From 2a1fa7be507ebc76d634df5b18549b0f79a0f832 Mon Sep 17 00:00:00 2001
From: mzernova <mzernova@opencascade.com>
Date: Fri, 22 Nov 2024 12:47:20 +0000
Subject: [PATCH] Fix grid flickering

---
 src/Graphic3d/Graphic3d_ShaderManager.cxx |  3 ++-
 src/OpenGl/OpenGl_View.cxx                | 12 ++++++++++--
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/Graphic3d/Graphic3d_ShaderManager.cxx b/src/Graphic3d/Graphic3d_ShaderManager.cxx
index 9cd5380c64..694ed3f2a1 100644
--- a/src/Graphic3d/Graphic3d_ShaderManager.cxx
+++ b/src/Graphic3d/Graphic3d_ShaderManager.cxx
@@ -2280,7 +2280,8 @@ Handle(Graphic3d_ShaderProgram) Graphic3d_ShaderManager::getGridProgram() const
     EOL"    aColor.a *= aFading;"
     EOL"  }"
 
-    EOL"  gl_FragDepth = uIsBackground ? 1.0 : min (aDepth, 1.0);"
+    EOL"  float aMaxDepth = 1.0 - 1e-5;"
+    EOL"  gl_FragDepth = uIsBackground ? aMaxDepth : min (aDepth, aMaxDepth);"
     EOL"  occFragColor = aColor;"
     EOL"}";
 
diff --git a/src/OpenGl/OpenGl_View.cxx b/src/OpenGl/OpenGl_View.cxx
index 65b5a1ecaf..06dea367c8 100644
--- a/src/OpenGl/OpenGl_View.cxx
+++ b/src/OpenGl/OpenGl_View.cxx
@@ -2597,10 +2597,14 @@ void OpenGl_View::renderGrid()
   aContext->ApplyWorldViewMatrix();
 
   aContext->core11fwd->glEnable (GL_DEPTH_TEST);
-  aContext->core11fwd->glDepthFunc (GL_LEQUAL);
+  aContext->core11fwd->glDepthFunc (GL_LESS);
   aContext->core11fwd->glDepthMask (GL_TRUE);
   aContext->core11fwd->glEnable (GL_BLEND);
-  aContext->core20fwd->glBlendFuncSeparate (GL_SRC_ALPHA, GL_DST_ALPHA, GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+  const bool wasDepthClamped = aContext->arbDepthClamp && aContext->core11fwd->glIsEnabled (GL_DEPTH_CLAMP);
+  if (aContext->arbDepthClamp && !wasDepthClamped)
+  {
+    aContext->core11fwd->glEnable (GL_DEPTH_CLAMP);
+  }
 
   const Standard_Real aCameraScale = aContext->Camera()->Scale();
   Standard_Real aScale = myGridParams.IsInfinity()
@@ -2625,6 +2629,10 @@ void OpenGl_View::renderGrid()
   aContext->Camera()->SetZRange (aZNear, aZFar);
   aContext->Camera()->SetProjectionType (aProjectionType);
   aContext->core11fwd->glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+  if (aContext->arbDepthClamp && !wasDepthClamped)
+  {
+    aContext->core11fwd->glDisable (GL_DEPTH_CLAMP);
+  }
 
   aContext->WorldViewState.Pop();
   aContext->ProjectionState.Pop();