Implement support for KHR_blend_equation_advanced

src/gpu/effects/GrAdvancedEquationXferProcessor.cpp

Index: src/gpu/effects/GrAdvancedEquationXferProcessor.cpp
diff --git a/src/gpu/effects/GrAdvancedEquationXferProcessor.cpp b/src/gpu/effects/GrAdvancedEquationXferProcessor.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..cc8f6e7b615ae29b647c133fdd7fec7035c3be50
--- /dev/null
+++ b/src/gpu/effects/GrAdvancedEquationXferProcessor.cpp
@@ -0,0 +1,316 @@
+/*
+ * 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/GrAdvancedEquationXferProcessor.h"
+
+#include "GrDrawTargetCaps.h"
+#include "GrGpu.h"
+#include "gl/GrGLXferProcessor.h"
+#include "gl/builders/GrGLFragmentShaderBuilder.h"
+#include "gl/builders/GrGLProgramBuilder.h"
+
+class GrAdvancedEquationXPBase : public GrXferProcessor {
+public:
+    GrAdvancedEquationXPBase(GrBlendEquation equation) : fEquation(equation) {}
+
+    const char* name() const override { return "Blend Equation Advanced"; }
+    bool hasSecondaryOutput() const override { return false; }
+
+    GrXferProcessor::OptFlags getOptimizations(const GrProcOptInfo&, const GrProcOptInfo&, bool,
+                                               GrColor*, const GrDrawTargetCaps&) override {
+        return GrXferProcessor::kNone_Opt;
+    }
+
+    bool willNeedXferBarrier(const GrRenderTarget* rt, const GrDrawTargetCaps&,
+                             GrXferBarrierType* outBarrierType) const override;
+
+protected:
+    void onGetGLProcessorKey(const GrGLCaps&, GrProcessorKeyBuilder*) const override;
+
+    void onGetBlendInfo(BlendInfo*) const override;
+
+    bool onIsEqual(const GrXferProcessor& xpBase) const override {
+        const GrAdvancedEquationXPBase& xp = xpBase.cast<GrAdvancedEquationXPBase>();
+        return fEquation == xp.fEquation;
+    }
+
+    const GrBlendEquation fEquation;
+
+    typedef GrXferProcessor INHERITED;
+};
+
+template<bool HasCoverage> class GrAdvancedEquationXferProcessor : public GrAdvancedEquationXPBase {
+public:
+    GrAdvancedEquationXferProcessor(GrBlendEquation equation) : INHERITED(equation) {
+        this->initClassID<GrAdvancedEquationXferProcessor>();
+    }
+
+    GrGLXferProcessor* createGLInstance() const override;
+
+private:
+    typedef GrAdvancedEquationXPBase INHERITED;
+};
+
+
+bool GrAdvancedEquationXPFactory::IsSupported(const GrContext* context, SkXfermode::Mode mode) {
+    if (!context->getGpu()->caps()->advancedBlendEquationSupport()) {
+        return false;
+    }
+    if (mode > SkXfermode::kLastMode) {
+        return false;
+    }
+    return mode == SkXfermode::kScreen_Mode || mode > SkXfermode::kLastCoeffMode;
+}
+
+GrXPFactory* GrAdvancedEquationXPFactory::Create(const GrContext* context, SkXfermode::Mode mode) {
+    if (!context->getGpu()->caps()->advancedBlendEquationSupport()) {
+        return NULL;
+    }
+
+    switch (mode) {
+        default: break;
+        case SkXfermode::kScreen_Mode: return RefFactory<kScreen_GrBlendEquation>();
+        case SkXfermode::kOverlay_Mode: return RefFactory<kOverlay_GrBlendEquation>();
+        case SkXfermode::kDarken_Mode: return RefFactory<kDarken_GrBlendEquation>();
+        case SkXfermode::kLighten_Mode: return RefFactory<kLighten_GrBlendEquation>();
+        case SkXfermode::kColorDodge_Mode: return RefFactory<kColorDodge_GrBlendEquation>();
+        case SkXfermode::kColorBurn_Mode: return RefFactory<kColorBurn_GrBlendEquation>();
+        case SkXfermode::kHardLight_Mode: return RefFactory<kHardLight_GrBlendEquation>();
+        case SkXfermode::kSoftLight_Mode: return RefFactory<kSoftLight_GrBlendEquation>();
+        case SkXfermode::kDifference_Mode: return RefFactory<kDifference_GrBlendEquation>();
+        case SkXfermode::kExclusion_Mode: return RefFactory<kExclusion_GrBlendEquation>();
+        case SkXfermode::kMultiply_Mode: return RefFactory<kMultiply_GrBlendEquation>();
+        case SkXfermode::kHue_Mode: return RefFactory<kHSLHue_GrBlendEquation>();
+        case SkXfermode::kSaturation_Mode: return RefFactory<kHSLSaturation_GrBlendEquation>();
+        case SkXfermode::kColor_Mode: return RefFactory<kHSLColor_GrBlendEquation>();
+        case SkXfermode::kLuminosity_Mode: return RefFactory<kHSLLuminosity_GrBlendEquation>();
+    }
+
+    return NULL;
+}
+
+template<GrBlendEquation Equation> GrXPFactory* GrAdvancedEquationXPFactory::RefFactory() {
+    GR_STATIC_ASSERT(GrBlendEquationIsAdvanced(Equation));
+    static GrAdvancedEquationXPFactory* factory;
+    if (!factory) {
+        factory = SkNEW_ARGS(GrAdvancedEquationXPFactory, (Equation));
+    }
+    return SkRef(factory);
+}
+
+GrAdvancedEquationXPFactory::GrAdvancedEquationXPFactory(GrBlendEquation equation)
+    : fEquation(equation),
+      fXferProcessor(SkNEW_ARGS(GrAdvancedEquationXferProcessor<false>, (fEquation))),
+      fXferProcessorWithCoverage(SkNEW_ARGS(GrAdvancedEquationXferProcessor<true>, (fEquation))) {
+}
+
+GrAdvancedEquationXPFactory::~GrAdvancedEquationXPFactory() {
+}
+
+bool GrAdvancedEquationXPFactory::canTweakAlphaForCoverage() const {
+   /*
+    The general SVG blend equation is defined in the spec as follows:
+
+      Dca' = B(Sc, Dc) * Sa * Da + Y * Sca * (1-Da) + Z * Dca * (1-Sa)
+      Da'  = X * Sa * Da + Y * Sa * (1-Da) + Z * Da * (1-Sa)
+
+    (Note that Sca, Dca indicate RGB vectors that are premultiplied by alpha,
+     and that B(Sc, Dc) is a mode-specific function that accepts non-multiplied
+     RGB colors.)
+
+    For every "advanced" blend mode, X=Y=Z=1 and this equation reduces to the
+    PDF blend equation.
+
+    It can be shown that when X=Y=Z=1, canTweakAlphaForCoverage() is true.
+
+
+    == Color ==
+
+    We substitute Y=Z=1 and define a blend() function that calculates Dca' in
+    terms of premultiplied alpha only:
+
+      blend(Sca, Dca, Sa, Da) = {Dca : if Sa == 0,
+                                 Sca : if Da == 0,
+                                 B(Sca/Sa, Dca/Da) * Sa * Da + Sca * (1-Da) + Dca * (1-Sa) : if Sa,Da != 0}
+
+    And for coverage modulation, we use a post blend src-over model:
+
+      Dca'' = f * blend(Sca, Dca, Sa, Da) + (1-f) * Dca
+
+    (Where f is the fractional coverage.)
+
+    Next we show that canTweakAlphaForCoverage() is true by proving the
+    following relationship:
+
+      blend(f*Sca, Dca, f*Sa, Da) == f * blend(Sca, Dca, Sa, Da) + (1-f) * Dca
+
+    General case (f,Sa,Da != 0):
+
+      f * blend(Sca, Dca, Sa, Da) + (1-f) * Dca
+        = f * (B(Sca/Sa, Dca/Da) * Sa * Da + Sca * (1-Da) + Dca * (1-Sa)) + (1-f) * Dca  [Sa,Da != 0, definition of blend()]
+        = B(Sca/Sa, Dca/Da) * f*Sa * Da + f*Sca * (1-Da) + f*Dca * (1-Sa) + Dca - f*Dca
+        = B(Sca/Sa, Dca/Da) * f*Sa * Da + f*Sca - f*Sca * Da + f*Dca - f*Dca * Sa + Dca - f*Dca
+        = B(Sca/Sa, Dca/Da) * f*Sa * Da + f*Sca - f*Sca * Da - f*Dca * Sa + Dca
+        = B(Sca/Sa, Dca/Da) * f*Sa * Da + f*Sca * (1-Da) - f*Dca * Sa + Dca
+        = B(Sca/Sa, Dca/Da) * f*Sa * Da + f*Sca * (1-Da) + Dca * (1 - f*Sa)
+        = B(f*Sca/f*Sa, Dca/Da) * f*Sa * Da + f*Sca * (1-Da) + Dca * (1 - f*Sa)  [f!=0]
+        = blend(f*Sca, Dca, f*Sa, Da)  [definition of blend()]
+
+    Corner cases (Sa=0, Da=0, and f=0):
+
+      Sa=0: f * blend(Sca, Dca, Sa, Da) + (1-f) * Dca
+              = f * Dca + (1-f) * Dca  [Sa=0, definition of blend()]
+              = Dca
+              = blend(0, Dca, 0, Da)  [definition of blend()]
+              = blend(f*Sca, Dca, f*Sa, Da)  [Sa=0]
+
+      Da=0: f * blend(Sca, Dca, Sa, Da) + (1-f) * Dca
+              = f * Sca + (1-f) * Dca  [Da=0, definition of blend()]
+              = f * Sca  [Da=0]
+              = blend(f*Sca, 0, f*Sa, 0)  [definition of blend()]
+              = blend(f*Sca, Dca, f*Sa, Da)  [Da=0]
+
+      f=0: f * blend(Sca, Dca, Sa, Da) + (1-f) * Dca
+             = Dca  [f=0]
+             = blend(0, Dca, 0, Da)  [definition of blend()]
+             = blend(f*Sca, Dca, f*Sa, Da)  [f=0]
+
+    == Alpha ==
+
+    We substitute X=Y=Z=1 and define a blend() function that calculates Da':
+
+      blend(Sa, Da) = Sa * Da + Sa * (1-Da) + Da * (1-Sa)
+                    = Sa * Da + Sa - Sa * Da + Da - Da * Sa
+                    = Sa + Da - Sa * Da
+
+    We use the same model for coverage modulation as we did with color:
+
+      Da'' = f * blend(Sa, Da) + (1-f) * Da
+
+    And show that canTweakAlphaForCoverage() is true by proving the following
+    relationship:
+
+      blend(f*Sa, Da) == f * blend(Sa, Da) + (1-f) * Da
+
+
+      f * blend(Sa, Da) + (1-f) * Da
+        = f * (Sa + Da - Sa * Da) + (1-f) * Da
+        = f*Sa + f*Da - f*Sa * Da + Da - f*Da
+        = f*Sa - f*Sa * Da + Da
+        = f*Sa + Da - f*Sa * Da
+        = blend(f*Sa, Da)
+   */
+
+    return true;
+}
+
+bool GrAdvancedEquationXPFactory::supportsRGBCoverage(GrColor, uint32_t) const {
+   /*
+    We do coverage modulation by multiplying it into the src color before
+    blending. The GPU runs the blend equation *after* the fragment shader, so
+    it is not within our control to apply coverage at that point. This model
+    is mathematically correct, but it only works with scalar coverage. It's easy
+    to see why it won't work when coverage is unique per component:
+
+      blend(fc*Sca, Dca, fa*Sa, Da)
+        = B((fc*Sca)/(fa*Sa), Dca/Da) * ...
+        != B(Sc, Dc) * ...
+
+    The arguments for B() no longer reduce to (Sc, Dc). And when Sc == 0, the
+    arguments for B() work, but the equation still doesn't:
+
+      fc * blend(0, Dca, Sa, Da) + (1-fc) * Dca
+        = ...
+        = B(0, Dca/Da) * fc*Sa * Da + fc*0 * (1-Da) + Dca * (1 - fc*Sa)
+        = blend(fc*0, Dca, fc*Sa, Da)
+        != blend(fc*0, Dca, fa*Sa, Da)
+
+    (Note that this could work if we knew the dst was transparent black.)
+   */
+
+    return false;
+}
+
+GrXferProcessor* GrAdvancedEquationXPFactory::onCreateXferProcessor(
+                                                        const GrDrawTargetCaps& caps,
+                                                        const GrProcOptInfo& colorPOI,
+                                                        const GrProcOptInfo& coveragePOI,
+                                                        const GrDeviceCoordTexture* dstCopy) const {
+    SkASSERT(caps.advancedBlendEquationSupport());
+    SkASSERT(!dstCopy || !dstCopy->texture());
+
+    if (coveragePOI.isFourChannelOutput()) {
+        // RGB coverage is not supported. (See supportsRGBCoverage())
+        return NULL;
+    }
+
+    return SkRef(coveragePOI.isSolidWhite() ? fXferProcessor.get()
+                                            : fXferProcessorWithCoverage.get());

[Chris Dalton, 2015/04/17 08:37:19]

TODO: This causes an assert:

  ../../src/gpu/GrMemoryPool.cpp:35: failed assertion "0 == fAllocationCnt"

Is there a workaround besides new-ing one every time?

+}
+
+bool GrAdvancedEquationXPBase::willNeedXferBarrier(const GrRenderTarget*,
+                                                   const GrDrawTargetCaps& caps,
+                                                   GrXferBarrierType* outBarrierType) const {
+    if (GrDrawTargetCaps::kAdvancedCoherent_BlendEquationSupport != caps.blendEquationSupport()) {
+        *outBarrierType = kBlend_GrXferBarrierType;
+        return true;
+    }
+    return false;
+}
+
+void GrAdvancedEquationXPBase::onGetGLProcessorKey(const GrGLCaps&, GrProcessorKeyBuilder*) const {
+    // Our XP's don't emit variable fragment code. (HasCoverage is accounted for by the class ID.)
+    return;
+}
+
+template</*HasCoverage = false*/>
+GrGLXferProcessor* GrAdvancedEquationXferProcessor<false>::createGLInstance() const {
+    class GLAdvancedEquationXP : public GrGLXferProcessor {
+    private:
+        void onEmitCode(const EmitArgs& args) override {
+            GrGLFPFragmentBuilder* fsBuilder = args.fPB->getFragmentShaderBuilder();
+            fsBuilder->codeAppendf("%s = %s;", args.fOutputPrimary, args.fInputColor);
+        }
+        void onSetData(const GrGLProgramDataManager&, const GrXferProcessor&) override {}
+    };
+    return SkNEW(GLAdvancedEquationXP);
+}
+
+template</*HasCoverage = true*/>
+GrGLXferProcessor* GrAdvancedEquationXferProcessor<true>::createGLInstance() const {
+    class GLAdvancedEquationXPWithCoverage : public GrGLXferProcessor {
+    private:
+        void onEmitCode(const EmitArgs& args) override {
+            // We do coverage modulation by multiplying it into the src color before blending.
+            // (See canTweakAlphaForCoverage())
+            GrGLFPFragmentBuilder* fsBuilder = args.fPB->getFragmentShaderBuilder();
+            fsBuilder->codeAppendf("%s = %s * %s;",
+                                   args.fOutputPrimary, args.fInputColor, args.fInputCoverage);
+        }
+        void onSetData(const GrGLProgramDataManager&, const GrXferProcessor&) override {}
+    };
+    return SkNEW(GLAdvancedEquationXPWithCoverage);
+}
+
+void GrAdvancedEquationXPBase::onGetBlendInfo(BlendInfo* blendInfo) const {
+    SkASSERT(GrBlendEquationIsAdvanced(fEquation));
+    blendInfo->fEquation = fEquation;
+}
+
+
+GR_DEFINE_XP_FACTORY_TEST(GrAdvancedEquationXPFactory);
+
+GrXPFactory* GrAdvancedEquationXPFactory::TestCreate(SkRandom* random,
+                                                     GrContext* context,
+                                                     const GrDrawTargetCaps& caps,
+                                                     GrTexture*[]) {
+    int mode = random->nextRangeU(SkXfermode::kLastCoeffMode, SkXfermode::kLastMode);
+    if (SkXfermode::kLastCoeffMode == mode) {
+        mode = SkXfermode::kScreen_Mode;
+    }
+    return GrAdvancedEquationXPFactory::Create(context, static_cast<SkXfermode::Mode>(mode));
+}