src/gpu/ccpr/GrCCPRCubicShader.h

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

#ifndef GrCCPRCubicShader_DEFINED
#define GrCCPRCubicShader_DEFINED

#include "ccpr/GrCCPRCoverageProcessor.h"

/**
 * This class renders the coverage of convex closed cubic segments using the techniques outlined in
 * "Resolution Independent Curve Rendering using Programmable Graphics Hardware" by Charles Loop and
 * Jim Blinn:
 *
 * https://www.microsoft.com/en-us/research/wp-content/uploads/2005/01/p1000-loop.pdf
 *
 * The provided curve segments must be convex, monotonic with respect to the vector of their closing
 * edge [P3 - P0], and must not contain or be near any inflection points or loop intersections.
 * (Use GrCCPRGeometry.)
 */
class GrCCPRCubicShader : public GrCCPRCoverageProcessor::Shader {
public:
    enum class CubicType {
        kSerpentine,
        kLoop
    };

protected:
    GrCCPRCubicShader(CubicType cubicType) : fCubicType(cubicType) {}

    int getNumInputPoints() const final { return 4; }

    void appendInputPointFetch(const GrCCPRCoverageProcessor&, GrGLSLShaderBuilder*,
                               const TexelBufferHandle& pointsBuffer,
                               const char* pointId) const final;

    void emitWind(GrGLSLShaderBuilder*, const char* pts, const char* rtAdjust,
                  const char* outputWind) const final;

    void emitSetupCode(GrGLSLShaderBuilder*, const char* pts, const char* segmentId,
                       const char* bloat, const char* wind, const char* rtAdjust,
                       GeometryVars*) const final;

    virtual void onEmitSetupCode(GrGLSLShaderBuilder*, const char* pts, const char* segmentId,
                                 const char* rtAdjust, GeometryVars*) const = 0;

    WindHandling onEmitVaryings(GrGLSLVaryingHandler*, SkString* code, const char* position,
                                const char* coverage, const char* wind) final;

    virtual void onEmitVaryings(GrGLSLVaryingHandler*, SkString* code) = 0;

    const CubicType   fCubicType;
    GrShaderVar       fKLMMatrix{"klm_matrix", kFloat3x3_GrSLType};
    GrShaderVar       fKLMDerivatives{"klm_derivatives", kFloat2_GrSLType, 3};
    GrShaderVar       fEdgeDistanceEquation{"edge_distance_equation", kFloat3_GrSLType};
    GrGLSLGeoToFrag   fKLMD{kFloat4_GrSLType};
};

class GrCCPRCubicHullShader : public GrCCPRCubicShader {
public:
    GrCCPRCubicHullShader(CubicType cubicType) : GrCCPRCubicShader(cubicType) {}

private:
    GeometryType getGeometryType() const override { return GeometryType::kHull; }
    int getNumSegments() const override { return 4; } // 4 wedges.
    void onEmitSetupCode(GrGLSLShaderBuilder*, const char* pts, const char* wedgeId,
                         const char* rtAdjust, GeometryVars*) const override;
    void onEmitVaryings(GrGLSLVaryingHandler*, SkString* code) override;
    void onEmitFragmentCode(GrGLSLPPFragmentBuilder*, const char* outputCoverage) const override;

    GrGLSLGeoToFrag fGradMatrix{kFloat2x2_GrSLType};
};

class GrCCPRCubicCornerShader : public GrCCPRCubicShader {
public:
    GrCCPRCubicCornerShader(CubicType cubicType) : GrCCPRCubicShader(cubicType) {}

private:
    GeometryType getGeometryType() const override { return GeometryType::kCorners; }
    int getNumSegments() const override { return 2; } // 2 corners.
    void onEmitSetupCode(GrGLSLShaderBuilder*, const char* pts, const char* cornerId,
                         const char* rtAdjust, GeometryVars*) const override;
    void onEmitVaryings(GrGLSLVaryingHandler*, SkString* code) override;
    void onEmitFragmentCode(GrGLSLPPFragmentBuilder*, const char* outputCoverage) const override;

    GrShaderVar        fEdgeDistanceDerivatives{"edge_distance_derivatives", kFloat2_GrSLType};
    GrGLSLGeoToFrag    fdKLMDdx{kFloat4_GrSLType};
    GrGLSLGeoToFrag    fdKLMDdy{kFloat4_GrSLType};
};

#endif