/*
**  Usage:
**      intersection = lines_intersect(x0, y0, x1, y1, x2, y2, x3, y3);
**
**  Description:
**      Determines if two given lines intersect.
**
**  Arguments:
**      x0, y0    1st coordinate pair for the first line
**      x1, y1    2nd coordinate pair for the first line
**      x2, y2    1st coordinate pair for the second line
**      x3, y3    2nd coordinate pair for the second line
**
**  Returns:
**      TRUE when the lines intersect,
**      or FALSE otherwise.
**
**  Dependences:
**      is_clockwise()
**
**  copyright (c) 2006, John Leffingwell
**  www.planetxot.com
*/
var x0, y0, x1, y1, x2, y2, x3, y3;
x0 = argument[0];
y0 = argument[1];
x1 = argument[2];
y1 = argument[3];
x2 = argument[4];
y2 = argument[5];
x3 = argument[6];
y3 = argument[7];
return ((is_clockwise(x0, y0, x1, y1, x2, y2) != is_clockwise(x0, y0, x1, y1, x3, y3))
&& (is_clockwise(x2, y2, x3, y3, x0, y0) != is_clockwise(x2, y2, x3, y3, x1, y1)));