public static bool CircleLineIntersection(Circle2D c, Line2D l)
{
var a1 = new Vector2D(c.Point.X - c.Radius, c.Point.Y - c.Radius);
var a2 = new Vector2D(c.Point.X + c.Radius, c.Point.Y + c.Radius);
if (BoundingBoxIntersection(a1, a2, l.A, l.B))
{
var slope = l.Slope;
double inverseSlope;
if (slope == null || (double) slope == 0)
{
// the bounding box already determined that an intersection has been made.
return true;
}
// slightly more complicated... need to create a tangent line. and find the distance.
inverseSlope = 1 / (double)slope;
// y= mx+b
// b = circle.y, x = circle .x
Line2D l2 = new Line2D();
l2.A = new Vector2D(c.Point.X, c.Point.Y);
l2.B.X = c.Point.X + c.Radius;
l2.B.Y = c.Point.Y + inverseSlope * (c.Point.X + c.Radius);
var p = LineLineIntersection(l, l2);
if (p != null)
{
var d = new Line2D(c.Point, p);
if (d.Length < c.Radius)
return true;
return false;
}
Line2D l3 = new Line2D();
l2.A = new Vector2D(c.Point.X, c.Point.Y);
l2.B.X = c.Point.X - c.Radius;
l2.B.Y = c.Point.Y + inverseSlope * (c.Point.X - c.Radius);
var q = LineLineIntersection(l, l2);
if (q != null)
{
var d = new Line2D(c.Point, q);
if (d.Length < c.Radius)
return true;
return false;
}
}
return false;
}
public static bool CircleCircleIntersection(Circle2D a, Circle2D b)
{
var l = new Line2D(a.Point, b.Point);
return l.Length < (a.Radius + b.Radius);
}
public static bool CircleContainsVertex(Circle2D a, Vector2D b)
{
var l = new Line2D(a.Point, b);
return l.Length < a.Radius;
}
// private static int FindLineCircleIntersections(double cx, double cy, double radius,
//Vector2D point1, Vector2D point2)
// {
// double dx, dy, A, B, C, det;
// dx = point2.X - point1.X;
// dy = point2.Y - point1.Y;
// A = dx * dx + dy * dy;
// B = 2 * (dx * (point1.X - cx) + dy * (point1.Y - cy));
// C = (point1.X - cx) * (point1.X - cx) + (point1.Y - cy) * (point1.Y - cy) - radius * radius;
// det = B * B - 4 * A * C;
// if ((A <= 0.0000001) || (det < 0))
// {
// return 0;
// }
// else if (det == 0)
// {
// return 1;
// }
// else
// {
// return 2;
// }
// }
// public static bool CirclePolygonIntersecton(Circle2D c, Polygon2D p)
// {
// foreach (var l in p.Lines)
// {
// var count = FindLineCircleIntersections(c.Point.X, c.Point.Y, c.Radius, l.A, l.B);
// if (count == 2)
// return true;
// else if (count == 1 && IsPointInPolygon(p, c.Point))
// return true;
// }
// if (IsPointInPolygon(p, c.Point))
// return true;
// return false;
// }
public static bool CirclePolygonIntersection(Circle2D c, Polygon2D p)
{
if (IsPointInPolygon(p, c.Point))
return true;
foreach (var l in p.Lines)
{
if (CircleLineIntersection(c, l))
return true;
}
return false;
}
