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 "SkEdgeClipper.h"
#include "SkLineClipper.h"
#include "SkGeometry.h"

template <typename T> static T* typedAllocThrow(SkChunkAlloc& alloc) {
    return static_cast<T*>(alloc.allocThrow(sizeof(T)));
}

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

SkEdgeBuilder::SkEdgeBuilder() : fAlloc(16*1024) {
    fEdgeList = NULL;
}

void SkEdgeBuilder::addLine(const SkPoint pts[]) {
    SkEdge* edge = typedAllocThrow<SkEdge>(fAlloc);
    if (edge->setLine(pts[0], pts[1], fShiftUp)) {
        fList.push(edge);
    } else {
        // TODO: unallocate edge from storage...
    }
}

void SkEdgeBuilder::addQuad(const SkPoint pts[]) {
    SkQuadraticEdge* edge = typedAllocThrow<SkQuadraticEdge>(fAlloc);
    if (edge->setQuadratic(pts, fShiftUp)) {
        fList.push(edge);
    } else {
        // TODO: unallocate edge from storage...
    }
}

void SkEdgeBuilder::addCubic(const SkPoint pts[]) {
    SkCubicEdge* edge = typedAllocThrow<SkCubicEdge>(fAlloc);
    if (edge->setCubic(pts, NULL, 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));
}

int SkEdgeBuilder::buildPoly(const SkPath& path, const SkIRect* iclip,
                             int shiftUp) {
    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 maxEdgeSize = maxEdgeCount * sizeof(SkEdge);
    size_t maxEdgePtrSize = maxEdgeCount * sizeof(SkEdge*);

    // lets store the edges and their pointers in the same block
    char* storage = (char*)fAlloc.allocThrow(maxEdgeSize + maxEdgePtrSize);
    SkEdge* edge = reinterpret_cast<SkEdge*>(storage);
    SkEdge** edgePtr = reinterpret_cast<SkEdge**>(storage + maxEdgeSize);
    // Record the beginning of our pointers, so we can return them to the caller
    fEdgeList = 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);
                    SkASSERT(lineCount <= SkLineClipper::kMaxClippedLineSegments);
                    for (int i = 0; i < lineCount; i++) {
                        if (edge->setLine(lines[i], lines[i + 1], shiftUp)) {
                            *edgePtr++ = edge++;
                        }
                    }
                    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:
                    if (edge->setLine(pts[0], pts[1], shiftUp)) {
                        *edgePtr++ = edge++;
                    }
                    break;
                default:
                    SkDEBUGFAIL("unexpected verb");
                    break;
            }
        }
    }
    SkASSERT((char*)edge <= (char*)fEdgeList);
    SkASSERT(edgePtr - fEdgeList <= maxEdgeCount);
    return SkToInt(edgePtr - 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) {
    fAlloc.reset();
    fList.reset();
    fShiftUp = shiftUp;

    SkScalar conicTol = SK_ScalarHalf * (1 << shiftUp);

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

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

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

        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);
                    for (int i = 0; i < lineCount; i++) {
                        this->addLine(&lines[i]);
                    }
                    break;
                }
                case SkPath::kQuad_Verb:
                    if (clipper.clipQuad(pts, clip)) {
                        this->addClipper(&clipper);
                    }
                    break;
                case SkPath::kConic_Verb: {
                    const int MAX_POW2 = 4;
                    const int MAX_QUADS = 1 << MAX_POW2;
                    const int MAX_QUAD_PTS = 1 + 2 * MAX_QUADS;
                    SkPoint storage[MAX_QUAD_PTS];

                    SkConic conic;
                    conic.set(pts, iter.conicWeight());
                    int pow2 = conic.computeQuadPOW2(conicTol);
                    pow2 = SkMin32(pow2, MAX_POW2);
                    int quadCount = conic.chopIntoQuadsPOW2(storage, pow2);
                    SkASSERT(quadCount <= MAX_QUADS);
                    for (int i = 0; i < quadCount; ++i) {
                        if (clipper.clipQuad(&storage[i * 2], clip)) {
                            this->addClipper(&clipper);
                        }
                    }
                } 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 int MAX_POW2 = 4;
                    const int MAX_QUADS = 1 << MAX_POW2;
                    const int MAX_QUAD_PTS = 1 + 2 * MAX_QUADS;
                    SkPoint storage[MAX_QUAD_PTS];

                    SkConic conic;
                    conic.set(pts, iter.conicWeight());
                    int pow2 = conic.computeQuadPOW2(conicTol);
                    pow2 = SkMin32(pow2, MAX_POW2);
                    int quadCount = conic.chopIntoQuadsPOW2(storage, pow2);
                    SkASSERT(quadCount <= MAX_QUADS);
                    for (int i = 0; i < quadCount; ++i) {
                        handle_quad(this, &storage[i * 2]);
                    }
                } break;
                case SkPath::kCubic_Verb: {
                    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();
}