2D line intersection test

intersect.cljc

(defn intersection-2D
  "Intersection of two lines in 2D space. No checks for parallel or coincident lines."
  [[[x1 y1] [x2 y2]]
   [[x3 y3] [x4 y4]]]
  (let [denom (- (* (- x1 x2) (- y3 y4))
                 (* (- y1 y2) (- x3 x4)))
        x1y2-y1x2 (- (* x1 y2) (* y1 x2))
        x3y4-y3x4 (- (* x3 y4) (* y3 x4))
        px-num (- (* x1y2-y1x2 (- x3 x4))
                  (* (- x1 x2) x3y4-y3x4))
        py-num (- (* x1y2-y1x2 (- y3 y4))
                  (* (- y1 y2) x3y4-y3x4))]
    [(/ px-num denom)
     (/ py-num denom)]))

Thanks, I have blatantly stolen that here

No problem. I can't remember offhand whether I actually wrote it or just found it somewhere.