gfxLineSegment.h (2711B)
1 /* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*- 2 * This Source Code Form is subject to the terms of the Mozilla Public 3 * License, v. 2.0. If a copy of the MPL was not distributed with this 4 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ 5 6 #ifndef GFX_LINESEGMENT_H 7 #define GFX_LINESEGMENT_H 8 9 #include "gfxTypes.h" 10 #include "gfxPoint.h" 11 12 struct gfxLineSegment { 13 gfxLineSegment() {} 14 gfxLineSegment(const gfxPoint& aStart, const gfxPoint& aEnd) 15 : mStart(aStart), mEnd(aEnd) {} 16 17 bool PointsOnSameSide(const gfxPoint& aOne, const gfxPoint& aTwo) { 18 // Solve the equation 19 // y - mStart.y - ((mEnd.y - mStart.y)/(mEnd.x - mStart.x))(x - mStart.x) 20 // for both points 21 22 gfxFloat deltaY = (mEnd.y - mStart.y); 23 gfxFloat deltaX = (mEnd.x - mStart.x); 24 25 gfxFloat one = deltaX * (aOne.y - mStart.y) - deltaY * (aOne.x - mStart.x); 26 gfxFloat two = deltaX * (aTwo.y - mStart.y) - deltaY * (aTwo.x - mStart.x); 27 28 // If both results have the same sign, then we're on the correct side of the 29 // line. 0 (on the line) is always considered in. 30 31 if ((one >= 0 && two >= 0) || (one <= 0 && two <= 0)) return true; 32 return false; 33 } 34 35 /** 36 * Determines if two line segments intersect, and returns the intersection 37 * point in aIntersection if they do. 38 * 39 * Coincident lines are considered not intersecting as they don't have an 40 * intersection point. 41 */ 42 bool Intersects(const gfxLineSegment& aOther, gfxPoint& aIntersection) { 43 gfxFloat denominator = 44 (aOther.mEnd.y - aOther.mStart.y).value * (mEnd.x - mStart.x).value - 45 (aOther.mEnd.x - aOther.mStart.x).value * (mEnd.y - mStart.y).value; 46 47 // Parallel or coincident. We treat coincident as not intersecting since 48 // these lines are guaranteed to have corners that intersect instead. 49 if (!denominator) { 50 return false; 51 } 52 53 gfxFloat anumerator = (aOther.mEnd.x - aOther.mStart.x).value * 54 (mStart.y - aOther.mStart.y).value - 55 (aOther.mEnd.y - aOther.mStart.y).value * 56 (mStart.x - aOther.mStart.x).value; 57 58 gfxFloat bnumerator = 59 (mEnd.x - mStart.x).value * (mStart.y - aOther.mStart.y).value - 60 (mEnd.y - mStart.y).value * (mStart.x - aOther.mStart.x).value; 61 62 gfxFloat ua = anumerator / denominator; 63 gfxFloat ub = bnumerator / denominator; 64 65 if (ua <= 0.0 || ua >= 1.0 || ub <= 0.0 || ub >= 1.0) { 66 // Intersection is outside of the segment 67 return false; 68 } 69 70 aIntersection = mStart + (mEnd - mStart) * ua; 71 return true; 72 } 73 74 gfxPoint mStart; 75 gfxPoint mEnd; 76 }; 77 78 #endif /* GFX_LINESEGMENT_H */