;; Echo effect - motion trails using frame buffer
;; @param num_echoes int [1, 20] default 4
;; @param decay float [0, 1] default 0.5

(define-effect echo
  ((num_echoes 4) (decay 0.5))
  (let* ((buffer (state-get 'buffer (list)))
         (new-buffer (take (cons frame buffer) (+ num_echoes 1))))
    (begin
      (state-set 'buffer new-buffer)
      ;; Blend frames with decay
      (if (< (length new-buffer) 2)
          frame
          (let ((result (copy frame)))
            ;; Simple blend of first two frames for now
            ;; Full version would fold over all frames
            (blend-images frame (nth new-buffer 1) (* decay 0.5)))))))