Gimp - Perl extension for writing Gimp Extensions/Plug-ins/Load & Save-Handlers
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...
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.
If you don't specify any import tags, Gimp assumes
qw/:consts main xlfd_size/ which is usually what you want.
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!
Import PARAM_* constants (PDB_INT32, PDB_STRING etc.) only.
All constants from gimpenums.h (BG_IMAGE_FILL, RUN_NONINTERACTIVE, NORMAL_MODE, PDB_INT32 etc.).
Set default spawn options to options, see Gimp::Net.
The default set (see below).
The default (unless '' is specified) is
'main', 'xlfd_size', ':consts', '__'. (
'__' is used for i18n purposes).
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
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...
noteworthy limitations (subject to be changed):
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.
Gimp::Fu-script, you should call
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
If you need to do cleanups before exiting you should use the
quit callback (which is not yet available if you use Gimp::Fu).
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
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.
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.
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.
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 ;)
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!):
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
You can drop the
Gimp:: when using the
:auto-import-tag. Very (very!) old perls may need:
(unfortunately. the plug-in in this example is actually called "plug_in_the_egg" *sigh*)
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 (
Should be called immediately when perl is initialized. Arguments are not yet supported. Initializations can later be done in the init function.
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;
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...).
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.
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.
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.
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)
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.
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).
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 (
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\"].
Initializes a progress bar. In networked modules this is a no-op.
Updates the progress bar. No-op in networked modules.
With these functions you can access the raw pixel data of drawables. They are documented in Gimp::Pixel, to keep this manual page short.
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.:
is replaced by
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.
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.
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).
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 Gimp::OO for details.
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:
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.
nothing is printed.
all pdb calls (and only pdb calls!) are printed with arguments and return values.
the parameter types are printed additionally.
the parameter names are printed.
the parameter descriptions.
all of the above.
set_trace returns the old tracemask.
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.
write trace to FILEHANDLE instead of STDERR.
Gimp supports different data types like colors, regions, strings. In perl, these are represented as:
normal perl scalars. Anything except STRING will be mapped to a perl-double.
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.
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).
these will be mapped to corresponding objects (IMAGE => Gimp::Image). In trace output you will see small integers (the image/layer/etc..-ID)
represented as an array ref [name, flags, data], where name and data should be perl strings and flags is the numerical flag value.
Not yet supported (and might never be).
Marc Lehmann <firstname.lastname@example.org>