1 /* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*- 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 { gfxLineSegmentgfxLineSegment13 gfxLineSegment(const gfxPoint &aStart, const gfxPoint &aEnd) 14 : mStart(aStart) 15 , mEnd(aEnd) 16 {} 17 PointsOnSameSidegfxLineSegment18 bool PointsOnSameSide(const gfxPoint& aOne, const gfxPoint& aTwo) 19 { 20 // Solve the equation y - mStart.y - ((mEnd.y - mStart.y)/(mEnd.x - mStart.x))(x - mStart.x) 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 line. 29 // 0 (on the line) is always considered in. 30 31 if ((one >= 0 && two >= 0) || (one <= 0 && two <= 0)) 32 return true; 33 return false; 34 } 35 36 /** 37 * Determines if two line segments intersect, and returns the intersection 38 * point in aIntersection if they do. 39 * 40 * Coincident lines are considered not intersecting as they don't have an 41 * intersection point. 42 */ IntersectsgfxLineSegment43 bool Intersects(const gfxLineSegment& aOther, gfxPoint& aIntersection) 44 { 45 gfxFloat denominator = (aOther.mEnd.y - aOther.mStart.y) * (mEnd.x - mStart.x ) - 46 (aOther.mEnd.x - aOther.mStart.x ) * (mEnd.y - mStart.y); 47 48 // Parallel or coincident. We treat coincident as not intersecting since 49 // these lines are guaranteed to have corners that intersect instead. 50 if (!denominator) { 51 return false; 52 } 53 54 gfxFloat anumerator = (aOther.mEnd.x - aOther.mStart.x) * (mStart.y - aOther.mStart.y) - 55 (aOther.mEnd.y - aOther.mStart.y) * (mStart.x - aOther.mStart.x); 56 57 gfxFloat bnumerator = (mEnd.x - mStart.x) * (mStart.y - aOther.mStart.y) - 58 (mEnd.y - mStart.y) * (mStart.x - aOther.mStart.x); 59 60 gfxFloat ua = anumerator / denominator; 61 gfxFloat ub = bnumerator / denominator; 62 63 if (ua <= 0.0 || ua >= 1.0 || 64 ub <= 0.0 || ub >= 1.0) { 65 //Intersection is outside of the segment 66 return false; 67 } 68 69 aIntersection = mStart + (mEnd - mStart) * ua; 70 return true; 71 } 72 73 gfxPoint mStart; 74 gfxPoint mEnd; 75 }; 76 77 #endif /* GFX_LINESEGMENT_H */ 78