Troubles with guide position

[alvk]

Hello everyone!

I'm using gimp to make figures for my scientific papers. Often I need to place a guide in a certain position relative to a selected layer. I'm trying to write a pretty simple script, that do the job. However, I have a problem with it. I want to have a checkbox, with indicates whether the guide should be placed within the selected layer or not. But it doesn't work. Every time, the script return negative value for guide position. If I have a multilayer image, this means that the guide is placed outside the active layer, regardless of the state of the checkbox. If I have a single layer image, I get an error, that the guide is outside the image. Could anyone help me to solve this problem? The full script is below. Thank you!

Code:

(define (script-fu-custom-guide image
                        drawable
                        orientation
                        position
                        in_toggle)

 (let* (
        (lwidth (car (gimp-drawable-get-width image)))
        (lheight (car (gimp-drawable-get-height image)))

        (offx (car (gimp-drawable-get-offsets drawable)))
        (offy (cadr (gimp-drawable-get-offsets drawable)))

        (if (= in_toggle TRUE) (position (* -1 position)))

        (guide_position
          (cond ((= orientation 0) (- offx position)) ; guide on left
                ((= orientation 1) (+ offx lwidth position)) ; guide on right
                ((= orientation 2) (- offy position)) ; guide on top
                ((= orientation 3) (+ offy lheight position)) ; guide on bottom
                )
          )
        )

   (if (< 1 orientation)
     (gimp-image-add-hguide image guide_position)
     )
   (if (> 2 orientation)
     (gimp-image-add-vguide image guide_position)
     )
   (gimp-displays-flush)
   )
 )

(script-fu-register "script-fu-custom-guide"
 _"_Custom guide"
 _"Adds a vertical or horizontal guide to the image"
 ""
 ""
 ""
 "*"
 SF-IMAGE       "Input image"    0
 SF-DRAWABLE    "Input drawable" 0
 SF-OPTION _"_Orientation"         '(_"Left" _"Right" _"Top" _"Bottom")
 SF-ADJUSTMENT _"_Position"         (list 20 0 MAX-IMAGE-SIZE 1 10 0 1)
 SF-TOGGLE     _"Within a layer?"  FALSE
)

(script-fu-menu-register "script-fu-custom-guide"
                        "<Image>/Figures")