src/effects/SkGaussianEdgeShader.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 "SkGaussianEdgeShader.h"
#include "SkReadBuffer.h"
#include "SkWriteBuffer.h"

 /** \class SkGaussianEdgeShaderImpl
 This subclass of shader applies a Gaussian to shadow edge

 The radius of the Gaussian blur is specified by the g and b values of the color,
 where g is the integer component and b is the fractional component. The r value
 represents the max final alpha.
 */
class SkGaussianEdgeShaderImpl : public SkShader {
public:
    SkGaussianEdgeShaderImpl() {}

    bool isOpaque() const override;

#if SK_SUPPORT_GPU
    sk_sp<GrFragmentProcessor> asFragmentProcessor(const AsFPArgs&) const override;
#endif

    SK_TO_STRING_OVERRIDE()
    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkGaussianEdgeShaderImpl)

protected:
    void flatten(SkWriteBuffer&) const override;

private:
    friend class SkGaussianEdgeShader;

    typedef SkShader INHERITED;
};

////////////////////////////////////////////////////////////////////////////

#if SK_SUPPORT_GPU

#include "GrCoordTransform.h"
#include "GrFragmentProcessor.h"
#include "GrInvariantOutput.h"
#include "glsl/GrGLSLFragmentProcessor.h"
#include "glsl/GrGLSLFragmentShaderBuilder.h"
#include "glsl/GrGLSLProgramDataManager.h"
#include "glsl/GrGLSLUniformHandler.h"
#include "SkGr.h"
#include "SkGrPriv.h"

class GaussianEdgeFP : public GrFragmentProcessor {
public:
    GaussianEdgeFP() {
        this->initClassID<GaussianEdgeFP>();

        // enable output of distance information for shape
        fUsesDistanceVectorField = true;
    }

    class GLSLGaussianEdgeFP : public GrGLSLFragmentProcessor {
    public:
        GLSLGaussianEdgeFP() {}

        void emitCode(EmitArgs& args) override {

            GrGLSLFPFragmentBuilder* fragBuilder = args.fFragBuilder;

            fragBuilder->codeAppendf("vec4 color = %s;", args.fInputColor);
            fragBuilder->codeAppend("float radius = color.g*255.0 + color.b;");

            fragBuilder->codeAppendf("float factor = 1.0 - clamp(%s.z/radius, 0.0, 1.0);",
                                     fragBuilder->distanceVectorName());
            fragBuilder->codeAppend("factor = exp(-factor * factor * 4.0) - 0.018;");
            fragBuilder->codeAppendf("%s = factor*vec4(0.0, 0.0, 0.0, color.r);", args.fOutputColor);
        }

        static void GenKey(const GrProcessor& proc, const GrGLSLCaps&,
                           GrProcessorKeyBuilder* b) {
            // only one shader generated currently
            b->add32(0x0);
        }

    protected:
        void onSetData(const GrGLSLProgramDataManager& pdman, const GrProcessor& proc) override {}
    };

    void onGetGLSLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const override {
        GLSLGaussianEdgeFP::GenKey(*this, caps, b);
    }

    const char* name() const override { return "GaussianEdgeFP"; }

    void onComputeInvariantOutput(GrInvariantOutput* inout) const override {
        inout->mulByUnknownFourComponents();
    }

private:
    GrGLSLFragmentProcessor* onCreateGLSLInstance() const override { return new GLSLGaussianEdgeFP; }

    bool onIsEqual(const GrFragmentProcessor& proc) const override { return true; }
};

////////////////////////////////////////////////////////////////////////////

sk_sp<GrFragmentProcessor> SkGaussianEdgeShaderImpl::asFragmentProcessor(const AsFPArgs& args) const {
    return sk_make_sp<GaussianEdgeFP>();
}

#endif

////////////////////////////////////////////////////////////////////////////

bool SkGaussianEdgeShaderImpl::isOpaque() const {
    return false;
}

////////////////////////////////////////////////////////////////////////////

#ifndef SK_IGNORE_TO_STRING
void SkGaussianEdgeShaderImpl::toString(SkString* str) const {
    str->appendf("GaussianEdgeShader: ()");
}
#endif

sk_sp<SkFlattenable> SkGaussianEdgeShaderImpl::CreateProc(SkReadBuffer& buf) {
    return sk_make_sp<SkGaussianEdgeShaderImpl>();
}

void SkGaussianEdgeShaderImpl::flatten(SkWriteBuffer& buf) const {
    this->INHERITED::flatten(buf);
}

///////////////////////////////////////////////////////////////////////////////

sk_sp<SkShader> SkGaussianEdgeShader::Make() {
    return sk_make_sp<SkGaussianEdgeShaderImpl>();
}

///////////////////////////////////////////////////////////////////////////////

SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkGaussianEdgeShader)
SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkGaussianEdgeShaderImpl)
SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END

///////////////////////////////////////////////////////////////////////////////