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