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..753141fad14e1958baa765848bbe7f647c34d3bc
--- /dev/null
+++ b/src/gpu/effects/GrAdvancedEquationXferProcessor.cpp
@@ -0,0 +1,326 @@
+/*
+ * 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 AdvancedEquationXPBase : public GrXferProcessor {
+public:
+    static AdvancedEquationXPBase* Create(bool hasCoverage, GrBlendEquation equation);
+    AdvancedEquationXPBase(GrBlendEquation equation) : fEquation(equation) {}
+
+    const char* name() const override { return "Blend Equation Advanced"; }
+    bool hasSecondaryOutput() const override { return false; }
+
+    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 AdvancedEquationXPBase& xp = xpBase.cast<AdvancedEquationXPBase>();
+        return fEquation == xp.fEquation;
+    }
+
+    const GrBlendEquation fEquation;
+
+    typedef GrXferProcessor INHERITED;
+};
+
+template<bool HasCoverage> class AdvancedEquationXP: public AdvancedEquationXPBase {
+public:
+    AdvancedEquationXP(GrBlendEquation equation) : INHERITED(equation) {
+        this->initClassID<AdvancedEquationXP>();
+    }
+
+    OptFlags getOptimizations(const GrProcOptInfo&, const GrProcOptInfo&, bool, GrColor*,
+                              const GrDrawTargetCaps&) override;
+
+    GrGLXferProcessor* createGLInstance() const override;
+
+private:
+    typedef AdvancedEquationXPBase 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(SkXfermode::Mode mode) {
+    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(Equation > kLastBasicGrBlendEquation);
+    static GrAdvancedEquationXPFactory* factory;
+    if (!factory) {
+        factory = SkNEW_ARGS(GrAdvancedEquationXPFactory, (Equation));
+    }
+    return SkRef(factory);
+}
+
+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(!dstCopy || !dstCopy->texture());
+
+    if (!caps.advancedBlendEquationSupport()) {
+        return NULL;
+    }
+    if (coveragePOI.isFourChannelOutput()) {
+        // RGB coverage is not supported. (See supportsRGBCoverage())
+        return NULL;
+    }
+    return AdvancedEquationXPBase::Create(!coveragePOI.isSolidWhite(), fEquation);
+}
+
+AdvancedEquationXPBase* AdvancedEquationXPBase::Create(bool hasCoverage, GrBlendEquation equation) {

[egdaniel, 2015/04/27 15:28:25]

Okay so it seems like I may have confused things with my set of comments from
before. In your original implementation for a given equation, you would only
ever make a single XPFactory that would always make exactly 2 XferProcessors. In
this new version you will make a new XferProcessor everytime an XP for a given
equation is used.

So maybe we could you go back to your original way of having the 2 SkAutoTUnrefs
on the XPFactory. But instead of making the 2 XferProcessors in the XPFactory
ctor, we just let the SkAutoTUnref default its object to NULL. Then in
onCreateXferProcessor we check if fXferProcessor.get() == NULL, and if so we
create it (using SkNew and reset on AutoTUnref) there before returning it? Same
with the coverage one. Does this approach seem reasonable?

[Chris Dalton, 2015/04/27 18:25:39]

This is also how I would prefer to do it, and I like your suggestion to create
the individual XP's lazily.

I did manage to fix the assert by storing the factories as static SkAutoTUnrefs,
which causes them to get cleaned up on exit. However, I think this only works
because we got lucky and the factories get cleaned up before the GrMemoryPool,
which is what asserts that the global allocation count is zero. I don't know how
fragile this is and if the destruction order will change on different compilers
or OS's, but I'm not comfortable with it. Below is the assert for reference.
I'll start looking into a better way to handle this, and am open to suggestions.

 0x00000000008e1cc6 in GrMemoryPool::~GrMemoryPool (
     this=0xf47c00 <_ZZNK12_GLOBAL__N_118MemoryPoolAccessor4poolEvE5gPool>,
__in_chrg=<optimized out>)
     at ../../src/gpu/GrMemoryPool.cpp:35
 35	    SkASSERT(0 == fAllocationCnt);
 (gdb) bt
 #0  0x00000000008e1cc6 in GrMemoryPool::~GrMemoryPool (
     this=0xf47c00 <_ZZNK12_GLOBAL__N_118MemoryPoolAccessor4poolEvE5gPool>,
__in_chrg=<optimized out>)
     at ../../src/gpu/GrMemoryPool.cpp:35
 #1  0x00007ffff65ad259 in __run_exit_handlers (status=0, listp=0x7ffff692f6c8
<__exit_funcs>, 
     run_list_atexit=run_list_atexit@entry=true) at exit.c:82
 #2  0x00007ffff65ad2a5 in __GI_exit (status=<optimized out>) at exit.c:104
 #3  0x00007ffff6592ecc in __libc_start_main (main=0x5d4841 <main(int, char**)>,
argc=3, argv=0x7fffffffdaf8, 
     init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>,
stack_end=0x7fffffffdae8) at libc-start.c:321
 #4  0x0000000000406209 in _start ()

+    if (hasCoverage) {
+        return SkNEW_ARGS(AdvancedEquationXP<true>, (equation));
+    } else {
+        return SkNEW_ARGS(AdvancedEquationXP<false>, (equation));
+    }
+}
+
+bool AdvancedEquationXPBase::willNeedXferBarrier(const GrRenderTarget*,
+                                                 const GrDrawTargetCaps& caps,
+                                                 GrXferBarrierType* outBarrierType) const {
+    if (GrDrawTargetCaps::kAdvancedCoherent_BlendEquationSupport != caps.blendEquationSupport()) {
+        *outBarrierType = kBlend_GrXferBarrierType;
+        return true;
+    }
+    return false;
+}
+
+void AdvancedEquationXPBase::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*/>
+GrXferProcessor::OptFlags AdvancedEquationXP<false>::getOptimizations(const GrProcOptInfo&,
+                                                                      const GrProcOptInfo&,
+                                                                      bool, GrColor*,
+                                                                      const GrDrawTargetCaps&) {
+    return kIgnoreCoverage_OptFlag;
+}
+
+template</*HasCoverage = false*/>
+GrGLXferProcessor* AdvancedEquationXP<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*/>
+GrXferProcessor::OptFlags AdvancedEquationXP<true>::getOptimizations(const GrProcOptInfo&,
+                                                                     const GrProcOptInfo&,
+                                                                     bool, GrColor*,
+                                                                     const GrDrawTargetCaps&) {
+    return kNone_Opt;
+}
+
+template</*HasCoverage = true*/>
+GrGLXferProcessor* AdvancedEquationXP<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 AdvancedEquationXPBase::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(static_cast<SkXfermode::Mode>(mode));
+}