﻿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; } } }