/// <summary>
/// Test if two line segments intersect.
/// </summary>
/// <remarks>
/// Refer to http://stackoverflow.com/a/565282/695964 for explanation
/// </remarks>
public bool IsIntersectWith(LineSegment other)
{
double RxS = XProd(this.to, other.to);
double qpr = XProd(other.start - this.start, this.to);
if (RxS == 0)
{
if (qpr == 0)
{
return true;
}
else
{
return false;
}
}
else
{
double t = XProd(other.start - this.start, other.to) / RxS;
double u = qpr / RxS;
if (t>=0 && t<=1 && u>=0 && u <=1)
{
return true;
}
else
{
return false;
}
}
}
/// <summary>
/// Test cases
/// </summary>
static void Main(string[] args)
{
LineSegment s1, s2;
// case 1: intersected
s1 = new LineSegment(new Vector(17, -14), new Vector(61, -58));
s2 = new LineSegment(new Vector(23, -34), new Vector(54, -34));
Debug.Assert(s1.IsIntersectWith(s2));
// case 2: intersected at two line segments' ends
s1 = new LineSegment(new Vector(84, -27), new Vector(119, -27));
s2 = new LineSegment(new Vector(119, -27), new Vector(101, -45));
Debug.Assert(s1.IsIntersectWith(s2));
// case 3: intersected at one line segment's end
/* Fails due to floating point equality comparison. This is expected.
* (NOTE: both this approach and my straightforward approach fail on this case)
s1 = new LineSegment(new Vector(13, -78), new Vector(31, -113));
s2 = new LineSegment(new Vector(20, -91), new Vector(30, -76));
Debug.Assert(s1.IsIntersectWith(s2));
*/
// case 4: no intersection
s1 = new LineSegment(new Vector(52, -78), new Vector(74, -78));
s2 = new LineSegment(new Vector(79, -74), new Vector(70, -91));
Debug.Assert(!s1.IsIntersectWith(s2));
// case 5: overlapped horizontally
s1 = new LineSegment(new Vector(79, -108), new Vector(104, -108));
s2 = new LineSegment(new Vector(90, -108), new Vector(116, -108));
Debug.Assert(s1.IsIntersectWith(s2));
// case 6: overlapped vertically
s1 = new LineSegment(new Vector(107, -55), new Vector(107, -71));
s2 = new LineSegment(new Vector(107, -65), new Vector(107, -79));
Debug.Assert(s1.IsIntersectWith(s2));
// case 7: horizonally parallel
s1 = new LineSegment(new Vector(42, -114), new Vector(63, -114));
s2 = new LineSegment(new Vector(54, -121), new Vector(62, -121));
Debug.Assert(!s1.IsIntersectWith(s2));
}
