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Il plugin filtro

We used a procedure plug-in for the First Step tutorial. Those types of plug-ins work without needing an image or drawable as input. Usually, we use a plug-in to change an image and its drawables. Plug-ins like these are called filter plug-ins.

Cos’è un Drawable?

A drawable in Lumi refers to an image element that can be drawn on, such as a layer or channel. Filter plug-ins typically operate on these elements.

Un semplice esempio di plug-in di filtro 

# !/usr/bin/env lumi-scheme-interpreter-0.1

(define (scheme-simple-filter-plug-in image drawables)
  ;; Use a let statement to define a message variable and core code
  (let ((message "hello, world"))
    ;; Display the message in Lumi's error console
    (lumi-message message)
    ;; Invert the colors of the first selected drawable
    (lumi-drawable-invert (vector-ref drawables 0) 1)))

;; Register the plug-in
(scheme-register-filter
  "scheme-simple-filter-plug-in"           ;; Main procedure name
  "Simple Filter Plug-in Demo"             ;; The name as it appears in the Lumi menu
  "Tests a basic Scheme filter plug-in"    ;; Tool-tip description
  "Author Name"                            ;; Give yourself some credit
  "License"                                ;; License
  "Date written"                           ;; Date written
  "*"                                      ;; Indicates this plug-in requires an image
  SF-ONE-OR-MORE-DRAWABLE)                 ;; Requires one or more selected drawables

;; Specify the menu location for the plug-in
(scheme-menu-register
  "scheme-simple-filter-plug-in"
  "<Image>/Plug-in")

Copy the text and save it as simple-filter-plug-in.scm in a folder called simple-filter-plug-in within one of Lumi’s plug-ins folders. A Lumi plug-ins folder is any folder listed under: Lumi > Edit > Preferences > Folders > Plug-ins

In Linux, right-click the simple-filter-plug-in.scm file, go to Properties > Permissions, and check Allow executing file as program. Una volta che il file è nel posto giusto, eseguibile e privo di errori di sintassi, al riavvio di Lumi apparirà nella barra di intestazione del menu in alto, all’interno di un menu chiamato Plug-in.

Esecuzione del plug-in

  1. Open an image (this filter plug-in requires an image to work).
  2. Open Tools > Debug > Message console to see a message.
  3. Select Simple Filter Plug-in Demo from the Plug-in menu.
  4. One of the selected layers will have its colors inverted and a message will be printed to the error console.

Modifica del plug-in

You can customize the plug-in by editing its .scm file. Ad esempio, per modificare il messaggio visualizzato:

  1. Open the file and locate the line defining message.
  2. Replace "hello, world" with your custom text.
  3. Salvare il file.

In Lumi version 3, plug-ins do not need refreshing for saved changes to take effect. Simply re-run the plug-in to see the updated message.

Esame dei plug-in

Shebang Line

The first line ensures the script works as a plug-in in Lumi 3:

# !/usr/bin/env lumi-scheme-interpreter-0.1

Definizione della procedura

The procedure accepts two arguments: the active image and the selected drawables.

(define (scheme-simple-filter-plug-in image drawables)

Logica fondamentale

A let statement defines a variable and performs operations on the drawable.

(let ((message "hello, world"))
  (lumi-message message) ;; Displays a message in Lumi's error console
  (lumi-drawable-invert (vector-ref drawables 0) 1)) ;; Inverts the colors of the first selected drawable

Registrazione del plug-in

The plug-in is registered with Lumi as a filter plug-in:

(scheme-register-filter
  "scheme-simple-filter-plug-in"           ;; Register the main procedure
  "Simple Filter Plug-in Demo"             ;; The name as it appears in the Lumi menu
  "Tests a basic Scheme filter plug-in"    ;; Tool-tip description
  "Author Name"                            ;; Author's name
  "License"                                ;; License type
  "Date written"                           ;; Date written
  "*"                                      ;; Indicates the plug-in requires an image
  SF-ONE-OR-MORE-DRAWABLE)                 ;; Requires one or more selected drawables

Registrazione nel menu

This line specifies the menu location for the plug-in:

(scheme-menu-register
  "scheme-simple-filter-plug-in"
  "<Image>/Plug-in")

Risoluzione dei problemi

If a plug-in does not appear, check its location, name, and executable property.

La posizione deve trovarsi in un percorso di ricerca del plug-in. The file name must match the name of the containing folder. Il file deve essere impostato come eseguibile.

The Message console is a valuable tool for troubleshooting custom plug-ins. If your plug-in doesn’t behave as expected, check here for error messages or logs. The Terminal window can also provide debugging information and report loading issues.

Avvolgimento