// port of this JavaScript code with some changes:
// http://www.kevlindev.com/gui/math/intersection/Intersection.js
// found here:
// http://stackoverflow.com/questions/563198/how-do-you-detect-where-two-line-segments-intersect/563240#563240
public class Intersector
{
static double MyEpsilon = 0.00001;
private static float[] OverlapIntervals(float ub1, float ub2)
{
float l = Math.Min(ub1, ub2);
float r = Math.Max(ub1, ub2);
float A = Math.Max(0, l);
float B = Math.Min(1, r);
if (A > B) // no intersection
return new float[] { };
else if (A == B)
return new float[] { A };
else // if (A < B)
return new float[] { A, B };
}
// IMPORTANT: a1 and a2 cannot be the same, e.g. a1--a2 is a true segment, not a point
// b1/b2 may be the same (b1--b2 is a point)
private static PointF[] OneD_Intersection(PointF a1, PointF a2, PointF b1, PointF b2)
{
//float ua1 = 0.0f; // by definition
//float ua2 = 1.0f; // by definition
float ub1, ub2;
float denomx = a2.X - a1.X;
float denomy = a2.Y - a1.Y;
if (Math.Abs(denomx) > Math.Abs(denomy))
{
ub1 = (b1.X - a1.X)/denomx;
ub2 = (b2.X - a1.X)/denomx;
}
else
{
ub1 = (b1.Y - a1.Y)/denomy;
ub2 = (b2.Y - a1.Y)/denomy;
}
List<PointF> ret = new List<PointF>();
float[] interval = OverlapIntervals(ub1, ub2);
foreach (float f in interval)
{
float x = a2.X * f + a1.X * (1.0f - f);
float y = a2.Y * f + a1.Y * (1.0f - f);
PointF p = new PointF(x, y);
ret.Add(p);
}
return ret.ToArray();
}
private static bool PointOnLine(PointF p, PointF a1, PointF a2)
{
float dummyU = 0.0f;
double d = DistFromSeg(p, a1, a2, MyEpsilon, ref dummyU);
return d < MyEpsilon;
}
private static double DistFromSeg(PointF p, PointF q0, PointF q1, double radius, ref float u)
{
// formula here:
//http://mathworld.wolfram.com/Point-LineDistance2-Dimensional.html
// where x0,y0 = p
// x1,y1 = q0
// x2,y2 = q1
double dx21 = q1.X - q0.X;
double dy21 = q1.Y - q0.Y;
double dx10 = q0.X - p.X;
double dy10 = q0.Y - p.Y;
double segLength = Math.Sqrt(dx21 * dx21 + dy21 * dy21);
if (segLength < MyEpsilon)
throw new Exception("Expected line segment, not point.");
double num = Math.Abs(dx21 * dy10 - dx10 * dy21);
double d = num/segLength;
return d;
}
// this is the general case. Really really general
public static PointF[] Intersection(PointF a1, PointF a2, PointF b1, PointF b2)
{
if (a1.Equals(a2) && b1.Equals(b2))
{
// both "segments" are points, return either point
if (a1.Equals(b1))
return new PointF[] { a1 };
else // both "segments" are different points, return empty set
return new PointF[] { };
}
else if (b1.Equals(b2)) // b is a point, a is a segment
{
if (PointOnLine(b1, a1, a2))
return new PointF[] { b1 };
else
return new PointF[] { };
}
else if (a1.Equals(a2)) // a is a point, b is a segment
{
if (PointOnLine(a1, b1, b2))
return new PointF[] { a1 };
else
return new PointF[] { };
}
// at this point we know both a and b are actual segments
float ua_t = (b2.X - b1.X) * (a1.Y - b1.Y) - (b2.Y - b1.Y) * (a1.X - b1.X);
float ub_t = (a2.X - a1.X) * (a1.Y - b1.Y) - (a2.Y - a1.Y) * (a1.X - b1.X);
float u_b = (b2.Y - b1.Y) * (a2.X - a1.X) - (b2.X - b1.X) * (a2.Y - a1.Y);
// Infinite lines intersect somewhere
if (!(-MyEpsilon < u_b && u_b < MyEpsilon)) // e.g. u_b != 0.0
{
float ua = ua_t/u_b;
float ub = ub_t/u_b;
if (0.0f <= ua && ua <= 1.0f && 0.0f <= ub && ub <= 1.0f)
{
// Intersection
return new PointF[] {
new PointF(a1.X + ua * (a2.X - a1.X),
a1.Y + ua * (a2.Y - a1.Y)) };
}
else
{
// No Intersection
return new PointF[] { };
}
}
else // lines (not just segments) are parallel or the same line
{
// Coincident
// find the common overlapping section of the lines
// first find the distance (squared) from one point (a1) to each point
if ((-MyEpsilon < ua_t && ua_t < MyEpsilon)
|| (-MyEpsilon < ub_t && ub_t < MyEpsilon))
{
if (a1.Equals(a2)) // danger!
return OneD_Intersection(b1, b2, a1, a2);
else // safe
return OneD_Intersection(a1, a2, b1, b2);
}
else
{
// Parallel
return new PointF[] { };
}
}
}
}
Hier ist der Testcode:
public class IntersectTest
{
public static void PrintPoints(PointF[] pf)
{
if (pf == null || pf.Length < 1)
System.Console.WriteLine("Doesn't intersect");
else if (pf.Length == 1)
{
System.Console.WriteLine(pf[0]);
}
else if (pf.Length == 2)
{
System.Console.WriteLine(pf[0] + " -- " + pf[1]);
}
}
public static void TestIntersect(PointF a1, PointF a2, PointF b1, PointF b2)
{
System.Console.WriteLine("----------------------------------------------------------");
System.Console.WriteLine("Does " + a1 + " -- " + a2);
System.Console.WriteLine("intersect " + b1 + " -- " + b2 + " and if so, where?");
System.Console.WriteLine("");
PointF[] result = Intersect.Intersection(a1, a2, b1, b2);
PrintPoints(result);
}
public static void Main()
{
System.Console.WriteLine("----------------------------------------------------------");
System.Console.WriteLine("line segments intersect");
TestIntersect(new PointF(0, 0),
new PointF(100, 100),
new PointF(100, 0),
new PointF(0, 100));
TestIntersect(new PointF(5, 17),
new PointF(100, 100),
new PointF(100, 29),
new PointF(8, 100));
System.Console.WriteLine("----------------------------------------------------------");
System.Console.WriteLine("");
System.Console.WriteLine("----------------------------------------------------------");
System.Console.WriteLine("just touching points and lines cross");
TestIntersect(new PointF(0, 0),
new PointF(25, 25),
new PointF(25, 25),
new PointF(100, 75));
System.Console.WriteLine("----------------------------------------------------------");
System.Console.WriteLine("");
System.Console.WriteLine("----------------------------------------------------------");
System.Console.WriteLine("parallel");
TestIntersect(new PointF(0, 0),
new PointF(0, 100),
new PointF(100, 0),
new PointF(100, 100));
System.Console.WriteLine("----------------------------------------------------------");
System.Console.WriteLine("");
System.Console.WriteLine("----");
System.Console.WriteLine("lines cross but segments don't intersect");
TestIntersect(new PointF(50, 50),
new PointF(100, 100),
new PointF(0, 25),
new PointF(25, 0));
System.Console.WriteLine("----------------------------------------------------------");
System.Console.WriteLine("");
System.Console.WriteLine("----------------------------------------------------------");
System.Console.WriteLine("coincident but do not overlap!");
TestIntersect(new PointF(0, 0),
new PointF(25, 25),
new PointF(75, 75),
new PointF(100, 100));
System.Console.WriteLine("----------------------------------------------------------");
System.Console.WriteLine("");
System.Console.WriteLine("----------------------------------------------------------");
System.Console.WriteLine("touching points and coincident!");
TestIntersect(new PointF(0, 0),
new PointF(25, 25),
new PointF(25, 25),
new PointF(100, 100));
System.Console.WriteLine("----------------------------------------------------------");
System.Console.WriteLine("");
System.Console.WriteLine("----------------------------------------------------------");
System.Console.WriteLine("overlap/coincident");
TestIntersect(new PointF(0, 0),
new PointF(75, 75),
new PointF(25, 25),
new PointF(100, 100));
TestIntersect(new PointF(0, 0),
new PointF(100, 100),
new PointF(0, 0),
new PointF(100, 100));
System.Console.WriteLine("----------------------------------------------------------");
System.Console.WriteLine("");
while (!System.Console.KeyAvailable) { }
}
}
und hier ist der Ausgang:
----------------------------------------------------------
line segments intersect
----------------------------------------------------------
Does {X=0, Y=0} -- {X=100, Y=100}
intersect {X=100, Y=0} -- {X=0, Y=100} and if so, where?
{X=50, Y=50}
----------------------------------------------------------
Does {X=5, Y=17} -- {X=100, Y=100}
intersect {X=100, Y=29} -- {X=8, Y=100} and if so, where?
{X=56.85001, Y=62.30054}
----------------------------------------------------------
----------------------------------------------------------
just touching points and lines cross
----------------------------------------------------------
Does {X=0, Y=0} -- {X=25, Y=25}
intersect {X=25, Y=25} -- {X=100, Y=75} and if so, where?
{X=25, Y=25}
----------------------------------------------------------
----------------------------------------------------------
parallel
----------------------------------------------------------
Does {X=0, Y=0} -- {X=0, Y=100}
intersect {X=100, Y=0} -- {X=100, Y=100} and if so, where?
Doesn't intersect
----------------------------------------------------------
----
lines cross but segments don't intersect
----------------------------------------------------------
Does {X=50, Y=50} -- {X=100, Y=100}
intersect {X=0, Y=25} -- {X=25, Y=0} and if so, where?
Doesn't intersect
----------------------------------------------------------
----------------------------------------------------------
coincident but do not overlap!
----------------------------------------------------------
Does {X=0, Y=0} -- {X=25, Y=25}
intersect {X=75, Y=75} -- {X=100, Y=100} and if so, where?
Doesn't intersect
----------------------------------------------------------
----------------------------------------------------------
touching points and coincident!
----------------------------------------------------------
Does {X=0, Y=0} -- {X=25, Y=25}
intersect {X=25, Y=25} -- {X=100, Y=100} and if so, where?
{X=25, Y=25}
----------------------------------------------------------
----------------------------------------------------------
overlap/coincident
----------------------------------------------------------
Does {X=0, Y=0} -- {X=75, Y=75}
intersect {X=25, Y=25} -- {X=100, Y=100} and if so, where?
{X=25, Y=25} -- {X=75, Y=75}
----------------------------------------------------------
Does {X=0, Y=0} -- {X=100, Y=100}
intersect {X=0, Y=0} -- {X=100, Y=100} and if so, where?
{X=0, Y=0} -- {X=100, Y=100}
----------------------------------------------------------
Ich weiß, dass diese Frage nur gestellt wird, damit Sie Ihre Antwort posten können. Sie sollten es als die akzeptierte Antwort markieren. Es würde nicht schaden, weniger konfrontative Sprache in der Frage zu verwenden, FWIW. – tfinniga
@tfinniga: Ich wusste nicht, dass es konfrontativ war, bis ich es umgeschrieben habe und es wie ein Puzzle statt einer Nachfrage klingen ließ. Mein Ziel war nicht, dass andere Leute die Arbeit für mich erledigen, sondern dass ich beweisen muss, dass keine andere Implementierung funktioniert hat. (Wenn du mich verzeihen kannst und eine wirklich gute Lösung findest (das ist jetzt SO), die einwandfrei funktioniert, würde ich dir gerne 100 Rep geben). –
Danke, ich denke das ist viel besser. Eine kugelsichere Implementierung für dieses gemeinsame Bedürfnis ist wertvoll, und die umformulierte Frage ist viel angenehmer. – tfinniga