Create fragment processor for performing input color blend with child processor

src/gpu/GrBlend.cpp

Index: src/gpu/GrBlend.cpp
diff --git a/src/gpu/GrBlend.cpp b/src/gpu/GrBlend.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..72a89d838ddb29d9bc0a096f439b8edcab5cdba3
--- /dev/null
+++ b/src/gpu/GrBlend.cpp
@@ -0,0 +1,124 @@
+/*
+* Copyright 2015 Google Inc.
+*
+* Use of this source code is governed by a BSD-style license that can be
+* found in the LICENSE file.
+*/
+
+#include "GrBlend.h"
+
+/**
+ * MaskedColor is used to evaluate the color and valid color component flags through the
+ * blending equation. Could possibly extend this to be used more broadly.
+ */
+class MaskedColor {
+public:
+    MaskedColor(GrColor color, GrColorComponentFlags flags)
+        : fColor(color)
+        , fFlags(flags) {}
+
+    MaskedColor() {}
+
+    void set(GrColor color, GrColorComponentFlags flags) {
+        fColor = color;
+        fFlags = flags;
+    }
+
+    static MaskedColor Invert(const MaskedColor& in) {
+        return MaskedColor(GrInvertColor(in.fColor), in.fFlags);
+    }
+
+    static MaskedColor ExtractAlpha(const MaskedColor& in) {
+        GrColorComponentFlags flags = (in.fFlags & kA_GrColorComponentFlag) ?
+            kRGBA_GrColorComponentFlags : kNone_GrColorComponentFlags;
+        return MaskedColor(GrColorPackA4(GrColorUnpackA(in.fColor)), flags);
+    }
+
+    static MaskedColor ExtractInverseAlpha(const MaskedColor& in) {
+        GrColorComponentFlags flags = (in.fFlags & kA_GrColorComponentFlag) ?
+            kRGBA_GrColorComponentFlags : kNone_GrColorComponentFlags;
+        return MaskedColor(GrColorPackA4(0xFF - GrColorUnpackA(in.fColor)), flags);
+    }
+
+    static MaskedColor Mul(const MaskedColor& a, const MaskedColor& b) {
+        GrColorComponentFlags outFlags = (a.fFlags & b.fFlags) | a.componentsWithValue(0) |
+                                         b.componentsWithValue(0);
+        return MaskedColor(GrColorMul(a.fColor, b.fColor), outFlags);
+    }
+
+    static MaskedColor SatAdd(const MaskedColor& a, const MaskedColor& b) {
+        GrColorComponentFlags outFlags = (a.fFlags & b.fFlags) | a.componentsWithValue(0xFF) |
+                                         b.componentsWithValue(0xFF);
+        return MaskedColor(GrColorSatAdd(a.fColor, b.fColor), outFlags);
+    }
+
+    GrColor color() const { return fColor; }
+
+    GrColorComponentFlags validFlags () const { return fFlags; }
+
+private:
+    GrColorComponentFlags componentsWithValue(unsigned value) const {
+        GrColorComponentFlags flags = kNone_GrColorComponentFlags;
+        if ((kR_GrColorComponentFlag & fFlags) && value == GrColorUnpackR(fColor)) {
+            flags |= kR_GrColorComponentFlag;
+        }
+        if ((kG_GrColorComponentFlag & fFlags) && value == GrColorUnpackG(fColor)) {
+            flags |= kG_GrColorComponentFlag;
+        }
+        if ((kB_GrColorComponentFlag & fFlags) && value == GrColorUnpackB(fColor)) {
+            flags |= kB_GrColorComponentFlag;
+        }
+        if ((kA_GrColorComponentFlag & fFlags) && value == GrColorUnpackA(fColor)) {
+            flags |= kA_GrColorComponentFlag;
+        }
+        return flags;
+    }
+
+    GrColor                 fColor;
+    GrColorComponentFlags   fFlags;
+};
+
+static MaskedColor get_term(GrBlendCoeff coeff, const MaskedColor& src, const MaskedColor& dst,
+                            const MaskedColor& value) {
+    switch (coeff) {
+        case kZero_GrBlendCoeff:
+            return MaskedColor(0, kRGBA_GrColorComponentFlags);
+        case kOne_GrBlendCoeff:
+            return value;
+        case kDC_GrBlendCoeff:
+            return MaskedColor::Mul(dst, value);
+        case kIDC_GrBlendCoeff:
+            return MaskedColor::Mul(MaskedColor::Invert(dst), value);
+        case kDA_GrBlendCoeff:
+            return MaskedColor::Mul(MaskedColor::ExtractAlpha(dst), value);
+        case kIDA_GrBlendCoeff:
+            return MaskedColor::Mul(MaskedColor::ExtractInverseAlpha(dst), value);
+        case kSC_GrBlendCoeff:
+            return MaskedColor::Mul(src, value);
+        case kISC_GrBlendCoeff:
+            return MaskedColor::Mul(MaskedColor::Invert(src), value);
+        case kSA_GrBlendCoeff:
+            return MaskedColor::Mul(MaskedColor::ExtractAlpha(src), value);
+        case kISA_GrBlendCoeff:
+            return MaskedColor::Mul(MaskedColor::ExtractInverseAlpha(src), value);
+        default:
+            SkFAIL("Illegal coefficient");
+            return MaskedColor();
+    }
+}
+
+void GrGetCoeffBlendKnownComponents(GrBlendCoeff srcCoeff, GrBlendCoeff dstCoeff,
+                                    GrColor srcColor, GrColorComponentFlags srcColorFlags,
+                                    GrColor dstColor, GrColorComponentFlags dstColorFlags,
+                                    GrColor* outColor,
+                                    GrColorComponentFlags* outFlags) {
+    MaskedColor src(srcColor, srcColorFlags);
+    MaskedColor dst(dstColor, dstColorFlags);
+
+    MaskedColor srcTerm = get_term(srcCoeff, src, dst, src);
+    MaskedColor dstTerm = get_term(dstCoeff, src, dst, dst);
+
+    MaskedColor output = MaskedColor::SatAdd(srcTerm, dstTerm);
+    *outColor = output.color();
+    *outFlags = output.validFlags();
+}