Add "sample locations" feature to GrProcessor

src/gpu/GrPipelineBuilder.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrPipelineBuilder_DEFINED
 #define GrPipelineBuilder_DEFINED
 
@@ skipping 273 matching lines @@
          * or smooth-line rendering if a line primitive is drawn and line smoothing is supported by
          * the 3D API.
          */
         kHWAntialias_Flag   = 0x01,
 
         /**
          * Modifies the vertex shader so that vertices will be positioned at pixel centers.
          */
         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.
      *
      * @param flags bitfield of Flags specifying the states to enable
      */
     void enableState(uint32_t flags) { fFlags |= flags; }
         
     /**
      * Disable render state settings.
@@ skipping 69 matching lines @@
     mutable SkAutoTUnref<const GrXPFactory> fXPFactory;
     FragmentProcessorArray                  fColorFragmentProcessors;
     FragmentProcessorArray                  fCoverageFragmentProcessors;
     GrClip                                  fClip;
 
     friend class GrPipeline;
     friend class GrDrawTarget;
 };
 
 #endif