Script-Fu & Scheme

Scheme

a variant on LISP.

processes LISTS

each list is a function with it's arguments

evaluate functions to return values

 
(+ 3 4) => 7

 
(* 7 6) => 42

 
(+

 
  (* 3 4)

 
  (/ 1 3)) => 4

 
(define (borne x)

 
	(cond ((< x 0) 0)

 
	      ((> x 255) 255)

 
       (T x)))

 
(borne 278) => 255

 
(borne -12) => 0

 
(borne 236) => 236

Literals

Quoted values:

 
	'this

 
	'(255 127 63)

 
	(* '5 '5)

 
	(borne '235)

Variables

 
(set! orange '(255 277 0))

 
(gimp-set-background-color orange)

 
(gimp-set-background-color 'orange)

 
(gimp-set-background-color '(255 127 0))

Local variables(*)

 
(let* ((a 3)

 
       (b 4)

 
       (

 
        (/ a b)

 
        )

 
       )

 
      )

 
)

List Processing

Lists are made up of

a first element (head) -- possibly a list

the rest of the list (tail) -- always a list

 
(1 2 3) = (1 (2 (3 ())))

 
() 

The empty list () is a list!

(car '(1 2 3)) => 1

(car '((a b) 2 3)) = > (a b)

(cdr '(1 2 3)) => (2 3)

More list processing

 
(cdr (cdr '(1 2 3 4))) => (3 4)

 
(cddr '(1 2 3 4)) => (3 4)

 
(car (cdr (cdr '(1 2 3 4)))) => 3

 
(caddr '(1 2 3 4)) => 3

 
(cadr (quote (1 2 3 4))) => 2

NOTE: ALL GIMP FUNCTIONS RETURN LISTS

Loops

 
The only looping construct that exists in Script-Fu is while 

 
[Note: this constraint is due to the current scheme interpreter SIOD used for Script-Fu. Once the scheme interpreter as planned is changed to Guile,

 
more looping constructs will probably be added.] The while loop looks as follows: 

 
(while       (condition)

 
      (statement1)

 
      (statement2)

 
      :

)

Registering functions with Script-Fu

Places script in interface menu

registers parameter types and default values

places command in PDB

 
(script-fu-register

 
 "my-func"	         ; name of func

 
 "Xtns/Script-Fu/My/Func" ; menu posn.

 
 "Does something"  ; help string

 
 "I. Am"           ; author

 
 "It's mine"       ; copyright

 
 "Today"           ; date

 
 ""                ;accepts any image type

 
 SF-VALUE "a" "0"  ; value param

 
 SF-COLOR "bk" '(0 0 0) ; color param

 
 SF-TOGGLE "inv" 0      ; boolean

 
)

Defining Script-Fu functions

 
(define (my-func a bk inv)

 
	 ; create image and layer

 
	 (set! img 

 
        (car (gimp-image-new a a RGB)))

 
  (set! layer

 
        (car (gimp-layer-new img a a

 
              RGB "layer 1" 100 NORMAL)))

 
  (gimp-image-disable-undo img)

 
  (gimp-image-add-layer img layer 0)

 
  (cond ((equalp inv 0)

 
         (gimp-palette-set-background bk))

 
	       (T

 
         (gimp-palette-set-background

 
          (invert bk))))

 
  (gimp-edit-fill img layer)

 
  (gimp-display-new img)

 
  (gimp-image-enable-undo img))

Working on current image

 
(script-fu-register "doit"

 
 "<Image>/Script-Fu/Me/doit"

 
 "Do something"

 
 "Me" "Mime" "today"

 
 "RGB*, GRAY*"

 
 SF-IMAGE "Image" 0

 
 SF-DRAWABLE "Layer" 0

 
 SF-VALUE "with" 5)

 
(define (doit img layer with)...)

Exemple1.

 
The following script uni.scm receives two parameters from the user, the size of the image, and a color and goes on to produce a uniform image of the requested size and the requested color. Not very useful, but it shows the essential steps in producing a script-fu script. (";" is a mark that the following is a comment)

 
; Define the function of the script and ;list its parameters

 
; The parameters will be matched with the ;parameters listed

 
; below in script-fu-register.

 
(define (uni-img size color)

 
   ; Create an img and a layer

 
   (set! img (car (gimp-image-new size size RGB)))

 
   (set! layer (car (gimp-layer-new img size size RGB "layer 1" 100 NORMAL)))

 
   ; The following is done for all scripts

 
   (gimp-image-disable-undo img)

 
   (gimp-image-add-layer img layer 0)

 
   ; Here is where the painting starts. We ;now have an image

 
   ; and layer and may paint in the layer ;through the PDB functions

 
   (gimp-palette-set-background color)

 
   (gimp-edit-fill img layer)

 
   ; The following is also done for all ;script

 
   (gimp-display-new img)

 
   (gimp-image-enable-undo img))

 
   ; Finally register our script with ;script-fu. 

 
   (script-fu-register "uni-img" 

 
      "<toolbox>/Xtns/Script-Fu/Tutorials/Uniform image"

 
      "Creates a uniform image"

 
      "Dov Grobgeld"

 
      "Dov Grobgeld"

 
      "1997"

 
      "" 

 
      SF-VALUE "size" "100"

 
      SF-COLOR "color" '(255 127 0))

Exemple2.

 
	Here is an example script which copies the current layer to a new layer, blurs it and inverts it. 

 
(define (script-fu-copy-blur                img drawable  blur-radius)

 
    ; Create a new layer

 
   (set! new-layer (car (gimp-layer-copy drawable 0)))

 
   ; Give it a name

 
   (gimp-layer-set-name new-layer "Gauss-blurred")

 
   ; Add the new layer to the image

 
   (gimp-image-add-layer img new-layer 0)

 
   ; Call a plugin to blur the image

 
   (plug-in-gauss-rle 1 img new-layer blur-radius 1 1)

 
   ; Invert the new layer

 
   (gimp-invert img new-layer)

 
   ; Flush the display 

 
   (gimp-displays-flush)   

 
)

 
(script-fu-register "script-fu-copy-blur"

 
      "<Image>/Script-Fu/Tutorial/copy-blur"

 
      "Copy and blur a layer"

 
      "Dov Grobgeld"

 
      "Dov Grobgeld"

 
      "1998"

 
      "RGB*, GRAY*"

 
      SF-IMAGE "Image" 0

 
      SF-DRAWABLE "Layer to blur" 0

 
      SF-VALUE "Blur strength" "5")

Exemple3.

 
Here's an example which draws horizontal lines, 16 pixels high, on an image: 

 
(set! y 0)

 
(while (< y size)

 
      (gimp-rect-select img 0 y size 16 REPLACE 0 0)

 
      (gimp-edit-fill img layer-one)

 
      (set! y (+ y 32)))

Exemple4.

 
Hereis an exemple to write a text in an image.

 
(define (script-fu-hello-world img drawable)

 
   ; Start an undo group. Everything between the start and the end 

 
   ; will be carried out if an undo command is issued.

 
   (gimp-undo-push-group-start img)

 
   ; Create the text. See DBbrowser for parameters of gimp-text.

 
   (set! text-float (car (gimp-text

 
            img

 
            drawable

 
            10 10

 
            "Hello world"

 
            0

 
            1

 
            30

 
            1

 
            "*" "Helvetica" "medium" "r" "*" "*")))

 
   ; Anchor the selection

 
   (gimp-floating-sel-anchor text-float)

 
   ; Complete the undo group

 
   (gimp-undo-push-group-end img)

 
   ; Flush output

 
   (gimp-displays-flush))

 
(script-fu-register "script-fu-hello-world"

 
      "<Image>/Script-Fu/Tutorial/Hello World"

 
      "Write Hello World in the current image"

 
      "Dov Grobgeld"

 
      "Dov Grobgeld"

 
      "1998"

 
      "RGB*, GRAY*"

 
      SF-IMAGE "Image" 0

 
      SF-DRAWABLE "Layer" 0)

Exemple5.

 
Copying a selection

 
To copy a selection, the command gimp-edit-copy is used. It places a copy of the selection contents in the cut-buffer. The contents of the

 
cut-buffer may then be pasted into a layer, the same layer or another one, and it is then pasted as a floating layer. 

 
In the following example the selection is copied, pasted into the same layer, offset a fixed distance, finally anchored. Try it by drawing a small blob in the

 
middle of the image, select the blob, and then call this script. 

 
(define (script-fu-sel-copy img

 
                            drawable)

 
   (gimp-undo-push-group-start img)

 
   (gimp-edit-copy img drawable)

 
   (set! sel-float (car (gimp-edit-paste img drawable FALSE)))

 
   (gimp-layer-set-offsets sel-float 100 50)

 
   ; Anchor the selection

 
   (gimp-floating-sel-anchor sel-float)

 
   ; Complete the undo group

 
   (gimp-undo-push-group-end img)

 
   ; Flush output

 
   (gimp-displays-flush))

 
(script-fu-register "script-fu-sel-copy"

 
      "<Image>/Script-Fu/Tutorial/Selection Copy"

 
      "Copy the selection into the same layer"

 
      "Dov Grobgeld"

 
      "Dov Grobgeld"

 
      "1998"

 
      "RGB*, GRAY*"

 
      SF-IMAGE "Image" 0

 
      SF-DRAWABLE "Layer" 0)