;; Outline effect - shows only edges
(require-primitives "image")

(define-effect outline
  :params (
    (thickness :type int :default 2 :range [1 10])
    (threshold :type int :default 100 :range [20 300])
    (color :type list :default (list 0 0 0))
    (fill_mode :type string :default "original")
  )
  (let* ((edge-img (image:edge-detect frame (/ threshold 2) threshold))
         (dilated (if (> thickness 1)
                      (dilate edge-img thickness)
                      edge-img))
         (base (cond
                 ((= fill_mode "original") (copy frame))
                 ((= fill_mode "white") (make-image (image:width frame) (image:height frame) (list 255 255 255)))
                 (else (make-image (image:width frame) (image:height frame) (list 0 0 0))))))
    (map-pixels base
      (lambda (x y c)
        (let ((edge-val (luminance (pixel dilated x y))))
          (if (> edge-val 128)
              color
              c))))))