;; Layer effect - composite frame-b over frame-a at position
;; Multi-input effect: uses frame-a (background) and frame-b (overlay)
;; Params: x, y (position), opacity (0-1), mode (blend mode)

(define-effect layer
  :params (
    (x :type int :default 0)
    (y :type int :default 0)
    (opacity :type float :default 1.0)
    (mode :type string :default "alpha")
  )
  (let [bg (copy frame-a)
        fg frame-b
        ;; Resize fg if needed to fit
        fg-w (width fg)
        fg-h (height fg)]
    (if (= opacity 1.0)
      ;; Simple paste
      (paste bg fg x y)
      ;; Blend with opacity
      (let [blended (if (= mode "alpha")
                      (blend-images (crop bg x y fg-w fg-h) fg opacity)
                      (blend-images (crop bg x y fg-w fg-h)
                                   (blend-mode (crop bg x y fg-w fg-h) fg mode)
                                   opacity))]
        (paste bg blended x y)))))