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:
Create()22 static GrEffectRef* Create() {
23 return CreateEffectRef(AutoEffectUnref(SkNEW(DitherEffect)));
24 }
25
~DitherEffect()26 virtual ~DitherEffect() {};
Name()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
getFactory() const33 virtual const GrBackendEffectFactory& getFactory() const SK_OVERRIDE {
34 return GrTBackendEffectFactory<DitherEffect>::getInstance();
35 }
36
37 private:
DitherEffect()38 DitherEffect() {
39 this->setWillReadFragmentPosition();
40 }
41
42 // All dither effects are equal
onIsEqual(const GrEffect &) const43 virtual bool onIsEqual(const GrEffect&) const SK_OVERRIDE { return true; }
44
45 GR_DECLARE_EFFECT_TEST;
46
47 typedef GrEffect INHERITED;
48 };
49
getConstantColorComponents(GrColor * color,uint32_t * validFlags) const50 void DitherEffect::getConstantColorComponents(GrColor* color, uint32_t* validFlags) const {
51 *validFlags = 0;
52 }
53
54 //////////////////////////////////////////////////////////////////////////////
55
56 GR_DEFINE_EFFECT_TEST(DitherEffect);
57
TestCreate(SkRandom *,GrContext *,const GrDrawTargetCaps &,GrTexture * [])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
GLDitherEffect(const GrBackendEffectFactory & factory,const GrDrawEffect & drawEffect)83 GLDitherEffect::GLDitherEffect(const GrBackendEffectFactory& factory,
84 const GrDrawEffect& drawEffect)
85 : INHERITED (factory) {
86 }
87
emitCode(GrGLShaderBuilder * builder,const GrDrawEffect & drawEffect,EffectKey key,const char * outputColor,const char * inputColor,const TransformedCoordsArray &,const TextureSamplerArray & samplers)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 ,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
Create()113 GrEffectRef* GrDitherEffect::Create() {
114 return DitherEffect::Create();
115 }
116