;; CRT effect - old monitor simulation
;; @param line_spacing int [1, 10] default 2
;; @param line_opacity float [0, 1] default 0.3
;; @param vignette float [0, 1] default 0.2

(define-effect crt
  ((line_spacing 2) (line_opacity 0.3) (vignette_amount 0.2))
  (let* ((w (width frame))
         (h (height frame))
         (cx (/ w 2))
         (cy (/ h 2))
         (max-dist (sqrt (+ (* cx cx) (* cy cy)))))
    (map-pixels frame
      (lambda (x y c)
        (let* (;; Scanline darkening
               (scanline-factor (if (= 0 (mod y line_spacing))
                                    (- 1 line_opacity)
                                    1))
               ;; Vignette
               (dx (- x cx))
               (dy (- y cy))
               (dist (sqrt (+ (* dx dx) (* dy dy))))
               (vignette-factor (- 1 (* (/ dist max-dist) vignette_amount)))
               ;; Combined
               (factor (* scanline-factor vignette-factor)))
          (rgb (* (red c) factor)
               (* (green c) factor)
               (* (blue c) factor)))))))