/*
 * 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 "ccpr/GrCCPRGeometry.h"

using TriangleInstance = GrCCPRCoverageProcessor::TriangleInstance;
using CubicInstance = GrCCPRCoverageProcessor::CubicInstance;

void GrCCPRCoverageOpsBuilder::parsePath(const SkMatrix& m, const SkPath& path, SkRect* devBounds,
                                         SkRect* devBounds45) {
    const SkPoint* pts = SkPathPriv::PointData(path);
    int numPts = path.countPoints();
    SkASSERT(numPts + 1 <= fLocalDevPtsBuffer.count());

    if (!numPts) {
        devBounds->setEmpty();
        devBounds45->setEmpty();
        this->parsePath(path, nullptr);
        return;
    }

    // m45 transforms path points into "45 degree" device space. A bounding box in this space gives
    // the circumscribing octagon's diagonals. We could use SK_ScalarRoot2Over2, but an orthonormal
    // transform is not necessary as long as the shader uses the correct inverse.
    SkMatrix m45;
    m45.setSinCos(1, 1);
    m45.preConcat(m);

    // X,Y,T are two parallel view matrices that accumulate two bounding boxes as they map points:
    // device-space bounds and "45 degree" device-space bounds (| 1 -1 | * devCoords).
    //                                                          | 1  1 |
    Sk4f X = Sk4f(m.getScaleX(), m.getSkewY(), m45.getScaleX(), m45.getSkewY());
    Sk4f Y = Sk4f(m.getSkewX(), m.getScaleY(), m45.getSkewX(), m45.getScaleY());
    Sk4f T = Sk4f(m.getTranslateX(), m.getTranslateY(), m45.getTranslateX(), m45.getTranslateY());

    // Map the path's points to device space and accumulate bounding boxes.
    Sk4f devPt = SkNx_fma(Y, Sk4f(pts[0].y()), T);
    devPt = SkNx_fma(X, Sk4f(pts[0].x()), devPt);
    Sk4f topLeft = devPt;
    Sk4f bottomRight = devPt;

    // Store all 4 values [dev.x, dev.y, dev45.x, dev45.y]. We are only interested in the first two,
    // and will overwrite [dev45.x, dev45.y] with the next point. This is why the dst buffer must
    // be at least one larger than the number of points.
    devPt.store(&fLocalDevPtsBuffer[0]);

    for (int i = 1; i < numPts; ++i) {
        devPt = SkNx_fma(Y, Sk4f(pts[i].y()), T);
        devPt = SkNx_fma(X, Sk4f(pts[i].x()), devPt);
        topLeft = Sk4f::Min(topLeft, devPt);
        bottomRight = Sk4f::Max(bottomRight, devPt);
        devPt.store(&fLocalDevPtsBuffer[i]);
    }

    SkPoint topLeftPts[2], bottomRightPts[2];
    topLeft.store(topLeftPts);
    bottomRight.store(bottomRightPts);
    devBounds->setLTRB(topLeftPts[0].x(), topLeftPts[0].y(),
                       bottomRightPts[0].x(), bottomRightPts[0].y());
    devBounds45->setLTRB(topLeftPts[1].x(), topLeftPts[1].y(),
                         bottomRightPts[1].x(), bottomRightPts[1].y());

    this->parsePath(path, fLocalDevPtsBuffer.get());
}

void GrCCPRCoverageOpsBuilder::parseDeviceSpacePath(const SkPath& deviceSpacePath) {
    this->parsePath(deviceSpacePath, SkPathPriv::PointData(deviceSpacePath));
}

void GrCCPRCoverageOpsBuilder::parsePath(const SkPath& path, const SkPoint* deviceSpacePts) {
    SkASSERT(!fParsingPath);
    SkDEBUGCODE(fParsingPath = true);
    SkASSERT(path.isEmpty() || deviceSpacePts);

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

    fGeometry.beginPath();

    if (path.isEmpty()) {
        return;
    }

    int ptsIdx = 0;
    bool insideContour = false;

    for (SkPath::Verb verb : SkPathPriv::Verbs(path)) {
        switch (verb) {
            case SkPath::kMove_Verb:
                this->endContourIfNeeded(insideContour);
                fGeometry.beginContour(deviceSpacePts[ptsIdx]);
                ++ptsIdx;
                insideContour = true;
                continue;
            case SkPath::kClose_Verb:
                this->endContourIfNeeded(insideContour);
                insideContour = false;
                continue;
            case SkPath::kLine_Verb:
                fGeometry.lineTo(deviceSpacePts[ptsIdx]);
                ++ptsIdx;
                continue;
            case SkPath::kQuad_Verb:
                fGeometry.quadraticTo(deviceSpacePts[ptsIdx], deviceSpacePts[ptsIdx + 1]);
                ptsIdx += 2;
                continue;
            case SkPath::kCubic_Verb:
                fGeometry.cubicTo(deviceSpacePts[ptsIdx], deviceSpacePts[ptsIdx + 1],
                                  deviceSpacePts[ptsIdx + 2]);
                ptsIdx += 3;
                continue;
            case SkPath::kConic_Verb:
                SK_ABORT("Conics are not supported.");
            default:
                SK_ABORT("Unexpected path verb.");
        }
    }

    this->endContourIfNeeded(insideContour);
}

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,
        atlasOffsetX, atlasOffsetY,
        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(const SkTArray<SkPoint, true>& pts,
                                            SkTArray<int32_t, true>& indices, int firstIndex,
                                            int indexCount, const Sk2f& atlasOffset,
                                            TriangleInstance out[]) {
    if (indexCount < 3) {
        return out;
    }

    const int32_t oneThirdCount = indexCount / 3;
    const int32_t twoThirdsCount = (2 * indexCount) / 3;
    out++->set(pts[indices[firstIndex]],
               pts[indices[firstIndex + oneThirdCount]],
               pts[indices[firstIndex + twoThirdsCount]], atlasOffset);

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

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

    return out;
}

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

    // Here we build a single instance buffer to share with every draw call from every CoverageOP we
    // plan to produce.
    //
    // CoverageOps process 4 different types of primitives (triangles, quadratics, serpentines,
    // loops), and each primitive type is further divided into instances that require a scissor and
    // those that don't. This leaves us with 8 independent instance arrays to build for the GPU.
    //
    // Rather than placing each instance array in its own GPU buffer, we allocate a single
    // megabuffer and lay them all out side-by-side. We can offset the "baseInstance" parameter in
    // our draw calls to direct the GPU to the applicable elements within a given array.
    //
    // We already know how big to make each of the 8 arrays from fTallies[kNumScissorModes], so
    // layout is straightforward.
    PrimitiveTallies baseInstances[kNumScissorModes];

    // Start with triangles and quadratics. They both view the instance buffer as an array of
    // TriangleInstance[], so we can just start at zero and lay them out one after the other.
    baseInstances[0].fTriangles = 0;
    baseInstances[1].fTriangles = baseInstances[0].fTriangles + fTallies[0].fTriangles;
    baseInstances[0].fQuadratics = baseInstances[1].fTriangles + fTallies[1].fTriangles;
    baseInstances[1].fQuadratics = baseInstances[0].fQuadratics + fTallies[0].fQuadratics;
    int triEndIdx = baseInstances[1].fQuadratics + fTallies[1].fQuadratics;

    // Cubics (loops and serpentines) view the same instance buffer as an array of CubicInstance[].
    // So, reinterpreting the instance data as CubicInstance[], we start them on the first index
    // that will not overwrite previous TriangleInstance data.
    int cubicBaseIdx = GR_CT_DIV_ROUND_UP(triEndIdx * sizeof(TriangleInstance),
                                          sizeof(CubicInstance));
    baseInstances[0].fCubics = cubicBaseIdx;
    baseInstances[1].fCubics = baseInstances[0].fCubics + fTallies[0].fCubics;
    int cubicEndIdx = baseInstances[1].fCubics + fTallies[1].fCubics;

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

    TriangleInstance* triangleInstanceData = static_cast<TriangleInstance*>(instanceBuffer->map());
    CubicInstance* cubicInstanceData = reinterpret_cast<CubicInstance*>(triangleInstanceData);
    SkASSERT(cubicInstanceData);

    PathInfo* currPathInfo = fPathsInfo.begin();
    float atlasOffsetX, atlasOffsetY;
    Sk2f atlasOffset;
    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

    const SkTArray<SkPoint, true>& pts = fGeometry.points();

    // 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];
                atlasOffsetX = static_cast<float>(currPathInfo->fAtlasOffsetX);
                atlasOffsetY = static_cast<float>(currPathInfo->fAtlasOffsetY);
                atlasOffset = {atlasOffsetX, atlasOffsetY};
#ifdef SK_DEBUG
                if (ScissorMode::kScissored == currPathInfo->fScissorMode) {
                    ++numScissoredPaths;
                }
#endif
                if (auto op = std::move(currPathInfo->fTerminatingOp)) {
                    op->setInstanceBuffer(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());
                triangleInstanceData[currIndices->fQuadratics++].set(&pts[ptsIdx], atlasOffset);
                currFan.push_back(ptsIdx += 2);
                continue;

            case GrCCPRGeometry::Verb::kMonotonicCubicTo:
                SkASSERT(!currFan.empty());
                cubicInstanceData[currIndices->fCubics++].set(&pts[ptsIdx],
                                                              atlasOffsetX, atlasOffsetY);
                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(pts, currFan, 0, fanSize, atlasOffset,
                                       triangleInstanceData + currIndices->fTriangles);
                    currIndices->fTriangles += fanSize - 2;
                    SkASSERT(triangleInstanceData + currIndices->fTriangles == end);
                }
                currFan.reset();
                continue;
        }
    }

    instanceBuffer->unmap();

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

    SkASSERT(currPathInfo == fPathsInfo.end());
    SkASSERT(ptsIdx == pts.count() - 1);
    SkASSERT(numScissoredPaths == numScissorBatches);
    SkASSERT(instanceIndices[0].fTriangles == initialBaseInstances[1].fTriangles);
    SkASSERT(instanceIndices[1].fTriangles == initialBaseInstances[0].fQuadratics);
    SkASSERT(instanceIndices[0].fQuadratics == initialBaseInstances[1].fQuadratics);
    SkASSERT(instanceIndices[1].fQuadratics == triEndIdx);
    SkASSERT(instanceIndices[0].fCubics == initialBaseInstances[1].fCubics);
    SkASSERT(instanceIndices[1].fCubics == cubicEndIdx);
    return true;
}

void GrCCPRCoverageOp::setInstanceBuffer(sk_sp<GrBuffer> instanceBuffer,
                                         const PrimitiveTallies baseInstances[kNumScissorModes],
                                         const PrimitiveTallies endInstances[kNumScissorModes]) {
    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 RenderPass = GrCCPRCoverageProcessor::RenderPass;

    SkASSERT(fInstanceBuffer);

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

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

    // Triangles.
    this->drawMaskPrimitives(flushState, pipeline, RenderPass::kTriangleHulls,
                             &PrimitiveTallies::fTriangles);
    this->drawMaskPrimitives(flushState, pipeline, RenderPass::kTriangleEdges,
                             &PrimitiveTallies::fTriangles);
    this->drawMaskPrimitives(flushState, pipeline, RenderPass::kTriangleCorners,
                             &PrimitiveTallies::fTriangles);

    // Quadratics.
    this->drawMaskPrimitives(flushState, pipeline, RenderPass::kQuadraticHulls,
                             &PrimitiveTallies::fQuadratics);
    this->drawMaskPrimitives(flushState, pipeline, RenderPass::kQuadraticCorners,
                             &PrimitiveTallies::fQuadratics);

    // Cubics.
    this->drawMaskPrimitives(flushState, pipeline, RenderPass::kCubicHulls,
                             &PrimitiveTallies::fCubics);
    this->drawMaskPrimitives(flushState, pipeline, RenderPass::kCubicCorners,
                             &PrimitiveTallies::fCubics);
}

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

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

    GrCCPRCoverageProcessor proc(renderPass);

    if (const int instanceCount = fInstanceCounts[(int)ScissorMode::kNonScissored].*instanceType) {
        SkASSERT(instanceCount > 0);
        const int baseInstance = fBaseInstances[(int)ScissorMode::kNonScissored].*instanceType;
        proc.appendMesh(fInstanceBuffer.get(), instanceCount, baseInstance, &fMeshesScratchBuffer);
        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);
            proc.appendMesh(fInstanceBuffer.get(), instanceCount, baseInstance,
                            &fMeshesScratchBuffer);
            fDynamicStatesScratchBuffer.push_back().fScissorRect = batch.fScissor;
            baseInstance += instanceCount;
        }
    }

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

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