Implement support for KHR_blend_equation_advanced

include/gpu/GrXferProcessor.h

Index: include/gpu/GrXferProcessor.h
diff --git a/include/gpu/GrXferProcessor.h b/include/gpu/GrXferProcessor.h
index 12042d3f74617beca61710e19f1a75bccdf18aa7..3eeedcfebf7e5db7c0cf5a3267ac98972a4e4f52 100644
--- a/include/gpu/GrXferProcessor.h
+++ b/include/gpu/GrXferProcessor.h
@@ -20,6 +20,43 @@ class GrGLXferProcessor;
 class GrProcOptInfo;
 
 /**
+ * Equations for alpha-blending.
+ */
+enum GrBlendEquation {
+    kInvalid_GrBlendEquation = -1,
+
+    // Basic blend equations.
+    kAdd_GrBlendEquation,             //<! Cs*S + Cd*D
+    kSubtract_GrBlendEquation,        //<! Cs*S - Cd*D
+    kReverseSubtract_GrBlendEquation, //<! Cd*D - Cs*S
+
+    kLastBasicGrBlendEquation = kReverseSubtract_GrBlendEquation,
+
+    // Advanced blend equations. These are described in the SVG and PDF specs.
+    kScreen_GrBlendEquation,
+    kOverlay_GrBlendEquation,
+    kDarken_GrBlendEquation,
+    kLighten_GrBlendEquation,
+    kColorDodge_GrBlendEquation,
+    kColorBurn_GrBlendEquation,
+    kHardLight_GrBlendEquation,
+    kSoftLight_GrBlendEquation,
+    kDifference_GrBlendEquation,
+    kExclusion_GrBlendEquation,
+    kMultiply_GrBlendEquation,
+    kHSLHue_GrBlendEquation,
+    kHSLSaturation_GrBlendEquation,
+    kHSLColor_GrBlendEquation,
+    kHSLLuminosity_GrBlendEquation,
+
+    kTotalGrBlendEquationCount
+};
+
+bool constexpr GrBlendEquationIsAdvanced(GrBlendEquation equation) {
+    return equation > kLastBasicGrBlendEquation;
+}
+
+/**
  * Coeffecients for alpha-blending.
  */
 enum GrBlendCoeff {
@@ -48,6 +85,15 @@ enum GrBlendCoeff {
 };
 
 /**
+ * Barriers for blending. When a shader reads the dst directly, an Xfer barrier is sometimes
+ * required after a pixel has been written, before it can be safely read again.
+ */
+enum GrXferBarrierType {
+    kTexture_GrXferBarrierType, //<! Required when a shader reads and renders to the same texture.
+    kBlend_GrXferBarrierType,   //<! Required by certain blend extensions.
+};
+
+/**
  * GrXferProcessor is responsible for implementing the xfer mode that blends the src color and dst
  * color. It does this by emitting fragment shader code and controlling the fixed-function blend
  * state. The inputs to its shader code are the final computed src color and fractional pixel
@@ -124,14 +170,24 @@ public:
                                       GrColor* overrideColor,
                                       const GrDrawTargetCaps& caps) = 0;
 
+    /**
+     * Returns whether this XP will require an Xfer barrier on the given rt. If true, outBarrierType
+     * is updated to contain the type of barrier needed.
+     */
+    virtual bool willNeedXferBarrier(const GrRenderTarget* rt,
+                                     const GrDrawTargetCaps& caps,
+                                     GrXferBarrierType* outBarrierType) const;
+
     struct BlendInfo {
-        GrBlendCoeff fSrcBlend;
-        GrBlendCoeff fDstBlend;
-        GrColor      fBlendConstant;
-        bool         fWriteColor;
+        GrBlendEquation fEquation;
+        GrBlendCoeff    fSrcBlend;
+        GrBlendCoeff    fDstBlend;
+        GrColor         fBlendConstant;
+        bool            fWriteColor;
     };
 
     void getBlendInfo(BlendInfo* blendInfo) const {
+        blendInfo->fEquation = kAdd_GrBlendEquation;
         blendInfo->fSrcBlend = kOne_GrBlendCoeff;
         blendInfo->fDstBlend = kZero_GrBlendCoeff;
         blendInfo->fBlendConstant = 0;