;; Swirl effect - spiral vortex distortion
;; @param strength float [-10, 10] default 1
;; @param radius float [0.1, 2] default 0.5
;; @param center_x float [0, 1] default 0.5
;; @param center_y float [0, 1] default 0.5
;; @param falloff string default "quadratic"

(define-effect swirl
  ((strength 1) (radius 0.5) (center_x 0.5) (center_y 0.5) (falloff "quadratic"))
  (let* ((w (width frame))
         (h (height frame))
         (cx (* w center_x))
         (cy (* h center_y))
         (coords (swirl-displace w h strength radius cx cy falloff)))
    (remap frame (coords-x coords) (coords-y coords))))