;; Trails effect - persistent motion trails

(define-effect trails
  :params (
    (persistence :type float :default 0.8 :range [0 0.99])
  )
  (let* ((buffer (state-get 'buffer nil))
         (current frame))
    (if (= buffer nil)
        (begin
          (state-set 'buffer (copy frame))
          frame)
        (let* ((faded (blend-images buffer
                                    (make-image (width frame) (height frame) (list 0 0 0))
                                    (- 1 persistence)))
               (result (blend-mode faded current "lighten")))
          (begin
            (state-set 'buffer result)
            result)))))