Create fragment processor for performing input color blend with child processor

tests/GrGetCoeffBlendKnownComponentsTest.cpp

+/*
+ * 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 "Test.h"
+
+#if SK_SUPPORT_GPU
+
+#include "GrBlend.h"
+#include "SkGr.h"
+#include "SkRandom.h"
+#include "SkXfermode.h"
+
+static GrColor make_baseline_color(GrColor src, GrColor dst, const SkXfermode* xm) {
+    SkPMColor skSrc = GrColorToSkPMColor(src);
+    SkPMColor skDst = GrColorToSkPMColor(dst);
+    if (xm) {
+        xm->xfer32(&skDst, &skSrc, 1, nullptr);
+    } else {
+        // null means src-over
+        skDst = SkPMSrcOver(skSrc, skDst);
+    }
+    return SkPMColorToGrColor(skDst);
+}
+
+DEF_TEST(GrGetCoeffBlendKnownComponents, reporter) {
+    SkRandom random;
+    for (int i = 0; i < SkXfermode::kLastCoeffMode; ++i) {
+        SkXfermode::Mode mode = (SkXfermode::Mode)i;
+        SkAutoTUnref<SkXfermode> xm(SkXfermode::Create(mode));
+        SkXfermode::Coeff srcCoeff, dstCoeff;
+        SkAssertResult(SkXfermode::ModeAsCoeff(mode, &srcCoeff, &dstCoeff));
+        for (int j = 0; j < 1000; ++j) {
+            GrColor src = GrPremulColor(random.nextU());
+            GrColor dst = GrPremulColor(random.nextU());
+            GrColor outColor;
+            GrColorComponentFlags outFlags;
+            GrGetCoeffBlendKnownComponents(SkXfermodeCoeffToGrBlendCoeff(srcCoeff),
+                                           SkXfermodeCoeffToGrBlendCoeff(dstCoeff),
+                                           src, kRGBA_GrColorComponentFlags,
+                                           dst, kRGBA_GrColorComponentFlags,
+                                           &outColor, &outFlags);
+            GrColor baselineColor = make_baseline_color(src, dst, xm);
+            if (SkAbs32(GrColorUnpackA(baselineColor) - GrColorUnpackA(outColor)) > 1 ||
+                SkAbs32(GrColorUnpackR(baselineColor) - GrColorUnpackR(outColor)) > 1 ||
+                SkAbs32(GrColorUnpackG(baselineColor) - GrColorUnpackG(outColor)) > 1 ||
+                SkAbs32(GrColorUnpackB(baselineColor) - GrColorUnpackB(outColor)) > 1) {
+                ERRORF(reporter, "Blended color is 0x%08x, expected 0x%08x", outColor,
+                       baselineColor);
+            }
+            GrColorIsPMAssert(outColor);
+        }
+    }
+}
+
+#endif