text: /* -*- 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 THEBES_API 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 */
  