Move XferEffects class to GrCustomXfermode file

src/gpu/effects/GrCustomXfermode.cpp

Index: src/gpu/effects/GrCustomXfermode.cpp
diff --git a/src/gpu/effects/GrCustomXfermode.cpp b/src/gpu/effects/GrCustomXfermode.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..a78f304850b0c16f90233ecc1e076d20c3f0b287
--- /dev/null
+++ b/src/gpu/effects/GrCustomXfermode.cpp
@@ -0,0 +1,492 @@
+/*
+ * 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 "effects/GrCustomXfermode.h"
+#include "effects/GrCustomXfermodePriv.h"
+
+#include "GrCoordTransform.h"
+#include "GrContext.h"
+#include "GrFragmentProcessor.h"
+#include "GrInvariantOutput.h"
+#include "GrProcessor.h"
+#include "GrTexture.h"
+#include "GrTextureAccess.h"
+#include "SkXfermode.h"
+#include "gl/GrGLCaps.h"
+#include "gl/GrGLProcessor.h"
+#include "gl/GrGLProgramDataManager.h"
+#include "gl/builders/GrGLProgramBuilder.h"
+
+bool GrCustomXfermode::IsSupportedMode(SkXfermode::Mode mode) {
+    return mode > SkXfermode::kLastCoeffMode && mode <= SkXfermode::kLastMode;
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Static helpers
+///////////////////////////////////////////////////////////////////////////////
+
+static void hard_light(GrGLFPFragmentBuilder* fsBuilder,
+                       const char* final,
+                       const char* src,
+                       const char* dst) {
+    static const char kComponents[] = {'r', 'g', 'b'};
+    for (size_t i = 0; i < SK_ARRAY_COUNT(kComponents); ++i) {
+        char component = kComponents[i];
+        fsBuilder->codeAppendf("if (2.0 * %s.%c <= %s.a) {", src, component, src);
+        fsBuilder->codeAppendf("%s.%c = 2.0 * %s.%c * %s.%c;",
+                               final, component, src, component, dst, component);
+        fsBuilder->codeAppend("} else {");
+        fsBuilder->codeAppendf("%s.%c = %s.a * %s.a - 2.0 * (%s.a - %s.%c) * (%s.a - %s.%c);",
+                               final, component, src, dst, dst, dst, component, src, src,
+                               component);
+        fsBuilder->codeAppend("}");
+    }
+    fsBuilder->codeAppendf("%s.rgb += %s.rgb * (1.0 - %s.a) + %s.rgb * (1.0 - %s.a);",
+                           final, src, dst, dst, src);
+}
+
+// Does one component of color-dodge
+static void color_dodge_component(GrGLFPFragmentBuilder* fsBuilder,
+                                  const char* final,
+                                  const char* src,
+                                  const char* dst,
+                                  const char component) {
+    fsBuilder->codeAppendf("if (0.0 == %s.%c) {", dst, component);
+    fsBuilder->codeAppendf("%s.%c = %s.%c * (1.0 - %s.a);",
+                           final, component, src, component, dst);
+    fsBuilder->codeAppend("} else {");
+    fsBuilder->codeAppendf("float d = %s.a - %s.%c;", src, src, component);
+    fsBuilder->codeAppend("if (0.0 == d) {");
+    fsBuilder->codeAppendf("%s.%c = %s.a * %s.a + %s.%c * (1.0 - %s.a) + %s.%c * (1.0 - %s.a);",
+                           final, component, src, dst, src, component, dst, dst, component,
+                           src);
+    fsBuilder->codeAppend("} else {");
+    fsBuilder->codeAppendf("d = min(%s.a, %s.%c * %s.a / d);",
+                           dst, dst, component, src);
+    fsBuilder->codeAppendf("%s.%c = d * %s.a + %s.%c * (1.0 - %s.a) + %s.%c * (1.0 - %s.a);",
+                           final, component, src, src, component, dst, dst, component, src);
+    fsBuilder->codeAppend("}");
+    fsBuilder->codeAppend("}");
+}
+
+// Does one component of color-burn
+static void color_burn_component(GrGLFPFragmentBuilder* fsBuilder,
+                                 const char* final,
+                                 const char* src,
+                                 const char* dst,
+                                 const char component) {
+    fsBuilder->codeAppendf("if (%s.a == %s.%c) {", dst, dst, component);
+    fsBuilder->codeAppendf("%s.%c = %s.a * %s.a + %s.%c * (1.0 - %s.a) + %s.%c * (1.0 - %s.a);",
+                           final, component, src, dst, src, component, dst, dst, component,
+                           src);
+    fsBuilder->codeAppendf("} else if (0.0 == %s.%c) {", src, component);
+    fsBuilder->codeAppendf("%s.%c = %s.%c * (1.0 - %s.a);",
+                           final, component, dst, component, src);
+    fsBuilder->codeAppend("} else {");
+    fsBuilder->codeAppendf("float d = max(0.0, %s.a - (%s.a - %s.%c) * %s.a / %s.%c);",
+                           dst, dst, dst, component, src, src, component);
+    fsBuilder->codeAppendf("%s.%c = %s.a * d + %s.%c * (1.0 - %s.a) + %s.%c * (1.0 - %s.a);",
+                           final, component, src, src, component, dst, dst, component, src);
+    fsBuilder->codeAppend("}");
+}
+
+// Does one component of soft-light. Caller should have already checked that dst alpha > 0.
+static void soft_light_component_pos_dst_alpha(GrGLFPFragmentBuilder* fsBuilder,
+                                               const char* final,
+                                               const char* src,
+                                               const char* dst,
+                                               const char component) {
+    // if (2S < Sa)
+    fsBuilder->codeAppendf("if (2.0 * %s.%c <= %s.a) {", src, component, src);
+    // (D^2 (Sa-2 S))/Da+(1-Da) S+D (-Sa+2 S+1)
+    fsBuilder->codeAppendf("%s.%c = (%s.%c*%s.%c*(%s.a - 2.0*%s.%c)) / %s.a +"
+                                   "(1.0 - %s.a) * %s.%c + %s.%c*(-%s.a + 2.0*%s.%c + 1.0);",
+                           final, component, dst, component, dst, component, src, src,
+                           component, dst, dst, src, component, dst, component, src, src,
+                           component);
+    // else if (4D < Da)
+    fsBuilder->codeAppendf("} else if (4.0 * %s.%c <= %s.a) {",
+                           dst, component, dst);
+    fsBuilder->codeAppendf("float DSqd = %s.%c * %s.%c;",
+                           dst, component, dst, component);
+    fsBuilder->codeAppendf("float DCub = DSqd * %s.%c;", dst, component);
+    fsBuilder->codeAppendf("float DaSqd = %s.a * %s.a;", dst, dst);
+    fsBuilder->codeAppendf("float DaCub = DaSqd * %s.a;", dst);
+    // (Da^3 (-S)+Da^2 (S-D (3 Sa-6 S-1))+12 Da D^2 (Sa-2 S)-16 D^3 (Sa-2 S))/Da^2
+    fsBuilder->codeAppendf("%s.%c ="
+                           "(-DaCub*%s.%c + DaSqd*(%s.%c - %s.%c * (3.0*%s.a - 6.0*%s.%c - 1.0)) +"
+                           " 12.0*%s.a*DSqd*(%s.a - 2.0*%s.%c) - 16.0*DCub * (%s.a - 2.0*%s.%c)) /"
+                           "DaSqd;",
+                           final, component, src, component, src, component, dst, component,
+                           src, src, component, dst, src, src, component, src, src,
+                           component);
+    fsBuilder->codeAppendf("} else {");
+    // -sqrt(Da * D) (Sa-2 S)-Da S+D (Sa-2 S+1)+S
+    fsBuilder->codeAppendf("%s.%c = -sqrt(%s.a*%s.%c)*(%s.a - 2.0*%s.%c) - %s.a*%s.%c +"
+                                   "%s.%c*(%s.a - 2.0*%s.%c + 1.0) + %s.%c;",
+                           final, component, dst, dst, component, src, src, component, dst,
+                           src, component, dst, component, src, src, component, src,
+                           component);
+    fsBuilder->codeAppendf("}");
+}
+
+// Adds a function that takes two colors and an alpha as input. It produces a color with the
+// hue and saturation of the first color, the luminosity of the second color, and the input
+// alpha. It has this signature:
+//      vec3 set_luminance(vec3 hueSatColor, float alpha, vec3 lumColor).
+static void add_lum_function(GrGLFPFragmentBuilder* fsBuilder, SkString* setLumFunction) {
+    // Emit a helper that gets the luminance of a color.
+    SkString getFunction;
+    GrGLShaderVar getLumArgs[] = {
+        GrGLShaderVar("color", kVec3f_GrSLType),
+    };
+    SkString getLumBody("return dot(vec3(0.3, 0.59, 0.11), color);");
+    fsBuilder->emitFunction(kFloat_GrSLType,
+                            "luminance",
+                            SK_ARRAY_COUNT(getLumArgs), getLumArgs,
+                            getLumBody.c_str(),
+                            &getFunction);
+
+    // Emit the set luminance function.
+    GrGLShaderVar setLumArgs[] = {
+        GrGLShaderVar("hueSat", kVec3f_GrSLType),
+        GrGLShaderVar("alpha", kFloat_GrSLType),
+        GrGLShaderVar("lumColor", kVec3f_GrSLType),
+    };
+    SkString setLumBody;
+    setLumBody.printf("float diff = %s(lumColor - hueSat);", getFunction.c_str());
+    setLumBody.append("vec3 outColor = hueSat + diff;");
+    setLumBody.appendf("float outLum = %s(outColor);", getFunction.c_str());
+    setLumBody.append("float minComp = min(min(outColor.r, outColor.g), outColor.b);"
+                      "float maxComp = max(max(outColor.r, outColor.g), outColor.b);"
+                      "if (minComp < 0.0 && outLum != minComp) {"
+                      "outColor = outLum + ((outColor - vec3(outLum, outLum, outLum)) * outLum) /"
+                                          "(outLum - minComp);"
+                      "}"
+                      "if (maxComp > alpha && maxComp != outLum) {"
+                      "outColor = outLum +"
+                                 "((outColor - vec3(outLum, outLum, outLum)) * (alpha - outLum)) /"
+                                 "(maxComp - outLum);"
+                      "}"
+                      "return outColor;");
+    fsBuilder->emitFunction(kVec3f_GrSLType,
+                            "set_luminance",
+                            SK_ARRAY_COUNT(setLumArgs), setLumArgs,
+                            setLumBody.c_str(),
+                            setLumFunction);
+}
+
+// Adds a function that creates a color with the hue and luminosity of one input color and
+// the saturation of another color. It will have this signature:
+//      float set_saturation(vec3 hueLumColor, vec3 satColor)
+static void add_sat_function(GrGLFPFragmentBuilder* fsBuilder, SkString* setSatFunction) {
+    // Emit a helper that gets the saturation of a color
+    SkString getFunction;
+    GrGLShaderVar getSatArgs[] = { GrGLShaderVar("color", kVec3f_GrSLType) };
+    SkString getSatBody;
+    getSatBody.printf("return max(max(color.r, color.g), color.b) - "
+                      "min(min(color.r, color.g), color.b);");
+    fsBuilder->emitFunction(kFloat_GrSLType,
+                            "saturation",
+                            SK_ARRAY_COUNT(getSatArgs), getSatArgs,
+                            getSatBody.c_str(),
+                            &getFunction);
+
+    // Emit a helper that sets the saturation given sorted input channels. This used
+    // to use inout params for min, mid, and max components but that seems to cause
+    // problems on PowerVR drivers. So instead it returns a vec3 where r, g ,b are the
+    // adjusted min, mid, and max inputs, respectively.
+    SkString helperFunction;
+    GrGLShaderVar helperArgs[] = {
+        GrGLShaderVar("minComp", kFloat_GrSLType),
+        GrGLShaderVar("midComp", kFloat_GrSLType),
+        GrGLShaderVar("maxComp", kFloat_GrSLType),
+        GrGLShaderVar("sat", kFloat_GrSLType),
+    };
+    static const char kHelperBody[] = "if (minComp < maxComp) {"
+        "vec3 result;"
+        "result.r = 0.0;"
+        "result.g = sat * (midComp - minComp) / (maxComp - minComp);"
+        "result.b = sat;"
+        "return result;"
+        "} else {"
+        "return vec3(0, 0, 0);"
+        "}";
+    fsBuilder->emitFunction(kVec3f_GrSLType,
+                            "set_saturation_helper",
+                            SK_ARRAY_COUNT(helperArgs), helperArgs,
+                            kHelperBody,
+                            &helperFunction);
+
+    GrGLShaderVar setSatArgs[] = {
+        GrGLShaderVar("hueLumColor", kVec3f_GrSLType),
+        GrGLShaderVar("satColor", kVec3f_GrSLType),
+    };
+    const char* helpFunc = helperFunction.c_str();
+    SkString setSatBody;
+    setSatBody.appendf("float sat = %s(satColor);"
+                       "if (hueLumColor.r <= hueLumColor.g) {"
+                       "if (hueLumColor.g <= hueLumColor.b) {"
+                       "hueLumColor.rgb = %s(hueLumColor.r, hueLumColor.g, hueLumColor.b, sat);"
+                       "} else if (hueLumColor.r <= hueLumColor.b) {"
+                       "hueLumColor.rbg = %s(hueLumColor.r, hueLumColor.b, hueLumColor.g, sat);"
+                       "} else {"
+                       "hueLumColor.brg = %s(hueLumColor.b, hueLumColor.r, hueLumColor.g, sat);"
+                       "}"
+                       "} else if (hueLumColor.r <= hueLumColor.b) {"
+                       "hueLumColor.grb = %s(hueLumColor.g, hueLumColor.r, hueLumColor.b, sat);"
+                       "} else if (hueLumColor.g <= hueLumColor.b) {"
+                       "hueLumColor.gbr = %s(hueLumColor.g, hueLumColor.b, hueLumColor.r, sat);"
+                       "} else {"
+                       "hueLumColor.bgr = %s(hueLumColor.b, hueLumColor.g, hueLumColor.r, sat);"
+                       "}"
+                       "return hueLumColor;",
+                       getFunction.c_str(), helpFunc, helpFunc, helpFunc, helpFunc,
+                       helpFunc, helpFunc);
+    fsBuilder->emitFunction(kVec3f_GrSLType,
+                            "set_saturation",
+                            SK_ARRAY_COUNT(setSatArgs), setSatArgs,
+                            setSatBody.c_str(),
+                            setSatFunction);
+
+}
+
+static void emit_custom_xfermode_code(SkXfermode::Mode mode,
+                                      GrGLFPFragmentBuilder* fsBuilder,
+                                      const char* outputColor,
+                                      const char* inputColor,
+                                      const char* dstColor) {
+    // We don't try to optimize for this case at all
+    if (NULL == inputColor) {
+        fsBuilder->codeAppendf("const vec4 ones = vec4(1);");
+        inputColor = "ones";
+    }
+    fsBuilder->codeAppendf("// SkXfermode::Mode: %s\n", SkXfermode::ModeName(mode));
+
+    // These all perform src-over on the alpha channel.
+    fsBuilder->codeAppendf("%s.a = %s.a + (1.0 - %s.a) * %s.a;",
+                           outputColor, inputColor, inputColor, dstColor);
+
+    switch (mode) {
+        case SkXfermode::kOverlay_Mode:
+            // Overlay is Hard-Light with the src and dst reversed
+            hard_light(fsBuilder, outputColor, dstColor, inputColor);
+            break;
+        case SkXfermode::kDarken_Mode:
+            fsBuilder->codeAppendf("%s.rgb = min((1.0 - %s.a) * %s.rgb + %s.rgb, "
+                                   "(1.0 - %s.a) * %s.rgb + %s.rgb);",
+                                   outputColor,
+                                   inputColor, dstColor, inputColor,
+                                   dstColor, inputColor, dstColor);
+            break;
+        case SkXfermode::kLighten_Mode:
+            fsBuilder->codeAppendf("%s.rgb = max((1.0 - %s.a) * %s.rgb + %s.rgb, "
+                                   "(1.0 - %s.a) * %s.rgb + %s.rgb);",
+                                   outputColor,
+                                   inputColor, dstColor, inputColor,
+                                   dstColor, inputColor, dstColor);
+            break;
+        case SkXfermode::kColorDodge_Mode:
+            color_dodge_component(fsBuilder, outputColor, inputColor, dstColor, 'r');
+            color_dodge_component(fsBuilder, outputColor, inputColor, dstColor, 'g');
+            color_dodge_component(fsBuilder, outputColor, inputColor, dstColor, 'b');
+            break;
+        case SkXfermode::kColorBurn_Mode:
+            color_burn_component(fsBuilder, outputColor, inputColor, dstColor, 'r');
+            color_burn_component(fsBuilder, outputColor, inputColor, dstColor, 'g');
+            color_burn_component(fsBuilder, outputColor, inputColor, dstColor, 'b');
+            break;
+        case SkXfermode::kHardLight_Mode:
+            hard_light(fsBuilder, outputColor, inputColor, dstColor);
+            break;
+        case SkXfermode::kSoftLight_Mode:
+            fsBuilder->codeAppendf("if (0.0 == %s.a) {", dstColor);
+            fsBuilder->codeAppendf("%s.rgba = %s;", outputColor, inputColor);
+            fsBuilder->codeAppendf("} else {");
+            soft_light_component_pos_dst_alpha(fsBuilder, outputColor, inputColor, dstColor, 'r');
+            soft_light_component_pos_dst_alpha(fsBuilder, outputColor, inputColor, dstColor, 'g');
+            soft_light_component_pos_dst_alpha(fsBuilder, outputColor, inputColor, dstColor, 'b');
+            fsBuilder->codeAppendf("}");
+            break;
+        case SkXfermode::kDifference_Mode:
+            fsBuilder->codeAppendf("%s.rgb = %s.rgb + %s.rgb -"
+                                   "2.0 * min(%s.rgb * %s.a, %s.rgb * %s.a);",
+                                   outputColor, inputColor, dstColor, inputColor, dstColor,
+                                   dstColor, inputColor);
+            break;
+        case SkXfermode::kExclusion_Mode:
+            fsBuilder->codeAppendf("%s.rgb = %s.rgb + %s.rgb - "
+                                   "2.0 * %s.rgb * %s.rgb;",
+                                   outputColor, dstColor, inputColor, dstColor, inputColor);
+            break;
+        case SkXfermode::kMultiply_Mode:
+            fsBuilder->codeAppendf("%s.rgb = (1.0 - %s.a) * %s.rgb + "
+                                   "(1.0 - %s.a) * %s.rgb + "
+                                   "%s.rgb * %s.rgb;",
+                                   outputColor, inputColor, dstColor, dstColor, inputColor,
+                                   inputColor, dstColor);
+            break;
+        case SkXfermode::kHue_Mode: {
+            //  SetLum(SetSat(S * Da, Sat(D * Sa)), Sa*Da, D*Sa) + (1 - Sa) * D + (1 - Da) * S
+            SkString setSat, setLum;
+            add_sat_function(fsBuilder, &setSat);
+            add_lum_function(fsBuilder, &setLum);
+            fsBuilder->codeAppendf("vec4 dstSrcAlpha = %s * %s.a;",
+                                   dstColor, inputColor);
+            fsBuilder->codeAppendf("%s.rgb = %s(%s(%s.rgb * %s.a, dstSrcAlpha.rgb),"
+                                               "dstSrcAlpha.a, dstSrcAlpha.rgb);",
+                                   outputColor, setLum.c_str(), setSat.c_str(), inputColor,
+                                   dstColor);
+            fsBuilder->codeAppendf("%s.rgb += (1.0 - %s.a) * %s.rgb + (1.0 - %s.a) * %s.rgb;",
+                                   outputColor, inputColor, dstColor, dstColor, inputColor);
+            break;
+        }
+        case SkXfermode::kSaturation_Mode: {
+            // SetLum(SetSat(D * Sa, Sat(S * Da)), Sa*Da, D*Sa)) + (1 - Sa) * D + (1 - Da) * S
+            SkString setSat, setLum;
+            add_sat_function(fsBuilder, &setSat);
+            add_lum_function(fsBuilder, &setLum);
+            fsBuilder->codeAppendf("vec4 dstSrcAlpha = %s * %s.a;",
+                                   dstColor, inputColor);
+            fsBuilder->codeAppendf("%s.rgb = %s(%s(dstSrcAlpha.rgb, %s.rgb * %s.a),"
+                                               "dstSrcAlpha.a, dstSrcAlpha.rgb);",
+                                   outputColor, setLum.c_str(), setSat.c_str(), inputColor,
+                                   dstColor);
+            fsBuilder->codeAppendf("%s.rgb += (1.0 - %s.a) * %s.rgb + (1.0 - %s.a) * %s.rgb;",
+                                   outputColor, inputColor, dstColor, dstColor, inputColor);
+            break;
+        }
+        case SkXfermode::kColor_Mode: {
+            //  SetLum(S * Da, Sa* Da, D * Sa) + (1 - Sa) * D + (1 - Da) * S
+            SkString setLum;
+            add_lum_function(fsBuilder, &setLum);
+            fsBuilder->codeAppendf("vec4 srcDstAlpha = %s * %s.a;",
+                                   inputColor, dstColor);
+            fsBuilder->codeAppendf("%s.rgb = %s(srcDstAlpha.rgb, srcDstAlpha.a, %s.rgb * %s.a);",
+                                   outputColor, setLum.c_str(), dstColor, inputColor);
+            fsBuilder->codeAppendf("%s.rgb += (1.0 - %s.a) * %s.rgb + (1.0 - %s.a) * %s.rgb;",
+                                   outputColor, inputColor, dstColor, dstColor, inputColor);
+            break;
+        }
+        case SkXfermode::kLuminosity_Mode: {
+            //  SetLum(D * Sa, Sa* Da, S * Da) + (1 - Sa) * D + (1 - Da) * S
+            SkString setLum;
+            add_lum_function(fsBuilder, &setLum);
+            fsBuilder->codeAppendf("vec4 srcDstAlpha = %s * %s.a;",
+                                   inputColor, dstColor);
+            fsBuilder->codeAppendf("%s.rgb = %s(%s.rgb * %s.a, srcDstAlpha.a, srcDstAlpha.rgb);",
+                                   outputColor, setLum.c_str(), dstColor, inputColor);
+            fsBuilder->codeAppendf("%s.rgb += (1.0 - %s.a) * %s.rgb + (1.0 - %s.a) * %s.rgb;",
+                                   outputColor, inputColor, dstColor, dstColor, inputColor);
+            break;
+        }
+        default:
+            SkFAIL("Unknown Custom Xfer mode.");
+            break;
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Fragment Processor
+///////////////////////////////////////////////////////////////////////////////
+
+GrFragmentProcessor* GrCustomXfermode::CreateFP(SkXfermode::Mode mode, GrTexture* background) {
+    if (!GrCustomXfermode::IsSupportedMode(mode)) {
+        return NULL;
+    } else {
+        return SkNEW_ARGS(GrCustomXferFP, (mode, background));
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+class GLCustomXferFP : public GrGLFragmentProcessor {
+public:
+    GLCustomXferFP(const GrFragmentProcessor&) {}
+    ~GLCustomXferFP() SK_OVERRIDE {};
+
+    void emitCode(GrGLFPBuilder* builder,
+                  const GrFragmentProcessor& fp,
+                  const char* outputColor,
+                  const char* inputColor,
+                  const TransformedCoordsArray& coords,
+                  const TextureSamplerArray& samplers) SK_OVERRIDE {
+        SkXfermode::Mode mode = fp.cast<GrCustomXferFP>().mode();
+        const GrTexture* backgroundTex =
+            fp.cast<GrCustomXferFP>().backgroundAccess().getTexture();
+        GrGLFPFragmentBuilder* fsBuilder = builder->getFragmentShaderBuilder();
+        const char* dstColor;
+        if (backgroundTex) {
+            dstColor = "bgColor";
+            fsBuilder->codeAppendf("vec4 %s = ", dstColor);
+            fsBuilder->appendTextureLookup(samplers[0], coords[0].c_str(), coords[0].getType());
+            fsBuilder->codeAppendf(";");
+        } else {
+            dstColor = fsBuilder->dstColor();
+        }
+        SkASSERT(dstColor);
+
+        emit_custom_xfermode_code(mode, fsBuilder, outputColor, inputColor, dstColor); 
+    }
+
+    void setData(const GrGLProgramDataManager&, const GrProcessor&) SK_OVERRIDE {}
+
+    static void GenKey(const GrFragmentProcessor& proc, const GrGLCaps&, GrProcessorKeyBuilder* b) {
+        // The background may come from the dst or from a texture.
+        uint32_t key = proc.numTextures();
+        SkASSERT(key <= 1);
+        key |= proc.cast<GrCustomXferFP>().mode() << 1;
+        b->add32(key);
+    }
+
+private:
+    typedef GrGLFragmentProcessor INHERITED;
+};
+
+///////////////////////////////////////////////////////////////////////////////
+
+GrCustomXferFP::GrCustomXferFP(SkXfermode::Mode mode, GrTexture* background)
+    : fMode(mode) {
+    this->initClassID<GrCustomXferFP>();
+    if (background) {
+        fBackgroundTransform.reset(kLocal_GrCoordSet, background, 
+                                   GrTextureParams::kNone_FilterMode);
+        this->addCoordTransform(&fBackgroundTransform);
+        fBackgroundAccess.reset(background);
+        this->addTextureAccess(&fBackgroundAccess);
+    } else {
+        this->setWillReadDstColor();
+    }
+}
+
+void GrCustomXferFP::getGLProcessorKey(const GrGLCaps& caps, GrProcessorKeyBuilder* b) const {
+    GLCustomXferFP::GenKey(*this, caps, b);
+}
+
+GrGLFragmentProcessor* GrCustomXferFP::createGLInstance() const {
+    return SkNEW_ARGS(GLCustomXferFP, (*this));
+}
+
+bool GrCustomXferFP::onIsEqual(const GrFragmentProcessor& other) const {
+    const GrCustomXferFP& s = other.cast<GrCustomXferFP>();
+    return fMode == s.fMode;
+}
+
+void GrCustomXferFP::onComputeInvariantOutput(GrInvariantOutput* inout) const {
+    inout->setToUnknown(GrInvariantOutput::kWill_ReadInput);
+}
+
+GR_DEFINE_FRAGMENT_PROCESSOR_TEST(GrCustomXferFP);
+GrFragmentProcessor* GrCustomXferFP::TestCreate(SkRandom* rand,
+                                                GrContext*,
+                                                const GrDrawTargetCaps&,
+                                                GrTexture*[]) {
+    int mode = rand->nextRangeU(SkXfermode::kLastCoeffMode + 1, SkXfermode::kLastSeparableMode);
+
+    return SkNEW_ARGS(GrCustomXferFP, (static_cast<SkXfermode::Mode>(mode), NULL));
+}
+