Final Thoughts

Introduction

What a journey! We started with a simple plug-in, hello-world.scm, and explored key programming concepts that help create powerful tools for GIMP, such as:

Functions: The building blocks of our plug-ins.
Refactoring: Improving code structure while maintaining functionality.
Code Libraries: Centralizing reusable functions to keep our code clean and modular.
Validation Techniques: Ensuring that inputs are valid before executing our core logic.

Along the way, you’ve likely also gained familiarity with Git, version control using GitHub, and setting up folder structures for repositories. These tools not only help with code organization but also allow you to maintain a clean, shareable workflow. This journey took me years to make, so take your time. Learning to write good plug-ins, like mastering any craft, is an ongoing process.

Here’s the final version of our main plug-in code:

#!/usr/bin/env gimp-script-fu-interpreter-3.0

(load "/home/your-name/code/path/to/repo/funky-library/messages.scm")

(define (script-fu-hello-world)
  (let ((message "Hello world!"))
    (send-message message 'status-bar)
    (send-message message 'dialog-box)
    (send-message message 'error-console)
    (send-message message 'terminal)))

(script-fu-register-procedure "script-fu-hello-world"
  "Hello world!"
  "A Script-Fu procedure plug-in example"
  "Mark Sweeney"
  "Under GNU GENERAL PUBLIC LICENSE Version 3"
  "2024")

(script-fu-menu-register
  "script-fu-hello-world"
  "<Image>/Funky")

Library code:

;; Purpose: Sends a message to the status bar, returns #t if successful
(define (send-to-status-bar message)
  (if (is-valid-string? message)
    (begin
      (gimp-message-set-handler MESSAGE-BOX)
      (gimp-message message)
      (gimp-message-set-handler ERROR-CONSOLE)
      #t)
    #f))

;; Purpose: Sends a message to the dialog box, returns #t if successful
(define (send-to-dialog-box message)
  (if (is-valid-string? message)
    (begin
      (gimp-message-set-handler MESSAGE-BOX)
      (gimp-message (string-append message "\n"))
      (gimp-message-set-handler ERROR-CONSOLE)
      #t)
    #f))

;; Purpose: Sends a message to the error console, returns #t if successful
(define (send-to-error-console message)
  (if (is-valid-string? message)
    (begin
      (gimp-message-set-handler ERROR-CONSOLE)
      (gimp-message message)
      #t)
    #f))

;; Purpose: Sends a message to the terminal, returns #t if successful
(define (send-to-terminal message)
  (if (is-valid-string? message)
    (begin
      (display message)
      (gimp-message-set-handler ERROR-CONSOLE)
      #t)
    #f))

;; Purpose: Dispatches a message to the appropriate output, returns #t if successful
(define (send-message message output)
  (if (is-valid-string-output? output)
    (cond
      ((eq? output 'error-console) (send-to-error-console message))
      ((eq? output 'dialog-box) (send-to-dialog-box message))
      ((eq? output 'status-bar) (send-to-status-bar message))
      ((eq? output 'terminal) (send-to-terminal message)))
    #f))

;; Purpose: Validates that the message is a non-empty string, returns #t if valid
(define (is-valid-string? message)
  (if (or (not (string? message)) (string=? message ""))
    (begin
      (error "Message must be a non-empty string")
      #f)
    #t))

;; Purpose: Validates that the output is a valid destination, returns #t if valid
(define (is-valid-string-output? output)
  (if (not (member output '(dialog-box status-bar error-console terminal)))
    (begin
      (error "Invalid output destination: " output)
      #f)
    #t))

Conclusion

By reworking our messaging library and refining the code step by step, we’ve created a system that is both robust and reusable. From simple message outputs to a fully structured library, the code now handles multiple outputs cleanly and with validation to ensure correctness. The core of our plug-in needs no comments, it is simply readable. It also has a custom set of debug messages, so that when our code fails, we can tell ourselves why.

(message "Hello world!")
(send-message message 'status-bar)
(send-message message 'dialog-box)
(send-message message 'error-console)
(send-message message 'terminal)

As you continue to build your own plug-ins, develop your own libraries or borrow from the ones I put on this site. Take your time, experiment with the code, and keep iterating—you’ll find that with each improvement, your coding skills and your understanding of the process will deepen.

Good luck on your journey!

hello-world.zip
funky-library.zip

Return Values