From 57357010a86ad38ab1e740e21ed5bb903eaa0ca2 Mon Sep 17 00:00:00 2001
From: kgv <kgv@opencascade.com>
Date: Thu, 15 Apr 2021 15:34:52 +0300
Subject: [PATCH] 0032301: Visualization, TKOpenGl - depth peeling is broken
 with OpenGl_Caps::buffersOpaqueAlpha option

OpenGl_LayerList::renderTransparent() - color mask is now set to write into Alpha channel of depth peeling FBOs.
OpenGl_View::blitBuffers() - avoid using undefined color for glClear(GL_COLOR_BUFFER_BIT) operation.
---
 src/OpenGl/OpenGl_LayerList.cxx    | 2 ++
 src/OpenGl/OpenGl_View.cxx         | 1 +
 tests/opengl/data/transparency/oit | 5 +++++
 3 files changed, 8 insertions(+)

diff --git a/src/OpenGl/OpenGl_LayerList.cxx b/src/OpenGl/OpenGl_LayerList.cxx
index 563bc6726b..53d616fb94 100644
--- a/src/OpenGl/OpenGl_LayerList.cxx
+++ b/src/OpenGl/OpenGl_LayerList.cxx
@@ -966,6 +966,7 @@ void OpenGl_LayerList::renderTransparent (const Handle(OpenGl_Workspace)&   theW
       // initialize min/max depth buffer
       aGlBlendBackFBO->BindDrawBuffer (aCtx);
       aCtx->SetDrawBuffers (1, THE_DRAW_BUFFERS0);
+      aCtx->SetColorMaskRGBA (NCollection_Vec4<bool> (true)); // force writes into all components, including alpha
       aCtx->core20fwd->glClearColor (0.0f, 0.0f, 0.0f, 0.0f);
       aCtx->core20fwd->glClear (GL_COLOR_BUFFER_BIT);
 
@@ -1122,6 +1123,7 @@ void OpenGl_LayerList::renderTransparent (const Handle(OpenGl_Workspace)&   theW
         theReadDrawFbo->BindBuffer (aCtx);
       }
       aCtx->SetDrawBuffers (1, THE_DRAW_BUFFERS0);
+      aCtx->SetColorMask (true); // update writes into alpha component
       break;
     }
   }
diff --git a/src/OpenGl/OpenGl_View.cxx b/src/OpenGl/OpenGl_View.cxx
index 3f6b63bad8..2900289ea5 100644
--- a/src/OpenGl/OpenGl_View.cxx
+++ b/src/OpenGl/OpenGl_View.cxx
@@ -2558,6 +2558,7 @@ bool OpenGl_View::blitBuffers (OpenGl_FrameBuffer*    theReadFbo,
 
   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
 
diff --git a/tests/opengl/data/transparency/oit b/tests/opengl/data/transparency/oit
index 3c47477845..a6f004731b 100644
--- a/tests/opengl/data/transparency/oit
+++ b/tests/opengl/data/transparency/oit
@@ -36,6 +36,11 @@ vdump $imagedir/${casename}_weight.png
 vrenderparams -oit peeling 4
 vdump $imagedir/${casename}_peel.png
 
+# test opaqueAlpha option - result should be the same
+vcaps -opaqueAlpha 1
+vdump $imagedir/${casename}_peel_rgb.png
+vcaps -opaqueAlpha 0
+
 # VTK viewer, just for comparison
 set hasVtk 0
 if { [vdriver -default] == "TKOpenGl" } {