Make GrGammaEffect have explicit sRGB modes, plus exponential mode.

src/gpu/effects/GrGammaEffect.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrGammaEffect.h"
 
 #include "GrContext.h"
 #include "GrCoordTransform.h"
 #include "GrFragmentProcessor.h"
 #include "GrInvariantOutput.h"
 #include "GrProcessor.h"
 #include "glsl/GrGLSLFragmentProcessor.h"
 #include "glsl/GrGLSLFragmentShaderBuilder.h"
 
 class GrGLGammaEffect : public GrGLSLFragmentProcessor {
 public:
     void emitCode(EmitArgs& args) override {
         const GrGammaEffect& ge = args.fFp.cast<GrGammaEffect>();
         GrGLSLFPFragmentBuilder* fragBuilder = args.fFragBuilder;
         GrGLSLUniformHandler* uniformHandler = args.fUniformHandler;
 
         const char* gammaUniName = nullptr;
-        if (!ge.gammaIsSRGB()) {
+        if (GrGammaEffect::Mode::kExponential == ge.mode()) {
             fGammaUni = uniformHandler->addUniform(kFragment_GrShaderFlag, kFloat_GrSLType,
                                                    kDefault_GrSLPrecision, "Gamma", &gammaUniName);
         }
 
-        GrGLSLShaderVar tmpVar("tmpColor", kVec4f_GrSLType, 0, kHigh_GrSLPrecision);
-        SkString tmpDecl;
-        tmpVar.appendDecl(args.fGLSLCaps, &tmpDecl);
-
         SkString srgbFuncName;
-        if (ge.gammaIsSRGB()) {
-            static const GrGLSLShaderVar gSrgbArgs[] = {
-                GrGLSLShaderVar("x", kFloat_GrSLType),
-            };
-
-            fragBuilder->emitFunction(kFloat_GrSLType,
-                                        "linear_to_srgb",
-                                        SK_ARRAY_COUNT(gSrgbArgs),
-                                        gSrgbArgs,
-                                        "return (x <= 0.0031308) ? (x * 12.92) "
-                                        ": (1.055 * pow(x, 0.416666667) - 0.055);",
-                                        &srgbFuncName);
+        static const GrGLSLShaderVar gSrgbArgs[] = {
+            GrGLSLShaderVar("x", kFloat_GrSLType),
+        };
+        switch (ge.mode()) {
+            case GrGammaEffect::Mode::kLinearToSRGB:
+                fragBuilder->emitFunction(kFloat_GrSLType,
+                                          "linear_to_srgb",
+                                          SK_ARRAY_COUNT(gSrgbArgs),
+                                          gSrgbArgs,
+                                          "return (x <= 0.0031308) ? (x * 12.92) "
+                                          ": (1.055 * pow(x, 0.416666667) - 0.055);",
+                                          &srgbFuncName);
+                break;
+            case GrGammaEffect::Mode::kSRGBToLinear:
+                fragBuilder->emitFunction(kFloat_GrSLType,
+                                          "srgb_to_linear",
+                                          SK_ARRAY_COUNT(gSrgbArgs),
+                                          gSrgbArgs,
+                                          "return (x <= 0.04045) ? (x / 12.92) "
+                                          ": pow((x + 0.055) / 1.055, 2.4);",
+                                          &srgbFuncName);
+            default:
+                // No helper function needed
+                break;
         }
 
-        fragBuilder->codeAppendf("%s;", tmpDecl.c_str());
+        if (nullptr == args.fInputColor) {
+            args.fInputColor = "vec4(1)";
+        }
 
-        fragBuilder->codeAppendf("%s = ", tmpVar.c_str());
-        fragBuilder->appendTextureLookup(args.fTexSamplers[0], args.fCoords[0].c_str(),
-                                            args.fCoords[0].getType());
-        fragBuilder->codeAppend(";");
-
-        if (ge.gammaIsSRGB()) {
+        if (GrGammaEffect::Mode::kExponential == ge.mode()) {
+            fragBuilder->codeAppendf("%s = vec4(pow(%s.rgb, vec3(%s)), %s.a);",
+                                     args.fOutputColor, args.fInputColor, gammaUniName,
+                                     args.fInputColor);
+        } else {
             fragBuilder->codeAppendf("%s = vec4(%s(%s.r), %s(%s.g), %s(%s.b), %s.a);",
-                                        args.fOutputColor,
-                                        srgbFuncName.c_str(), tmpVar.c_str(),
-                                        srgbFuncName.c_str(), tmpVar.c_str(),
-                                        srgbFuncName.c_str(), tmpVar.c_str(),
-                                        tmpVar.c_str());
-        } else {
-            fragBuilder->codeAppendf("%s = vec4(pow(%s.rgb, vec3(%s)), %s.a);",
-                                        args.fOutputColor, tmpVar.c_str(), gammaUniName,
-                                        tmpVar.c_str());
+                                     args.fOutputColor,
+                                     srgbFuncName.c_str(), args.fInputColor,
+                                     srgbFuncName.c_str(), args.fInputColor,
+                                     srgbFuncName.c_str(), args.fInputColor,
+                                     args.fInputColor);
         }
     }
 
     void onSetData(const GrGLSLProgramDataManager& pdman, const GrProcessor& proc) override {
         const GrGammaEffect& ge = proc.cast<GrGammaEffect>();
-        if (!ge.gammaIsSRGB()) {
+        if (GrGammaEffect::Mode::kExponential == ge.mode()) {
             pdman.set1f(fGammaUni, ge.gamma());
         }
     }
 
     static inline void GenKey(const GrProcessor& processor, const GrGLSLCaps&,
                               GrProcessorKeyBuilder* b) {
         const GrGammaEffect& ge = processor.cast<GrGammaEffect>();
-        uint32_t key = ge.gammaIsSRGB() ? 0x1 : 0x0;
+        uint32_t key = static_cast<uint32_t>(ge.mode());
         b->add32(key);
     }
 
 private:
     GrGLSLProgramDataManager::UniformHandle fGammaUni;
 
     typedef GrGLSLFragmentProcessor INHERITED;
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
-GrGammaEffect::GrGammaEffect(GrTexture* texture, SkScalar gamma)
-    : INHERITED(texture, GrCoordTransform::MakeDivByTextureWHMatrix(texture)) {
+GrGammaEffect::GrGammaEffect(Mode mode, SkScalar gamma)
+    : fMode(mode)
+    , fGamma(gamma) {
     this->initClassID<GrGammaEffect>();
-
-    fGamma = gamma;
-    fGammaIsSRGB = SkScalarNearlyEqual(gamma, 1.0f / 2.2f);
 }
 
 bool GrGammaEffect::onIsEqual(const GrFragmentProcessor& s) const {
     const GrGammaEffect& other = s.cast<GrGammaEffect>();
     return
-        other.fGammaIsSRGB == fGammaIsSRGB &&
-        other.fGamma == fGamma;
+        other.fMode == fMode &&
+        (fMode != Mode::kExponential || other.fGamma == fGamma);
 }
 
 void GrGammaEffect::onComputeInvariantOutput(GrInvariantOutput* inout) const {
     inout->setToUnknown(GrInvariantOutput::kWill_ReadInput);
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 GR_DEFINE_FRAGMENT_PROCESSOR_TEST(GrGammaEffect);
 
 const GrFragmentProcessor* GrGammaEffect::TestCreate(GrProcessorTestData* d) {
     // We want to be sure and test sRGB sometimes
-    bool srgb = d->fRandom->nextBool();
-    return new GrGammaEffect(d->fTextures[GrProcessorUnitTest::kSkiaPMTextureIdx],
-                             srgb ? 1.0f / 2.2f : d->fRandom->nextRangeScalar(0.5f, 2.0f));
+    Mode testMode = static_cast<Mode>(d->fRandom->nextRangeU(0, 2));
+    SkScalar gamma = d->fRandom->nextRangeScalar(0.5f, 2.0f);
+    return new GrGammaEffect(testMode, gamma);
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 void GrGammaEffect::onGetGLSLProcessorKey(const GrGLSLCaps& caps,
                                                GrProcessorKeyBuilder* b) const {
     GrGLGammaEffect::GenKey(*this, caps, b);
 }
 
 GrGLSLFragmentProcessor* GrGammaEffect::onCreateGLSLInstance() const {
     return new GrGLGammaEffect();
 }
 
-const GrFragmentProcessor* GrGammaEffect::Create(GrTexture* texture, SkScalar gamma) {
-    return new GrGammaEffect(texture, gamma);
+const GrFragmentProcessor* GrGammaEffect::Create(SkScalar gamma) {
+    // TODO: Once our public-facing API for specifying gamma curves settles down, expose this,
+    // and allow clients to explicitly request sRGB, rather than inferring from the exponent.
+    // Note that AdobeRGB (for example) is speficied as x^2.2, not the Rec.709 curves.
+    if (SkScalarNearlyEqual(gamma, 2.2f)) {
+        return new GrGammaEffect(Mode::kSRGBToLinear, 2.2f);
+    } else if (SkScalarNearlyEqual(gamma, 1.0f / 2.2f)) {
+        return new GrGammaEffect(Mode::kLinearToSRGB, 1.0f / 2.2f);
+    } else {
+        return new GrGammaEffect(Mode::kExponential, gamma);
+    }
 }