Workaround for ATI driver bug when using QGraphicsEffect with GL.

If you forward declare a shader function which takes a sampler as
argument, the shader program will fail to link on ATI cards under
Windows.

Task-number: QTBUG-10510
Reviewed-by: Trond

2 files changed, 6 insertions, 5 deletions

diff --git a/src/opengl/gl2paintengineex/qglengineshadermanager.cpp b/src/opengl/gl2paintengineex/qglengineshadermanager.cpp
index 8183f08..0c98e3b 100644
--- a/src/opengl/gl2paintengineex/qglengineshadermanager.cpp
+++ b/src/opengl/gl2paintengineex/qglengineshadermanager.cpp
@@ -265,10 +265,12 @@ QGLEngineShaderProg *QGLEngineSharedShaders::findProgramInCache(const QGLEngineS
 
     do {
         QByteArray source;
-        source.append(qShaderSnippets[prog.mainFragShader]);
-        source.append(qShaderSnippets[prog.srcPixelFragShader]);
+        // Insert the custom stage before the srcPixel shader to work around an ATI driver bug
+        // where you cannot forward declare a function that takes a sampler as argument.
         if (prog.srcPixelFragShader == CustomImageSrcFragmentShader)
             source.append(prog.customStageSource);
+        source.append(qShaderSnippets[prog.mainFragShader]);
+        source.append(qShaderSnippets[prog.srcPixelFragShader]);
         if (prog.compositionFragShader)
             source.append(qShaderSnippets[prog.compositionFragShader]);
         if (prog.maskFragShader)
@@ -765,8 +767,8 @@ bool QGLEngineShaderManager::useCorrectShaderProg()
     // doesn't use are disabled)
     QGLContextPrivate* ctx_d = ctx->d_func();
     ctx_d->setVertexAttribArrayEnabled(QT_VERTEX_COORDS_ATTR, true);
-    ctx_d->setVertexAttribArrayEnabled(QT_TEXTURE_COORDS_ATTR, currentShaderProg->useTextureCoords);
-    ctx_d->setVertexAttribArrayEnabled(QT_OPACITY_ATTR, currentShaderProg->useOpacityAttribute);
+    ctx_d->setVertexAttribArrayEnabled(QT_TEXTURE_COORDS_ATTR, currentShaderProg && currentShaderProg->useTextureCoords);
+    ctx_d->setVertexAttribArrayEnabled(QT_OPACITY_ATTR, currentShaderProg && currentShaderProg->useOpacityAttribute);
 
     shaderProgNeedsChanging = false;
     return true;
diff --git a/src/opengl/gl2paintengineex/qglengineshadersource_p.h b/src/opengl/gl2paintengineex/qglengineshadersource_p.h
index c88c041..c963265 100644
--- a/src/opengl/gl2paintengineex/qglengineshadersource_p.h
+++ b/src/opengl/gl2paintengineex/qglengineshadersource_p.h
@@ -343,7 +343,6 @@ static const char* const qglslImageSrcFragmentShader = "\n\
 static const char* const qglslCustomSrcFragmentShader = "\n\
     varying   highp   vec2      textureCoords; \n\
     uniform   lowp    sampler2D imageTexture; \n\
-    lowp vec4 customShader(lowp sampler2D texture, highp vec2 coords); \n\
     lowp vec4 srcPixel() \n\
     { \n\
         return customShader(imageTexture, textureCoords); \n\