Gimp(3pm)

NAME

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

This is a release of gimp-perl for gimp-2.0. It is not compatible with version 1.2.x or below of The Gimp.

This is mostly a reference manual. For a quick intro, look at Gimp::Fu.

SYNOPSIS

use Gimp;
use Gimp::Fu;         # easy scripting environment

IMPORT TAGS

Place these in your "use Gimp qw(...)" command to have added features
available to your plug-in.

:auto
Import useful constants, like RGB, RUN_NONINTERACTIVE... as well as
all libgimp and pdb functions automagically into the caller's
namespace.  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 Gimp::Net.

:DEFAULT
The default set (see below).

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

GETTING STARTED

Gimp::Fu is recommended for scripts not requiring custom interfaces or speciailized execution. Lots of examples are in the "examples/"
directory of your gimp-perl source tree, or installed in your plug-ins directory if you are running from a package.

Using the "Xtns->DB Browser" is a good way to learn The GIMP's
Procedural Database(pdb). For referencing functions you already know
of, the included script gimpdoc is useful.

DESCRIPTION

Gimp-Perl is a module for writing plug-ins, extensions, standalone
scripts, and file-handlers for The GNU Image Manipulation Program (The GIMP). It can be used to automate repetitive tasks, acheive a
precision hard to get through manual use of The GIMP, interface to a
web server, or other tasks that involve Gimp.

It is developed on Linux, and should work with similar OSes.

Some hilights:

o Access to The GIMP's Procedural Database (pdb) for manipulation of: most objects.
o Use either a plain pdb (scheme-like) interface or an object-oriented: syntax, i.e. "gimp_image_new(600,300,RGB)" is the same as "new
Image(600,300,RGB)"
o Networked plug-ins look/behave the same as those running from within: gimp.
o Gimp::Fu will start The GIMP for you, if it cannot connect to an: existing GIMP process.
o You can access the pixel-data functions using piddles (see Gimp::PDL): giving the same level of control as a C plug-in, with a data language wrapper.
o Over 50 example scripts to give you a good starting point, or use as: is.

OUTLINE OF A GIMP PLUG-IN

All plug-ins (with the exception of those using "Gimp::init") 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, it will actually call "Gimp::Fu::main" instead of "Gimp::main":: exit main; # Gimp::Fu::main is exported by default when using Gimp::Fu
This is similar to Gtk, Tk or similar modules, where you have to call the main eventloop.
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.
CALLBACKS
The Gimp module provides routines to be optionally filled in by a plugin writer. This does not apply if using "Gimp::Fu", as these are done automatically.
Gimp::on_query: Do any activities that must be performed at Gimp startup, when the
procedure is queried. Should typically have at least one call to
gimp_install_procedure.
Gimp::on_net: Run when called from a network interface (from the Perl-Server or
from running it standalone).
Gimp::on_lib: Run only when called itneractively from within Gimp.
Gimp::on_run: Run when anything calls it (network or lib).

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 to change: "-" (dashes) to "_" (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 and hopefully clearer to read.

SPECIAL FUNCTIONS

In this section, you can find descriptions of special functions,
functions having different calling conventions/semantics than might be expected or otherwise 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 supported. Initializations can later be done in the init
function.
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.; This function has not been well tested.
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 (Gimp::Net), 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 Gimp::Net. Calling "Gimp::end" is optional.
This is used in the process of testing the module ('make test').
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 do nothing 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 call 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 function 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).
Gimp::canonicalize_colour/Gimp::canonicalize_color: Take in a color specifier in a variety of different formats, and
return a valid gimp color specifier, consisting of 3 or 4 numbers
in the range between 0 and 1.0.; For example:

$color = canonicalize_colour ("#ff00bb");
$color = canonicalize_colour ([255,255,34]);
$color = canonicalize_colour ([255,255,34,255]);
$color = canonicalize_colour ([1.0,1.0,0.32]);
$color = canonicalize_colour ('red');; Note that bounds checking is excessively lax; this assumes
relatively good input

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 from the C library. 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 Gimp::Pixel, 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. See Gimp::OO for details on using the object
oritented syntax. The 'gimpdoc' script will also return OO varients
when functions are described. For example:

gimpdoc image_new

has a section:

SOME SYNTAX ALTERNATIVES: image = Gimp->image_new (width,height,type)
image = new Image (width,height,type)
image = image_new Display (width,height,type)

DEBUGGING AIDS

How to debug your scripts:

Gimp::set_trace (tracemask): Tracking down bugs in gimp scripts is difficult, due to a lack of
reasonable error messages. Often, if anything goes wrong, you only get an execution failure.; You can switch on tracing to see which parameters are used to call pdb functions, so you can at least see what was called to cause the error.; 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 (default).
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 or 4 elements (i.e.
[0.1,0.4,0.9] or [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.

AUTHOR

Marc Lehmann <pcg@goof.com> (pre-2.0)

Seth Burgess <sjburge@gimp.org> (2.0+)

POD ERRORS

Hey! The above document had some coding errors, which are explained below:

Around line 680:: =cut found outside a pod block. Skipping to next block.

docs.sk

comprehensive documentation repository

In section

See also