private KeyValuePair <HalfEdge, float>?FindFirstParallelEdge(Seed seed, float length, float distance, float parallelThreshold)
{
Contract.Requires(seed != null);
var start = seed.Origin.Position;
var end = seed.Origin.Position + seed.Direction * length;
var segment = new LineSegment2(start, end);
//Calculate the expanded bounds to query. This is as wide as the parallel check distance
var p = seed.Direction.Perpendicular() * distance / 2;
var a = start + p;
var b = start - p;
var c = end + p;
var d = end - p;
var queryBounds = new BoundingRectangle(
Vector2.Min(Vector2.Min(a, b), Vector2.Min(c, d)),
Vector2.Max(Vector2.Max(a, b), Vector2.Max(c, d))
);
//now get all lines which intersect this bounds and check them for parallelism
var candidates = _mesh.FindEdges(queryBounds);
KeyValuePair <HalfEdge, float>?firstParallel = null;
foreach (var candidate in candidates)
{
var dirCandidate = candidate.Segment.Line.Direction;
var dir = segment.Line.Direction;
//Dot product directions of lines to check parallelism (compare with threshold)
var dot = Math.Abs(Vector2.Dot(dir, dirCandidate));
if (dot > parallelThreshold)
{
//Our query bounds were larger than the actual area we wanted to query (because we're limited to axis aligned bounds)
//Check that this line enters the smaller OABB area
//We'll do this check by checking if the line segment intersects any of the four OABB segments (AB, BC, CD, DA)
if (new LineSegment2(a, b).Intersects(candidate.Segment).HasValue ||
new LineSegment2(b, c).Intersects(candidate.Segment).HasValue ||
new LineSegment2(c, d).Intersects(candidate.Segment).HasValue ||
new LineSegment2(d, a).Intersects(candidate.Segment).HasValue)
{
//check how far along this segment the parallelism starts
var startDist = segment.ClosestPointDistanceAlongSegment(candidate.StartVertex.Position);
var endDist = segment.ClosestPointDistanceAlongSegment(candidate.EndVertex.Position);
var minDist = Math.Min(startDist, endDist);
if (firstParallel == null || minDist < firstParallel.Value.Value)
{
firstParallel = new KeyValuePair <HalfEdge, float>(candidate, minDist);
}
}
}
}
return(firstParallel);
}
