Update (18 Nov): bug fix - guides go up to both edges, if width/height is a multiple of the separation distance.
max was set to height (if vertical guide) when it should have been width and vice versa for vertical.
The GIMP photo/image manipulation program allows you to add guides as an aid to image editing. It is fairly simple to add them - Image > Guides > New Guide or click on one of the rulers and drag onto the canvas. However, this can be time consuming if you need to add multiple guides, equally spaced.
Script-Fu however, allows you to do this via scripting. First of all, create a scm file (e.g. guides-repeat.scm) in your script folder (on Windows this would be C:\Program Files\GIMP-2.0\share\gimp\2.0\scripts (all users) or %USERPROFILE%\.gimp-2.6\scripts, then paste in the following code (use a plain text editor like Notepad)
(define (script-fu-guide-repeat image drawable direction separation) (let* ( (width (car (gimp-image-width image))) (height (car (gimp-image-height image))) (position 0) ) ; set maximum otherwise the guides will be added indefinitely (if (= direction 0) (set! max height) (set! max width) ) ; while the position is less than the maximum (while (<= position max) (if (= direction 0) ;; check position is inside the image boundaries (if (<= position height) (gimp-image-add-hguide image position)) (if (<= position width) (gimp-image-add-vguide image position)) ) ; increment position by defined separation (set! position (+ position separation))) (gimp-displays-flush) ) ) (script-fu-register "script-fu-guide-repeat" _"R_epeating Guide" _"Add multiple guides separated by specified number of pixels" "Sam Collett" "Sam Collett" "2008-11-18" "*" SF-IMAGE "Image" 0 SF-DRAWABLE "Drawable" 0 SF-OPTION _"Direction" '(_"Horizontal" _"Vertical") SF-ADJUSTMENT _"Separation" (list 40 1 MAX-IMAGE-SIZE 1 10 0 1) ) (script-fu-menu-register "script-fu-guide-repeat" "<Image>/Image/Guides")
After saving the script, either restart GIMP or Filters > Script-Fu > Refresh Scripts (GIMP 2.6, earlier versions use Xtns instead of Filters). Repeating Guides should now appear under Image > Guides