Implement support for KHR_blend_equation_advanced

include/gpu/effects/GrAdvancedEquationXferProcessor.h

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrAdvancedEquationXferProcessor_DEFINED
+#define GrAdvancedEquationXferProcessor_DEFINED
+
+#include "GrTypes.h"
+#include "GrXferProcessor.h"
+
+/**
+ * Provides Xfer processors that implement advanced SVG/PDF blend modes in hardware, without the
+ * need for a dst texture. Can only be used if supported by the GPU.
+ */
+class GrAdvancedEquationXPFactory : public GrXPFactory {
+public:
+    static bool IsSupported(const GrContext*, SkXfermode::Mode);
+    static GrXPFactory* Create(SkXfermode::Mode);
+
+    bool canTweakAlphaForCoverage() const override;
+    bool supportsRGBCoverage(GrColor, uint32_t) const override;
+
+    void getInvariantOutput(const GrProcOptInfo&, const GrProcOptInfo&,
+                            GrXPFactory::InvariantOutput* output) const override {
+        // Advanced blend modes all use the dst color, even when src alpha is 1, so we can't make
+        // any conclusions about the output without knowing something about the dst.
+        output->fWillBlendWithDst = true;
+        output->fBlendedColorFlags = 0;
+    }
+
+private:
+    template<GrBlendEquation> static GrXPFactory* RefFactory();
+
+    GrAdvancedEquationXPFactory(GrBlendEquation equation) : fEquation(equation) {}
+
+    GrXferProcessor* onCreateXferProcessor(const GrDrawTargetCaps& caps,
+                                           const GrProcOptInfo& colorPOI,
+                                           const GrProcOptInfo& coveragePOI,
+                                           const GrDeviceCoordTexture* dstCopy) const override;
+
+    bool willReadDstColor(const GrDrawTargetCaps&, const GrProcOptInfo&,
+                          const GrProcOptInfo&) const override {
+        return false;
+    }
+
+    bool onIsEqual(const GrXPFactory& xpfBase) const override {
+        const GrAdvancedEquationXPFactory& xpf = xpfBase.cast<GrAdvancedEquationXPFactory>();
+        return fEquation == xpf.fEquation;
+    }
+
+    const GrBlendEquation           fEquation;
+
+    GR_DECLARE_XP_FACTORY_TEST;
+
+    typedef GrXPFactory INHERITED;
+};
+
+#endif