src/gpu/tessellate/GrTessellatePathOp.h

/*
 * Copyright 2019 Google LLC.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef GrTessellatePathOp_DEFINED
#define GrTessellatePathOp_DEFINED

#include "src/gpu/ops/GrMeshDrawOp.h"
#include "src/gpu/tessellate/GrTessellationPathRenderer.h"

class GrAppliedHardClip;
class GrStencilPathShader;
class GrResolveLevelCounter;

// Renders paths using a hybrid "Red Book" (stencil, then cover) method. Curves get linearized by
// either GPU tessellation shaders or indirect draws. This Op doesn't apply analytic AA, so it
// requires a render target that supports either MSAA or mixed samples if AA is desired.
class GrTessellatePathOp : public GrDrawOp {
private:
    DEFINE_OP_CLASS_ID

    GrTessellatePathOp(const SkMatrix& viewMatrix, const SkPath& path, GrPaint&& paint,
                       GrAAType aaType, GrTessellationPathRenderer::OpFlags opFlags)
            : GrDrawOp(ClassID())
            , fOpFlags(opFlags)
            , fViewMatrix(viewMatrix)
            , fPath(path)
            , fAAType(aaType)
            , fColor(paint.getColor4f())
            , fProcessors(std::move(paint)) {
        SkRect devBounds;
        fViewMatrix.mapRect(&devBounds, path.getBounds());
        this->setBounds(devBounds, HasAABloat(GrAAType::kCoverage == fAAType), IsHairline::kNo);
    }

    const char* name() const override { return "GrTessellatePathOp"; }
    void visitProxies(const VisitProxyFunc& fn) const override { fProcessors.visitProxies(fn); }
    GrProcessorSet::Analysis finalize(const GrCaps& caps, const GrAppliedClip* clip,
                                      bool hasMixedSampledCoverage,
                                      GrClampType clampType) override {
        return fProcessors.finalize(
                fColor, GrProcessorAnalysisCoverage::kNone, clip, &GrUserStencilSettings::kUnused,
                hasMixedSampledCoverage, caps, clampType, &fColor);
    }

    FixedFunctionFlags fixedFunctionFlags() const override;
    void onPrePrepare(GrRecordingContext*, const GrSurfaceProxyView*, GrAppliedClip*,
                      const GrXferProcessor::DstProxyView&) override;
    void onPrepare(GrOpFlushState* state) override;

    // Produces a non-overlapping triangulation of the path's inner polygon(s). The inner polygons
    // connect the endpoints of each verb. (i.e., they are the path that would result from
    // collapsing all curves to single lines.) If this succeeds, then we will be able to fill the
    // triangles directly and bypass stencilling them.
    //
    // Returns false if the inner triangles do not form a simple polygon (e.g., self intersection,
    // double winding). Non-simple polygons would need to split edges in order to avoid overlap,
    // and this is not an option as it would introduce T-junctions with the outer cubics.
    bool prepareNonOverlappingInnerTriangles(GrMeshDrawOp::Target*, int* numCountedCurves);

    // Produces a "Red Book" style triangulation of the SkPath's inner polygon(s) using a
    // "middle-out" topology (See GrMiddleOutPolygonTriangulator), and then prepares outer cubics in
    // the cubic buffer. The inner triangles and outer cubics stencilled together define the
    // complete path.
    //
    // If a resolveLevel counter is provided, this method resets it and uses it to count and
    // prepares the outer cubics as indirect draws. Otherwise they are prepared as hardware
    // tessellation patches.
    //
    // If drawTrianglesAsIndirectCubicDraw is true, then the resolveLevel counter must be non-null,
    // and we express the inner triangles as an indirect cubic draw and sneak them in alongside the
    // other cubic draws.
    void prepareMiddleOutTrianglesAndCubics(GrMeshDrawOp::Target*, GrResolveLevelCounter* = nullptr,
                                            bool drawTrianglesAsIndirectCubicDraw = false);

    // Prepares a list of indirect draw commands and instance data for the path's "outer cubics",
    // converting any quadratics to cubics. An outer cubic is an independent, 4-point closed contour
    // consisting of a single cubic curve. Stencilled together with the inner triangles, these
    // define the complete path.
    void prepareIndirectOuterCubics(GrMeshDrawOp::Target*, const GrResolveLevelCounter&);

    // For performance reasons we can often express triangles as an indirect cubic draw and sneak
    // them in alongside the other indirect draws. This prepareIndirectOuterCubics variant allows
    // the caller to provide a mapped cubic buffer with triangles already written into 4-point
    // instances at the beginning. If numTrianglesAtBeginningOfData is nonzero, we add an extra
    // indirect draw that renders these triangles.
    void prepareIndirectOuterCubicsAndTriangles(GrMeshDrawOp::Target*, const GrResolveLevelCounter&,
                                                SkPoint* cubicData,
                                                int numTrianglesAtBeginningOfData);

    // Writes an array of "outer cubic" tessellation patches from each bezier in the SkPath,
    // converting any quadratics to cubics. An outer cubic is an independent, 4-point closed contour
    // consisting of a single cubic curve. Stencilled together with the inner triangles, these
    // define the complete path.
    void prepareTessellatedOuterCubics(GrMeshDrawOp::Target*, int numCountedCurves);

    // Writes an array of cubic "wedges" from the SkPath, converting any lines or quadratics to
    // cubics. A wedge is an independent, 5-point closed contour consisting of 4 cubic control
    // points plus an anchor point fanning from the center of the curve's resident contour. Once
    // stencilled, these wedges alone define the complete path.
    //
    // TODO: Eventually we want to use rational cubic wedges in order to support conics.
    void prepareTessellatedCubicWedges(GrMeshDrawOp::Target*);

    void onExecute(GrOpFlushState*, const SkRect& chainBounds) override;
    void drawStencilPass(GrOpFlushState*);
    void drawCoverPass(GrOpFlushState*);

    const GrTessellationPathRenderer::OpFlags fOpFlags;
    const SkMatrix fViewMatrix;
    const SkPath fPath;
    const GrAAType fAAType;
    SkPMColor4f fColor;
    GrProcessorSet fProcessors;

    sk_sp<const GrBuffer> fTriangleBuffer;
    int fBaseTriangleVertex;
    int fTriangleVertexCount;

    // These switches specify how the above fTriangleBuffer should be drawn (if at all).
    //
    // If stencil=true and fill=false:
    //
    //     We just stencil the triangles (with cubics) during the stencil step. The path gets filled
    //     later using a simple bounding box if needed.
    //
    // If stencil=true and fill=true:
    //
    //     We still stencil the triangles and cubics normally, but during the *fill* step we fill
    //     the triangles plus local convex hulls around each cubic instead of a bounding box.
    //
    // If stencil=false and fill=true:
    //
    //     This means that fTriangleBuffer contains non-overlapping geometry that can be filled
    //     directly to the final render target. We only need to stencil *curves*, and during the
    //     fill step we draw the triangles directly with a stencil test that accounts for curves
    //     (see drawCoverPass()), and then finally fill the curves with local convex hulls.
    bool fDoStencilTriangleBuffer = false;
    bool fDoFillTriangleBuffer = false;

    // The cubic buffer defines either standalone cubics or wedges. These are stencilled by
    // tessellation shaders, and may also be used do fill local convex hulls around each cubic.
    sk_sp<const GrBuffer> fCubicBuffer;
    int fBaseCubicVertex;
    int fCubicVertexCount;
    GrStencilPathShader* fStencilCubicsShader = nullptr;

    // If fIndirectDrawBuffer is non-null, then we issue an indexed-indirect draw instead of using
    // hardware tessellation. This is oftentimes faster than tessellation, and other times it serves
    // as a polyfill when tessellation just isn't supported.
    sk_sp<const GrBuffer> fIndirectDrawBuffer;
    size_t fIndirectDrawOffset;
    int fIndirectDrawCount;
    sk_sp<const GrBuffer> fIndirectIndexBuffer;

    friend class GrOpMemoryPool;  // For ctor.

public:
    // This serves as a base class for benchmarking individual methods on GrTessellatePathOp.
    class TestingOnly_Benchmark;
};

#endif