Notes about the Scheme language

checker.scm

;; https://docs.gimp.org/2.10/en/gimp-using-script-fu-tutorial-first-script.html
(define (checker image drawable color-bg color-fg)
  (let* ((width (car (gimp-image-width image)))
         (height (car (gimp-image-height image)))
         (width-str (number->string width))
         (height-str (number->string height))
         (message (string-append "Image size: " width-str "x" height-str "px"))
         (x 0)
         (y 0))

    ;; fill layer with background color (light gray)
    (gimp-context-set-background color-bg)
    (gimp-drawable-fill drawable BACKGROUND-FILL)

    ;; draw checker
    (while (< y height)
      (set! x (if (even? y) 0 1))

      (while (< x width)
        (gimp-drawable-set-pixel drawable x y 3 (list->vector color-fg))
        (set! x (+ x 2)))

      (set! y (+ y 1)))

    (gimp-displays-flush)))

(script-fu-register
  "checker"                                   ;function name
  "Checker"                                   ;menu label
  "Draws a checker."                          ;description
  "Hakim Benoudjit"                           ;author
  "Copyright 2026, Hakim Benoudjit"           ;copyright notice
  "February 2026"                             ;date created
  "RGB"                                       ;image type that the script works on
  SF-IMAGE      "Image"             0
  SF-DRAWABLE   "Drawable"          0
  SF-COLOR      "Background-color"             '(0 0 #xff)
  SF-COLOR      "Foreground-color"             '(#xff 0 0)
)

(script-fu-menu-register "checker" "<Image>/Filters/Hakim's")

scheme.md

Installation

$ sudo apt install guile-3.0

Help

From the command line:

$ sudo apt install guile-3.0-doc
$ info --vi-keys guile  # to use vim keybindings in info

• h: Show shortcuts.
• [ and ]: Go to the previous/next node.
• g and G: Go to the start/end of the document.
• Tab: Jump to hyperlinks (in order).
• Alt-g and ': Follow the hyperlink, and return to where we were.
• j and k: Scroll one line down/up.
• u and d: Scroll half a page up/down.
• /<text>: Search for occurrences of text.
• n and N: Jump to the next/previous occurrence.

Gimp script-fu

• Run TinyScheme from terminal: gimp-console -b -.
• PDB (Procedure Database): internal registry of all Gimp functions that can be called.
• E.g.: (gimp-image-scale image new-width new-height)
• Image: While gimp image (canvas, layers...).
• Drawable: Usually one layer (active one).
• Browse plugins:

$ apt-get source gimp
$ cd <gimp>/plug-ins/script-fu

• Scripts are installed in ~/.config/GIMP/2.10/scripts/.
• Functions (script-fu ...): for registering plugins.

Script-fu functions

All of these functions return a list not a number:

• gimp-image-list
• gimp-image-width
• gimp-image-height

The following function are used to change the background:

• gimp-context-set-background: set the background color.
• gimp-drawable-fill: fill active drawable (active layer) using foreground/background color.
• gimp-displays-flush: modification won't be visible without flushing them to UI.