src/core/SkEdgeBuilder.cpp

/*
 * Copyright 2011 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
#include "SkEdgeBuilder.h"
#include "SkPath.h"
#include "SkEdge.h"
#include "SkAnalyticEdge.h"
#include "SkEdgeClipper.h"
#include "SkLineClipper.h"
#include "SkGeometry.h"

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

SkEdgeBuilder::SkEdgeBuilder() {
    fEdgeList = nullptr;
}

SkEdgeBuilder::Combine SkEdgeBuilder::CombineVertical(const SkEdge* edge, SkEdge* last) {
    if (last->fCurveCount || last->fDX || edge->fX != last->fX) {
        return kNo_Combine;
    }
    if (edge->fWinding == last->fWinding) {
        if (edge->fLastY + 1 == last->fFirstY) {
            last->fFirstY = edge->fFirstY;
            return kPartial_Combine;
        }
        if (edge->fFirstY == last->fLastY + 1) {
            last->fLastY = edge->fLastY;
            return kPartial_Combine;
        }
        return kNo_Combine;
    }
    if (edge->fFirstY == last->fFirstY) {
        if (edge->fLastY == last->fLastY) {
            return kTotal_Combine;
        }
        if (edge->fLastY < last->fLastY) {
            last->fFirstY = edge->fLastY + 1;
            return kPartial_Combine;
        }
        last->fFirstY = last->fLastY + 1;
        last->fLastY = edge->fLastY;
        last->fWinding = edge->fWinding;
        return kPartial_Combine;
    }
    if (edge->fLastY == last->fLastY) {
        if (edge->fFirstY > last->fFirstY) {
            last->fLastY = edge->fFirstY - 1;
            return kPartial_Combine;
        }
        last->fLastY = last->fFirstY - 1;
        last->fFirstY = edge->fFirstY;
        last->fWinding = edge->fWinding;
        return kPartial_Combine;
    }
    return kNo_Combine;
}

static inline bool approximatelyEqual(SkFixed a, SkFixed b) {
    return SkAbs32(a - b) < 0x100;
}

SkEdgeBuilder::Combine SkEdgeBuilder::CombineVertical(
        const SkAnalyticEdge* edge, SkAnalyticEdge* last) {
    SkASSERT(fEdgeType == kAnalyticEdge);
    if (last->fCurveCount || last->fDX || edge->fX != last->fX) {
        return kNo_Combine;
    }
    if (edge->fWinding == last->fWinding) {
        if (edge->fLowerY == last->fUpperY) {
            last->fUpperY = edge->fUpperY;
            last->fY = last->fUpperY;
            return kPartial_Combine;
        }
        if (approximatelyEqual(edge->fUpperY, last->fLowerY)) {
            last->fLowerY = edge->fLowerY;
            return kPartial_Combine;
        }
        return kNo_Combine;
    }
    if (approximatelyEqual(edge->fUpperY, last->fUpperY)) {
        if (approximatelyEqual(edge->fLowerY, last->fLowerY)) {
            return kTotal_Combine;
        }
        if (edge->fLowerY < last->fLowerY) {
            last->fUpperY = edge->fLowerY;
            last->fY = last->fUpperY;
            return kPartial_Combine;
        }
        last->fUpperY = last->fLowerY;
        last->fY = last->fUpperY;
        last->fLowerY = edge->fLowerY;
        last->fWinding = edge->fWinding;
        return kPartial_Combine;
    }
    if (approximatelyEqual(edge->fLowerY, last->fLowerY)) {
        if (edge->fUpperY > last->fUpperY) {
            last->fLowerY = edge->fUpperY;
            return kPartial_Combine;
        }
        last->fLowerY = last->fUpperY;
        last->fUpperY = edge->fUpperY;
        last->fY = last->fUpperY;
        last->fWinding = edge->fWinding;
        return kPartial_Combine;
    }
    return kNo_Combine;
}

bool SkEdgeBuilder::vertical_line(const SkEdge* edge) {
    return !edge->fDX && !edge->fCurveCount;
}

bool SkEdgeBuilder::vertical_line(const SkAnalyticEdge* edge) {
    SkASSERT(fEdgeType == kAnalyticEdge);
    return !edge->fDX && !edge->fCurveCount;
}

void SkEdgeBuilder::addLine(const SkPoint pts[]) {
    if (fEdgeType == kBezier) {
        SkLine* line = fAlloc.make<SkLine>();
        if (line->set(pts)) {
            fList.push(line);
        }
    } else if (fEdgeType == kAnalyticEdge) {
        SkAnalyticEdge* edge = fAlloc.make<SkAnalyticEdge>();
        if (edge->setLine(pts[0], pts[1])) {
            if (vertical_line(edge) && fList.count()) {
                Combine combine = CombineVertical(edge, (SkAnalyticEdge*)*(fList.end() - 1));
                if (kNo_Combine != combine) {
                    if (kTotal_Combine == combine) {
                        fList.pop();
                    }
                    goto unallocate_analytic_edge;
                }
            }
            fList.push(edge);
        } else {
unallocate_analytic_edge:
            ;
            // TODO: unallocate edge from storage...
        }
    } else {
        SkEdge* edge = fAlloc.make<SkEdge>();
        if (edge->setLine(pts[0], pts[1], fShiftUp)) {
            if (vertical_line(edge) && fList.count()) {
                Combine combine = CombineVertical(edge, (SkEdge*)*(fList.end() - 1));
                if (kNo_Combine != combine) {
                    if (kTotal_Combine == combine) {
                        fList.pop();
                    }
                    goto unallocate_edge;
                }
            }
            fList.push(edge);
        } else {
unallocate_edge:
            ;
            // TODO: unallocate edge from storage...
        }
    }
}

void SkEdgeBuilder::addQuad(const SkPoint pts[]) {
    if (fEdgeType == kBezier) {
        SkQuad* quad = fAlloc.make<SkQuad>();
        if (quad->set(pts)) {
            fList.push(quad);
        }
    } else if (fEdgeType == kAnalyticEdge) {
        SkAnalyticQuadraticEdge* edge = fAlloc.make<SkAnalyticQuadraticEdge>();
        if (edge->setQuadratic(pts)) {
            fList.push(edge);
        } else {
            // TODO: unallocate edge from storage...
        }
    } else {
        SkQuadraticEdge* edge = fAlloc.make<SkQuadraticEdge>();
        if (edge->setQuadratic(pts, fShiftUp)) {
            fList.push(edge);
        } else {
            // TODO: unallocate edge from storage...
        }
    }
}

void SkEdgeBuilder::addCubic(const SkPoint pts[]) {
    if (fEdgeType == kBezier) {
        SkCubic* cubic = fAlloc.make<SkCubic>();
        if (cubic->set(pts)) {
            fList.push(cubic);
        }
    } else if (fEdgeType == kAnalyticEdge) {
        SkAnalyticCubicEdge* edge = fAlloc.make<SkAnalyticCubicEdge>();
        if (edge->setCubic(pts)) {
            fList.push(edge);
        } else {
            // TODO: unallocate edge from storage...
        }
    } else {
        SkCubicEdge* edge = fAlloc.make<SkCubicEdge>();
        if (edge->setCubic(pts, fShiftUp)) {
            fList.push(edge);
        } else {
            // TODO: unallocate edge from storage...
        }
    }
}

void SkEdgeBuilder::addClipper(SkEdgeClipper* clipper) {
    SkPoint      pts[4];
    SkPath::Verb verb;

    while ((verb = clipper->next(pts)) != SkPath::kDone_Verb) {
        switch (verb) {
            case SkPath::kLine_Verb:
                this->addLine(pts);
                break;
            case SkPath::kQuad_Verb:
                this->addQuad(pts);
                break;
            case SkPath::kCubic_Verb:
                this->addCubic(pts);
                break;
            default:
                break;
        }
    }
}

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

static void setShiftedClip(SkRect* dst, const SkIRect& src, int shift) {
    dst->set(SkIntToScalar(src.fLeft >> shift),
             SkIntToScalar(src.fTop >> shift),
             SkIntToScalar(src.fRight >> shift),
             SkIntToScalar(src.fBottom >> shift));
}

SkEdgeBuilder::Combine SkEdgeBuilder::checkVertical(const SkEdge* edge, SkEdge** edgePtr) {
    return !vertical_line(edge) || edgePtr <= (SkEdge**)fEdgeList ? kNo_Combine :
            CombineVertical(edge, edgePtr[-1]);
}

SkEdgeBuilder::Combine SkEdgeBuilder::checkVertical(const SkAnalyticEdge* edge,
        SkAnalyticEdge** edgePtr) {
    SkASSERT(fEdgeType == kAnalyticEdge);
    return !vertical_line(edge) || edgePtr <= (SkAnalyticEdge**)fEdgeList ? kNo_Combine :
            CombineVertical(edge, edgePtr[-1]);
}

int SkEdgeBuilder::buildPoly(const SkPath& path, const SkIRect* iclip, int shiftUp,
                             bool canCullToTheRight) {
    SkPath::Iter    iter(path, true);
    SkPoint         pts[4];
    SkPath::Verb    verb;

    int maxEdgeCount = path.countPoints();
    if (iclip) {
        // clipping can turn 1 line into (up to) kMaxClippedLineSegments, since
        // we turn portions that are clipped out on the left/right into vertical
        // segments.
        maxEdgeCount *= SkLineClipper::kMaxClippedLineSegments;
    }

    size_t edgeSize;
    char* edge;
    switch (fEdgeType) {
        case kEdge:
            edgeSize = sizeof(SkEdge);
            edge = (char*)fAlloc.makeArrayDefault<SkEdge>(maxEdgeCount);
            break;
        case kAnalyticEdge:
            edgeSize = sizeof(SkAnalyticEdge);
            edge = (char*)fAlloc.makeArrayDefault<SkAnalyticEdge>(maxEdgeCount);
            break;
        case kBezier:
            edgeSize = sizeof(SkLine);
            edge = (char*)fAlloc.makeArrayDefault<SkLine>(maxEdgeCount);
            break;
    }

    SkDEBUGCODE(char* edgeStart = edge);
    char** edgePtr = fAlloc.makeArrayDefault<char*>(maxEdgeCount);
    fEdgeList = (void**)edgePtr;

    if (iclip) {
        SkRect clip;
        setShiftedClip(&clip, *iclip, shiftUp);

        while ((verb = iter.next(pts, false)) != SkPath::kDone_Verb) {
            switch (verb) {
                case SkPath::kMove_Verb:
                case SkPath::kClose_Verb:
                    // we ignore these, and just get the whole segment from
                    // the corresponding line/quad/cubic verbs
                    break;
                case SkPath::kLine_Verb: {
                    SkPoint lines[SkLineClipper::kMaxPoints];
                    int lineCount = SkLineClipper::ClipLine(pts, clip, lines, canCullToTheRight);
                    SkASSERT(lineCount <= SkLineClipper::kMaxClippedLineSegments);
                    for (int i = 0; i < lineCount; i++) {
                        this->addPolyLine(lines + i, edge, edgeSize, edgePtr, shiftUp);
                    }
                    break;
                }
                default:
                    SkDEBUGFAIL("unexpected verb");
                    break;
            }
        }
    } else {
        while ((verb = iter.next(pts, false)) != SkPath::kDone_Verb) {
            switch (verb) {
                case SkPath::kMove_Verb:
                case SkPath::kClose_Verb:
                    // we ignore these, and just get the whole segment from
                    // the corresponding line/quad/cubic verbs
                    break;
                case SkPath::kLine_Verb: {
                    this->addPolyLine(pts, edge, edgeSize, edgePtr, shiftUp);
                    break;
                }
                default:
                    SkDEBUGFAIL("unexpected verb");
                    break;
            }
        }
    }
    SkASSERT((size_t)(edge - edgeStart) <= maxEdgeCount * edgeSize);
    SkASSERT(edgePtr - (char**)fEdgeList <= maxEdgeCount);
    return SkToInt(edgePtr - (char**)fEdgeList);
}

static void handle_quad(SkEdgeBuilder* builder, const SkPoint pts[3]) {
    SkPoint monoX[5];
    int n = SkChopQuadAtYExtrema(pts, monoX);
    for (int i = 0; i <= n; i++) {
        builder->addQuad(&monoX[i * 2]);
    }
}

int SkEdgeBuilder::build(const SkPath& path, const SkIRect* iclip, int shiftUp,
                         bool canCullToTheRight, EdgeType edgeType) {
    fAlloc.reset();
    fList.reset();
    fShiftUp = shiftUp;
    fEdgeType = edgeType;

    if (SkPath::kLine_SegmentMask == path.getSegmentMasks()) {
        return this->buildPoly(path, iclip, shiftUp, canCullToTheRight);
    }

    SkAutoConicToQuads quadder;
    const SkScalar conicTol = SK_Scalar1 / 4;

    SkPath::Iter    iter(path, true);
    SkPoint         pts[4];
    SkPath::Verb    verb;

    if (iclip) {
        SkRect clip;
        setShiftedClip(&clip, *iclip, shiftUp);
        SkEdgeClipper clipper(canCullToTheRight);

        while ((verb = iter.next(pts, false)) != SkPath::kDone_Verb) {
            switch (verb) {
                case SkPath::kMove_Verb:
                case SkPath::kClose_Verb:
                    // we ignore these, and just get the whole segment from
                    // the corresponding line/quad/cubic verbs
                    break;
                case SkPath::kLine_Verb:
                    if (clipper.clipLine(pts[0], pts[1], clip)) {
                        this->addClipper(&clipper);
                    }
                    break;
                case SkPath::kQuad_Verb:
                    if (clipper.clipQuad(pts, clip)) {
                        this->addClipper(&clipper);
                    }
                    break;
                case SkPath::kConic_Verb: {
                    const SkPoint* quadPts = quadder.computeQuads(
                                          pts, iter.conicWeight(), conicTol);
                    for (int i = 0; i < quadder.countQuads(); ++i) {
                        if (clipper.clipQuad(quadPts, clip)) {
                            this->addClipper(&clipper);
                        }
                        quadPts += 2;
                    }
                } break;
                case SkPath::kCubic_Verb:
                    if (clipper.clipCubic(pts, clip)) {
                        this->addClipper(&clipper);
                    }
                    break;
                default:
                    SkDEBUGFAIL("unexpected verb");
                    break;
            }
        }
    } else {
        while ((verb = iter.next(pts, false)) != SkPath::kDone_Verb) {
            switch (verb) {
                case SkPath::kMove_Verb:
                case SkPath::kClose_Verb:
                    // we ignore these, and just get the whole segment from
                    // the corresponding line/quad/cubic verbs
                    break;
                case SkPath::kLine_Verb:
                    this->addLine(pts);
                    break;
                case SkPath::kQuad_Verb: {
                    handle_quad(this, pts);
                    break;
                }
                case SkPath::kConic_Verb: {
                    const SkPoint* quadPts = quadder.computeQuads(
                                          pts, iter.conicWeight(), conicTol);
                    for (int i = 0; i < quadder.countQuads(); ++i) {
                        handle_quad(this, quadPts);
                        quadPts += 2;
                    }
                } break;
                case SkPath::kCubic_Verb: {
                    if (fEdgeType == kBezier) {
                        this->addCubic(pts);
                        break;
                    }
                    SkPoint monoY[10];
                    int n = SkChopCubicAtYExtrema(pts, monoY);
                    for (int i = 0; i <= n; i++) {
                        this->addCubic(&monoY[i * 3]);
                    }
                    break;
                }
                default:
                    SkDEBUGFAIL("unexpected verb");
                    break;
            }
        }
    }
    fEdgeList = fList.begin();
    return fList.count();
}

int SkEdgeBuilder::build_edges(const SkPath& path, const SkIRect* shiftedClip,
        int shiftEdgesUp, bool pathContainedInClip, EdgeType edgeType) {
    // If we're convex, then we need both edges, even the right edge is past the clip
    const bool canCullToTheRight = !path.isConvex();

    const SkIRect* builderClip = pathContainedInClip ? nullptr : shiftedClip;
    int count = this->build(path, builderClip, shiftEdgesUp, canCullToTheRight, edgeType);
    SkASSERT(count >= 0);

    // canCullToRight == false should imply count != 1 if edgeType != kBezier.
    // If edgeType == kBezier (DAA), we don't chop edges at y extrema so count == 1 is valid.
    // For example, a single cubic edge with a valley shape \_/ is fine for DAA.
    SkASSERT(edgeType == kBezier || canCullToTheRight || count != 1);

    return count;
}