src/gpu/effects/GrBlurredEdgeFragmentProcessor.cpp

/*
 * Copyright 2017 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "effects/GrBlurredEdgeFragmentProcessor.h"
#include "GrInvariantOutput.h"

#include "glsl/GrGLSLFragmentProcessor.h"
#include "glsl/GrGLSLFragmentShaderBuilder.h"

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

    void emitCode(EmitArgs& args) override {

        GrBlurredEdgeFP::Mode mode = args.fFp.cast<GrBlurredEdgeFP>().mode();

        GrGLSLFPFragmentBuilder* fragBuilder = args.fFragBuilder;

        fragBuilder->codeAppendf("vec4 color = %s;", args.fInputColor);
        if (!args.fGpImplementsDistanceVector) {
            fragBuilder->codeAppendf("// assuming interpolant is set in vertex colors\n");
            fragBuilder->codeAppendf("float factor = 1.0 - color.b;");
        } else {
            fragBuilder->codeAppendf("// using distance to edge to compute interpolant\n");
            fragBuilder->codeAppend("float radius = color.r*256.0*64.0 + color.g*64.0;");
            fragBuilder->codeAppend("float pad = color.b*64.0;");

            fragBuilder->codeAppendf("float factor = 1.0 - clamp((%s.z - pad)/radius, 0.0, 1.0);",
                                     fragBuilder->distanceVectorName());
        }
        switch (mode) {
            case GrBlurredEdgeFP::kGaussian_Mode:
                fragBuilder->codeAppend("factor = exp(-factor * factor * 4.0) - 0.018;");
                break;
            case GrBlurredEdgeFP::kSmoothstep_Mode:
                fragBuilder->codeAppend("factor = smoothstep(factor, 0.0, 1.0);");
                break;
        }
        if (!args.fGpImplementsDistanceVector) {
            fragBuilder->codeAppendf("%s = factor*vec4(0.0, 0.0, 0.0, color.g);",
                                     args.fOutputColor);
        } else {
            fragBuilder->codeAppendf("%s = factor*vec4(0.0, 0.0, 0.0, color.a);",
                                     args.fOutputColor);
        }
    }

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

    GrBlurredEdgeFP::Mode fMode;
};

GrGLSLFragmentProcessor* GrBlurredEdgeFP::onCreateGLSLInstance() const {
    return new GLSLBlurredEdgeFP();
}

void GrBlurredEdgeFP::onGetGLSLProcessorKey(const GrShaderCaps& caps, 
                                            GrProcessorKeyBuilder* b) const {
    b->add32(fMode);
}

bool GrBlurredEdgeFP::onIsEqual(const GrFragmentProcessor& other) const {
    const GrBlurredEdgeFP& that = other.cast<GrBlurredEdgeFP>();
    return that.fMode == fMode;
}

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