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
18class GLDitherEffect;
19
20class DitherEffect : public GrEffect {
21public:
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
37private:
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
50void DitherEffect::getConstantColorComponents(GrColor* color, uint32_t* validFlags) const {
51    *validFlags = 0;
52}
53
54//////////////////////////////////////////////////////////////////////////////
55
56GR_DEFINE_EFFECT_TEST(DitherEffect);
57
58GrEffectRef* DitherEffect::TestCreate(SkRandom*,
59                                      GrContext*,
60                                      const GrDrawTargetCaps&,
61                                      GrTexture*[]) {
62    return DitherEffect::Create();
63}
64
65//////////////////////////////////////////////////////////////////////////////
66
67class GLDitherEffect : public GrGLEffect {
68public:
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
79private:
80    typedef GrGLEffect INHERITED;
81};
82
83GLDitherEffect::GLDitherEffect(const GrBackendEffectFactory& factory,
84                               const GrDrawEffect& drawEffect)
85    : INHERITED (factory) {
86}
87
88void 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
113GrEffectRef* GrDitherEffect::Create() {
114    return DitherEffect::Create();
115}
116