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/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef GFX_LINESEGMENT_H
#define GFX_LINESEGMENT_H
#include "gfxTypes.h"
#include "gfxPoint.h"
struct gfxLineSegment {
gfxLineSegment(const gfxPoint &aStart, const gfxPoint &aEnd)
: mStart(aStart)
, mEnd(aEnd)
{}
bool PointsOnSameSide(const gfxPoint& aOne, const gfxPoint& aTwo)
{
// Solve the equation y - mStart.y - ((mEnd.y - mStart.y)/(mEnd.x - mStart.x))(x - mStart.x) for both points
gfxFloat deltaY = (mEnd.y - mStart.y);
gfxFloat deltaX = (mEnd.x - mStart.x);
gfxFloat one = deltaX * (aOne.y - mStart.y) - deltaY * (aOne.x - mStart.x);
gfxFloat two = deltaX * (aTwo.y - mStart.y) - deltaY * (aTwo.x - mStart.x);
// If both results have the same sign, then we're on the correct side of the line.
// 0 (on the line) is always considered in.
if ((one >= 0 && two >= 0) || (one <= 0 && two <= 0))
return true;
return false;
}
/**
* Determines if two line segments intersect, and returns the intersection
* point in aIntersection if they do.
*
* Coincident lines are considered not intersecting as they don't have an
* intersection point.
*/
bool Intersects(const gfxLineSegment& aOther, gfxPoint& aIntersection)
{
gfxFloat denominator = (aOther.mEnd.y - aOther.mStart.y) * (mEnd.x - mStart.x ) -
(aOther.mEnd.x - aOther.mStart.x ) * (mEnd.y - mStart.y);
// Parallel or coincident. We treat coincident as not intersecting since
// these lines are guaranteed to have corners that intersect instead.
if (!denominator) {
return false;
}
gfxFloat anumerator = (aOther.mEnd.x - aOther.mStart.x) * (mStart.y - aOther.mStart.y) -
(aOther.mEnd.y - aOther.mStart.y) * (mStart.x - aOther.mStart.x);
gfxFloat bnumerator = (mEnd.x - mStart.x) * (mStart.y - aOther.mStart.y) -
(mEnd.y - mStart.y) * (mStart.x - aOther.mStart.x);
gfxFloat ua = anumerator / denominator;
gfxFloat ub = bnumerator / denominator;
if (ua <= 0.0 || ua >= 1.0 ||
ub <= 0.0 || ub >= 1.0) {
//Intersection is outside of the segment
return false;
}
aIntersection = mStart + (mEnd - mStart) * ua;
return true;
}
gfxPoint mStart;
gfxPoint mEnd;
};
#endif /* GFX_LINESEGMENT_H */
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