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77 lines
2.6 KiB
C
77 lines
2.6 KiB
C
/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef GFX_LINESEGMENT_H
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#define GFX_LINESEGMENT_H
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#include "gfxTypes.h"
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#include "gfxPoint.h"
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struct gfxLineSegment {
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gfxLineSegment() : mStart(gfxPoint()), mEnd(gfxPoint()) {}
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gfxLineSegment(const gfxPoint& aStart, const gfxPoint& aEnd)
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: mStart(aStart), mEnd(aEnd) {}
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bool PointsOnSameSide(const gfxPoint& aOne, const gfxPoint& aTwo) {
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// Solve the equation
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// y - mStart.y - ((mEnd.y - mStart.y)/(mEnd.x - mStart.x))(x - mStart.x)
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// for both points
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gfxFloat deltaY = (mEnd.y - mStart.y);
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gfxFloat deltaX = (mEnd.x - mStart.x);
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gfxFloat one = deltaX * (aOne.y - mStart.y) - deltaY * (aOne.x - mStart.x);
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gfxFloat two = deltaX * (aTwo.y - mStart.y) - deltaY * (aTwo.x - mStart.x);
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// If both results have the same sign, then we're on the correct side of the
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// line. 0 (on the line) is always considered in.
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if ((one >= 0 && two >= 0) || (one <= 0 && two <= 0)) return true;
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return false;
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}
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/**
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* Determines if two line segments intersect, and returns the intersection
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* point in aIntersection if they do.
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*
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* Coincident lines are considered not intersecting as they don't have an
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* intersection point.
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*/
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bool Intersects(const gfxLineSegment& aOther, gfxPoint& aIntersection) {
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gfxFloat denominator =
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(aOther.mEnd.y - aOther.mStart.y) * (mEnd.x - mStart.x) -
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(aOther.mEnd.x - aOther.mStart.x) * (mEnd.y - mStart.y);
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// Parallel or coincident. We treat coincident as not intersecting since
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// these lines are guaranteed to have corners that intersect instead.
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if (!denominator) {
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return false;
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}
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gfxFloat anumerator =
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(aOther.mEnd.x - aOther.mStart.x) * (mStart.y - aOther.mStart.y) -
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(aOther.mEnd.y - aOther.mStart.y) * (mStart.x - aOther.mStart.x);
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gfxFloat bnumerator = (mEnd.x - mStart.x) * (mStart.y - aOther.mStart.y) -
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(mEnd.y - mStart.y) * (mStart.x - aOther.mStart.x);
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gfxFloat ua = anumerator / denominator;
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gfxFloat ub = bnumerator / denominator;
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if (ua <= 0.0 || ua >= 1.0 || ub <= 0.0 || ub >= 1.0) {
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// Intersection is outside of the segment
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return false;
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}
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aIntersection = mStart + (mEnd - mStart) * ua;
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return true;
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}
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gfxPoint mStart;
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gfxPoint mEnd;
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};
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#endif /* GFX_LINESEGMENT_H */
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