1/*
2 * Copyright 2016 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 "GrSRGBEffect.h"
9
10#include "GrFragmentProcessor.h"
11#include "GrProcessor.h"
12#include "glsl/GrGLSLFragmentProcessor.h"
13#include "glsl/GrGLSLFragmentShaderBuilder.h"
14
15class GrGLSRGBEffect : public GrGLSLFragmentProcessor {
16public:
17    void emitCode(EmitArgs& args) override {
18        const GrSRGBEffect& srgbe = args.fFp.cast<GrSRGBEffect>();
19        GrGLSLFPFragmentBuilder* fragBuilder = args.fFragBuilder;
20
21        SkString srgbFuncName;
22        static const GrShaderVar gSrgbArgs[] = {
23            GrShaderVar("x", kHalf_GrSLType),
24        };
25        switch (srgbe.mode()) {
26            case GrSRGBEffect::Mode::kLinearToSRGB:
27                fragBuilder->emitFunction(kHalf_GrSLType,
28                                          "linear_to_srgb",
29                                          SK_ARRAY_COUNT(gSrgbArgs),
30                                          gSrgbArgs,
31                                          "return (x <= 0.0031308) ? (x * 12.92) "
32                                          ": (1.055 * pow(x, 0.416666667) - 0.055);",
33                                          &srgbFuncName);
34                break;
35            case GrSRGBEffect::Mode::kSRGBToLinear:
36                fragBuilder->emitFunction(kHalf_GrSLType,
37                                          "srgb_to_linear",
38                                          SK_ARRAY_COUNT(gSrgbArgs),
39                                          gSrgbArgs,
40                                          "return (x <= 0.04045) ? (x / 12.92) "
41                                          ": pow((x + 0.055) / 1.055, 2.4);",
42                                          &srgbFuncName);
43                break;
44        }
45
46        if (nullptr == args.fInputColor) {
47            args.fInputColor = "half4(1)";
48        }
49
50        // Mali Bifrost uses fp16 for mediump. Making the intermediate color variable highp causes
51        // calculations to be performed with sufficient precision.
52        fragBuilder->codeAppendf("float4 color = %s;", args.fInputColor);
53        if (srgbe.alpha() == GrSRGBEffect::Alpha::kPremul) {
54            fragBuilder->codeAppendf("half nonZeroAlpha = max(color.a, 0.00001);");
55            fragBuilder->codeAppendf("color = half4(color.rgb / nonZeroAlpha, color.a);");
56        }
57        fragBuilder->codeAppendf("color = half4(%s(color.r), %s(color.g), %s(color.b), color.a);",
58                                    srgbFuncName.c_str(),
59                                    srgbFuncName.c_str(),
60                                    srgbFuncName.c_str());
61        if (srgbe.alpha() == GrSRGBEffect::Alpha::kPremul) {
62            fragBuilder->codeAppendf("color = half4(color.rgb, 1) * color.a;");
63        }
64        fragBuilder->codeAppendf("%s = color;", args.fOutputColor);
65    }
66
67    static inline void GenKey(const GrProcessor& processor, const GrShaderCaps&,
68                              GrProcessorKeyBuilder* b) {
69        const GrSRGBEffect& srgbe = processor.cast<GrSRGBEffect>();
70        uint32_t key = static_cast<uint32_t>(srgbe.mode()) |
71                      (static_cast<uint32_t>(srgbe.alpha()) << 1);
72        b->add32(key);
73    }
74
75private:
76    typedef GrGLSLFragmentProcessor INHERITED;
77};
78
79///////////////////////////////////////////////////////////////////////////////
80
81GrSRGBEffect::GrSRGBEffect(Mode mode, Alpha alpha)
82    : INHERITED(kGrSRGBEffect_ClassID, kPreservesOpaqueInput_OptimizationFlag |
83                kConstantOutputForConstantInput_OptimizationFlag)
84    , fMode(mode)
85    , fAlpha(alpha)
86{
87}
88
89std::unique_ptr<GrFragmentProcessor> GrSRGBEffect::clone() const { return Make(fMode, fAlpha); }
90
91bool GrSRGBEffect::onIsEqual(const GrFragmentProcessor& s) const {
92    const GrSRGBEffect& other = s.cast<GrSRGBEffect>();
93    return other.fMode == fMode;
94}
95
96static inline float srgb_to_linear(float srgb) {
97    return (srgb <= 0.04045f) ? srgb / 12.92f : powf((srgb + 0.055f) / 1.055f, 2.4f);
98}
99static inline float linear_to_srgb(float linear) {
100    return (linear <= 0.0031308) ? linear * 12.92f : 1.055f * powf(linear, 1.f / 2.4f) - 0.055f;
101}
102
103GrColor4f GrSRGBEffect::constantOutputForConstantInput(GrColor4f color) const {
104    color = color.unpremul();
105    switch (fMode) {
106        case Mode::kLinearToSRGB:
107            color = GrColor4f(linear_to_srgb(color.fRGBA[0]), linear_to_srgb(color.fRGBA[1]),
108                              linear_to_srgb(color.fRGBA[2]), color.fRGBA[3]);
109            break;
110        case Mode::kSRGBToLinear:
111            color = GrColor4f(srgb_to_linear(color.fRGBA[0]), srgb_to_linear(color.fRGBA[1]),
112                              srgb_to_linear(color.fRGBA[2]), color.fRGBA[3]);
113            break;
114    }
115    return color.premul();
116}
117
118///////////////////////////////////////////////////////////////////////////////
119
120GR_DEFINE_FRAGMENT_PROCESSOR_TEST(GrSRGBEffect);
121
122#if GR_TEST_UTILS
123std::unique_ptr<GrFragmentProcessor> GrSRGBEffect::TestCreate(GrProcessorTestData* d) {
124    Mode testMode = static_cast<Mode>(d->fRandom->nextRangeU(0, 1));
125    return GrSRGBEffect::Make(testMode, Alpha::kPremul);
126}
127#endif
128
129///////////////////////////////////////////////////////////////////////////////
130
131void GrSRGBEffect::onGetGLSLProcessorKey(const GrShaderCaps& caps,
132                                          GrProcessorKeyBuilder* b) const {
133    GrGLSRGBEffect::GenKey(*this, caps, b);
134}
135
136GrGLSLFragmentProcessor* GrSRGBEffect::onCreateGLSLInstance() const {
137    return new GrGLSRGBEffect;
138}
139
140