Programming blog

So I ventured into Scheme today (or a variant of it anyway) and started learning how to create scripts to control the behavior of Gimp, the open source image editor. The script I created today takes an image, and creates 360 rotations of the image offset by 1 degree each and saves each of them in the current folder (I couldn't work out how to change folders in Script-fu, so oh well, you'll have to move the images elsewhere).

The myrotate function was actually created by David M. MacMillan but released under the GNU, as is this script.

; Define the image rotation function
;rotate the images in here and save them to the rotation directory
(define (myrotate rotatedegrees infile outfile)
   (let* ((image (car (file-png-load 1 infile infile)))
          (drawable (car (gimp-image-active-drawable image)))
          (rotateradians (* rotatedegrees (/ 3.14159 180)))
         )

         (gimp-drawable-transform-rotate-default drawable rotateradians 0 150 150 0 1)

         (file-png-save 1 image drawable outfile outfile 
              1 0 0 0 0 0 0 )
            ; 1 Adam7 interlacing?
            ;   0 deflate compression factor (0-9)
            ;     0 Write bKGD chunk?
            ;       0 Write gAMMA chunk?
            ;         0 Write oFFs chunk?
            ;           0 Write tIME chunk?    ?? backwards in DB Browser
            ;             0 Write pHYS chunk?  ?? backwards in DB Browser
   )
)
; Define the looping function
(define (rotate-img Infile) 
	; Define the initial value of the rotation
	(set! xx 0)
	; Loop through each value of xx from 0 to 360 and do the image rotation for it.
	(while (< xx 360)
	; set the name of the current outfile
                (set! sx (number->string xx))
		(set! outfile (string-append sx ".png"))
		(myrotate xx Infile outfile)
		; Increment xx
		(set! xx (+ xx 1))
	)
)
; Finally register our script with script-fu.
(script-fu-register "rotate-img"
                    "Rotate image"
                    "Rotates an image through each of 0 to 360 degrees and saves a copy in the subdirectory of rotations"
                    "David Wees<dweesdesign@gmail.com>"
                    "David Wees - released under the GNU"
                    "2007-06-11"
                    ""
		    SF-FILENAME "Infile" "infile.png"
)
(script-fu-menu-register "rotate-img" "<Toolbox>/Xtns/Script-Fu/Misc")

You need to save this to a file, call it rotate-img.scm and then place that file in your scripts folder of your Gimp installation. Hope it works for you!

Next post will be an application using files created with this script.