Remove hasMixedSamples() from GrPipelineBuilder

src/gpu/effects/GrPorterDuffXferProcessor.cpp

Index: src/gpu/effects/GrPorterDuffXferProcessor.cpp
diff --git a/src/gpu/effects/GrPorterDuffXferProcessor.cpp b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
index 733e552eea7bc1298d1ad07fae918111ae6564d7..f609cd2b8e19bdf266c846872b1f42923fc8a071 100644
--- a/src/gpu/effects/GrPorterDuffXferProcessor.cpp
+++ b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
@@ -799,8 +799,7 @@ void GrPorterDuffXPFactory::getInvariantBlendedColor(const GrProcOptInfo& colorP
 }
 
 bool GrPorterDuffXPFactory::onWillReadDstColor(const GrCaps& caps,
-                                               const GrPipelineOptimizations& optimizations,
-                                               bool hasMixedSamples) const {
+                                               const GrPipelineOptimizations& optimizations) const {
     if (caps.shaderCaps()->dualSourceBlendingSupport()) {
         return false;
     }
@@ -816,9 +815,12 @@ bool GrPorterDuffXPFactory::onWillReadDstColor(const GrCaps& caps,
         }
         return get_lcd_blend_formula(optimizations.fCoveragePOI, fXfermode).hasSecondaryOutput();
     }
+
     // We fallback on the shader XP when the blend formula would use dual source blending but we
     // don't have support for it.
-    return get_blend_formula(optimizations.fColorPOI, optimizations.fCoveragePOI, hasMixedSamples,
+    static const bool kHasMixedSamples = false;
+    SkASSERT(!caps.usesMixedSamples()); // Dual source blending is a prerequisite for mixed samples.
+    return get_blend_formula(optimizations.fColorPOI, optimizations.fCoveragePOI, kHasMixedSamples,
                              fXfermode).hasSecondaryOutput();
 }
 
@@ -897,8 +899,7 @@ GrXferProcessor* GrPorterDuffXPFactory::CreateSrcOverXferProcessor(
 }
 
 bool GrPorterDuffXPFactory::SrcOverWillNeedDstTexture(const GrCaps& caps,
-                                                      const GrPipelineOptimizations& optimizations,
-                                                      bool hasMixedSamples) {
+                                                     const GrPipelineOptimizations& optimizations) {
     if (caps.shaderCaps()->dstReadInShaderSupport() ||
         caps.shaderCaps()->dualSourceBlendingSupport()) {
         return false;
@@ -915,8 +916,11 @@ bool GrPorterDuffXPFactory::SrcOverWillNeedDstTexture(const GrCaps& caps,
         return get_lcd_blend_formula(optimizations.fCoveragePOI,
                                      SkXfermode::kSrcOver_Mode).hasSecondaryOutput();
     }
+
     // We fallback on the shader XP when the blend formula would use dual source blending but we
     // don't have support for it.
+    static const bool kHasMixedSamples = false;
+    SkASSERT(!caps.usesMixedSamples());

[egdaniel, 2016/05/05 20:04:56]

can you add the same dual source blending comment here as above. Otherwise I'll
forget and some time down the road be staring at this way to long trying to
figure out why we don't have mixedSamples.

On a related note, when you set usesMixedSamples on caps are you explictly
checking or asserting dual source blending is available? Or are you just
assuming that is the case knowing how the extension works? If it is the latter,
I would request adding an assert there since we are now relying on that property
here.

[Chris Dalton, 2016/05/06 16:06:50]

Oops, I didn't notice I missed this one.
Yeah, we check when building the caps. It's possible to have one extension
without the other, but if dual source blending is not supported then we ignore
NV_framebuffer_mixed_samples.

The reason is because HW coverage modulation happens in ROP (after fragment
shading), so it would be impossible to make certain xfer modes work without dual
source blending when using mixed samples.

[egdaniel, 2016/05/06 16:10:04]

Sounds good. Just wanted to make sure we had some check.

     return get_blend_formula(optimizations.fColorPOI, optimizations.fCoveragePOI,
-                             hasMixedSamples, SkXfermode::kSrcOver_Mode).hasSecondaryOutput();
+                             kHasMixedSamples, SkXfermode::kSrcOver_Mode).hasSecondaryOutput();
 }