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       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 {
      13           0 :   gfxLineSegment(const gfxPoint &aStart, const gfxPoint &aEnd) 
      14           0 :     : mStart(aStart)
      15           0 :     , mEnd(aEnd)
      16           0 :   {}
      17             : 
      18           0 :   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           0 :     gfxFloat deltaY = (mEnd.y - mStart.y);
      23           0 :     gfxFloat deltaX = (mEnd.x - mStart.x);
      24             :   
      25           0 :     gfxFloat one = deltaX * (aOne.y - mStart.y) - deltaY * (aOne.x - mStart.x);
      26           0 :     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           0 :     if ((one >= 0 && two >= 0) || (one <= 0 && two <= 0))
      32           0 :       return true;
      33           0 :     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             :    */
      43           0 :   bool Intersects(const gfxLineSegment& aOther, gfxPoint& aIntersection)
      44             :   {
      45           0 :     gfxFloat denominator = (aOther.mEnd.y - aOther.mStart.y) * (mEnd.x - mStart.x ) - 
      46           0 :                            (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           0 :     if (!denominator) {
      51           0 :       return false;
      52             :     }
      53             : 
      54           0 :     gfxFloat anumerator = (aOther.mEnd.x - aOther.mStart.x) * (mStart.y - aOther.mStart.y) -
      55           0 :                          (aOther.mEnd.y - aOther.mStart.y) * (mStart.x - aOther.mStart.x);
      56             :   
      57           0 :     gfxFloat bnumerator = (mEnd.x - mStart.x) * (mStart.y - aOther.mStart.y) -
      58           0 :                          (mEnd.y - mStart.y) * (mStart.x - aOther.mStart.x);
      59             : 
      60           0 :     gfxFloat ua = anumerator / denominator;
      61           0 :     gfxFloat ub = bnumerator / denominator;
      62             : 
      63           0 :     if (ua <= 0.0 || ua >= 1.0 ||
      64           0 :         ub <= 0.0 || ub >= 1.0) {
      65             :       //Intersection is outside of the segment
      66           0 :       return false;
      67             :     }
      68             : 
      69           0 :     aIntersection = mStart + (mEnd - mStart) * ua;  
      70           0 :     return true;
      71             :   }
      72             : 
      73             :   gfxPoint mStart;
      74             :   gfxPoint mEnd;
      75             : };
      76             : 
      77             : #endif /* GFX_LINESEGMENT_H */