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/*
* Copyright 2013 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "SkLumaColorFilter.h"
#include "SkColorPriv.h"
#include "SkRasterPipeline.h"
#include "SkString.h"
#if SK_SUPPORT_GPU
#include "GrContext.h"
#include "GrInvariantOutput.h"
#include "glsl/GrGLSLFragmentProcessor.h"
#include "glsl/GrGLSLFragmentShaderBuilder.h"
#endif
void SkLumaColorFilter::filterSpan(const SkPMColor src[], int count,
SkPMColor dst[]) const {
for (int i = 0; i < count; ++i) {
SkPMColor c = src[i];
/*
* While LuminanceToAlpha is defined to operate on un-premultiplied
* inputs, due to the final alpha scaling it can be computed based on
* premultipled components:
*
* LumA = (k1 * r / a + k2 * g / a + k3 * b / a) * a
* LumA = (k1 * r + k2 * g + k3 * b)
*/
unsigned luma = SkComputeLuminance(SkGetPackedR32(c),
SkGetPackedG32(c),
SkGetPackedB32(c));
dst[i] = SkPackARGB32(luma, 0, 0, 0);
}
}
bool SkLumaColorFilter::onAppendStages(SkRasterPipeline* p,
SkColorSpace* dst,
SkArenaAlloc* scratch,
bool shaderIsOpaque) const {
p->append(SkRasterPipeline::luminance_to_alpha);
return true;
}
sk_sp<SkColorFilter> SkLumaColorFilter::Make() {
return sk_sp<SkColorFilter>(new SkLumaColorFilter);
}
SkLumaColorFilter::SkLumaColorFilter() : INHERITED() {}
sk_sp<SkFlattenable> SkLumaColorFilter::CreateProc(SkReadBuffer&) {
return Make();
}
void SkLumaColorFilter::flatten(SkWriteBuffer&) const {}
#ifndef SK_IGNORE_TO_STRING
void SkLumaColorFilter::toString(SkString* str) const {
str->append("SkLumaColorFilter ");
}
#endif
#if SK_SUPPORT_GPU
class LumaColorFilterEffect : public GrFragmentProcessor {
public:
static sk_sp<GrFragmentProcessor> Make() {
return sk_sp<GrFragmentProcessor>(new LumaColorFilterEffect);
}
const char* name() const override { return "Luminance-to-Alpha"; }
class GLSLProcessor : public GrGLSLFragmentProcessor {
public:
static void GenKey(const GrProcessor&, const GrShaderCaps&, GrProcessorKeyBuilder*) {}
void emitCode(EmitArgs& args) override {
if (nullptr == args.fInputColor) {
args.fInputColor = "vec4(1)";
}
GrGLSLFPFragmentBuilder* fragBuilder = args.fFragBuilder;
fragBuilder->codeAppendf("\tfloat luma = dot(vec3(%f, %f, %f), %s.rgb);\n",
SK_ITU_BT709_LUM_COEFF_R,
SK_ITU_BT709_LUM_COEFF_G,
SK_ITU_BT709_LUM_COEFF_B,
args.fInputColor);
fragBuilder->codeAppendf("\t%s = vec4(0, 0, 0, luma);\n",
args.fOutputColor);
}
private:
typedef GrGLSLFragmentProcessor INHERITED;
};
private:
LumaColorFilterEffect() : INHERITED(kConstantOutputForConstantInput_OptimizationFlag) {
this->initClassID<LumaColorFilterEffect>();
}
GrGLSLFragmentProcessor* onCreateGLSLInstance() const override {
return new GLSLProcessor;
}
virtual void onGetGLSLProcessorKey(const GrShaderCaps& caps,
GrProcessorKeyBuilder* b) const override {
GLSLProcessor::GenKey(*this, caps, b);
}
bool onIsEqual(const GrFragmentProcessor&) const override { return true; }
void onComputeInvariantOutput(GrInvariantOutput* inout) const override {
// The output is always black. The alpha value for the color passed in is arbitrary.
inout->setToOther(kRGB_GrColorComponentFlags, GrColorPackRGBA(0, 0, 0, 0));
}
GrColor4f constantOutputForConstantInput(GrColor4f input) const override {
float luma = SK_ITU_BT709_LUM_COEFF_R * input.fRGBA[0] +
SK_ITU_BT709_LUM_COEFF_G * input.fRGBA[1] +
SK_ITU_BT709_LUM_COEFF_B * input.fRGBA[2];
return GrColor4f(0, 0, 0, luma);
}
typedef GrFragmentProcessor INHERITED;
};
sk_sp<GrFragmentProcessor> SkLumaColorFilter::asFragmentProcessor(GrContext*, SkColorSpace*) const {
return LumaColorFilterEffect::Make();
}
#endif
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