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 "glsl/GrGLSLFragmentProcessor.h"
13 #include "glsl/GrGLSLFragmentShaderBuilder.h"
14
15 //////////////////////////////////////////////////////////////////////////////
16
17 class DitherEffect : public GrFragmentProcessor {
18 public:
Create()19 static GrFragmentProcessor* Create() {
20 return new DitherEffect;
21 }
22
~DitherEffect()23 virtual ~DitherEffect() {};
24
name() const25 const char* name() const override { return "Dither"; }
26
27 private:
DitherEffect()28 DitherEffect() {
29 this->initClassID<DitherEffect>();
30 this->setWillReadFragmentPosition();
31 }
32
33 GrGLSLFragmentProcessor* onCreateGLSLInstance() const override;
34
35 void onGetGLSLProcessorKey(const GrGLSLCaps&, GrProcessorKeyBuilder*) const override;
36
37 // All dither effects are equal
onIsEqual(const GrFragmentProcessor &) const38 bool onIsEqual(const GrFragmentProcessor&) const override { return true; }
39
40 void onComputeInvariantOutput(GrInvariantOutput* inout) const override;
41
42 GR_DECLARE_FRAGMENT_PROCESSOR_TEST;
43
44 typedef GrFragmentProcessor INHERITED;
45 };
46
onComputeInvariantOutput(GrInvariantOutput * inout) const47 void DitherEffect::onComputeInvariantOutput(GrInvariantOutput* inout) const {
48 inout->setToUnknown(GrInvariantOutput::kWill_ReadInput);
49 }
50
51 //////////////////////////////////////////////////////////////////////////////
52
53 GR_DEFINE_FRAGMENT_PROCESSOR_TEST(DitherEffect);
54
TestCreate(GrProcessorTestData *)55 const GrFragmentProcessor* DitherEffect::TestCreate(GrProcessorTestData*) {
56 return DitherEffect::Create();
57 }
58
59 //////////////////////////////////////////////////////////////////////////////
60
61 class GLDitherEffect : public GrGLSLFragmentProcessor {
62 public:
63 void emitCode(EmitArgs& args) override;
64
65 private:
66 typedef GrGLSLFragmentProcessor INHERITED;
67 };
68
emitCode(EmitArgs & args)69 void GLDitherEffect::emitCode(EmitArgs& args) {
70 GrGLSLFPFragmentBuilder* fragBuilder = args.fFragBuilder;
71 // Generate a random number based on the fragment position. For this
72 // random number generator, we use the "GLSL rand" function
73 // that seems to be floating around on the internet. It works under
74 // the assumption that sin(<big number>) oscillates with high frequency
75 // and sampling it will generate "randomness". Since we're using this
76 // for rendering and not cryptography it should be OK.
77
78 // For each channel c, add the random offset to the pixel to either bump
79 // it up or let it remain constant during quantization.
80 fragBuilder->codeAppendf("\t\tfloat r = "
81 "fract(sin(dot(%s.xy ,vec2(12.9898,78.233))) * 43758.5453);\n",
82 fragBuilder->fragmentPosition());
83 fragBuilder->codeAppendf("\t\t%s = (1.0/255.0) * vec4(r, r, r, r) + %s;\n",
84 args.fOutputColor, GrGLSLExpr4(args.fInputColor).c_str());
85 }
86
87 //////////////////////////////////////////////////////////////////////////////
88
onGetGLSLProcessorKey(const GrGLSLCaps & caps,GrProcessorKeyBuilder * b) const89 void DitherEffect::onGetGLSLProcessorKey(const GrGLSLCaps& caps,
90 GrProcessorKeyBuilder* b) const {
91 GLDitherEffect::GenKey(*this, caps, b);
92 }
93
onCreateGLSLInstance() const94 GrGLSLFragmentProcessor* DitherEffect::onCreateGLSLInstance() const {
95 return new GLDitherEffect;
96 }
97
Create()98 GrFragmentProcessor* GrDitherEffect::Create() { return DitherEffect::Create(); }
99