public static IEnumerable <Point2D> IntersectWithLine(this Circle2D circle, BoundaryLine2D line)
{
var offsetToCenter = line.HalfPlane.GetOffsetFromBoundaryTowardInside(circle.Center);
if (!(offsetToCenter.AbsoluteValue() <= circle.Radius))
{
return(Enumerable.Empty <Point2D>());
}
var intersectionOfLineWithPerpendicularRadius =
circle.Center + line.HalfPlane.DirectionTowardInterior.ToVector(-offsetToCenter);
var distanceFromPerpendicularRadiusToIntersectionsSquared =
circle.Radius.Square() - offsetToCenter.Square();
// If it's negative, the line doesn't quite intersect the circle.
if (distanceFromPerpendicularRadiusToIntersectionsSquared > Unit.ZeroArea)
{
var distanceFromPerpendicularRadiusToIntersections =
distanceFromPerpendicularRadiusToIntersectionsSquared.SquareRoot();
var intersectionPoints =
line
.ParallelDirections
.Select(direction =>
intersectionOfLineWithPerpendicularRadius
+ direction.ToVector(distanceFromPerpendicularRadiusToIntersections))
.ToList();
if (intersectionPoints.DistinctEquatable().Count() > 1)
{
return(intersectionPoints);
}
}
return(intersectionOfLineWithPerpendicularRadius.Singleton());
}
public static Either <Null, Point2D, Segment2D> IntersectWithDisk(this Segment2D segment, Circle2D diskBoundary)
{
var lineIntersectionsWithBoundary = diskBoundary.IntersectWithLine(segment.AsLine()).ToList();
if (lineIntersectionsWithBoundary.Count == 0)
{
return(Null.Instance);
}
if (lineIntersectionsWithBoundary.Count == 1)
{
var point = lineIntersectionsWithBoundary.Single();
if (segment.Contains(point))
{
return(point);
}
return(Null.Instance);
}
var segmentDirection = segment.GetDirection();
var(baseSideIntersection, endSideIntersection) =
(lineIntersectionsWithBoundary[0], lineIntersectionsWithBoundary[1]).ReverseIf(
(lineIntersectionsWithBoundary[0].DirectionTo(lineIntersectionsWithBoundary[1])
.Value
.DotProduct(segmentDirection)
) < 0);
var clipBase =
(baseSideIntersection - segment.BasePoint).GetComponentInDirection(segmentDirection)
> Unit.ZeroDistance;
var clipEnd =
(endSideIntersection - segment.EndPoint).GetComponentInDirection(segmentDirection) < Unit.ZeroDistance;
var clippedBase = clipBase ? baseSideIntersection : segment.BasePoint;
var clippedEnd = clipEnd ? endSideIntersection : segment.EndPoint;
if (clippedBase == clippedEnd)
{
return(clipBase ? segment.EndPoint : segment.BasePoint);
}
var signedDistance = (clippedEnd - clippedBase).GetComponentInDirection(segmentDirection);
if (signedDistance > Unit.ZeroDistance)
{
return(new Segment2D(clippedBase, clippedEnd));
}
return(Null.Instance);
}
public static IEnumerable <Point2D> IntersectWithLine(this Circle2D circle, Line2D line) => circle.IntersectWithLine(line.AsBoundaryLine());
