public bool Intersect(LineSegment a, LineSegment b, bool ignoreEndPointIntersects, out List <LineSegmentIntersect> intersects)
{
float ua = (b.End.X - b.Start.X) * (a.Start.Y - b.Start.Y) - (b.End.Y - b.Start.Y) * (a.Start.X - b.Start.X);
float ub = (a.End.X - a.Start.X) * (a.Start.Y - b.Start.Y) - (a.End.Y - a.Start.Y) * (a.Start.X - b.Start.X);
float denominator = (b.End.Y - b.Start.Y) * (a.End.X - a.Start.X) - (b.End.X - b.Start.X) * (a.End.Y - a.Start.Y);
intersects = null;
const float small = 0.01f;
if (Math.Abs(denominator) <= small)
{
if (Math.Abs(ua) <= small && Math.Abs(ub) <= small)
{
// lines are coincident:
// lacking other algorithms which actually work,
// roll some expensive distance tests to find intersection points
if (a.Start.DistanceFromLineSegment(b) <= small)
{
intersects = new List <LineSegmentIntersect>();
intersects.Add(new LineSegmentIntersect(LineSegmentIntersectType.StartA, a.Start));
}
if (a.End.DistanceFromLineSegment(b) <= small)
{
if (intersects == null)
{
intersects = new List <LineSegmentIntersect>();
}
intersects.Add(new LineSegmentIntersect(LineSegmentIntersectType.EndA, a.End));
}
if (b.Start.DistanceFromLineSegment(a) <= small)
{
if (intersects == null)
{
intersects = new List <LineSegmentIntersect>();
}
intersects.Add(new LineSegmentIntersect(LineSegmentIntersectType.MidPointA, b.Start));
}
if (b.End.DistanceFromLineSegment(a) <= small)
{
if (intersects == null)
{
intersects = new List <LineSegmentIntersect>();
}
intersects.Add(new LineSegmentIntersect(LineSegmentIntersectType.MidPointA, b.End));
}
}
}
else
{
ua /= denominator;
ub /= denominator;
if (ua >= 0 && ua <= 1 && ub >= 0 && ub <= 1)
{
LineSegmentIntersectType type = LineSegmentIntersectType.MidPointA;
if (ua <= small)
{
type = LineSegmentIntersectType.StartA;
}
else if (1 - ua <= small)
{
type = LineSegmentIntersectType.EndA;
}
intersects = new List <LineSegmentIntersect>();
intersects.Add(new LineSegmentIntersect(type, a.Start + new Vector(ua * (a.End.X - a.Start.X), ua * (a.End.Y - a.Start.Y))));
}
}
if (intersects != null && ignoreEndPointIntersects)
{
for (int index = 0; index < intersects.Count; ++index)
{
var intersect = intersects[index];
if (intersect.Position.Distance(a.Start) <= small ||
intersect.Position.Distance(b.Start) <= small ||
intersect.Position.Distance(a.End) <= small ||
intersect.Position.Distance(b.End) <= small)
{
intersects.RemoveAt(index);
--index;
}
}
}
return(intersects != null);
}
public LineSegmentIntersect(LineSegmentIntersectType type, Vector pos)
{
Type = type;
Position = pos;
}
public LineSegmentIntersect(LineSegmentIntersectType type, Vector pos)
{
Type = type;
Position = pos;
}
