Add support for advanced blend equations to our OpenGL QPainter

Mesa and NVidia have been supporting these extensions several years now.
It also means we can get rid of the dead unused code we had for advanced
compositions.

Change-Id: I6a2fcda13490abd977eb4cc3d8b34f186d05ca25
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/gui/opengl/qopenglshaderprogram.cpp b/src/gui/opengl/qopenglshaderprogram.cpp
index 1fe30f7e0e..46963f0dbf 100644
--- a/src/gui/opengl/qopenglshaderprogram.cpp
+++ b/src/gui/opengl/qopenglshaderprogram.cpp
@@ -497,6 +497,13 @@ static const char redefineHighp[] =
     "#endif\n";
 #endif
 
+// Boiler-plate header to have the layout attributes available we need later
+static const char blendEquationAdvancedHeader[] =
+    "#ifdef GL_KHR_blend_equation_advanced\n"
+    "#extension GL_ARB_fragment_coord_conventions : enable\n"
+    "#extension GL_KHR_blend_equation_advanced : enable\n"
+    "#endif\n";
+
 struct QVersionDirectivePosition
 {
     Q_DECL_CONSTEXPR QVersionDirectivePosition(int position = 0, int line = -1)
@@ -637,6 +644,10 @@ bool QOpenGLShader::compileSourceCode(const char *source)
                 }
             }
         }
+        if (d->shaderType == Fragment) {
+            sourceChunks.append(blendEquationAdvancedHeader);
+            sourceChunkLengths.append(GLint(sizeof(blendEquationAdvancedHeader) - 1));
+        }
 
         // The precision qualifiers are useful on OpenGL/ES systems,
         // but usually not present on desktop systems.