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..933e0923b5057b2d99feea641bd3be705507f2d1 100644
--- a/include/gpu/GrRenderTarget.h
+++ b/include/gpu/GrRenderTarget.h
@@ -31,14 +31,55 @@ public:
 
     // GrRenderTarget
     /**
-     * @return true if the surface is multisampled, false otherwise
+     * On some hardware it is possible for a render target to have multisampling
+     * only in certain stages of the graphics pipeline. This enum allows
+     * the caller to query about specific stages in isMultisampled() and
+     * numSamples().
      */
-    bool isMultisampled() const { return 0 != fDesc.fSampleCnt; }
+    enum PipelineStage {
+        kColorBuffer_PipelineStage,
+        kStencilBuffer_PipelineStage,
+        // We only support two sample configs at the moment, unified and
+        // stencil. So we can query multisample info for everywhere/anywhere
+        // by checking the correct buffer.
+        kEverywhere_PipelineStage = kColorBuffer_PipelineStage,
+        kAnywhere_PipelineStage = kStencilBuffer_PipelineStage
+    };
+
+    /**
+     * @param  pipelineStage  specifies the pipeline stage for which
+     *                        multisampling is queried
+     * @return true if the surface is multisampled in the specified pipeline
+     *         stage(s), false otherwise
+     */
+    bool isMultisampled(PipelineStage pipelineStage =
+                                      kEverywhere_PipelineStage) const {
+        if (kStencil_GrSampleConfig == fSampleConfig &&
+            kColorBuffer_PipelineStage == pipelineStage) {
+            return false;
+        }
+        return 0 != fDesc.fSampleCnt;
+     }
+
+    /**
+     * @param  pipelineStage  specifies the pipeline stage for which
+     *                        multisampling is queried
+     * @return the number of samples-per-pixel, or zero if the render target
+     *         is not multisampled in the specified pipeline stage(s)
+     */
+    int numSamples(PipelineStage pipelineStage =
+                                 kEverywhere_PipelineStage) const {
+        return this->isMultisampled(pipelineStage) ? fDesc.fSampleCnt : 0;
+    }
 
     /**
-     * @return the number of samples-per-pixel or zero if non-MSAA.
+     * @return sample config: kUnified_GrSampleConfig if both color and stencil
+               buffers are MSAA, or kStencil_GrSampleConfig if only stencil
+               buffer is MSAA.
      */
-    int numSamples() const { return fDesc.fSampleCnt; }
+    GrSampleConfig sampleConfig() const {
+        return fSampleConfig;
+    }
 
     /**
      * Call to indicate the multisample contents were modified such that the
@@ -94,8 +135,10 @@ 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 +153,8 @@ private:
 
     friend class GrRenderTargetPriv;
 
+    GrSampleConfig    fSampleConfig;
+
     GrStencilBuffer*  fStencilBuffer;
 
     SkIRect           fResolveRect;