Gimp Panel-Merger Script-Fu

; A simple script to merge seperated panels of a vertical comic.
; Install this script by copy pasting its contents into notepad, saving as panel-merger.scm,
; and putting it into GIMPs script folder (which is usually found at C\Program Files\GIMP x.x\share\gimp\x.x\scripts).
; Then restart GIMP or click Filters > Script-Fu > Refresh Scripts.
; Simply add the image of each panel of the comic to GIMP such that the 1st panel is at the top of the layer list
; and the last panel is at the bottom, then run this script by navigating to Image > Merge Panels, and you're done!

; Works best when panels are all of same height and width. Doesn't (usually) explode if they're not,
; just might require some manual canvas resizing or layer offsetting to fix it up.


(define (script-fu-panel-merger imagevariable)
(let*   ( ;declare ALL the variables!
    (layercount (car (gimp-image-get-layers imagevariable)))
    (templayercount 0)
    (behindtlc 0)
    (layerlist (cadr (gimp-image-get-layers imagevariable)))
    (heightlist (cadr (gimp-image-get-layers imagevariable)))
    (tempheightvalue 0)
    (lastlayerheight 0)
    (lastlayercount 0)
    (canvaswidth (car (gimp-image-width imagevariable)))
    )

(gimp-undo-push-group-start imagevariable)  ;sets where to revert to when you hit the undo button

(while (< templayercount layercount) ;gets height value to resize canvas to, and populates vector with list of layer heights for later
    (set! tempheightvalue (+ tempheightvalue (car (gimp-drawable-height (vector-ref layerlist templayercount)))))
    (vector-set! heightlist templayercount (gimp-drawable-height (vector-ref layerlist templayercount)))
    (set! templayercount (+ templayercount 1))
)
    (gimp-image-resize imagevariable canvaswidth tempheightvalue 0 0)   ;resizes the canvas to combined height of layers

(set! templayercount 0)
(while (< templayercount layercount)    ;adds alpha channels to each layer
    (gimp-layer-add-alpha (vector-ref layerlist templayercount))
    (set! templayercount (+ templayercount 1))
)

(set! templayercount 0)
(while (< templayercount layercount)    ;resizes each layer to canvas size
    (gimp-layer-resize-to-image-size (vector-ref layerlist templayercount))
    (set! templayercount (+ templayercount 1))
)

(set! templayercount 1)
(if (> layercount 1)
    (while (< templayercount layercount)    ;offsets each layer by the appropiate height
        (set! lastlayerheight (+ lastlayerheight (car (vector-ref heightlist behindtlc))))
        (gimp-layer-set-offsets (vector-ref layerlist templayercount) 0 lastlayerheight)
        (set! templayercount (+ templayercount 1))
        (set! behindtlc (+ behindtlc 1))
    )
)

(gimp-undo-push-group-end imagevariable)
(gimp-displays-flush)

);paren let*
);paren define

    (script-fu-register
    "script-fu-panel-merger"
    "Merge Panels"
    "Merges panels of a comic vertically: \
    first arrange each panel as a layer,\
    with the first panel as the first layer,\
    and so on, before running the script."
    "Anon"
    "No restrictions on use/modfication."
    "March 29th, 2017"
    ""
    SF-IMAGE    "SF-IMAGE" 0
    )
    (script-fu-menu-register "script-fu-panel-merger" "<Image>/Image") ;puts "Merge Panels" under the Image menu in GIMP GUI