Implement support for mixed sampled render targets

src/gpu/GrPipeline.cpp

Index: src/gpu/GrPipeline.cpp
diff --git a/src/gpu/GrPipeline.cpp b/src/gpu/GrPipeline.cpp
index 906426caaaecc0699dd8d878ee2ccdfa9bdfd6dd..d1ebad03104b3b19b24ac0df37f6c34c4bf06dea 100644
--- a/src/gpu/GrPipeline.cpp
+++ b/src/gpu/GrPipeline.cpp
@@ -29,11 +29,30 @@ GrPipeline::GrPipeline(const GrPipelineBuilder& pipelineBuilder,
         overrideColor = colorPOI.inputColorToEffectiveStage();
     }
 
+    fRenderTarget.reset(pipelineBuilder.fRenderTarget.get());
+    SkASSERT(fRenderTarget);
+
+    fFlags = 0;
+    if (pipelineBuilder.isHWAntialias()) {
+        fFlags |= kHWAA_Flag;
+    }
+    if (pipelineBuilder.isDither()) {
+        fFlags |= kDither_Flag;
+    }
+
     GrXferProcessor::OptFlags optFlags;
     if (xferProcessor) {
         fXferProcessor.reset(xferProcessor.get());
 
-        optFlags = xferProcessor->getOptimizations(colorPOI,
+        GrProcOptInfo localColorPOI = colorPOI;
+        // Optimizations will try to turn off blending which is required by mixed
+        // sampled modes.
+        bool isMixedSampledTarget =
+            (this->getRenderTarget()->sampleConfig() == kStencil_GrSampleConfig);
+        localColorPOI.setNeedsCoverageModulation(this->isHWAntialiasState() &&
+                                                 isMixedSampledTarget);
+
+        optFlags = xferProcessor->getOptimizations(localColorPOI,

[Mark Kilgard, 2015/03/24 14:05:08]

For Google:  enabling/disabling GL_BLEND when using
GL_ONE,GL_ONE_MINUS_SRC_ALPHA or GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA blending is
probably just costing you CPU drivers doing driver validation if the alpha from
shader is guaranteed 1.0

NVIDIA GPUs for the last 5+ years should be able to render "just as fast" for
these blend modes when source alpha==1.0 as having blending disabled.  The GPU
recognizes the blend optimization automatically and avoids read-modify-writes
during alpha==1.0 blending.  But calling glEnable(GL_BLEND)/glDisable(GL_BLEND)
is going to cause driver validations.

Please consider having a mode so K1 and other GPUs can simply not excessively
enable/disable blending.

                                                    coveragePOI,
                                                    pipelineBuilder.getStencil().doesWrite(),
                                                    &overrideColor,
@@ -51,20 +70,10 @@ GrPipeline::GrPipeline(const GrPipelineBuilder& pipelineBuilder,
         return;
     }
 
-    fRenderTarget.reset(pipelineBuilder.fRenderTarget.get());
-    SkASSERT(fRenderTarget);
     fScissorState = scissorState;
     fStencilSettings = pipelineBuilder.getStencil();
     fDrawFace = pipelineBuilder.getDrawFace();
 
-    fFlags = 0;
-    if (pipelineBuilder.isHWAntialias()) {
-        fFlags |= kHWAA_Flag;
-    }
-    if (pipelineBuilder.isDither()) {
-        fFlags |= kDither_Flag;
-    }
-
     int firstColorStageIdx = colorPOI.firstEffectiveStageIndex();
 
     // TODO: Once we can handle single or four channel input into coverage stages then we can use