using System;
using System.Windows;
using System.Windows.Shapes;
namespace AnimatingObjectsAlongAPath
{
public static class Helpers
{
///
/// This is based off an explanation and expanded math presented by Paul Bourke:
///
/// It takes two lines as inputs and returns true if they intersect, false if they
/// don't.
/// If they do, ptIntersection returns the point where the two lines intersect.
///
/// The first line
/// The second line
/// The point where both lines intersect (if they do).
///
/// See http://local.wasp.uwa.edu.au/~pbourke/geometry/lineline2d/
public static bool DoLinesIntersect(Line L1, Line L2, ref Point ptIntersection)
{
// Denominator for ua and ub are the same, so store this calculation
double d =
(L2.Y2  L2.Y1) * (L1.X2  L1.X1)

(L2.X2  L2.X1) * (L1.Y2  L1.Y1);
//n_a and n_b are calculated as seperate values for readability
double n_a =
(L2.X2  L2.X1) * (L1.Y1  L2.Y1)

(L2.Y2  L2.Y1) * (L1.X1  L2.X1);
double n_b =
(L1.X2  L1.X1) * (L1.Y1  L2.Y1)

(L1.Y2  L1.Y1) * (L1.X1  L2.X1);
// Make sure there is not a division by zero  this also indicates that
// the lines are parallel.
// If n_a and n_b were both equal to zero the lines would be on top of each
// other (coincidental). This check is not done because it is not
// necessary for this implementation (the parallel check accounts for this).
if (d == 0)
return false;
// Calculate the intermediate fractional point that the lines potentially intersect.
double ua = n_a / d;
double ub = n_b / d;
// The fractional point will be between 0 and 1 inclusive if the lines
// intersect. If the fractional calculation is larger than 1 or smaller
// than 0 the lines would need to be longer to intersect.
if (ua >= 0d && ua <= 1d && ub >= 0d && ub <= 1d)
{
ptIntersection.X = L1.X1 + (ua * (L1.X2  L1.X1));
ptIntersection.Y = L1.Y1 + (ua * (L1.Y2  L1.Y1));
return true;
}
return false;
}
}
}