Implement support for mixed sampled render targets

include/gpu/GrRenderTarget.h

Index: include/gpu/GrRenderTarget.h
diff --git a/include/gpu/GrRenderTarget.h b/include/gpu/GrRenderTarget.h
index 40e006aa8aec8edb70b28cec5a3274f5b7f0e110..5144748fabda79f8d0b5527f4aade84c19dd2082 100644
--- a/include/gpu/GrRenderTarget.h
+++ b/include/gpu/GrRenderTarget.h
@@ -31,14 +31,39 @@ public:
 
     // GrRenderTarget
     /**
-     * @return true if the surface is multisampled, false otherwise
+     * @param  pipelineStage  specifies the buffer(s) for which multisampling
+                              is queried
+     * @return true if the surface is multisampled in all of the buffers
+     *         specified by the sample config, false if any are non-MSAA
      */

[Chris Dalton, 2015/03/19 12:07:40]

Maybe pipeline stage would be better to say than buffer. For example, raster is
a pipeline stage that could be multisampled, but not a buffer... 

-    bool isMultisampled() const { return 0 != fDesc.fSampleCnt; }
+    bool isMultisampled(GrPipelineStage pipelineStage =
+                                        kEverywhere_GrPipelineStage) const {
+        return 0 != numSamples(pipelineStage);
+    }
 
     /**
-     * @return the number of samples-per-pixel or zero if non-MSAA.
+     * @param  pipelineStage  specifies the buffer(s) for which sample count
+                              is queried
+     * @return the number of samples-per-pixel or zero if any of the specified
+     *         buffers is non-MSAA.
      */
-    int numSamples() const { return fDesc.fSampleCnt; }
+    int numSamples(GrPipelineStage pipelineStage =
+                                   kEverywhere_GrPipelineStage) const {
+        if (kStencil_GrSampleConfig == fSampleConfig &&
+            kColorBuffer_GrPipelineStage == pipelineStage) {
+            return 0;
+        }
+        return fDesc.fSampleCnt;
+    }
+
+    /**
+     * @return sample config: kUnified_GrSampleConfig if both color and stencil
+               buffers are MSAA, or kStencil_GrSampleConfig if only stencil
+               buffer is MSAA.
+     */
+    GrSampleConfig sampleConfig() const {
+        return fSampleConfig;
+    }
 
     /**
      * Call to indicate the multisample contents were modified such that the
@@ -94,8 +119,10 @@ public:
     const GrRenderTargetPriv renderTargetPriv() const;
 
 protected:
-    GrRenderTarget(GrGpu* gpu, LifeCycle lifeCycle, const GrSurfaceDesc& desc)
+    GrRenderTarget(GrGpu* gpu, LifeCycle lifeCycle, const GrSurfaceDesc& desc,
+                   GrSampleConfig sampleConfig)
         : INHERITED(gpu, lifeCycle, desc)
+        , fSampleConfig(sampleConfig)
         , fStencilBuffer(NULL) {
         fResolveRect.setLargestInverted();
     }
@@ -110,6 +137,8 @@ private:
 
     friend class GrRenderTargetPriv;
 
+    GrSampleConfig    fSampleConfig;
+
     GrStencilBuffer*  fStencilBuffer;
 
     SkIRect           fResolveRect;