Added SkComposeShader GPU implementation

src/core/SkComposeShader.cpp

Index: src/core/SkComposeShader.cpp
diff --git a/src/core/SkComposeShader.cpp b/src/core/SkComposeShader.cpp
index c16d7ffc578f352f948d432934c68c41851c6623..15c556c76ce80c96f0254ef8ae0751b1bd5a7e08 100644
--- a/src/core/SkComposeShader.cpp
+++ b/src/core/SkComposeShader.cpp
@@ -194,6 +194,160 @@ void SkComposeShader::ComposeShaderContext::shadeSpan(int x, int y, SkPMColor re
     }
 }
 
+#if SK_SUPPORT_GPU
+
+#include "SkGr.h"
+#include "GrProcessor.h"
+#include "gl/GrGLBlend.h"
+#include "gl/builders/GrGLProgramBuilder.h"
+
+/////////////////////////////////////////////////////////////////////
+
+class GrComposeEffect : public GrFragmentProcessor {
+public:
+
+    static GrFragmentProcessor* Create(GrFragmentProcessor* fpA, GrFragmentProcessor* fpB,
+                                       SkXfermode::Mode mode) {
+        return SkNEW_ARGS(GrComposeEffect, (fpA, fpB, mode));
+    }
+    const char* name() const override {return fName.c_str(); }
+    void onGetGLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const override;
+
+    SkXfermode::Mode getMode() const { return fMode; }
+    int getShaderAChildIndex() const { return fShaderAChildIndex; }
+    int getShaderBChildIndex() const { return fShaderBChildIndex; }
+
+protected:
+    bool onIsEqual(const GrFragmentProcessor&) const override;
+    void onComputeInvariantOutput(GrInvariantOutput* inout) const override;
+
+private:
+    GrComposeEffect(GrFragmentProcessor* fpA, GrFragmentProcessor* fpB, SkXfermode::Mode mode)
+        : fMode(mode) {
+        this->initClassID<GrComposeEffect>();
+        fShaderAChildIndex = this->registerChildProcessor(fpA);
+        fShaderBChildIndex = this->registerChildProcessor(fpB);
+        fName.printf("Compose Shader <%s, %s> (Mode: %s)", fpA->name(), fpB->name(),
+                     SkXfermode::ModeName(fMode));
+    }
+
+    GrGLFragmentProcessor* onCreateGLInstance() const override;
+
+    SkString fName;
+    int fShaderAChildIndex;
+    int fShaderBChildIndex;
+    SkXfermode::Mode fMode;
+
+    typedef GrFragmentProcessor INHERITED;
+};
+
+/////////////////////////////////////////////////////////////////////
+
+class GrGLComposeEffect : public GrGLFragmentProcessor {
+public:
+    GrGLComposeEffect(const GrProcessor& processor) {
+        const GrComposeEffect& cs = processor.cast<GrComposeEffect>();
+        fShaderAChildIndex = cs.getShaderAChildIndex();
+        fShaderBChildIndex = cs.getShaderBChildIndex();
+        fMode = cs.getMode();
+    }
+
+    void emitCode(EmitArgs&) override;
+
+private:
+    int fShaderAChildIndex;
+    int fShaderBChildIndex;
+    SkXfermode::Mode fMode;
+
+    typedef GrGLFragmentProcessor INHERITED;
+};
+
+bool GrComposeEffect::onIsEqual(const GrFragmentProcessor& other) const {
+    const GrComposeEffect& cs = other.cast<GrComposeEffect>();
+    return fMode == cs.fMode;
+}
+
+void GrComposeEffect::onComputeInvariantOutput(GrInvariantOutput* inout) const {
+    inout->setToUnknown(GrInvariantOutput::kWill_ReadInput);
+}
+
+void GrComposeEffect::onGetGLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const {
+    b->add32(fMode);
+}
+
+GrGLFragmentProcessor* GrComposeEffect::onCreateGLInstance() const{
+    return SkNEW_ARGS(GrGLComposeEffect, (*this));
+}
+
+/////////////////////////////////////////////////////////////////////
+
+void GrGLComposeEffect::emitCode(EmitArgs& args) {
+
+    GrGLFragmentBuilder* fsBuilder = args.fBuilder->getFragmentShaderBuilder();
+
+    // emit the code of the two child shaders
+    SkString mangledOutputColorA;
+    this->emitChild(fShaderAChildIndex, args.fInputColor, &mangledOutputColorA, args);
+    SkString mangledOutputColorB;
+    this->emitChild(fShaderBChildIndex, args.fInputColor, &mangledOutputColorB, args);
+
+    // emit blend code
+    fsBuilder->codeAppend("\t{\n");
+    fsBuilder->codeAppendf("\t\t// Compose Xfer Mode: %s\n", SkXfermode::ModeName(fMode));
+    GrGLBlend::AppendPorterDuffBlend(fsBuilder, mangledOutputColorB.c_str(),
+                                     mangledOutputColorA.c_str(), args.fOutputColor, fMode);
+    fsBuilder->codeAppend("\t}\n");
+}
+
+/////////////////////////////////////////////////////////////////////
+
+bool SkComposeShader::asFragmentProcessor(GrContext* context, const SkPaint& paint,
+                                          const SkMatrix& viewM, const SkMatrix* localMatrix,
+                                          GrColor* paintColor,
+                                          GrProcessorDataManager* procDataManager,
+                                          GrFragmentProcessor** fp) const {
+    // NULL fMode implies src-over
+    SkXfermode::Mode mode = SkXfermode::Mode::kSrcOver_Mode;
+    if (fMode) {
+        // Fragment processor will only support coefficient modes that aren't kClear_Mode.
+        // This is because GrGLBlend::AppendPorterDuffBlend(), which emits the blend code in the
+        // shader, only supports those xfer modes.
+        SkXfermode::Coeff srcCoeff, dstCoeff;
+        if (!fMode->asMode(&mode) || !SkXfermode::ModeAsCoeff(mode, &srcCoeff, &dstCoeff)
+            || mode == SkXfermode::Mode::kClear_Mode) {

[egdaniel, 2015/08/21 16:21:39]

nit: we put the variable on the right side of ==

+            return false;
+        }
+    }
+    GrFragmentProcessor* fpA = NULL;
+    if (!fShaderA->asFragmentProcessor(context, paint, viewM, localMatrix, paintColor,
+        procDataManager, &fpA) || !fpA) {

[egdaniel, 2015/08/21 16:21:39]

Can you line this up so that procDataMangeger, &fpA is aligned with the other
params in the function call.

+        return false;
+    }
+    GrFragmentProcessor* fpB = NULL;
+    if (!fShaderB->asFragmentProcessor(context, paint, viewM, localMatrix, paintColor,

[egdaniel, 2015/08/21 16:21:39]

same as above

+        procDataManager, &fpB) || !fpB) {
+        fpA->unref();
+        return false;
+    }
+
+    *fp = GrComposeEffect::Create(fpA, fpB, mode);

[egdaniel, 2015/08/21 16:21:39]

Is there any chance that this Create can fail and return null? If we don't plan
on this ever failing in the future maybe we should just go with a ctor.
Otherwise we need to check here that it is not null

+    fpA->unref();
+    fpB->unref();
+
+    return true;
+}
+
+
+
+#else
+bool SkComposeShader::asFragmentProcessor(GrContext*, const SkPaint&, const SkMatrix&,
+                                          const SkMatrix*, GrColor*, GrProcessorDataManager*,
+                                          GrFragmentProcessor**) const {
+    SkDEBUGFAIL("Should not call in GPU-less build");
+    return false;
+}
+#endif
+
 #ifndef SK_IGNORE_TO_STRING
 void SkComposeShader::toString(SkString* str) const {
     str->append("SkComposeShader: (");