Joncom

// Adapted from: http://stackoverflow.com/questions/563198/how-do-you-detect-where-two-line-segments-intersect/1968345#1968345
function line_intersects(p0_x, p0_y, p1_x, p1_y, p2_x, p2_y, p3_x, p3_y) {

    var s1_x, s1_y, s2_x, s2_y;
    s1_x = p1_x - p0_x;
    s1_y = p1_y - p0_y;
    s2_x = p3_x - p2_x;
    s2_y = p3_y - p2_y;

    var s, t;