Add "sample locations" feature to GrProcessor

src/gpu/GrPipelineBuilder.h

Index: src/gpu/GrPipelineBuilder.h
diff --git a/src/gpu/GrPipelineBuilder.h b/src/gpu/GrPipelineBuilder.h
index f5fe9f80dc38196d583183845a0990684b88eced..178dd6593edec32f6c5992e2ae19f7b82d3d421e 100644
--- a/src/gpu/GrPipelineBuilder.h
+++ b/src/gpu/GrPipelineBuilder.h
@@ -291,12 +291,18 @@ public:
          */
         kSnapVerticesToPixelCenters_Flag = 0x02,
 
-        kLast_Flag = kSnapVerticesToPixelCenters_Flag,
+        /**
+         * Adds a built-in fragment shader array that contains the pipeline's sample locations.
+         */
+        kSampleLocations_Flag = 0x04,

[bsalomon, 2016/02/22 20:28:26]

Where/how will this get set?

[Chris Dalton, 2016/02/22 21:19:11]

I envision it being set by the code that sets up the pipeline for a specific
type of batch.

e.g.

 batch = shapeRendering->createBatch(..., &pipelineBuilder);

Then ShapeRendering (or whatever it ends up being named) modifies the
HWAntialias and SampleLocations flags as needed.

For example, maybe somebody wants to draw something to a non-MSAA texture but
the view matrix has persective (not supported by coverage shaders). If
createBatch() notices you have EXT_raster_multisample, it can enable HW
antialias and sample locations in the builder, then return a batch for mixed
samples.

+
+        kLast_Flag = kSampleLocations_Flag,
     };
 
     bool isHWAntialias() const { return SkToBool(fFlags & kHWAntialias_Flag); }
     bool snapVerticesToPixelCenters() const {
         return SkToBool(fFlags & kSnapVerticesToPixelCenters_Flag); }
+    bool hasSampleLocations() const { return SkToBool(fFlags & kSampleLocations_Flag); }
 
     /**
      * Enable render state settings.