// Code snippet used from https://gist.github.com/Joncom/e8e8d18ebe7fe55c3894.
// Returns true if an intersection exists and false otherwise.
function intersection(p0_x, p0_y, p1_x, p1_y, p2_x, p2_y, p3_x, p3_y) {
  let 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;

  let 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);

  return (s >= 0 && s <= 1 && t >= 0 && t <= 1);
}