Gimp(3)

NAME
Gimp - Perl extension for writing Gimp Extensions/Plug-ins/Load & Save-Handlers

This is mostly a reference manual. For a quick intro, look at the Gimp::Fu manpage. For more information, including tutorials, look at the Gimp-Perl pages at http://gimp.pages.de.

RATIONALE
Well, scheme (which is used by script-fu), is IMnsHO the crappiest language ever (well, the crappiest language that one actually can use, so it's not _that_ bad). Scheme has the worst of all languages, no data types, but still using variables. Look at haskell (http://www.haskell.org) to see how functional is done right.

Since I was unable to write a haskell interface (and perl is the traditional scripting language), I wrote a Perl interface instead. Not too bad a decision I believe...

SYNOPSIS
  use Gimp;
  Other modules of interest:
  use Gimp::Fu;         # easy scripting environment
  use Gimp::PDL;        # interface to the Perl Data Language
  these have their own manpage.

  IMPORT TAGS
If you don't specify any import tags, Gimp assumes "qw/:consts main xlfd_size/" which is usually what you want.

:auto
    Import useful constants, like RGB, RUN_NONINTERACTIVE... as well as all libgimp and pdb functions automagically into the caller's namespace. BEWARE! This will overwrite your AUTOLOAD function, if you have one!

:param
    Import PARAM_* constants (PDB_INT32, PDB_STRING etc.) only.

:consts
    All constants from gimpenums.h (BG_IMAGE_FILL, RUN_NONINTERACTIVE, NORMAL_MODE, PDB_INT32 etc.).

spawn_options=options
    Set default spawn options to options, see the Gimp::Net manpage.

:DEFAULT
    The default set (see below).

The default (unless '' is specified) is "'main', 'xlfd_size', ':consts', '__'". ("'__'" is used for i18n purposes).

GETTING STARTED
You should first read the Gimp::Fu manpage and then come back. This manpage is mainly intended for reference purposes.

Also, Dov Grobgeld has written an excellent tutorial for Gimp-Perl. You can find it at http://imagic.weizmann.ac.il/~dov/gimp/perl-tut.html

DESCRIPTION
I think you already know what this is about: writing Gimp plug-ins/extensions/scripts/file-handlers/standalone-scripts, just about everything you can imagine in perl. If you are missing functionality (look into TODO first), please feel free contact the author...

Some hilights:

• Networked plug-ins and plug-ins using the libgimp interfaces (i.e. to be started from within The Gimp) look almost the same (if you use the Gimp::Fu interface, there will be no visible differences at all), you can easily create hybrid (networked & libgimp) scripts as well.
• Use either a plain pdb (scheme-like) interface or nice object-oriented syntax, i.e. ""gimp_image_new(600,300,RGB)"" is the same as ""new Image(600,300,RGB)""
• Gimp::Fu will start The Gimp for you, if it cannot connect to an existing gimp process.
• You can optionally overwrite the pixel-data functions by versions using piddles (see the Gimp::PDL manpage)

noteworthy limitations (subject to be changed):

• callback procedures do not poass return values to The Gimp.

OUTLINE OF A GIMP PLUG-IN
All plug-ins (and extensions etc.) _must_ contain a call to "Gimp::main". The return code should be immediately handed out to exit:

 exit main;             # Gimp::main is exported by default.
Before the call to "Gimp::main", no other PDB function must be called.

In a "Gimp::Fu"-script, you should call "Gimp::Fu::main" instead:

 exit main;             # Gimp::Fu::main is exported by default as well.
This is similar to Gtk, Tk or similar modules, where you have to call the main eventloop. Attention: although you call "exit" with the result of "main", the main function might not actually return. This depends on both the version of Gimp and the version of the Gimp-Perl module that is in use. Do not depend on "main" to return at all, but still call "exit" immediately.

If you need to do cleanups before exiting you should use the "quit" callback (which is not yet available if you use Gimp::Fu).

CALLBACKS
THIS SECTION IS OUTDATED AND WILL BE REWORKED SOON. USE Gimp::Fu or READ THE SOURCE :(

If you use the plain Gimp module (as opposed to Gimp::Fu), your program should only call one function: "main". Everything else is going to be called from The Gimp at a later stage. For this to work, you should define certain call-backs in the same module you called "Gimp::main":

init (), query (), quit ()
    the standard libgimp callback functions. "run"() is missing, because this module will directly call the function you registered with "gimp_install_procedure". Some only make sense for extensions, some only for normal plug-ins.

<installed_procedure>()
    The callback for a registered function ("gimp_install_procedure" and friends). The arguments from The Gimp are passed as normal arguments (with the exception of arrays being passed without a preceding count).

    The return values from <installed_procedure>() are checked against the specification, with the exception that a single "undef" is treated like no arguments. you can return less, but not more results than specified.

    If you "die" within the callback, the error will be reported to The Gimp (as soon as The Gimp implements such a functionality) as an execution error.

net ()
    this is called when the plug-in is not started directly from within the Gimp, but instead from the Net-Server (the perl network server extension you hopefully have installed and started ;)

CALLING GIMP FUNCTIONS
There are two different flavours of gimp-functions. Functions from the PDB (the Procedural DataBase), and functions from libgimp (the C-language interface library).

You can get a listing and description of every PDB function by starting the DB Browser extension in the Gimp-Xtns menu (but remember that DB Browser is buggy and displays "_" (underscores) as "-" (dashes), so you can't see the difference between gimp_quit and gimp-quit. As a rule of thumb, Script-Fu in gimp versions before 1.2 registers scripts with dashes, and everything else uses underscores).

libgimp functions can't be traced (and won't be traceable in the foreseeable future).

To call pdb functions (or equivalent libgimp functions), just treat them like normal perl (this requires the use of the ":auto" import tag, but see below for another possibility!):

 gimp_palette_set_foreground([20,5,7]);
 gimp_palette_set_background("cornsilk");
If you don't use the ":auto" import tag, you can call all Gimp functions using OO-Syntax:

 Gimp->gimp_palette_set_foreground([20,5,7]);
 Gimp->palette_set_background("cornsilk");
 Palette->set_foreground('#1230f0');
As you can see, you can also drop part of the name prefixes with this syntax, so its actually shorter to write.

"But how do I call functions containing dashes?". Well, get your favourite perl book and learn perl! Anyway, newer perls understand a nice syntax (see also the description for "gimp_call_procedure"):

 "Gimp::plug-in-the-egg"->(RUN_INTERACTIVE,$image,$drawable);
You can drop the "Gimp::" when using the ":auto"-import-tag. Very (very!) old perls may need:

 &{"Gimp::plug-in-the-egg"}("Gimp",RUN_INTERACTIVE,$image,$drawable);
(unfortunately. the plug-in in this example is actually called "plug_in_the_egg" *sigh*)

SPECIAL FUNCTIONS
In this section, you can find descriptions of special functions, functions having different calling conventions/semantics than I would expect (I cannot speak for you), or just plain interesting functions. All of these functions must either be imported explicitly or called using a namespace override ("Gimp::"), not as Methods ("Gimp->").

main(), Gimp::main()
    Should be called immediately when perl is initialized. Arguments are not yet supported. Initializations can later be done in the init function.

xlfd_size(fontname)
    This auxillary functions parses the XLFD (usually obtained from a "PF_FONT" parameter) and returns its size and unit (e.g. "(20,POINTS)"). This can conviniently used in the gimp_text_..._fontname functions, which ignore the size (no joke ;). Example:

     $drawable->text_fontname (50, 50, "The quick", 5, 1, xlfd_size $font, $font;

Gimp::gtk_init()
    Initialize Gtk in a similar way the Gimp itself did it. This automatically parses gimp's gtkrc and sets a variety of default settings (visual, colormap, gamma, shared memory...).

Gimp::gtk_init_add { init statements ... };
    Add a callback function that should be called when gtk is being initialized (i.e. when Gimp::gtk_init is called, which should therefore be done even in Gnome applications).

    This is different to Gtk->init_add, which only gets called in Gtk->main, which is too late for registering types.

Gimp::init([connection-argument]), Gimp::end()
    These is an alternative interface that replaces the call to Gimp::main and the net callback. At the moment it only works for the Net interface (the Gimp::Net manpage), and not as a native plug-in. Here's an example:

     use Gimp;
     Gimp::init;
     <do something with the gimp>
    The optional argument to init has the same format as the GIMP_HOST variable described in the Gimp::Net manpage. Calling "Gimp::end" is optional.

Gimp::lock(), Gimp::unlock()
    These functions can be used to gain exclusive access to the Gimp. After calling lock, all accesses by other clients will be blocked and executed after the call to unlock. Calls to lock and unlock can be nested.

    Currently, these functions only lock the current Perl-Server instance against exclusive access, they are nops when used via the Gimp::Lib interface.

Gimp::set_rgb_db(filespec)
    Use the given rgb database instead of the default one. The format is the same as the one used by the X11 Consortiums rgb database (you might have a copy in /usr/lib/X11/rgb.txt). You can view the default database with "perldoc -m Gimp", at the end of the file (the default database is similar, but not identical to the X11 default rgb.txt)

Gimp::initialized()
    this function returns true whenever it is safe to clal gimp functions. This is usually only the case after gimp_main or gimp_init have been called.

Gimp::register_callback(gimp_function_name,perl_function)
    Using this fucntion you can overwrite the standard Gimp behaviour of calling a perl subroutine of the same name as the gimp function.

    The first argument is the name of a registered gimp function that you want to overwrite ('perl_fu_make_something'), and the second argument can be either a name of the corresponding perl sub ('Elsewhere::make_something') or a code reference (\&my_make).

SPECIAL METHODS
This chapter descibes methods that behave differently than you might expect, or methods uniquely implemented in perl (that is, not in the PDB). All of these must be invoked using the method syntax ("Gimp->" or "$object->").

gimp_install_procedure(name, blurb, help, author, copyright, date, menu_path, image_types, type, [params], [return_vals])
    Mostly same as gimp_install_procedure. The parameters and return values for the functions are specified as an array ref containing either integers or array-refs with three elements, [PARAM_TYPE, \"NAME\", \"DESCRIPTION\"].

gimp_progress_init(message,[])
    Initializes a progress bar. In networked modules this is a no-op.

gimp_progress_update(percentage)
    Updates the progress bar. No-op in networked modules.

gimp_tile_*, gimp_pixel_rgn_*, gimp_drawable_get
    With these functions you can access the raw pixel data of drawables. They are documented in the Gimp::Pixel manpage, to keep this manual page short.

gimp_call_procedure(procname, arguments...)
    This function is actually used to implement the fancy stuff. Its your basic interface to the PDB. Every function call is eventually done through his function, i.e.:

     gimp_image_new(args...);
    is replaced by

     gimp_call_procedure "gimp_image_new",args...;
    at runtime.

gimp_list_images, gimp_image_get_layers, gimp_image_get_channels
    These functions return what you would expect: an array of images, layers or channels. The reason why this is documented is that the usual way to return "PDB_INT32ARRAY"'s would be to return a reference to an array of integers, rather than blessed objects.

gimp_drawable_bounds drawable/gdrawable
    Returns an array (x,y,w,h) containing the upper left corner and the size of currently selected parts of the drawable, just as needed by PixelRgn->new and similar functions.

server_eval(string)
    This evaluates the given string in array context and returns the results. It's similar to "eval", but with two important differences: the evaluating always takes place on the server side/server machine (which might be the same as the local one) and compilation/runtime errors are reported as runtime errors (i.e. throwing an exception).

OBJECT ORIENTED SYNTAX
In this manual, only the plain syntax (that lesser languages like C use) is described. Actually, the recommended way to write gimp scripts is to use the fancy OO-like syntax you are used to in perl (version 5 at least ;). As a fact, OO-syntax saves soooo much typing as well. See the Gimp::OO manpage for details.

DEBUGGING AIDS
No, I can't tell you how to cure immune deficiencies (which might well be uncurable, as AIDS virii might be able to survive in brain cells, among other unreachable (for medication) parts of your body), but I can tell you how Gimp can help you debugging your scripts:

Gimp::set_trace (tracemask)
    Tracking down bugs in gimp scripts is difficult: no sensible error messages. If anything goes wrong, you only get an execution failure. Switch on tracing to see which parameters are used to call pdb functions.

    This function is never exported, so you have to qualify it when calling.

    tracemask is any number of the following flags or'ed together.

    TRACE_NONE
        nothing is printed.

    TRACE_CALL
        all pdb calls (and only pdb calls!) are printed with arguments and return values.

    TRACE_TYPE
        the parameter types are printed additionally.

    TRACE_NAME
        the parameter names are printed.

    TRACE_DESC
        the parameter descriptions.

    TRACE_ALL
        all of the above.

    "set_trace" returns the old tracemask.

Gimp::set_trace(\$tracevar)
    write trace into $tracevar instead of printing it to STDERR. $tracevar only contains the last command traces, i.e. it's cleared on every PDB invocation invocation.

Gimp::set_trace(*FILEHANDLE)
    write trace to FILEHANDLE instead of STDERR.

SUPPORTED GIMP DATA TYPES
Gimp supports different data types like colors, regions, strings. In perl, these are represented as:

INT32, INT16, INT8, FLOAT, STRING
    normal perl scalars. Anything except STRING will be mapped to a perl-double.

INT32ARRAY, INT16ARRAY, INT8ARRAY, FLOATARRAY, STRINGARRAY
    array refs containing scalars of the same type, i.e. [1, 2, 3, 4]. Gimp implicitly swallows or generates a preceeding integer argument because the preceding argument usually (this is a de-facto standard) contains the number of elements.

COLOR
    on input, either an array ref with 3 elements (i.e. [233,40,40]), a X11-like string ("#rrggbb") or a colour name ("papayawhip") (see set_rgb_db).

DISPLAY, IMAGE, LAYER, CHANNEL, DRAWABLE, SELECTION
    these will be mapped to corresponding objects (IMAGE => Gimp::Image). In trace output you will see small integers (the image/layer/etc..-ID)

PARASITE
    represented as an array ref [name, flags, data], where name and data should be perl strings and flags is the numerical flag value.

REGION, BOUNDARY, PATH, STATUS
    Not yet supported (and might never be).

AUTHOR
Marc Lehmann <pcg@goof.com>

SEE ALSO
perl(1), gimp(1), the Gimp::OO manpage, the Gimp::Data manpage, the Gimp::Pixel manpage, the Gimp::PDL manpage, the Gimp::Util manpage, the Gimp::UI manpage, the Gimp::Feature manpage, the Gimp::Net manpage, the Gimp::Compat manpage, the Gimp::Config manpage, the Gimp::Lib manpage, the Gimp::Module manpage, the scm2perl manpage and the scm2scm manpage.