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 #include "GrFragmentProcessor.h"
  10 #include "GrInvariantOutput.h"
  11 #include "SkRect.h"
  12 #include "gl/GrGLProcessor.h"
  13 #include "gl/GrGLSL.h"
  14 #include "gl/builders/GrGLProgramBuilder.h"
  15
  16 //////////////////////////////////////////////////////////////////////////////
  17
  18 class DitherEffect : public GrFragmentProcessor {
  19 public:
  20     static GrFragmentProcessor* Create() {
  21         GR_CREATE_STATIC_PROCESSOR(gDitherEffect, DitherEffect, ())
  22         return SkRef(gDitherEffect);
  23     }
  24
  25     virtual ~DitherEffect() {};
  26
  27     const char* name() const SK_OVERRIDE { return "Dither"; }
  28
  29     void getGLProcessorKey(const GrGLCaps&, GrProcessorKeyBuilder*) const SK_OVERRIDE;
  30
  31     GrGLFragmentProcessor* createGLInstance() const SK_OVERRIDE;
  32
  33 private:
  34     DitherEffect() {
  35         this->initClassID<DitherEffect>();
  36         this->setWillReadFragmentPosition();
  37     }
  38
  39     // All dither effects are equal
  40     bool onIsEqual(const GrFragmentProcessor&) const SK_OVERRIDE { return true; }
  41
  42     void onComputeInvariantOutput(GrInvariantOutput* inout) const SK_OVERRIDE;
  43
  44     GR_DECLARE_FRAGMENT_PROCESSOR_TEST;
  45
  46     typedef GrFragmentProcessor INHERITED;
  47 };
  48
  49 void DitherEffect::onComputeInvariantOutput(GrInvariantOutput* inout) const {
  50     inout->setToUnknown(GrInvariantOutput::kWill_ReadInput);
  51 }
  52
  53 //////////////////////////////////////////////////////////////////////////////
  54
  55 GR_DEFINE_FRAGMENT_PROCESSOR_TEST(DitherEffect);
  56
  57 GrFragmentProcessor* DitherEffect::TestCreate(SkRandom*,
  58                                               GrContext*,
  59                                               const GrDrawTargetCaps&,
  60                                               GrTexture*[]) {
  61     return DitherEffect::Create();
  62 }
  63
  64 //////////////////////////////////////////////////////////////////////////////
  65
  66 class GLDitherEffect : public GrGLFragmentProcessor {
  67 public:
  68     GLDitherEffect(const GrProcessor&);
  69
  70     virtual void emitCode(GrGLFPBuilder* builder,
  71                           const GrFragmentProcessor& fp,
  72                           const char* outputColor,
  73                           const char* inputColor,
  74                           const TransformedCoordsArray&,
  75                           const TextureSamplerArray&) SK_OVERRIDE;
  76
  77 private:
  78     typedef GrGLFragmentProcessor INHERITED;
  79 };
  80
  81 GLDitherEffect::GLDitherEffect(const GrProcessor&) {
  82 }
  83
  84 void GLDitherEffect::emitCode(GrGLFPBuilder* builder,
  85                               const GrFragmentProcessor& fp,
  86                               const char* outputColor,
  87                               const char* inputColor,
  88                               const TransformedCoordsArray&,
  89                               const TextureSamplerArray& samplers) {
  90     GrGLFPFragmentBuilder* fsBuilder = builder->getFragmentShaderBuilder();
  91     // Generate a random number based on the fragment position. For this
  92     // random number generator, we use the "GLSL rand" function
  93     // that seems to be floating around on the internet. It works under
  94     // the assumption that sin(<big number>) oscillates with high frequency
  95     // and sampling it will generate "randomness". Since we're using this
  96     // for rendering and not cryptography it should be OK.
  97
  98     // For each channel c, add the random offset to the pixel to either bump
  99     // it up or let it remain constant during quantization.
 100     fsBuilder->codeAppendf("\t\tfloat r = "
 101                            "fract(sin(dot(%s.xy ,vec2(12.9898,78.233))) * 43758.5453);\n",
 102                            fsBuilder->fragmentPosition());
 103     fsBuilder->codeAppendf("\t\t%s = (1.0/255.0) * vec4(r, r, r, r) + %s;\n",
 104                            outputColor, GrGLSLExpr4(inputColor).c_str());
 105 }
 106
 107 //////////////////////////////////////////////////////////////////////////////
 108
 109 void DitherEffect::getGLProcessorKey(const GrGLCaps& caps,
 110                                      GrProcessorKeyBuilder* b) const {
 111     GLDitherEffect::GenKey(*this, caps, b);
 112 }
 113
 114 GrGLFragmentProcessor* DitherEffect::createGLInstance() const  {
 115     return SkNEW_ARGS(GLDitherEffect, (*this));
 116 }
 117
 118 GrFragmentProcessor* GrDitherEffect::Create() { return DitherEffect::Create(); }