Source/core/platform/graphics/FloatPolygon.cpp

/*
 * Copyright (C) 2012 Adobe Systems Incorporated. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above
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 *    disclaimer.
 * 2. Redistributions in binary form must reproduce the above
 *    copyright notice, this list of conditions and the following
 *    disclaimer in the documentation and/or other materials
 *    provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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#include "config.h"
#include "core/platform/graphics/FloatPolygon.h"

#include "wtf/MathExtras.h"

namespace WebCore {

static inline float determinant(const FloatSize& a, const FloatSize& b)
{
    return a.width() * b.height() - a.height() * b.width();
}

static inline bool areCollinearPoints(const FloatPoint& p0, const FloatPoint& p1, const FloatPoint& p2)
{
    return !determinant(p1 - p0, p2 - p0);
}

static inline bool areCoincidentPoints(const FloatPoint& p0, const FloatPoint& p1)
{
    return p0.x() == p1.x() && p0.y() == p1.y();
}

static inline bool isPointOnLineSegment(const FloatPoint& vertex1, const FloatPoint& vertex2, const FloatPoint& point)
{
    return point.x() >= std::min(vertex1.x(), vertex2.x())
        && point.x() <= std::max(vertex1.x(), vertex2.x())
        && areCollinearPoints(vertex1, vertex2, point);
}

static inline unsigned nextVertexIndex(unsigned vertexIndex, unsigned nVertices, bool clockwise)
{
    return ((clockwise) ? vertexIndex + 1 : vertexIndex - 1 + nVertices) % nVertices;
}

static unsigned findNextEdgeVertexIndex(const FloatPolygon& polygon, unsigned vertexIndex1, bool clockwise)
{
    unsigned nVertices = polygon.numberOfVertices();
    unsigned vertexIndex2 = nextVertexIndex(vertexIndex1, nVertices, clockwise);

    while (vertexIndex2 && areCoincidentPoints(polygon.vertexAt(vertexIndex1), polygon.vertexAt(vertexIndex2)))
        vertexIndex2 = nextVertexIndex(vertexIndex2, nVertices, clockwise);

    while (vertexIndex2) {
        unsigned vertexIndex3 = nextVertexIndex(vertexIndex2, nVertices, clockwise);
        if (!areCollinearPoints(polygon.vertexAt(vertexIndex1), polygon.vertexAt(vertexIndex2), polygon.vertexAt(vertexIndex3)))
            break;
        vertexIndex2 = vertexIndex3;
    }

    return vertexIndex2;
}

FloatPolygon::FloatPolygon(PassOwnPtr<Vector<FloatPoint> > vertices, WindRule fillRule)
    : m_vertices(vertices)
    , m_fillRule(fillRule)
{
    unsigned nVertices = numberOfVertices();
    m_edges.resize(nVertices);
    m_empty = nVertices < 3;

    if (nVertices)
        m_boundingBox.setLocation(vertexAt(0));

    if (m_empty)
        return;

    unsigned minVertexIndex = 0;
    for (unsigned i = 1; i < nVertices; ++i) {
        const FloatPoint& vertex = vertexAt(i);
        if (vertex.y() < vertexAt(minVertexIndex).y() || (vertex.y() == vertexAt(minVertexIndex).y() && vertex.x() < vertexAt(minVertexIndex).x()))
            minVertexIndex = i;
    }
    FloatPoint nextVertex = vertexAt((minVertexIndex + 1) % nVertices);
    FloatPoint prevVertex = vertexAt((minVertexIndex + nVertices - 1) % nVertices);
    bool clockwise = determinant(vertexAt(minVertexIndex) - prevVertex, nextVertex - prevVertex) > 0;

    unsigned edgeIndex = 0;
    unsigned vertexIndex1 = 0;
    do {
        m_boundingBox.extend(vertexAt(vertexIndex1));
        unsigned vertexIndex2 = findNextEdgeVertexIndex(*this, vertexIndex1, clockwise);
        m_edges[edgeIndex].m_polygon = this;
        m_edges[edgeIndex].m_vertexIndex1 = vertexIndex1;
        m_edges[edgeIndex].m_vertexIndex2 = vertexIndex2;
        m_edges[edgeIndex].m_edgeIndex = edgeIndex;
        ++edgeIndex;
        vertexIndex1 = vertexIndex2;
    } while (vertexIndex1);

    if (edgeIndex > 3) {
        const FloatPolygonEdge& firstEdge = m_edges[0];
        const FloatPolygonEdge& lastEdge = m_edges[edgeIndex - 1];
        if (areCollinearPoints(lastEdge.vertex1(), lastEdge.vertex2(), firstEdge.vertex2())) {
            m_edges[0].m_vertexIndex1 = lastEdge.m_vertexIndex1;
            edgeIndex--;
        }
    }

    m_edges.resize(edgeIndex);
    m_empty = m_edges.size() < 3;

    if (m_empty)
        return;

    for (unsigned i = 0; i < m_edges.size(); ++i) {
        FloatPolygonEdge* edge = &m_edges[i];
        m_edgeTree.add(EdgeInterval(edge->minY(), edge->maxY(), edge));
    }
}

bool FloatPolygon::overlappingEdges(float minY, float maxY, Vector<const FloatPolygonEdge*>& result) const
{
    Vector<FloatPolygon::EdgeInterval> overlappingEdgeIntervals;
    m_edgeTree.allOverlaps(FloatPolygon::EdgeInterval(minY, maxY, 0), overlappingEdgeIntervals);
    unsigned overlappingEdgeIntervalsSize = overlappingEdgeIntervals.size();
    result.resize(overlappingEdgeIntervalsSize);
    for (unsigned i = 0; i < overlappingEdgeIntervalsSize; ++i) {
        const FloatPolygonEdge* edge = static_cast<const FloatPolygonEdge*>(overlappingEdgeIntervals[i].data());
        ASSERT(edge);
        result[i] = edge;
    }
    return overlappingEdgeIntervalsSize > 0;
}

static inline float leftSide(const FloatPoint& vertex1, const FloatPoint& vertex2, const FloatPoint& point)
{
    return ((point.x() - vertex1.x()) * (vertex2.y() - vertex1.y())) - ((vertex2.x() - vertex1.x()) * (point.y() - vertex1.y()));
}

bool FloatPolygon::containsEvenOdd(const FloatPoint& point) const
{
    unsigned crossingCount = 0;
    for (unsigned i = 0; i < numberOfEdges(); ++i) {
        const FloatPoint& vertex1 = edgeAt(i).vertex1();
        const FloatPoint& vertex2 = edgeAt(i).vertex2();
        if (isPointOnLineSegment(vertex1, vertex2, point))
            return true;
        if ((vertex1.y() <= point.y() && vertex2.y() > point.y()) || (vertex1.y() > point.y() && vertex2.y() <= point.y())) {
            float vt = (point.y()  - vertex1.y()) / (vertex2.y() - vertex1.y());
            if (point.x() < vertex1.x() + vt * (vertex2.x() - vertex1.x()))
                ++crossingCount;
        }
    }
    return crossingCount & 1;
}

bool FloatPolygon::containsNonZero(const FloatPoint& point) const
{
    int windingNumber = 0;
    for (unsigned i = 0; i < numberOfEdges(); ++i) {
        const FloatPoint& vertex1 = edgeAt(i).vertex1();
        const FloatPoint& vertex2 = edgeAt(i).vertex2();
        if (isPointOnLineSegment(vertex1, vertex2, point))
            return true;
        if (vertex2.y() < point.y()) {
            if ((vertex1.y() > point.y()) && (leftSide(vertex1, vertex2, point) > 0))
                ++windingNumber;
        } else if (vertex2.y() > point.y()) {
            if ((vertex1.y() <= point.y()) && (leftSide(vertex1, vertex2, point) < 0))
                --windingNumber;
        }
    }
    return windingNumber;
}

bool FloatPolygon::contains(const FloatPoint& point) const
{
    if (!m_boundingBox.contains(point))
        return false;
    return (fillRule() == RULE_NONZERO) ? containsNonZero(point) : containsEvenOdd(point);
}

bool VertexPair::overlapsRect(const FloatRect& rect) const
{
    bool boundsOverlap = (minX() < rect.maxX()) && (maxX() > rect.x()) && (minY() < rect.maxY()) && (maxY() > rect.y());
    if (!boundsOverlap)
        return false;

    float leftSideValues[4] = {
        leftSide(vertex1(), vertex2(), rect.minXMinYCorner()),
        leftSide(vertex1(), vertex2(), rect.maxXMinYCorner()),
        leftSide(vertex1(), vertex2(), rect.minXMaxYCorner()),
        leftSide(vertex1(), vertex2(), rect.maxXMaxYCorner())
    };

    int currentLeftSideSign = 0;
    for (unsigned i = 0; i < 4; ++i) {
        if (!leftSideValues[i])
            continue;
        int leftSideSign = leftSideValues[i] > 0 ? 1 : -1;
        if (!currentLeftSideSign)
            currentLeftSideSign = leftSideSign;
        else if (currentLeftSideSign != leftSideSign)
            return true;
    }

    return false;
}

bool VertexPair::intersection(const VertexPair& other, FloatPoint& point) const
{
    // See: http://paulbourke.net/geometry/pointlineplane/, "Intersection point of two lines in 2 dimensions"

    const FloatSize& thisDelta = vertex2() - vertex1();
    const FloatSize& otherDelta = other.vertex2() - other.vertex1();
    float denominator = determinant(thisDelta, otherDelta);
    if (!denominator)
        return false;

    // The two line segments: "this" vertex1,vertex2 and "other" vertex1,vertex2, have been defined
    // in parametric form. Each point on the line segment is: vertex1 + u * (vertex2 - vertex1),
    // when 0 <= u <= 1. We're computing the values of u for each line at their intersection point.

    const FloatSize& vertex1Delta = vertex1() - other.vertex1();
    float uThisLine = determinant(otherDelta, vertex1Delta) / denominator;
    float uOtherLine = determinant(thisDelta, vertex1Delta) / denominator;

    if (uThisLine < 0 || uOtherLine < 0 || uThisLine > 1 || uOtherLine > 1)
        return false;

    point = vertex1() + uThisLine * thisDelta;
    return true;
}

} // namespace WebCore