Implement support for mixed sampled render targets

Adds a new FBO type kStencil_MSFBOType that is selected whenever
NV_framebuffer_mixed_samples extension is available.  In this new
FBO type a non-msaa color buffer is created with a multisampled
stencil buffer attachment.

Replaces numSamples() with separate numColorSamples and numStencilSamples
methods in RenderTarget.

In mixed samples mode non-MSAA codepaths are used to draw simple shapes,
while NVPR-rendered paths and text are rendered with a multisampled
stencil.

BUG=skia:3177

Review URL: https://codereview.chromium.org/1001503002

1 files changed, 61 insertions, 6 deletions

diff --git a/include/gpu/GrRenderTarget.h b/include/gpu/GrRenderTarget.h
index 5984bf71d8..91a67ae133 100644
--- a/include/gpu/GrRenderTarget.h
+++ b/include/gpu/GrRenderTarget.h
@@ -31,14 +31,65 @@ 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.
+     * 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 = 0,
+        kStencil_SampleConfig = 1
+    };
+
+    /**
+     * @return true if the surface is multisampled in all buffers,
+     *         false otherwise
+     */
+    bool isUnifiedMultisampled() const {
+        if (fSampleConfig != kUnified_SampleConfig) {
+            return false;
+        }
+        return 0 != fDesc.fSampleCnt;
+    }
+
+    /**
+     * @return true if the surface is multisampled in the stencil buffer,
+     *         false otherwise
+     */
+    bool isStencilBufferMultisampled() const {
+        return 0 != fDesc.fSampleCnt;
+    }
+
+    /**
+     * @return the number of color samples-per-pixel, or zero if non-MSAA or
+     *         multisampled in the stencil buffer only.
      */
-    bool isMultisampled() const { return 0 != fDesc.fSampleCnt; }
+    int numColorSamples() const {
+        if (fSampleConfig == kUnified_SampleConfig) {
+            return fDesc.fSampleCnt;
+        }
+        return 0;
+    }
 
     /**
-     * @return the number of samples-per-pixel or zero if non-MSAA.
+     * @return the number of stencil samples-per-pixel, or zero if non-MSAA.
      */
-    int numSamples() const { return fDesc.fSampleCnt; }
+    int numStencilSamples() const {
+        return fDesc.fSampleCnt;
+    }
+
+    /**
+     * @return true if the surface is mixed sampled, false otherwise.
+     */
+    bool hasMixedSamples() const {
+        SkASSERT(kStencil_SampleConfig != fSampleConfig ||
+                 this->isStencilBufferMultisampled());
+        return kStencil_SampleConfig == fSampleConfig;
+    }
 
     /**
      * Call to indicate the multisample contents were modified such that the
@@ -94,9 +145,11 @@ 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)
-        , fStencilAttachment(NULL) {
+        , fStencilAttachment(NULL)
+        , fSampleConfig(sampleConfig) {
         fResolveRect.setLargestInverted();
     }
 
@@ -111,10 +164,12 @@ private:
     friend class GrRenderTargetPriv;
 
     GrStencilAttachment*  fStencilAttachment;
+    SampleConfig          fSampleConfig;
 
     SkIRect               fResolveRect;
 
     typedef GrSurface INHERITED;
 };
 
+
 #endif