src/third_party/skia/src/gpu/effects/GrDitherEffect.cpp

   1 /*
   2  * Copyright 2014 Google Inc.
   3  *
   4  * Use of this source code is governed by a BSD-style license that can be
   5  * found in the LICENSE file.
   6  */
   7
   8 #include "gl/builders/GrGLProgramBuilder.h"
   9 #include "GrDitherEffect.h"
  10
  11 #include "gl/GrGLProcessor.h"
  12 #include "gl/GrGLSL.h"
  13 #include "GrTBackendProcessorFactory.h"
  14
  15 #include "SkRect.h"
  16
  17 //////////////////////////////////////////////////////////////////////////////
  18
  19 class GLDitherEffect;
  20
  21 class DitherEffect : public GrFragmentProcessor {
  22 public:
  23     static GrFragmentProcessor* Create() {
  24         GR_CREATE_STATIC_FRAGMENT_PROCESSOR(gDitherEffect, DitherEffect, ())
  25         return SkRef(gDitherEffect);
  26     }
  27
  28     virtual ~DitherEffect() {};
  29     static const char* Name() { return "Dither"; }
  30
  31     typedef GLDitherEffect GLProcessor;
  32
  33     virtual void getConstantColorComponents(GrColor* color, uint32_t* validFlags) const SK_OVERRIDE;
  34
  35     virtual const GrBackendFragmentProcessorFactory& getFactory() const SK_OVERRIDE {
  36         return GrTBackendFragmentProcessorFactory<DitherEffect>::getInstance();
  37     }
  38
  39 private:
  40     DitherEffect() {
  41         this->setWillReadFragmentPosition();
  42     }
  43
  44     // All dither effects are equal
  45     virtual bool onIsEqual(const GrProcessor&) const SK_OVERRIDE { return true; }
  46
  47     GR_DECLARE_FRAGMENT_PROCESSOR_TEST;
  48
  49     typedef GrFragmentProcessor INHERITED;
  50 };
  51
  52 void DitherEffect::getConstantColorComponents(GrColor* color, uint32_t* validFlags) const {
  53     *validFlags = 0;
  54 }
  55
  56 //////////////////////////////////////////////////////////////////////////////
  57
  58 GR_DEFINE_FRAGMENT_PROCESSOR_TEST(DitherEffect);
  59
  60 GrFragmentProcessor* DitherEffect::TestCreate(SkRandom*,
  61                                               GrContext*,
  62                                               const GrDrawTargetCaps&,
  63                                               GrTexture*[]) {
  64     return DitherEffect::Create();
  65 }
  66
  67 //////////////////////////////////////////////////////////////////////////////
  68
  69 class GLDitherEffect : public GrGLFragmentProcessor {
  70 public:
  71     GLDitherEffect(const GrBackendProcessorFactory&, const GrProcessor&);
  72
  73     virtual void emitCode(GrGLProgramBuilder* builder,
  74                           const GrFragmentProcessor& fp,
  75                           const GrProcessorKey& key,
  76                           const char* outputColor,
  77                           const char* inputColor,
  78                           const TransformedCoordsArray&,
  79                           const TextureSamplerArray&) SK_OVERRIDE;
  80
  81 private:
  82     typedef GrGLFragmentProcessor INHERITED;
  83 };
  84
  85 GLDitherEffect::GLDitherEffect(const GrBackendProcessorFactory& factory,
  86                                const GrProcessor&)
  87     : INHERITED (factory) {
  88 }
  89
  90 void GLDitherEffect::emitCode(GrGLProgramBuilder* builder,
  91                               const GrFragmentProcessor& fp,
  92                               const GrProcessorKey& key,
  93                               const char* outputColor,
  94                               const char* inputColor,
  95                               const TransformedCoordsArray&,
  96                               const TextureSamplerArray& samplers) {
  97     GrGLFragmentShaderBuilder* fsBuilder = builder->getFragmentShaderBuilder();
  98     // Generate a random number based on the fragment position. For this
  99     // random number generator, we use the "GLSL rand" function
 100     // that seems to be floating around on the internet. It works under
 101     // the assumption that sin(<big number>) oscillates with high frequency
 102     // and sampling it will generate "randomness". Since we're using this
 103     // for rendering and not cryptography it should be OK.
 104
 105     // For each channel c, add the random offset to the pixel to either bump
 106     // it up or let it remain constant during quantization.
 107     fsBuilder->codeAppendf("\t\tfloat r = "
 108                            "fract(sin(dot(%s.xy ,vec2(12.9898,78.233))) * 43758.5453);\n",
 109                            fsBuilder->fragmentPosition());
 110     fsBuilder->codeAppendf("\t\t%s = (1.0/255.0) * vec4(r, r, r, r) + %s;\n",
 111                            outputColor, GrGLSLExpr4(inputColor).c_str());
 112 }
 113
 114 //////////////////////////////////////////////////////////////////////////////
 115
 116 GrFragmentProcessor* GrDitherEffect::Create() { return DitherEffect::Create(); }