Implement support for mixed sampled render targets

include/gpu/GrTypes.h

Index: include/gpu/GrTypes.h
diff --git a/include/gpu/GrTypes.h b/include/gpu/GrTypes.h
index 3f02c62bfd07aab21c647c673beef0850a782c32..868c8fe7bb05c85ff4b721aac17e13fb74121d13 100644
--- a/include/gpu/GrTypes.h
+++ b/include/gpu/GrTypes.h
@@ -423,6 +423,18 @@ enum GrSurfaceOrigin {
 };
 
 /**
+ * Sample config clarifies the meaning of samples count.
+ * In default kUnified_GrSampleConfig sample count refers to MSAA sample count.
+ * If NV_framebuffer_mixed_samples is available and sample config is chosen to be
+ * kStencil_GrSampleConfig, sample count refers to the stencil sample count only,
+ * and the color sample count is assumed to be zero.
+ */
+enum GrSampleConfig {
+    kUnified_GrSampleConfig,
+    kStencil_GrSampleConfig,
+};
+
+/**
  * Describes a surface to be created.
  */
 struct GrSurfaceDesc {
@@ -549,6 +561,13 @@ struct GrBackendRenderTargetDesc {
      */
     int                             fSampleCnt;
     /**
+     * If fSampleCnt is > 1, which buffers are multisampled (color and stencil,
+     * or just stencil?). The default is both. Note that mixing multisampled
+     * and aliased buffers is only possible if NV_framebuffer_mixed_samples is
+     * available.
+     */
+    GrSampleConfig                  fSampleConfig;
+    /**
      * Number of bits of stencil per-pixel.
      */
     int                             fStencilBits;