src/gpu/ccpr/GrCCPRCoverageOp.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 "GrCCPRCoverageOp.h"

#include "GrGpuCommandBuffer.h"
#include "GrOnFlushResourceProvider.h"
#include "GrOpFlushState.h"
#include "SkMathPriv.h"
#include "SkPath.h"
#include "SkPathPriv.h"
#include "SkPoint.h"
#include "SkNx.h"
#include "ccpr/GrCCPRGeometry.h"

using TriangleInstance = GrCCPRCoverageProcessor::TriangleInstance;
using CurveInstance = GrCCPRCoverageProcessor::CurveInstance;

/**
 * This is a view matrix that accumulates two bounding boxes as it maps points: device-space bounds
 * and "45 degree" device-space bounds (| 1 -1 | * devCoords).
 *                                      | 1  1 |
 */
class AccumulatingViewMatrix {
public:
    AccumulatingViewMatrix(const SkMatrix& m, const SkPoint& initialPoint);

    SkPoint transform(const SkPoint& pt);
    void getAccumulatedBounds(SkRect* devBounds, SkRect* devBounds45) const;

private:
    Sk4f fX;
    Sk4f fY;
    Sk4f fT;

    Sk4f fTopLeft;
    Sk4f fBottomRight;
};

inline AccumulatingViewMatrix::AccumulatingViewMatrix(const SkMatrix& m,
                                                      const SkPoint& initialPoint) {
    // m45 transforms into 45 degree space in order to find the octagon's diagonals. We could
    // use SK_ScalarRoot2Over2 if we wanted an orthonormal transform, but this is irrelevant as
    // long as the shader uses the correct inverse when coming back to device space.
    SkMatrix m45;
    m45.setSinCos(1, 1);
    m45.preConcat(m);

    fX = Sk4f(m.getScaleX(), m.getSkewY(), m45.getScaleX(), m45.getSkewY());
    fY = Sk4f(m.getSkewX(), m.getScaleY(), m45.getSkewX(), m45.getScaleY());
    fT = Sk4f(m.getTranslateX(), m.getTranslateY(), m45.getTranslateX(), m45.getTranslateY());

    Sk4f transformed = SkNx_fma(fY, Sk4f(initialPoint.y()), fT);
    transformed = SkNx_fma(fX, Sk4f(initialPoint.x()), transformed);
    fTopLeft = fBottomRight = transformed;
}

inline SkPoint AccumulatingViewMatrix::transform(const SkPoint& pt) {
    Sk4f transformed = SkNx_fma(fY, Sk4f(pt.y()), fT);
    transformed = SkNx_fma(fX, Sk4f(pt.x()), transformed);

    fTopLeft = Sk4f::Min(fTopLeft, transformed);
    fBottomRight = Sk4f::Max(fBottomRight, transformed);

    // TODO: vst1_lane_f32? (Sk4f::storeLane?)
    float data[4];
    transformed.store(data);
    return SkPoint::Make(data[0], data[1]);
}

inline void AccumulatingViewMatrix::getAccumulatedBounds(SkRect* devBounds,
                                                         SkRect* devBounds45) const {
    float topLeft[4], bottomRight[4];
    fTopLeft.store(topLeft);
    fBottomRight.store(bottomRight);
    devBounds->setLTRB(topLeft[0], topLeft[1], bottomRight[0], bottomRight[1]);
    devBounds45->setLTRB(topLeft[2], topLeft[3], bottomRight[2], bottomRight[3]);
}

void GrCCPRCoverageOpsBuilder::parsePath(const SkMatrix& viewMatrix, const SkPath& path,
                                         SkRect* devBounds, SkRect* devBounds45) {
    SkASSERT(!fParsingPath);
    SkDEBUGCODE(fParsingPath = true);

    fCurrPathPointsIdx = fGeometry.points().count();
    fCurrPathVerbsIdx = fGeometry.verbs().count();
    fCurrPathTallies = PrimitiveTallies();

    fGeometry.beginPath();

    if (path.isEmpty()) {
        devBounds->setEmpty();
        devBounds45->setEmpty();
        return;
    }

    const SkPoint* const pts = SkPathPriv::PointData(path);
    int ptsIdx = 0;
    bool insideContour = false;

    AccumulatingViewMatrix m(viewMatrix, pts[0]);

    for (SkPath::Verb verb : SkPathPriv::Verbs(path)) {
        switch (verb) {
            case SkPath::kMove_Verb:
                this->endContourIfNeeded(insideContour);
                fGeometry.beginContour(m.transform(pts[ptsIdx++]));
                insideContour = true;
                continue;
            case SkPath::kClose_Verb:
                this->endContourIfNeeded(insideContour);
                insideContour = false;
                continue;
            case SkPath::kLine_Verb:
                fGeometry.lineTo(m.transform(pts[ptsIdx++]));
                continue;
            case SkPath::kQuad_Verb:
                SkASSERT(ptsIdx >= 1); // SkPath should have inserted an implicit moveTo if needed.
                fGeometry.quadraticTo(m.transform(pts[ptsIdx]), m.transform(pts[ptsIdx + 1]));
                ptsIdx += 2;
                continue;
            case SkPath::kCubic_Verb:
                SkASSERT(ptsIdx >= 1); // SkPath should have inserted an implicit moveTo if needed.
                fGeometry.cubicTo(m.transform(pts[ptsIdx]), m.transform(pts[ptsIdx + 1]),
                                  m.transform(pts[ptsIdx + 2]));
                ptsIdx += 3;
                continue;
            case SkPath::kConic_Verb:
                SK_ABORT("Conics are not supported.");
            default:
                SK_ABORT("Unexpected path verb.");
        }
    }

    this->endContourIfNeeded(insideContour);
    m.getAccumulatedBounds(devBounds, devBounds45);
}

void GrCCPRCoverageOpsBuilder::endContourIfNeeded(bool insideContour) {
    if (insideContour) {
        fCurrPathTallies += fGeometry.endContour();
    }
}

void GrCCPRCoverageOpsBuilder::saveParsedPath(ScissorMode scissorMode,
                                              const SkIRect& clippedDevIBounds,
                                              int16_t atlasOffsetX, int16_t atlasOffsetY) {
    SkASSERT(fParsingPath);

    fPathsInfo.push_back() = {
        scissorMode,
        (int32_t) (((uint32_t) (int32_t) atlasOffsetY << 16) | (atlasOffsetX & 0xffff)),
        std::move(fTerminatingOp)
    };

    fTallies[(int)scissorMode] += fCurrPathTallies;

    if (ScissorMode::kScissored == scissorMode) {
        fScissorBatches.push_back() = {
            fCurrPathTallies,
            clippedDevIBounds.makeOffset(atlasOffsetX, atlasOffsetY)
        };
    }

    SkDEBUGCODE(fParsingPath = false);
}

void GrCCPRCoverageOpsBuilder::discardParsedPath() {
    SkASSERT(fParsingPath);

    // The code will still work whether or not the below assertion is true. It is just unlikely that
    // the caller would want this, and probably indicative of of a mistake. (Why emit an
    // intermediate Op (to switch to a new atlas?), just to then throw the path away?)
    SkASSERT(!fTerminatingOp);

    fGeometry.resize_back(fCurrPathPointsIdx, fCurrPathVerbsIdx);
    SkDEBUGCODE(fParsingPath = false);
}

void GrCCPRCoverageOpsBuilder::emitOp(SkISize drawBounds) {
    SkASSERT(!fTerminatingOp);
    fTerminatingOp.reset(new GrCCPRCoverageOp(std::move(fScissorBatches), drawBounds));
    SkASSERT(fScissorBatches.empty());
}

// Emits a contour's triangle fan.
//
// Classic Redbook fanning would be the triangles: [0  1  2], [0  2  3], ..., [0  n-2  n-1].
//
// This function emits the triangle: [0  n/3  n*2/3], and then recurses on all three sides. The
// advantage to this approach is that for a convex-ish contour, it generates larger triangles.
// Classic fanning tends to generate long, skinny triangles, which are expensive to draw since they
// have a longer perimeter to rasterize and antialias.
//
// The indices array indexes the fan's points (think: glDrawElements), and must have at least log3
// elements past the end for this method to use as scratch space.
//
// Returns the next triangle instance after the final one emitted.
static TriangleInstance* emit_recursive_fan(SkTArray<int32_t, true>& indices, int firstIndex,
                                            int indexCount, int32_t packedAtlasOffset,
                                            TriangleInstance out[]) {
    if (indexCount < 3) {
        return out;
    }

    const int32_t oneThirdCount = indexCount / 3;
    const int32_t twoThirdsCount = (2 * indexCount) / 3;
    *out++ = {
        indices[firstIndex],
        indices[firstIndex + oneThirdCount],
        indices[firstIndex + twoThirdsCount],
        packedAtlasOffset
    };

    out = emit_recursive_fan(indices, firstIndex, oneThirdCount + 1, packedAtlasOffset, out);
    out = emit_recursive_fan(indices, firstIndex + oneThirdCount,
                             twoThirdsCount - oneThirdCount + 1, packedAtlasOffset, out);

    int endIndex = firstIndex + indexCount;
    int32_t oldValue = indices[endIndex];
    indices[endIndex] = indices[firstIndex];
    out = emit_recursive_fan(indices, firstIndex + twoThirdsCount, indexCount - twoThirdsCount + 1,
                             packedAtlasOffset, out);
    indices[endIndex] = oldValue;

    return out;
}

bool GrCCPRCoverageOpsBuilder::finalize(GrOnFlushResourceProvider* onFlushRP,
                                        SkTArray<std::unique_ptr<GrCCPRCoverageOp>>* ops) {
    SkASSERT(!fParsingPath);

    const SkTArray<SkPoint, true>& points = fGeometry.points();
    sk_sp<GrBuffer> pointsBuffer = onFlushRP->makeBuffer(kTexel_GrBufferType,
                                                         points.count() * 2 * sizeof(float),
                                                         points.begin());
    if (!pointsBuffer) {
        return false;
    }

    // Configure the instance buffer layout.
    PrimitiveTallies baseInstances[kNumScissorModes];
    // int4 indices.
    baseInstances[0].fTriangles = 0;
    baseInstances[1].fTriangles = baseInstances[0].fTriangles + fTallies[0].fTriangles;
    // int2 indices (curves index the buffer as int2 rather than int4).
    baseInstances[0].fQuadratics = (baseInstances[1].fTriangles + fTallies[1].fTriangles) * 2;
    baseInstances[1].fQuadratics = baseInstances[0].fQuadratics + fTallies[0].fQuadratics;
    baseInstances[0].fSerpentines = baseInstances[1].fQuadratics + fTallies[1].fQuadratics;
    baseInstances[1].fSerpentines = baseInstances[0].fSerpentines + fTallies[0].fSerpentines;
    baseInstances[0].fLoops = baseInstances[1].fSerpentines + fTallies[1].fSerpentines;
    baseInstances[1].fLoops = baseInstances[0].fLoops + fTallies[0].fLoops;
    int instanceBufferSize = (baseInstances[1].fLoops + fTallies[1].fLoops) * sizeof(CurveInstance);

    sk_sp<GrBuffer> instanceBuffer = onFlushRP->makeBuffer(kVertex_GrBufferType,
                                                           instanceBufferSize);
    if (!instanceBuffer) {
        return false;
    }

    TriangleInstance* triangleInstanceData = static_cast<TriangleInstance*>(instanceBuffer->map());
    CurveInstance* curveInstanceData = reinterpret_cast<CurveInstance*>(triangleInstanceData);
    SkASSERT(curveInstanceData);

    PathInfo* currPathInfo = fPathsInfo.begin();
    int32_t packedAtlasOffset;
    int ptsIdx = -1;
    PrimitiveTallies instanceIndices[2] = {baseInstances[0], baseInstances[1]};
    PrimitiveTallies* currIndices;
    SkSTArray<256, int32_t, true> currFan;

#ifdef SK_DEBUG
    int numScissoredPaths = 0;
    int numScissorBatches = 0;
    PrimitiveTallies initialBaseInstances[] = {baseInstances[0], baseInstances[1]};
#endif

    // Expand the ccpr verbs into GPU instance buffers.
    for (GrCCPRGeometry::Verb verb : fGeometry.verbs()) {
        switch (verb) {
            case GrCCPRGeometry::Verb::kBeginPath:
                SkASSERT(currFan.empty());
                currIndices = &instanceIndices[(int)currPathInfo->fScissorMode];
                packedAtlasOffset = currPathInfo->fPackedAtlasOffset;
#ifdef SK_DEBUG
                if (ScissorMode::kScissored == currPathInfo->fScissorMode) {
                    ++numScissoredPaths;
                }
#endif
                if (auto op = std::move(currPathInfo->fTerminatingOp)) {
                    op->setBuffers(pointsBuffer, instanceBuffer, baseInstances, instanceIndices);
                    baseInstances[0] = instanceIndices[0];
                    baseInstances[1] = instanceIndices[1];
                    SkDEBUGCODE(numScissorBatches += op->fScissorBatches.count());
                    ops->push_back(std::move(op));
                }
                ++currPathInfo;
                continue;

            case GrCCPRGeometry::Verb::kBeginContour:
                SkASSERT(currFan.empty());
                currFan.push_back(++ptsIdx);
                continue;

            case GrCCPRGeometry::Verb::kLineTo:
                SkASSERT(!currFan.empty());
                currFan.push_back(++ptsIdx);
                continue;

            case GrCCPRGeometry::Verb::kMonotonicQuadraticTo:
                SkASSERT(!currFan.empty());
                curveInstanceData[currIndices->fQuadratics++] = {ptsIdx, packedAtlasOffset};
                currFan.push_back(ptsIdx += 2);
                continue;

            case GrCCPRGeometry::Verb::kMonotonicSerpentineTo:
                SkASSERT(!currFan.empty());
                curveInstanceData[currIndices->fSerpentines++] = {ptsIdx, packedAtlasOffset};
                currFan.push_back(ptsIdx += 3);
                continue;

            case GrCCPRGeometry::Verb::kMonotonicLoopTo:
                SkASSERT(!currFan.empty());
                curveInstanceData[currIndices->fLoops++] = {ptsIdx, packedAtlasOffset};
                currFan.push_back(ptsIdx += 3);
                continue;

            case GrCCPRGeometry::Verb::kEndClosedContour: // endPt == startPt.
                SkASSERT(!currFan.empty());
                currFan.pop_back();
                // fallthru.
            case GrCCPRGeometry::Verb::kEndOpenContour: // endPt != startPt.
                if (currFan.count() >= 3) {
                    int fanSize = currFan.count();
                    // Reserve space for emit_recursive_fan. Technically this can grow to
                    // fanSize + log3(fanSize), but we approximate with log2.
                    currFan.push_back_n(SkNextLog2(fanSize));
                    SkDEBUGCODE(TriangleInstance* end =)
                    emit_recursive_fan(currFan, 0, fanSize, packedAtlasOffset,
                                       triangleInstanceData + currIndices->fTriangles);
                    currIndices->fTriangles += fanSize - 2;
                    SkASSERT(triangleInstanceData + currIndices->fTriangles == end);
                }
                currFan.reset();
                continue;
        }
    }

    instanceBuffer->unmap();

    if (auto op = std::move(fTerminatingOp)) {
        op->setBuffers(std::move(pointsBuffer), std::move(instanceBuffer), baseInstances,
                       instanceIndices);
        SkDEBUGCODE(numScissorBatches += op->fScissorBatches.count());
        ops->push_back(std::move(op));
    }

    SkASSERT(currPathInfo == fPathsInfo.end());
    SkASSERT(ptsIdx == points.count() - 1);
    SkASSERT(numScissoredPaths == numScissorBatches);
    SkASSERT(instanceIndices[0].fTriangles == initialBaseInstances[1].fTriangles);
    SkASSERT(instanceIndices[1].fTriangles * 2 == initialBaseInstances[0].fQuadratics);
    SkASSERT(instanceIndices[0].fQuadratics == initialBaseInstances[1].fQuadratics);
    SkASSERT(instanceIndices[1].fQuadratics == initialBaseInstances[0].fSerpentines);
    SkASSERT(instanceIndices[0].fSerpentines == initialBaseInstances[1].fSerpentines);
    SkASSERT(instanceIndices[1].fSerpentines == initialBaseInstances[0].fLoops);
    SkASSERT(instanceIndices[0].fLoops == initialBaseInstances[1].fLoops);
    SkASSERT(instanceIndices[1].fLoops * (int) sizeof(CurveInstance) == instanceBufferSize);
    return true;
}

void GrCCPRCoverageOp::setBuffers(sk_sp<GrBuffer> pointsBuffer, sk_sp<GrBuffer> instanceBuffer,
                                  const PrimitiveTallies baseInstances[kNumScissorModes],
                                  const PrimitiveTallies endInstances[kNumScissorModes]) {
    fPointsBuffer = std::move(pointsBuffer);
    fInstanceBuffer = std::move(instanceBuffer);
    fBaseInstances[0] = baseInstances[0];
    fBaseInstances[1] = baseInstances[1];
    fInstanceCounts[0] = endInstances[0] - baseInstances[0];
    fInstanceCounts[1] = endInstances[1] - baseInstances[1];
}

void GrCCPRCoverageOp::onExecute(GrOpFlushState* flushState) {
    using Mode = GrCCPRCoverageProcessor::Mode;

    SkDEBUGCODE(GrCCPRCoverageProcessor::Validate(flushState->drawOpArgs().fProxy));
    SkASSERT(fPointsBuffer);
    SkASSERT(fInstanceBuffer);

    GrPipeline pipeline(flushState->drawOpArgs().fProxy, GrPipeline::ScissorState::kEnabled,
                        SkBlendMode::kPlus);

    fMeshesScratchBuffer.reserve(1 + fScissorBatches.count());
    fDynamicStatesScratchBuffer.reserve(1 + fScissorBatches.count());

    // Triangles.
    auto constexpr kTrianglesGrPrimitiveType = GrCCPRCoverageProcessor::kTrianglesGrPrimitiveType;
    this->drawMaskPrimitives(flushState, pipeline, Mode::kTriangleHulls,
                             kTrianglesGrPrimitiveType, 3, &PrimitiveTallies::fTriangles);
    this->drawMaskPrimitives(flushState, pipeline, Mode::kTriangleEdges,
                             kTrianglesGrPrimitiveType, 3, &PrimitiveTallies::fTriangles);
    this->drawMaskPrimitives(flushState, pipeline, Mode::kTriangleCorners,
                             kTrianglesGrPrimitiveType, 3, &PrimitiveTallies::fTriangles);

    // Quadratics.
    auto constexpr kQuadraticsGrPrimitiveType = GrCCPRCoverageProcessor::kQuadraticsGrPrimitiveType;
    this->drawMaskPrimitives(flushState, pipeline, Mode::kQuadraticHulls,
                             kQuadraticsGrPrimitiveType, 3, &PrimitiveTallies::fQuadratics);
    this->drawMaskPrimitives(flushState, pipeline, Mode::kQuadraticCorners,
                             kQuadraticsGrPrimitiveType, 3, &PrimitiveTallies::fQuadratics);

    // Cubics.
    auto constexpr kCubicsGrPrimitiveType = GrCCPRCoverageProcessor::kCubicsGrPrimitiveType;
    this->drawMaskPrimitives(flushState, pipeline, Mode::kSerpentineHulls,
                             kCubicsGrPrimitiveType, 4, &PrimitiveTallies::fSerpentines);
    this->drawMaskPrimitives(flushState, pipeline, Mode::kLoopHulls,
                             kCubicsGrPrimitiveType, 4, &PrimitiveTallies::fLoops);
    this->drawMaskPrimitives(flushState, pipeline, Mode::kSerpentineCorners,
                             kCubicsGrPrimitiveType, 4, &PrimitiveTallies::fSerpentines);
    this->drawMaskPrimitives(flushState, pipeline, Mode::kLoopCorners,
                             kCubicsGrPrimitiveType, 4, &PrimitiveTallies::fLoops);
}

void GrCCPRCoverageOp::drawMaskPrimitives(GrOpFlushState* flushState, const GrPipeline& pipeline,
                                          GrCCPRCoverageProcessor::Mode mode,
                                          GrPrimitiveType primType, int vertexCount,
                                          int PrimitiveTallies::* instanceType) const {
    using ScissorMode = GrCCPRCoverageOpsBuilder::ScissorMode;
    SkASSERT(pipeline.getScissorState().enabled());

    fMeshesScratchBuffer.reset();
    fDynamicStatesScratchBuffer.reset();

    if (const int instanceCount = fInstanceCounts[(int)ScissorMode::kNonScissored].*instanceType) {
        SkASSERT(instanceCount > 0);
        const int baseInstance = fBaseInstances[(int)ScissorMode::kNonScissored].*instanceType;
        GrMesh& mesh = fMeshesScratchBuffer.emplace_back(primType);
        mesh.setInstanced(fInstanceBuffer.get(), instanceCount, baseInstance, vertexCount);
        fDynamicStatesScratchBuffer.push_back().fScissorRect.setXYWH(0, 0, fDrawBounds.width(),
                                                                     fDrawBounds.height());
    }

    if (fInstanceCounts[(int)ScissorMode::kScissored].*instanceType) {
        int baseInstance = fBaseInstances[(int)ScissorMode::kScissored].*instanceType;
        for (const ScissorBatch& batch : fScissorBatches) {
            SkASSERT(this->bounds().contains(batch.fScissor));
            const int instanceCount = batch.fInstanceCounts.*instanceType;
            if (!instanceCount) {
                continue;
            }
            SkASSERT(instanceCount > 0);
            GrMesh& mesh = fMeshesScratchBuffer.emplace_back(primType);
            mesh.setInstanced(fInstanceBuffer.get(), instanceCount, baseInstance, vertexCount);
            fDynamicStatesScratchBuffer.push_back().fScissorRect = batch.fScissor;
            baseInstance += instanceCount;
        }
    }

    SkASSERT(fMeshesScratchBuffer.count() == fDynamicStatesScratchBuffer.count());

    if (!fMeshesScratchBuffer.empty()) {
        GrCCPRCoverageProcessor proc(mode, fPointsBuffer.get());
        SkASSERT(flushState->rtCommandBuffer());
        flushState->rtCommandBuffer()->draw(pipeline, proc, fMeshesScratchBuffer.begin(),
                                            fDynamicStatesScratchBuffer.begin(),
                                            fMeshesScratchBuffer.count(), this->bounds());
    }
}