/*

 * Copyright 2013 Google Inc.

 *

 * Use of this source code is governed by a BSD-style license that can be

 * found in the LICENSE file.

 */

#ifndef GrBezierEffect_DEFINED

#define GrBezierEffect_DEFINED

#include "include/core/SkMatrix.h"

#include "include/private/SkColorData.h"

#include "include/private/gpu/ganesh/GrTypesPriv.h"

#include "src/base/SkArenaAlloc.h"

#include "src/core/SkSLTypeShared.h"

#include "src/gpu/ganesh/GrCaps.h"

#include "src/gpu/ganesh/GrGeometryProcessor.h"

#include "src/gpu/ganesh/GrProcessorUnitTest.h"

#include "src/gpu/ganesh/GrShaderCaps.h"

#include <cstdint>

#include <memory>

namespace skgpu { class KeyBuilder; }

/**

 * Shader is based off of Loop-Blinn Quadratic GPU Rendering

 * The output of this effect is a hairline edge for conics.

 * Conics specified by implicit equation K^2 - LM.

 * K, L, and M, are the first three values of the vertex attribute,

 * the fourth value is not used. Distance is calculated using a

 * first order approximation from the taylor series.

 * Coverage for AA is max(0, 1-distance).

 *

 * Test were also run using a second order distance approximation.

 * There were two versions of the second order approx. The first version

 * is of roughly the form:

 * f(q) = |f(p)| - ||f'(p)||*||q-p|| - ||f''(p)||*||q-p||^2.

 * The second is similar:

 * f(q) = |f(p)| + ||f'(p)||*||q-p|| + ||f''(p)||*||q-p||^2.

 * The exact version of the equations can be found in the paper

 * "Distance Approximations for Rasterizing Implicit Curves" by Gabriel Taubin

 *

 * In both versions we solve the quadratic for ||q-p||.

 * Version 1:

 * gFM is magnitude of first partials and gFM2 is magnitude of 2nd partials (as derived from paper)

 * builder->fsCodeAppend("\t\tedgeAlpha = (sqrt(gFM*gFM+4.0*func*gF2M) - gFM)/(2.0*gF2M);\n");

 * Version 2:

 * builder->fsCodeAppend("\t\tedgeAlpha = (gFM - sqrt(gFM*gFM-4.0*func*gF2M))/(2.0*gF2M);\n");

 *

 * Also note that 2nd partials of k,l,m are zero

 *

 * When comparing the two second order approximations to the first order approximations,

 * the following results were found. Version 1 tends to underestimate the distances, thus it

 * basically increases all the error that we were already seeing in the first order

 * approx. So this version is not the one to use. Version 2 has the opposite effect

 * and tends to overestimate the distances. This is much closer to what we are

 * looking for. It is able to render ellipses (even thin ones) without the need to chop.

 * However, it can not handle thin hyperbolas well and thus would still rely on

 * chopping to tighten the clipping. Another side effect of the overestimating is

 * that the curves become much thinner and "ropey". If all that was ever rendered

 * were "not too thin" curves and ellipses then 2nd order may have an advantage since

 * only one geometry would need to be rendered. However no benches were run comparing

 * chopped first order and non chopped 2nd order.

 */

class GrConicEffect : public GrGeometryProcessor {

public:

    static GrGeometryProcessor* Make(SkArenaAlloc* arena,

                                     const SkPMColor4f& color,

                                     const SkMatrix& viewMatrix,

                                     const GrCaps& caps,

                                     const SkMatrix& localMatrix,

                                     bool usesLocalCoords,

                                     uint8_t coverage = 0xff) {

        if (!caps.shaderCaps()->fShaderDerivativeSupport) {

            return nullptr;

        }

        return arena->make([&](void* ptr) {

            return new (ptr) GrConicEffect(color, viewMatrix, coverage, localMatrix,

                                           usesLocalCoords);

        });

    }

    ~GrConicEffect() override;

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

    void addToKey(const GrShaderCaps& caps, skgpu::KeyBuilder* b) const override;

    std::unique_ptr<ProgramImpl> makeProgramImpl(const GrShaderCaps&) const override;

private:

    class Impl;

    GrConicEffect(const SkPMColor4f&, const SkMatrix& viewMatrix, uint8_t coverage,

                  const SkMatrix& localMatrix, bool usesLocalCoords);

    inline const Attribute& inPosition() const { return kAttributes[0]; }

    inline const Attribute& inConicCoeffs() const { return kAttributes[1]; }

    SkPMColor4f         fColor;

    SkMatrix            fViewMatrix;

    SkMatrix            fLocalMatrix;

    bool                fUsesLocalCoords;

    uint8_t             fCoverageScale;

    inline static constexpr Attribute kAttributes[] = {

        {"inPosition", kFloat2_GrVertexAttribType, SkSLType::kFloat2},

        {"inConicCoeffs", kFloat4_GrVertexAttribType, SkSLType::kHalf4}

    };

    GR_DECLARE_GEOMETRY_PROCESSOR_TEST

    using INHERITED = GrGeometryProcessor;

};

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

/**

 * The output of this effect is a hairline edge for quadratics.

 * Quadratic specified by 0=u^2-v canonical coords. u and v are the first

 * two components of the vertex attribute. At the three control points that define

 * the Quadratic, u, v have the values {0,0}, {1/2, 0}, and {1, 1} respectively.

 * Coverage for AA is min(0, 1-distance). 3rd & 4th cimponent unused.

 * Requires shader derivative instruction support.

 */

class GrQuadEffect : public GrGeometryProcessor {

public:

    static GrGeometryProcessor* Make(SkArenaAlloc* arena,

                                     const SkPMColor4f& color,

                                     const SkMatrix& viewMatrix,

                                     const GrCaps& caps,

                                     const SkMatrix& localMatrix,

                                     bool usesLocalCoords,

                                     uint8_t coverage = 0xff) {

        if (!caps.shaderCaps()->fShaderDerivativeSupport) {

            return nullptr;

        }

        return arena->make([&](void* ptr) {

            return new (ptr) GrQuadEffect(color, viewMatrix, coverage, localMatrix,

                                          usesLocalCoords);

        });

    }

    ~GrQuadEffect() override;

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

    void addToKey(const GrShaderCaps& caps, skgpu::KeyBuilder* b) const override;

    std::unique_ptr<ProgramImpl> makeProgramImpl(const GrShaderCaps&) const override;

private:

    class Impl;

    GrQuadEffect(const SkPMColor4f&, const SkMatrix& viewMatrix, uint8_t coverage,

                 const SkMatrix& localMatrix, bool usesLocalCoords);

    inline const Attribute& inPosition() const { return kAttributes[0]; }

    inline const Attribute& inHairQuadEdge() const { return kAttributes[1]; }

    SkPMColor4f fColor;

    SkMatrix fViewMatrix;

    SkMatrix fLocalMatrix;

    bool fUsesLocalCoords;

    uint8_t fCoverageScale;

    inline static constexpr Attribute kAttributes[] = {

        {"inPosition", kFloat2_GrVertexAttribType, SkSLType::kFloat2},

        {"inHairQuadEdge", kFloat4_GrVertexAttribType, SkSLType::kHalf4}

    };

    GR_DECLARE_GEOMETRY_PROCESSOR_TEST

    using INHERITED = GrGeometryProcessor;

};

#endif