Implement support for KHR_blend_equation_advanced

src/gpu/GrDrawTargetCaps.h

Index: src/gpu/GrDrawTargetCaps.h
diff --git a/src/gpu/GrDrawTargetCaps.h b/src/gpu/GrDrawTargetCaps.h
index 310703cacad1d4a23e1fc8b73977e8739f992811..efc3512bd0c6a4832870b21e8d598c548ecbdf8a 100644
--- a/src/gpu/GrDrawTargetCaps.h
+++ b/src/gpu/GrDrawTargetCaps.h
@@ -142,6 +142,26 @@ public:
     bool useDrawInsteadOfClear() const { return fUseDrawInsteadOfClear; }
 
     /**
+     * Indicates the capabilities of the fixed function blend unit.
+     */
+    enum BlendEquationSupport {

[egdaniel, 2015/05/05 21:20:01]

Can BlendEquationSupport and related functions be moved into GL?

[Chris Dalton, 2015/05/06 16:06:27]

Not easily, most the places where we add support for advanced blend equations
are not in GL (getBlendInfo, GrBlendEquation, willNeedXferBarrier, xferBarrier,
GrXferBarrierType, willNeedDstCopy, getOptimizations, etc.)

Advanced blend equations are a hardware feature, all the OpenGL extension does
is give you access to our dedicated blend unit in the ROP. They will definitely
be available in any non-proprietary API that skia ends up on, so I actually
think Gr (not GL) feels like the right spot for it.

(I did put "AdvancedBlendEqnInteraction" in GrGLSLCaps because that part of the
extension felt like an API-specific idiosyncrasy)

[egdaniel, 2015/05/06 17:57:46]

sgtm

+        kBasic_BlendEquationSupport,             //<! Support to select the operator that
+                                                 //   combines src and dst terms.
+        kAdvanced_BlendEquationSupport,          //<! Additional fixed function support for specific
+                                                 //   SVG/PDF blend modes. Requires blend barriers.
+        kAdvancedCoherent_BlendEquationSupport,  //<! Advanced blend equation support that does not
+                                                 //   require blend barriers, and permits overlap.
+
+        kLast_BlendEquationSupport = kAdvancedCoherent_BlendEquationSupport
+    };
+
+    BlendEquationSupport blendEquationSupport() const { return fBlendEquationSupport; }
+
+    bool advancedBlendEquationSupport() const {
+        return kBasic_BlendEquationSupport != fBlendEquationSupport;
+    }
+
+    /**
      * Indicates whether GPU->CPU memory mapping for GPU resources such as vertex buffers and
      * textures allows partial mappings or full mappings.
      */
@@ -192,6 +212,7 @@ protected:
     // Driver workaround
     bool fUseDrawInsteadOfClear         : 1;
 
+    BlendEquationSupport fBlendEquationSupport;
     uint32_t fMapBufferFlags;
 
     int fMaxRenderTargetSize;