I’ve implemented a small turtle script to perform simple drawings via usual turtle commands. How it looks:
How to draw?
To draw something with turtle, you should create a TinyScheme file somewhere containing a turtle-configuration variable like this:
(define turtle-configuration '(
(down)
(red)
(forward 30)
(left 90)
(green)
(forward 30)
(left 90)
(blue)
(forward 30)
(left 90)
(yellow)
(forward 30)
))
Then, this file should be chosen in the script UI available in File > Create menu. The code mentioned above draws a colorful square:
Source code
(define turtle-movement-commands '(forward backward))
(define turtle-rotation-commands '(left right))
(define turtle-color-commands '(black red green yellow blue magenta cyan gray))
(define turtle-pen-commands '(up down))
(define turtle-all-commands (append turtle-movement-commands
turtle-rotation-commands
turtle-color-commands
turtle-pen-commands))
(define (turtle-sequence-to-string-internal sequence delimiter)
(cond
((null? sequence) "")
((null? (cdr sequence)) (car sequence))
(else (string-append (car sequence) delimiter
(turtle-sequence-to-string-internal (cdr sequence) delimiter)))
)
)
(define (turtle-sequence-to-string sequence delimiter)
(string-append "(" (turtle-sequence-to-string-internal sequence delimiter)
")")
)
(define (turtle-to-string-with-delimiter value delimiter)
(cond
((number? value) (number->string value))
((symbol? value) (symbol->string value))
((char? value) (string-append "character with " (number->string
(char->integer value)) " code"))
((equal? value #t) "true")
((equal? value #f) "false")
((list? value) (turtle-sequence-to-string (map (lambda (value)
(turtle-to-string-with-delimiter value delimiter)) value) delimiter))
((vector? value) "{{vector}}")
(else value)
)
)
(define (turtle-to-string value)
(turtle-to-string-with-delimiter value ", ")
)
(define (turtle-make-error type source actual expected)
(string-append
"invalid " (turtle-to-string type)
" for " (turtle-to-string source)
" (expected: " (turtle-to-string expected)
", got: " (turtle-to-string actual) ")")
)
(define (member? value list)
(cond
((null? list) #f)
((equal? value (car list)) #t)
(else (member? value (cdr list)))
)
)
(define (all? predicate list)
(cond
((null? list) #t)
(else (and (predicate (car list)) (all? predicate (cdr list))))
)
)
(define (turtle-is-movement-command command)
(if (list? command)
(member? (car command) turtle-movement-commands)
#f)
)
(define (turtle-is-rotation-command command)
(if (list? command)
(member? (car command) turtle-rotation-commands)
#f)
)
(define (turtle-is-color-command command)
(if (list? command)
(member? (car command) turtle-color-commands)
#f)
)
(define (turtle-is-pen-command command)
(if (list? command)
(member? (car command) turtle-pen-commands)
#f)
)
(define (turtle-is-command command)
(if (list? command)
(member? (car command) turtle-all-commands)
#f)
)
(define (turtle-is-not-movement-command command)
(not (turtle-is-movement-command command))
)
(define (turtle-is-not-rotation-command command)
(not (turtle-is-rotation-command command))
)
(define (turtle-is-not-color-command command)
(not (turtle-is-color-command command))
)
(define (turtle-is-not-pen-command command)
(not (turtle-is-pen-command command))
)
(define (turtle-is-not-command command)
(not (turtle-is-command command))
)
(define (turtle-has-argument command)
(if (list? command)
(not (null? (cdr command)))
#f)
)
(define (turtle-has-no-argument command)
(not (turtle-has-argument command))
)
(define (turtle-argument command)
(cadr command)
)
(define (turtle-is-expected-command actual expected)
(if (list? actual)
(equal? (car actual) expected)
#f)
)
(define (turtle-validate-configuration configuration)
(cond
((not (list? configuration)) (list (turtle-make-error "type"
"configuration" configuration "{{list}}")))
(else (map (lambda (command)
(let* ((command-string (turtle-to-string-with-delimiter command " ")))
(cond
((null? command) (turtle-make-error "type" "configuration[...]"
"nothing" "{{list}}"))
((not (list? command)) (turtle-make-error "type"
"configuration[...]" command-string "{{list}}"))
((turtle-is-not-command command) (turtle-make-error "type"
"configuration[...]" command-string (string-append "one of "
(turtle-to-string-with-delimiter turtle-all-commands " | "))))
((and (or (turtle-is-color-command command)
(turtle-is-pen-command command)) (turtle-has-argument
command)) (turtle-make-error "argument" "configuration[...]"
command-string (string-append "no argument for "
(turtle-to-string-with-delimiter (append
turtle-color-commands turtle-pen-commands) " | "))))
((and (or (turtle-is-movement-command command)
(turtle-is-rotation-command command))
(turtle-has-no-argument command)) (turtle-make-error
"argument" "configuration[...]" command-string (string-append
"argument for " (turtle-to-string-with-delimiter (append
turtle-movement-commands turtle-rotation-commands) " | "))))
((and (or (turtle-is-movement-command command)
(turtle-is-rotation-command command))
(turtle-has-no-argument command)) (turtle-make-error
"argument" "configuration[...]" command-string
(string-append "argument for "
(turtle-to-string-with-delimiter (append
turtle-movement-commands turtle-rotation-commands) " | "))))
((and (or (turtle-is-movement-command command)
(turtle-is-rotation-command command)) (not (integer?
(turtle-argument command)))) (turtle-make-error "argument"
"configuration[...]" command-string (string-append
"integer argument for " (turtle-to-string-with-delimiter
(append turtle-movement-commands turtle-rotation-commands)
" | "))))
(else #t)
)
)) configuration))
)
)
(define (turtle-is-valid-configuration configuration)
(all? boolean? (turtle-validate-configuration configuration))
)
(define (turtle-color-to-rgb color)
(cond
((equal? 'black color) '(0 0 0))
((equal? 'red color) '(255 0 0))
((equal? 'green color) '(0 255 0))
((equal? 'yellow color) '(255 255 0))
((equal? 'blue color) '(0 0 255))
((equal? 'magenta color) '(255 0 138))
((equal? 'cyan color) '(2 247 243))
((equal? 'gray color) '(143 143 143))
(else #f)
)
)
(define (turtle-degrees-to-radians-internal degrees)
(* degrees (/ 3.1415926535897 180))
)
(define (turtle-point-to-string x y)
(string-append "(" (turtle-to-string x) ", " (turtle-to-string y) ")")
)
(define (turtle-draw configuration-path x y color pen-state angle line-width image-width image-height)
(load configuration-path)
(set! color (nth color turtle-color-commands))
(set! pen-state (nth pen-state turtle-pen-commands))
(cond
((and (integer? x)
(integer? y)
(member? color turtle-color-commands)
(member? pen-state turtle-pen-commands)
(turtle-is-valid-configuration turtle-configuration))
(let*
(
(image (car (gimp-image-new image-width image-height
RGB)))
(layer (car (gimp-layer-new image image-width
image-height RGB-IMAGE "drawing" 100 NORMAL-MODE)))
)
(gimp-image-insert-layer image layer 0 0)
(gimp-context-set-brush-size line-width)
(gimp-drawable-fill layer WHITE-FILL)
(map (lambda (command)
(cond
((turtle-is-expected-command command 'down)
(set! pen-state 'down)
(print "✏️ Pen is put down"))
((turtle-is-expected-command command 'up)
(set! pen-state 'up)
(print "✏️ Pen is up"))
((turtle-is-color-command command)
(gimp-context-set-foreground (turtle-color-to-rgb (car command)))
(print (string-append "🎨️ Color is set to " (symbol->string (car command)))))
((turtle-is-expected-command command 'left)
(set! angle (- angle (turtle-argument command)))
(print (string-append "↪️ Turned to the left at " (number->string (turtle-argument command)) " degrees")))
((turtle-is-expected-command command 'right)
(set! angle (+ angle (turtle-argument command)))
(print (string-append "↪️ Turned to the right at " (number->string (turtle-argument command)) " degrees")))
((turtle-is-expected-command command 'forward)
(if (equal? pen-state 'down)
(let*
(
(new-x (+ x (* (cos (turtle-degrees-to-radians-internal angle)) (turtle-argument command))))
(new-y (+ y (* (sin (turtle-degrees-to-radians-internal angle)) (turtle-argument command))))
(points (cons-array 4 'double))
)
(aset points 0 x)
(aset points 1 y)
(aset points 2 new-x)
(aset points 3 new-y)
(gimp-pencil layer 4 points)
(print (string-append "📝️ Drew a line from " (turtle-point-to-string x y) " to " (turtle-point-to-string new-x new-y)))
(set! x new-x)
(set! y new-y)
)
(print "❌️✏️ Can't draw, pen is up")
)
)
((turtle-is-expected-command command 'backward)
(if (equal? pen-state 'down)
(let*
(
(new-x (- x (* (cos (turtle-degrees-to-radians-internal angle)) (turtle-argument command))))
(new-y (- y (* (sin (turtle-degrees-to-radians-internal angle)) (turtle-argument command))))
(points (cons-array 4 'double))
)
(aset points 0 x)
(aset points 1 y)
(aset points 2 new-x)
(aset points 3 new-y)
(gimp-pencil layer 4 points)
(print (string-append "📝️ Drew a line from " (turtle-point-to-string x y) " to " (turtle-point-to-string new-x new-y)))
(set! x new-x)
(set! y new-y)
)
(print "❌️✏️ Can't draw, pen is up")
)
)
)
) turtle-configuration)
(gimp-display-new image)
)
#t)
(else #f)
)
)
(script-fu-register
"turtle-draw"
"Turtle draw"
(string-append "Creates a simple drawing with a turtle commands.\
\
Available commands: " (turtle-to-string turtle-all-commands) ".\
- " (turtle-to-string turtle-movement-commands) " require a single argument denoting amount of pixels to move the turtle on.\
- " (turtle-to-string turtle-rotation-commands) " require a single argument denoting amount of degrees to rotate the turtle at.\
- Other commands don't require any argument.\
\
All commands should be put in a list like this: '((red) (forward 30) (left 90) (forward 30))"
)
"Maisa Unbelievable"
"copyright 2024, Maisa Unbelievable"
"June 17, 2024"
"" ;image type that the script works on
SF-FILENAME "Path to a file with a 'turtle-configuration' variable with turtle commands" "/home/USER/.config/GIMP/2.10/scripts/NAME.scm"
SF-ADJUSTMENT "Initial X coordinate" '(0 0 1000 1 5 0 SF-SPINNER)
SF-ADJUSTMENT "Initial Y coordinate" '(0 0 1000 1 5 0 SF-SPINNER)
SF-OPTION "Initial color" (map symbol->string turtle-color-commands)
SF-OPTION "Initial pen state" (map symbol->string turtle-pen-commands)
SF-ADJUSTMENT "Initial rotation angle" '(0 0 360 1 5 0 SF-SPINNER)
SF-ADJUSTMENT "Line width" '(2 0 10 1 5 0 SF-SPINNER)
SF-ADJUSTMENT "Image width" '(100 0 1000 1 5 0 SF-SPINNER)
SF-ADJUSTMENT "Image height" '(100 0 1000 1 5 0 SF-SPINNER)
)
(script-fu-menu-register "turtle-draw" "<Image>/File/Create")
Suggestions how to better organize code and format it are welcome (this is my first GIMP script 
).
