Check if two line segments intersect

gistfile1.txt

// 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;
    s = (-s1_y * (p0_x - p2_x) + s1_x * (p0_y - p2_y)) / (-s2_x * s1_y + s1_x * s2_y);
    t = ( s2_x * (p0_y - p2_y) - s2_y * (p0_x - p2_x)) / (-s2_x * s1_y + s1_x * s2_y);

    if (s >= 0 && s <= 1 && t >= 0 && t <= 1)
    {
        // Collision detected
        return 1;
    }

    return 0; // No collision
}

You can merge the two returns into return (s >= 0 && s <= 1 && t >= 0 && t <= 1);

Thanks a lot

This is great. Thanks!