skia2/include/gpu/effects/GrPorterDuffXferProcessor.h
cdalton 6fd158ea47 Implement Porter Duff XP with a blend table
Removes the runtime logic used by PorterDuffXferProcessor to decide
blend coeffs and shader outputs, and instead uses a compile-time
constant table of pre-selected blend formulas. Separates out the dst
read fallback into its own XP.

Introduces a new blend strategy for srcCoeff=0 that can apply coverage
with a reverse subtract blend equation instead of dual source
blending.

Adds new macros in GrBlend.h to analyze blend formulas both runtime.

Removes kSetCoverageDrawing_OptFlag and GrSimplifyBlend as they are no
longer used.

Adds a GM that verifies all xfermodes, including arithmetic, with the
color/coverage invariants used by Porter Duff.

Adds a unit test that verifies each Porter Duff formula with every
color/coverage invariant.

Major changes:

 * Uses a reverse subtract blend equation for coverage when srcCoeff=0
   (clear, dst-out [Sa=1], dst-in, modulate). Platforms that don't
   support dual source blending no longer require a dst copy for
   dst-in and modulate.

 * Sets BlendInfo::fWriteColor to false when the blend does not modify
   the dst. GrGLGpu will now use glColorMask instead of blending for
   these modes (dst, dst-in [Sa=1], modulate ignored for [Sc=1]).

 * Converts all SA blend coeffs to One for opaque inputs, and ISA to
   Zero if there is also no coverage. (We keep ISA around when there
   is coverage because we use it to tweak alpha for coverage.)

 * Abandons solid white optimizations for the sake of simplicity
   (screen was the only mode that previous had solid white opts).

Minor differences:

 * Inconsequential differences in opt flags (e.g. we now return
   kCanTweakAlphaForCoverage_OptFlag even when there is no coverage).

 * Src coeffs when the shader outputs 0.

 * IS2C vs IS2A when the secondary output is scalar.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/9a70920db22b6309c671f8e5d519bb95570e4414

Review URL: https://codereview.chromium.org/1124373002
2015-05-27 15:08:33 -07:00

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C++

/*
* Copyright 2014 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef GrPorterDuffXferProcessor_DEFINED
#define GrPorterDuffXferProcessor_DEFINED
#include "GrTypes.h"
#include "GrXferProcessor.h"
#include "SkXfermode.h"
class GrProcOptInfo;
class GrPorterDuffXPFactory : public GrXPFactory {
public:
static GrXPFactory* Create(SkXfermode::Mode mode);
bool supportsRGBCoverage(GrColor knownColor, uint32_t knownColorFlags) const override;
void getInvariantOutput(const GrProcOptInfo& colorPOI, const GrProcOptInfo& coveragePOI,
GrXPFactory::InvariantOutput*) const override;
private:
GrPorterDuffXPFactory(SkXfermode::Mode);
GrXferProcessor* onCreateXferProcessor(const GrCaps& caps,
const GrProcOptInfo& colorPOI,
const GrProcOptInfo& coveragePOI,
const DstTexture*) const override;
bool willReadDstColor(const GrCaps& caps,
const GrProcOptInfo& colorPOI,
const GrProcOptInfo& coveragePOI) const override;
bool onIsEqual(const GrXPFactory& xpfBase) const override {
const GrPorterDuffXPFactory& xpf = xpfBase.cast<GrPorterDuffXPFactory>();
return fXfermode == xpf.fXfermode;
}
GR_DECLARE_XP_FACTORY_TEST;
static void TestGetXPOutputTypes(const GrXferProcessor*, int* outPrimary, int* outSecondary);
SkXfermode::Mode fXfermode;
friend class GrPorterDuffTest; // for TestGetXPOutputTypes()
typedef GrXPFactory INHERITED;
};
#endif