src/gpu/tessellate/GrPathShader.h

/*
 * Copyright 2020 Google LLC.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef GrPathShader_DEFINED
#define GrPathShader_DEFINED

#include "src/core/SkArenaAlloc.h"
#include "src/gpu/GrGeometryProcessor.h"
#include "src/gpu/GrOpFlushState.h"
#include "src/gpu/GrOpsRenderPass.h"
#include "src/gpu/GrProgramInfo.h"
#include "src/gpu/ops/GrSimpleMeshDrawOpHelper.h"
#include <limits>

 // This is a common base class for shaders in the GPU tessellator.
class GrPathShader : public GrGeometryProcessor {
public:
    GrPathShader(ClassID classID, const SkMatrix& viewMatrix, GrPrimitiveType primitiveType,
                 int tessellationPatchVertexCount)
            : GrGeometryProcessor(classID)
            , fViewMatrix(viewMatrix)
            , fPrimitiveType(primitiveType)
            , fTessellationPatchVertexCount(tessellationPatchVertexCount) {
        if (fTessellationPatchVertexCount) {
            this->setWillUseTessellationShaders();
        }
    }

    GrPrimitiveType primitiveType() const { return fPrimitiveType; }
    int tessellationPatchVertexCount() const { return fTessellationPatchVertexCount; }
    const SkMatrix& viewMatrix() const { return fViewMatrix; }

    struct ProgramArgs {
        SkArenaAlloc* fArena;
        const GrSurfaceProxyView& fWriteView;
        const GrXferProcessor::DstProxyView* fDstProxyView;
        GrXferBarrierFlags fXferBarrierFlags;
        GrLoadOp fColorLoadOp;
        const GrCaps* fCaps;
    };

    static GrProgramInfo* MakeProgram(const ProgramArgs& args, const GrPathShader* shader,
                                      const GrPipeline* pipeline,
                                      const GrUserStencilSettings* stencil) {
        return args.fArena->make<GrProgramInfo>(args.fWriteView, pipeline, stencil, shader,
                                                shader->fPrimitiveType,
                                                shader->fTessellationPatchVertexCount,
                                                args.fXferBarrierFlags, args.fColorLoadOp);
    }

    // Fills in a 4-point patch in such a way that the shader will recognize it as a conic.
    static void WriteConicPatch(const SkPoint pts[3], float w, SkPoint patch[4]) {
        // Write out the 3 conic points to patch[0..2], the weight to patch[3].x, and then set
        // patch[3].y as NaN to flag this patch as a conic.
        memcpy(patch, pts, sizeof(SkPoint) * 3);
        patch[3].set(w, std::numeric_limits<float>::infinity());
    }

private:
    const SkMatrix fViewMatrix;
    const GrPrimitiveType fPrimitiveType;
    const int fTessellationPatchVertexCount;

    class Impl;
};

#endif