Source/WebCore/platform/graphics/FloatQuad.cpp

/*
 * Copyright (C) 2008 Apple Inc. All rights reserved.
 * Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies)
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 *     from this software without specific prior written permission. 
 *
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 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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#include "config.h"
#include "FloatQuad.h"

#include <algorithm>
#include <limits>

using namespace std;

namespace WebCore {

static inline float min4(float a, float b, float c, float d)
{
    return min(min(a, b), min(c, d));
}

static inline float max4(float a, float b, float c, float d)
{
    return max(max(a, b), max(c, d));
}

inline float dot(const FloatSize& a, const FloatSize& b)
{
    return a.width() * b.width() + a.height() * b.height();
}

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

inline bool isPointInTriangle(const FloatPoint& p, const FloatPoint& t1, const FloatPoint& t2, const FloatPoint& t3)
{
    // Compute vectors        
    FloatSize v0 = t3 - t1;
    FloatSize v1 = t2 - t1;
    FloatSize v2 = p - t1;
    
    // Compute dot products
    float dot00 = dot(v0, v0);
    float dot01 = dot(v0, v1);
    float dot02 = dot(v0, v2);
    float dot11 = dot(v1, v1);
    float dot12 = dot(v1, v2);

    // Compute barycentric coordinates
    float invDenom = 1.0f / (dot00 * dot11 - dot01 * dot01);
    float u = (dot11 * dot02 - dot01 * dot12) * invDenom;
    float v = (dot00 * dot12 - dot01 * dot02) * invDenom;

    // Check if point is in triangle
    return (u >= 0) && (v >= 0) && (u + v <= 1);
}

FloatRect FloatQuad::boundingBox() const
{
    float left   = min4(m_p1.x(), m_p2.x(), m_p3.x(), m_p4.x());
    float top    = min4(m_p1.y(), m_p2.y(), m_p3.y(), m_p4.y());

    float right  = max4(m_p1.x(), m_p2.x(), m_p3.x(), m_p4.x());
    float bottom = max4(m_p1.y(), m_p2.y(), m_p3.y(), m_p4.y());
    
    return FloatRect(left, top, right - left, bottom - top);
}

static inline bool withinEpsilon(float a, float b)
{
    return fabs(a - b) < numeric_limits<float>::epsilon();
}

bool FloatQuad::isRectilinear() const
{
    return (withinEpsilon(m_p1.x(), m_p2.x()) && withinEpsilon(m_p2.y(), m_p3.y()) && withinEpsilon(m_p3.x(), m_p4.x()) && withinEpsilon(m_p4.y(), m_p1.y()))
        || (withinEpsilon(m_p1.y(), m_p2.y()) && withinEpsilon(m_p2.x(), m_p3.x()) && withinEpsilon(m_p3.y(), m_p4.y()) && withinEpsilon(m_p4.x(), m_p1.x()));
}

bool FloatQuad::containsPoint(const FloatPoint& p) const
{
    return isPointInTriangle(p, m_p1, m_p2, m_p3) || isPointInTriangle(p, m_p1, m_p3, m_p4);
} 

// Note that we only handle convex quads here.
bool FloatQuad::containsQuad(const FloatQuad& other) const
{
    return containsPoint(other.p1()) && containsPoint(other.p2()) && containsPoint(other.p3()) && containsPoint(other.p4());
}

static inline FloatPoint rightMostCornerToVector(const FloatRect& rect, const FloatSize& vector)
{
    // Return the corner of the rectangle that if it is to the left of the vector
    // would mean all of the rectangle is to the left of the vector.
    // The vector here represents the side between two points in a clockwise convex polygon.
    //
    //  Q  XXX
    // QQQ XXX   If the lower left corner of X is left of the vector that goes from the top corner of Q to
    //  QQQ      the right corner of Q, then all of X is left of the vector, and intersection impossible.
    //   Q
    //
    FloatPoint point;
    if (vector.width() >= 0)
        point.setY(rect.maxY());
    else
        point.setY(rect.y());
    if (vector.height() >= 0)
        point.setX(rect.x());
    else
        point.setX(rect.maxX());
    return point;
}

bool FloatQuad::intersectsRect(const FloatRect& rect) const
{
    // For each side of the quad clockwise we check if the rectangle is to the left of it
    // since only content on the right can onlap with the quad.
    // This only works if the quad is convex.
    FloatSize v1, v2, v3, v4;

    // Ensure we use clockwise vectors.
    if (!isCounterclockwise()) {
        v1 = m_p2 - m_p1;
        v2 = m_p3 - m_p2;
        v3 = m_p4 - m_p3;
        v4 = m_p1 - m_p4;
    } else {
        v1 = m_p4 - m_p1;
        v2 = m_p1 - m_p2;
        v3 = m_p2 - m_p3;
        v4 = m_p3 - m_p4;
    }

    FloatPoint p = rightMostCornerToVector(rect, v1);
    if (determinant(v1, p - m_p1) < 0)
        return false;

    p = rightMostCornerToVector(rect, v2);
    if (determinant(v2, p - m_p2) < 0)
        return false;

    p = rightMostCornerToVector(rect, v3);
    if (determinant(v3, p - m_p3) < 0)
        return false;

    p = rightMostCornerToVector(rect, v4);
    if (determinant(v4, p - m_p4) < 0)
        return false;

    // If not all of the rectangle is outside one of the quad's four sides, then that means at least
    // a part of the rectangle is overlapping the quad.
    return true;
}

bool FloatQuad::isCounterclockwise() const
{
    // Return if the two first vectors are turning clockwise. If the quad is convex then all following vectors will turn the same way.
    return determinant(m_p2 - m_p1, m_p3 - m_p2) < 0;
}

} // namespace WebCore