lineintersection.as

// ported from http://alienryderflex.com/intersect/

public static function LineIntersection(a:Point, b:Point, c:Point, d:Point):Point
{
	var distAB:Number, cos:Number, sin:Number, newX:Number, ABpos:Number;
	if ((a.x == b.x && a.y == b.y) || (c.x == d.x && c.y == d.y)) return null;

	if ( a == c || a == d || b == c || b == d ) return null;

	b = b.clone();
	c = c.clone();
	d = d.clone();

	b.offset( -a.x, -a.y);
	c.offset( -a.x, -a.y);
	d.offset( -a.x, -a.y);
	// a is now considered to be (0,0)

	distAB = b.length;
	cos = b.x / distAB;
	sin = b.y / distAB;

	c = new Point(c.x * cos + c.y * sin, c.y * cos - c.x * sin);
	d = new Point(d.x * cos + d.y * sin, d.y * cos - d.x * sin);

	if ((c.y < 0 && d.y < 0) || (c.y >= 0 && d.y >= 0)) return null;

	ABpos = d.x + (c.x - d.x) * d.y / (d.y - c.y); // what.
	if (ABpos < 0 || ABpos > distAB) return null;

	return new Point(a.x + ABpos * cos, a.y + ABpos * sin);			
}