : NULL;
  }

  if (aPair[0] == NULL
   || aPair[1] == NULL)
  {
    return;
  }

  if (aPair[0]->NbSamples() != 0)
  {
    // resolve MSAA buffers before drawing
    if (!myOpenGlFBO ->InitLazy (aCtx, aPair[0]->GetVPSize(), myFboColorFormat, myFboDepthFormat, 0)
     || !myOpenGlFBO2->InitLazy (aCtx, aPair[0]->GetVPSize(), myFboColorFormat, 0, 0))
    {
      aCtx->PushMessage (GL_DEBUG_SOURCE_APPLICATION, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH,
                         "Error! Unable to allocate FBO for blitting stereo pair");
      bindDefaultFbo (theDrawFbo);
      return;
    }

    if (!blitBuffers (aPair[0], myOpenGlFBO .operator->(), Standard_False)
     || !blitBuffers (aPair[1], myOpenGlFBO2.operator->(), Standard_False))
    {
      bindDefaultFbo (theDrawFbo);
      return;
    }

    aPair[0] = myOpenGlFBO .operator->();
    aPair[1] = myOpenGlFBO2.operator->();
    bindDefaultFbo (theDrawFbo);
  }

  struct
  {
    Standard_Integer left;
    Standard_Integer top;
    Standard_Integer right;
    Standard_Integer bottom;
    Standard_Integer dx() { return right  - left; }
    Standard_Integer dy() { return bottom - top; }
  } aGeom;

  myWindow->PlatformWindow()->Position (aGeom.left, aGeom.top, aGeom.right, aGeom.bottom);

  Standard_Boolean toReverse = myRenderParams.ToReverseStereo;
  const Standard_Boolean isOddY = (aGeom.top + aGeom.dy()) % 2 == 1;
  const Standard_Boolean isOddX =  aGeom.left % 2 == 1;
  if (isOddY
   && (myRenderParams.StereoMode == Graphic3d_StereoMode_RowInterlaced
    || myRenderParams.StereoMode == Graphic3d_StereoMode_ChessBoard))
  {
    toReverse = !toReverse;
  }
  if (isOddX
   && (myRenderParams.StereoMode == Graphic3d_StereoMode_ColumnInterlaced
    || myRenderParams.StereoMode == Graphic3d_StereoMode_ChessBoard))
  {
    toReverse = !toReverse;
  }

  if (toReverse)
  {
    std::swap (aPair[0], aPair[1]);
  }

  aCtx->core20fwd->glDepthFunc (GL_ALWAYS);
  aCtx->core20fwd->glDepthMask (GL_TRUE);
  aCtx->core20fwd->glEnable (GL_DEPTH_TEST);

  aCtx->BindTextures (Handle(OpenGl_TextureSet)(), Handle(OpenGl_ShaderProgram)());
  OpenGl_VertexBuffer* aVerts = initBlitQuad (myToFlipOutput);

  const Handle(OpenGl_ShaderManager)& aManager = aCtx->ShaderManager();
  if (!aVerts->IsValid()
   || !aManager->BindStereoProgram (myRenderParams.StereoMode))
  {
    aCtx->PushMessage (GL_DEBUG_SOURCE_APPLICATION, GL_DEBUG_TYPE_ERROR, 0, GL_DEBUG_SEVERITY_HIGH, "Error! Anaglyph has failed");
    return;
  }

  switch (myRenderParams.StereoMode)
  {
    case Graphic3d_StereoMode_Anaglyph:
    {
      OpenGl_Mat4 aFilterL, aFilterR;
      aFilterL.SetDiagonal (Graphic3d_Vec4 (0.0f, 0.0f, 0.0f, 0.0f));
      aFilterR.SetDiagonal (Graphic3d_Vec4 (0.0f, 0.0f, 0.0f, 0.0f));
      switch (myRenderParams.AnaglyphFilter)
      {
        case Graphic3d_RenderingParams::Anaglyph_RedCyan_Simple:
        {
          aFilterL.SetRow (0, Graphic3d_Vec4 (1.0f, 0.0f, 0.0f, 0.0f));
          aFilterR.SetRow (1, Graphic3d_Vec4 (0.0f, 1.0f, 0.0f, 0.0f));
          aFilterR.SetRow (2, Graphic3d_Vec4 (0.0f, 0.0f, 1.0f, 0.0f));
          break;
        }
        case Graphic3d_RenderingParams::Anaglyph_RedCyan_Optimized:
        {
          aFilterL.SetRow (0, Graphic3d_Vec4 ( 0.4154f,      0.4710f,      0.16666667f, 0.0f));
          aFilterL.SetRow (1, Graphic3d_Vec4 (-0.0458f,     -0.0484f,     -0.0257f,     0.0f));
          aFilterL.SetRow (2, Graphic3d_Vec4 (-0.0547f,     -0.0615f,      0.0128f,     0.0f));
          aFilterL.SetRow (3, Graphic3d_Vec4 ( 0.0f,         0.0f,         0.0f,        0.0f));
          aFilterR.SetRow (0, Graphic3d_Vec4 (-0.01090909f, -0.03636364f, -0.00606061f, 0.0f));
          aFilterR.SetRow (1, Graphic3d_Vec4 ( 0.37560000f,  0.73333333f,  0.01111111f, 0.0f));
          aFilterR.SetRow (2, Graphic3d_Vec4 (-0.06510000f, -0.12870000f,  1.29710000f, 0.0f));
          aFilterR.SetRow (3, Graphic3d_Vec4 ( 0.0f,                0.0f,  0.0f,        0.0f));
          break;
        }
        case Graphic3d_RenderingParams::Anaglyph_YellowBlue_Simple:
        {
          aFilterL.SetRow (0, Graphic3d_Vec4 (1.0f, 0.0f, 0.0f, 0.0f));
          aFilterL.SetRow (1, Graphic3d_Vec4 (0.0f, 1.0f, 0.0f, 0.0f));
          aFilterR.SetRow (2, Graphic3d_Vec4 (0.0f, 0.0f, 1.0f, 0.0f));
          break;
        }
        case Graphic3d_RenderingParams::Anaglyph_YellowBlue_Optimized:
        {
          aFilterL.SetRow (0, Graphic3d_Vec4 ( 1.062f, -0.205f,  0.299f, 0.0f));
          aFilterL.SetRow (1, Graphic3d_Vec4 (-0.026f,  0.908f,  0.068f, 0.0f));
          aFilterL.SetRow (2, Graphic3d_Vec4 (-0.038f, -0.173f,  0.022f, 0.0f));
          aFilterL.SetRow (3, Graphic3d_Vec4 ( 0.0f,    0.0f,    0.0f,   0.0f));
          aFilterR.SetRow (0, Graphic3d_Vec4 (-0.016f, -0.123f, -0.017f, 0.0f));
          aFilterR.SetRow (1, Graphic3d_Vec4 ( 0.006f,  0.062f, -0.017f, 0.0f));
          aFilterR.SetRow (2, Graphic3d_Vec4 ( 0.094f,  0.185f,  0.911f, 0.0f));
          aFilterR.SetRow (3, Graphic3d_Vec4 ( 0.0f,    0.0f,    0.0f,   0.0f));
          break;
        }
        case Graphic3d_RenderingParams::Anaglyph_GreenMagenta_Simple:
        {
          aFilterR.SetRow (0, Graphic3d_Vec4 (1.0f, 0.0f, 0.0f, 0.0f));
          aFilterL.SetRow (1, Graphic3d_Vec4 (0.0f, 1.0f, 0.0f, 0.0f));
          aFilterR.SetRow (2, Graphic3d_Vec4 (0.0f, 0.0f, 1.0f, 0.0f));
          break;
        }
        case Graphic3d_RenderingParams::Anaglyph_UserDefined:
        {
          aFilterL = myRenderParams.AnaglyphLeft;
          aFilterR = myRenderParams.AnaglyphRight;
          break;
        }
      }
      aCtx->ActiveProgram()->SetUniform (aCtx, "uMultL", aFilterL);
      aCtx->ActiveProgram()->SetUniform (aCtx, "uMultR", aFilterR);
      break;
    }
    case Graphic3d_StereoMode_RowInterlaced:
    {
      Graphic3d_Vec2 aTexOffset = myRenderParams.ToSmoothInterlacing
                                ? Graphic3d_Vec2 (0.0f, -0.5f / float(aPair[0]->GetSizeY()))
                                : Graphic3d_Vec2();
      aCtx->ActiveProgram()->SetUniform (aCtx, "uTexOffset", aTexOffset);
      break;
    }
    case Graphic3d_StereoMode_ColumnInterlaced:
    {
      Graphic3d_Vec2 aTexOffset = myRenderParams.ToSmoothInterlacing
                                ? Graphic3d_Vec2 (0.5f / float(aPair[0]->GetSizeX()), 0.0f)
                                : Graphic3d_Vec2();
      aCtx->ActiveProgram()->SetUniform (aCtx, "uTexOffset", aTexOffset);
      break;
    }
    case Graphic3d_StereoMode_ChessBoard:
    {
      Graphic3d_Vec2 aTexOffset = myRenderParams.ToSmoothInterlacing
                                ? Graphic3d_Vec2 (0.5f / float(aPair[0]->GetSizeX()),
                                                 -0.5f / float(aPair[0]->GetSizeY()))
                                : Graphic3d_Vec2();
      aCtx->ActiveProgram()->SetUniform (aCtx, "uTexOffset", aTexOffset);
      break;
    }
    default: break;
  }

  for (int anEyeIter = 0; anEyeIter < 2; ++anEyeIter)
  {
    OpenGl_FrameBuffer* anEyeFbo = aPair[anEyeIter];
    anEyeFbo->ColorTexture()->Bind (aCtx, (Graphic3d_TextureUnit )(Graphic3d_TextureUnit_0 + anEyeIter));
    if (anEyeFbo->ColorTexture()->Sampler()->Parameters()->Filter() != Graphic3d_TOTF_BILINEAR)
    {
      // force filtering
      anEyeFbo->ColorTexture()->Sampler()->Parameters()->SetFilter (Graphic3d_TOTF_BILINEAR);
      aCtx->core20fwd->glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
      aCtx->core20fwd->glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    }
  }
  aVerts->BindVertexAttrib (aCtx, 0);

  aCtx->core20fwd->glDrawArrays (GL_TRIANGLE_STRIP, 0, 4);

  aVerts->UnbindVertexAttrib (aCtx, 0);
  aPair[1]->ColorTexture()->Unbind (aCtx, Graphic3d_TextureUnit_1);
  aPair[0]->ColorTexture()->Unbind (aCtx, Graphic3d_TextureUnit_0);
}

// =======================================================================
// function : copyBackToFront
// purpose  :
// =======================================================================
bool OpenGl_View::copyBackToFront()
{
  myIsImmediateDrawn = Standard_False;
  const Handle(OpenGl_Context)& aCtx = myWorkspace->GetGlContext();
  if (aCtx->core11ffp == NULL)
  {
    return false;
  }

  OpenGl_Mat4 aProjectMat;
  Graphic3d_TransformUtils::Ortho2D (aProjectMat,
                                     0.0f, static_cast<GLfloat> (myWindow->Width()),
                                     0.0f, static_cast<GLfloat> (myWindow->Height()));

  aCtx->WorldViewState.Push();
  aCtx->ProjectionState.Push();

  aCtx->WorldViewState.SetIdentity();
  aCtx->ProjectionState.SetCurrent (aProjectMat);

  aCtx->ApplyProjectionMatrix();
  aCtx->ApplyWorldViewMatrix();

  // synchronize FFP state before copying pixels
  aCtx->BindProgram (Handle(OpenGl_ShaderProgram)());
  aCtx->ShaderManager()->PushState (Handle(OpenGl_ShaderProgram)());
  aCtx->DisableFeatures();

  switch (aCtx->DrawBuffer())
  {
    case GL_BACK_LEFT:
    {
      aCtx->SetReadBuffer (GL_BACK_LEFT);
      aCtx->SetDrawBuffer (GL_FRONT_LEFT);
      break;
    }
    case GL_BACK_RIGHT:
    {
      aCtx->SetReadBuffer (GL_BACK_RIGHT);
      aCtx->SetDrawBuffer (GL_FRONT_RIGHT);
      break;
    }
    default:
    {
      aCtx->SetReadBuffer (GL_BACK);
      aCtx->SetDrawBuffer (GL_FRONT);
      break;
    }
  }

  aCtx->core11ffp->glRasterPos2i (0, 0);
  aCtx->core11ffp->glCopyPixels  (0, 0, myWindow->Width() + 1, myWindow->Height() + 1, GL_COLOR);
  //aCtx->core11ffp->glCopyPixels  (0, 0, myWidth + 1, myHeight + 1, GL_DEPTH);

  aCtx->EnableFeatures();

  aCtx->WorldViewState.Pop();
  aCtx->ProjectionState.Pop();
  aCtx->ApplyProjectionMatrix();

  // read/write from front buffer now
  aCtx->SetReadBuffer (aCtx->DrawBuffer());
  return true;
}

// =======================================================================
// function : checkOitCompatibility
// purpose  :
// =======================================================================
Standard_Boolean OpenGl_View::checkOitCompatibility (const Handle(OpenGl_Context)& theGlContext,
                                                     const Standard_Boolean theMSAA)
{
  // determine if OIT is supported by current OpenGl context
  Standard_Boolean& aToDisableOIT = theMSAA ? myToDisableMSAA : myToDisableOIT;
  if (aToDisableOIT)
  {
    return Standard_False;
  }

  TCollection_ExtendedString aCompatibilityMsg;
  if (theGlContext->hasFloatBuffer     == OpenGl_FeatureNotAvailable
   && theGlContext->hasHalfFloatBuffer == OpenGl_FeatureNotAvailable)
  {
    aCompatibilityMsg += "OpenGL context does not support floating-point RGBA color buffer format.\n";
  }
  if (theMSAA && theGlContext->hasSampleVariables == OpenGl_FeatureNotAvailable)
  {
    aCompatibilityMsg += "Current version of GLSL does not support built-in sample variables.\n";
  }
  if (theGlContext->hasDrawBuffers == OpenGl_FeatureNotAvailable)
  {
    aCompatibilityMsg += "OpenGL context does not support multiple draw buffers.\n";
  }
  if (aCompatibilityMsg.IsEmpty())
  {
    return Standard_True;
  }

  aCompatibilityMsg += "  Blended order-independent transparency will not be available.\n";
  theGlContext->PushMessage (GL_DEBUG_SOURCE_APPLICATION,
                          GL_DEBUG_TYPE_ERROR,
                          0,
                          GL_DEBUG_SEVERITY_HIGH,
                          aCompatibilityMsg);

  aToDisableOIT = Standard_True;
  return Standard_False;
}

// =======================================================================
// function : updateSkydomeBg
// purpose  :
// =======================================================================
void OpenGl_View::updateSkydomeBg (const Handle(OpenGl_Context)& theCtx)
{
  if (!myToUpdateSkydome)
  {
    return;
  }

  myToUpdateSkydome = false;

  // Set custom shader
  Handle(OpenGl_ShaderProgram) aProg;
  Handle(Graphic3d_ShaderProgram) aProxy = theCtx->ShaderManager()->GetBgSkydomeProgram();
  TCollection_AsciiString anUnused;
  theCtx->ShaderManager()->Create (aProxy, anUnused, aProg);
  Handle(OpenGl_ShaderProgram) aPrevProgram = theCtx->ActiveProgram();
  theCtx->BindProgram (aProg);

  // Setup uniforms
  aProg->SetUniform (theCtx, "uSunDir", OpenGl_Vec3((float )mySkydomeAspect.SunDirection().X(),
                                                    (float )mySkydomeAspect.SunDirection().Y(),
                                                    (float )mySkydomeAspect.SunDirection().Z()));
  aProg->SetUniform (theCtx, "uCloudy", mySkydomeAspect.Cloudiness());
  aProg->SetUniform (theCtx, "uTime",   mySkydomeAspect.TimeParameter());
  aProg->SetUniform (theCtx, "uFog",    mySkydomeAspect.Fogginess());

  // Create and prepare framebuffer
  GLint aPrevFBO = 0;
  theCtx->core11fwd->glGetIntegerv (GL_FRAMEBUFFER_BINDING, &aPrevFBO);
  GLuint anFBO = 0;
  theCtx->arbFBO->glGenFramebuffers (1, &anFBO);
  theCtx->arbFBO->glBindFramebuffer (GL_FRAMEBUFFER, anFBO);

  const Standard_Integer anOldViewport[4] = {theCtx->Viewport()[0], theCtx->Viewport()[1], theCtx->Viewport()[2], theCtx->Viewport()[3]};
  const Standard_Integer aViewport[4] = {0, 0, mySkydomeAspect.Size(), mySkydomeAspect.Size()};
  theCtx->ResizeViewport (aViewport);

  // Fullscreen triangle
  Handle(OpenGl_VertexBuffer) aVBO = new OpenGl_VertexBuffer();
  const float aTriangle[] = {-1.0, -1.0, 3.0, -1.0, -1.0, 3.0};
  aVBO->Init (theCtx, 2, 3, aTriangle);
  aVBO->BindAttribute (theCtx, Graphic3d_TypeOfAttribute::Graphic3d_TOA_POS);
  aVBO->Bind (theCtx);

  if (mySkydomeTexture.IsNull())
  {
    mySkydomeTexture = new OpenGl_Texture();
    mySkydomeTexture->Sampler()->Parameters()->SetFilter (Graphic3d_TOTF_BILINEAR);
  }
  if (mySkydomeTexture->SizeX() != mySkydomeAspect.Size())
  {
    mySkydomeTexture->Release (theCtx.get());
    mySkydomeTexture->InitCubeMap (theCtx, NULL, mySkydomeAspect.Size(),
                                   Image_Format_RGB, false, false);
  }

  // init aspects if needed
  if (myCubeMapParams->TextureSet (theCtx).IsNull())
  {
    myCubeMapParams->Aspect()->SetInteriorStyle (Aspect_IS_SOLID);
    myCubeMapParams->Aspect()->SetFaceCulling (Graphic3d_TypeOfBackfacingModel_DoubleSided);
    myCubeMapParams->Aspect()->SetShadingModel (Graphic3d_TypeOfShadingModel_Unlit);
    myCubeMapParams->Aspect()->SetShaderProgram (theCtx->ShaderManager()->GetBgCubeMapProgram());
    Handle(Graphic3d_TextureSet) aTextureSet = new Graphic3d_TextureSet (1);
    myCubeMapParams->Aspect()->SetTextureSet (aTextureSet);
    myCubeMapParams->Aspect()->SetTextureMapOn (true);
    myCubeMapParams->SynchronizeAspects();
  }

  myCubeMapParams->Aspect()->ShaderProgram()->PushVariableInt ("uZCoeff", 1);
  myCubeMapParams->Aspect()->ShaderProgram()->PushVariableInt ("uYCoeff", 1);

  for (Standard_Integer aSideIter = 0; aSideIter < 6; aSideIter++)
  {
    aProg->SetUniform (theCtx, "uSide", aSideIter);
    theCtx->arbFBO->glFramebufferTexture2D (GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_CUBE_MAP_POSITIVE_X + aSideIter,
                                            mySkydomeTexture->TextureId(), 0);
    theCtx->core15->glDrawArrays (GL_TRIANGLES, 0, 3);
  }
  theCtx->arbFBO->glDeleteFramebuffers (1, &anFBO);
  aVBO->Release (theCtx.get());

  myCubeMapParams->TextureSet (theCtx)->ChangeFirst() = mySkydomeTexture;
  theCtx->BindProgram (aPrevProgram);
  theCtx->ResizeViewport (anOldViewport);
  theCtx->arbFBO->glBindFramebuffer (GL_FRAMEBUFFER, aPrevFBO);
}

// =======================================================================
// function : checkPBRAvailability
// purpose  :
// =======================================================================
Standard_Boolean OpenGl_View::checkPBRAvailability() const
{
  return myWorkspace->GetGlContext()->HasPBR()
      && !myPBREnvironment.IsNull();
}

// =======================================================================
// function : updatePBREnvironment
// purpose  :
// =======================================================================
void OpenGl_View::updatePBREnvironment (const Handle(OpenGl_Context)& theCtx)
{
  if (myBackgroundType == Graphic3d_TOB_CUBEMAP
   && myToUpdateSkydome)
  {
    updateSkydomeBg (theCtx);
  }

  if (myPBREnvState != OpenGl_PBREnvState_CREATED
  || !myPBREnvRequest)
  {
    myPBREnvRequest = false;
    return;
  }

  myPBREnvRequest = false;

  Handle(OpenGl_TextureSet) aGlTextureSet;
  OpenGl_Aspects* aTmpGlAspects = NULL;
  if (!myCubeMapIBL.IsNull()
    && myCubeMapIBL == myCubeMapBackground)
  {
    aGlTextureSet = myCubeMapParams->TextureSet (theCtx);
  }
  else if (!myCubeMapIBL.IsNull())
  {
    myCubeMapIBL->SetMipmapsGeneration (Standard_True);

    Handle(Graphic3d_AspectFillArea3d) anAspect = new Graphic3d_AspectFillArea3d();
    {
      Handle(Graphic3d_TextureSet) aTextureSet = new Graphic3d_TextureSet (myCubeMapIBL);
      anAspect->SetInteriorStyle (Aspect_IS_SOLID);
      anAspect->SetTextureSet (aTextureSet);
      anAspect->SetTextureMapOn (true);
    }

    aTmpGlAspects = new OpenGl_Aspects();
    aTmpGlAspects->SetAspect (anAspect);
    aGlTextureSet = aTmpGlAspects->TextureSet (theCtx);
  }

  if (!aGlTextureSet.IsNull()
   && !aGlTextureSet->IsEmpty())
  {
    myPBREnvironment->Bake (theCtx,
                            aGlTextureSet->First(),
                            myCubeMapIBL->ZIsInverted(),
                            myCubeMapIBL->IsTopDown(),
                            myRenderParams.PbrEnvBakingDiffNbSamples,
                            myRenderParams.PbrEnvBakingSpecNbSamples,
                            myRenderParams.PbrEnvBakingProbability);
  }
  else
  {
    myPBREnvironment->Clear (theCtx);
  }
  aGlTextureSet.Nullify();
  OpenGl_Element::Destroy (theCtx.get(), aTmpGlAspects);
}