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 ae420cea6c3aaa9e7c98c23af7185221dc5985b4..be16c59095df810c3cf16ab3c68e3402212922e3 100644
--- a/include/gpu/GrRenderTarget.h
+++ b/include/gpu/GrRenderTarget.h
@@ -31,14 +31,60 @@ 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 buffers. This enum allows the caller to query about
+     * specific buffers in isMultisampled() and numSamples().
      */
-    bool isMultisampled() const { return 0 != fDesc.fSampleCnt; }
+    enum BufferBits {
+        kAny_BufferBits = 0,
+        kColor_BufferBit = 1,
+        kStencil_BufferBit = (1 << 1),
+        kAll_BufferBits = kColor_BufferBit + kStencil_BufferBit
+    };
+
+    /**
+     * Enforce only two legal sample configs.
+     * kUnified_SampleConfig signifies multisampling in both color and stencil
+     * buffers and is available across all hardware.
+     * kStencil_SampleConfig means multisampling is present in stencil buffer
+     * only; this config requires hardware support of
+     * NV_framebuffer_mixed_samples.
+    */
+    enum SampleConfig {
+        kUnified_SampleConfig = kColor_BufferBit + kStencil_BufferBit,
+        kStencil_SampleConfig = kStencil_BufferBit
+    };
 
     /**
-     * @return the number of samples-per-pixel or zero if non-MSAA.
+     * @param  buffers  specifies the buffers for which multisampling is queried
+     * @return true if the surface is multisampled in the specified buffer(s),

[Chris Dalton, 2015/04/07 23:48:23]

Nit picking, but this is maybe ambiguous. How about:

"@return true if the surface is multisampled in every specified buffer"

[vbuzinov, 2015/04/08 12:05:30]

Done.

+     *         false otherwise
      */
-    int numSamples() const { return fDesc.fSampleCnt; }
+    bool isMultisampled(BufferBits buffers = kAll_BufferBits) const {
+        if (buffers != (fSampleConfig & buffers)) {
+            // One of the buffers is not in our msaa config.
+            return false;
+        }
+        return 0 != fDesc.fSampleCnt;
+    }
+
+    /**
+     * @param  buffers  specifies the buffers for which multisampling is queried
+     * @return the number of samples-per-pixel, or zero if the render target
+     *         is not multisampled in the specified buffer(s)

[Chris Dalton, 2015/04/07 23:48:23]

Here too:

"@return the number of samples-per-pixel, or zero if any of the specified
buffers is not multisampled."

[vbuzinov, 2015/04/08 12:05:30]

Done.

+     */
+    int numSamples(BufferBits buffers = kAll_BufferBits) const {
+        return this->isMultisampled(buffers) ? fDesc.fSampleCnt : 0;
+    }
+
+    /**
+     * @return sample config: kUnified_SampleConfig if both color and stencil
+               buffers are MSAA, or kStencil_SampleConfig if only stencil
+               buffer is MSAA.
+     */
+    SampleConfig sampleConfig() const {
+        return fSampleConfig;
+    }
 
     /**
      * Call to indicate the multisample contents were modified such that the
@@ -94,8 +140,10 @@ public:
     const GrRenderTargetPriv renderTargetPriv() const;
 
 protected:
-    GrRenderTarget(GrGpu* gpu, LifeCycle lifeCycle, const GrSurfaceDesc& desc)
+    GrRenderTarget(GrGpu* gpu, LifeCycle lifeCycle, const GrSurfaceDesc& desc,
+                   SampleConfig sampleConfig)
         : INHERITED(gpu, lifeCycle, desc)
+        , fSampleConfig(sampleConfig)
         , fStencilBuffer(NULL) {
         fResolveRect.setLargestInverted();
     }
@@ -110,6 +158,8 @@ private:
 
     friend class GrRenderTargetPriv;
 
+    SampleConfig      fSampleConfig;
+
     GrStencilBuffer*  fStencilBuffer;
 
     SkIRect           fResolveRect;
@@ -117,4 +167,6 @@ private:
     typedef GrSurface INHERITED;
 };
 
+GR_MAKE_BITFIELD_OPS(GrRenderTarget::BufferBits)
+
 #endif