The Structure Of A Plug-in

The majority of code in this package resides in gimpmodule.c , but this provides a poor interface for implementing some portions of a plugin. For this reason, there is a python module called plugin.py that sets out a structure for plug-ins and implements some things that were either too difficult or impossible to do in C.

The main purpose of plugin.py was to implement an object oriented structure for plug-ins. As well as this, it handles tracebacks, which are otherwise ignored by libgimp , and gives a method to call other GIMP-Python plug-ins without going through the procedural database.
An Example Plugin

As in a lot of manuals, the first thing you examine is an example, so here is an example. I have included it before explaining what it does to allow more advanced programmers to see the structure up front. It is a translation of the clothify Script-Fu extension:

#!/usr/bin/env python


import math
from gimpfu import *

def python_clothify(timg, tdrawable, bx=9, by=9,
azimuth=135, elevation=45, depth=3):
width = tdrawable.width
height = tdrawable.height

img = gimp.Image(width, height, RGB)
img.disable_undo()

layer_one = gimp.Layer(img, "X Dots", width, height, RGB_IMAGE,
100, NORMAL_MODE)
img.add_layer(layer_one, 0)
pdb.gimp_edit_fill(layer_one, BACKGROUND_FILL)

pdb.plug_in_noisify(img, layer_one, 0, 0.7, 0.7, 0.7, 0.7)

layer_two = layer_one.copy()
layer_two.mode = MULTIPLY_MODE
layer_two.name = "Y Dots"
img.add_layer(layer_two, 0)

pdb.plug_in_gauss_rle(img, layer_one, bx, 1, 0)
pdb.plug_in_gauss_rle(img, layer_two, by, 0, 1)

img.flatten()

bump_layer = img.active_layer

pdb.plug_in_c_astretch(img, bump_layer)
pdb.plug_in_noisify(img, bump_layer, 0, 0.2, 0.2, 0.2, 0.2)
pdb.plug_in_bump_map(img, tdrawable, bump_layer, azimuth,
elevation, depth, 0, 0, 0, 0, True, False, 0)

gimp.delete(img)

register(
"python_fu_clothify",
"Make the specified layer look like it is printed on cloth",
"Make the specified layer look like it is printed on cloth",
"James Henstridge",
"James Henstridge",
"1997-1999",
"<Image>/Filters/Artistic/_Clothify...",
"RGB*, GRAY*",
[
(PF_INT, "x_blur", "X blur", 9),
(PF_INT, "y_blur", "Y blur", 9),
(PF_INT, "azimuth", "Azimuth", 135),
(PF_INT, "elevation", "Elevation", 45),
(PF_INT, "depth", "Depth", 3)
],
[],
python_clothify)

main()

Import Modules

In this plugin, a number of modules are imported. The important ones are:

gimpfu : this module provides a simple interface for writing plug-ins, similar to what script-fu provides. It provides the GUI for entering in parameters in interactive mode and performs some sanity checks when registering the plugin.

By using "from gimpfu import *", this module also provides an easy way to get all the commonly used symbols into the plug-in's namespace.

gimp : the main part of the gimp extension. This is imported with gimpfu.

gimpenums : a number of useful constants. This is also automatically imported with gimpfu.

The pdb variable is a variable for accessing the procedural database. It is imported into the plug-in's namespace with gimpfu for convenience.
Plugin Framework

With pygimp-0.4, the gimpfu module was introduced. It simplifies writing plug-ins a lot. It handles the run mode (interactive, non interactive or run with last values), providing a GUI for interactive mode and saving the last used settings.

Using the gimpfu plugin, all you need to do is write the function that should be run, make a call to register, and finally a call to main to get the plugin started.

If the plugin is to be run on an image, the first parameter to the plugin function should be the image, and the second should be the current drawable (do not worry about the run_mode parameter). Plug-ins that do not act on an existing image (and hence go in the toolbox's menus) do not need these parameters. Any other parameters are specific to the plugin.

After defining the plugin function, you need to call register to register the plugin with gimp (When the plugin is run to query it, this information is passed to gimp. When it is run interactively, this information is used to construct the GUI). The parameters to register are:

name

blurb

help

author

copyright

date

menupath

imagetypes

params

results

function

Most of these parameters are quite self explanatory. The menupath option should start with <Image>;/ for image plug-ins and <Toolbox>/ for toolbox plug-ins. The remainder of the menupath is a slash separated path to its menu item.

The params parameter holds a list parameters for the function. It is a list of tuples. Note that you do not have to specify the run_type, image or drawable parameters, as gimpfu will add these automatically for you. The tuple format is (type, name, description, default [, extra]). The allowed type codes are:

PF_INT8

PF_INT16

PF_INT32

PF_INT

PF_FLOAT

PF_STRING

PF_VALUE

PF_COLOR

PF_COLOUR

PF_REGION

PF_IMAGE

PF_LAYER

PF_CHANNEL

PF_DRAWABLE

PF_TOGGLE

PF_BOOL

PF_RADIO

PF_SLIDER

PF_SPINNER

PF_ADJUSTMENT

PF_FONT

PF_FILE

PF_BRUSH

PF_PATTERN

PF_GRADIENT

PF_PALETTE

These values map onto the standard PARAM_* constants. The reason to use the extra constants is that they give gimpfu more information, so it can produce a better interface (for instance, the PF_FONT type is equivalent to PARAM_STRING, but in the GUI you get a small button that will bring up a font selection dialog).

The PF_SLIDER, PF_SPINNER and PF_ADJUSTMENT types require the extra parameter. It is of the form (min, max, step), and gives the limits for the spin button or slider.

The results parameter is a list of 3-tuples of the form (type, name, description). It defines the return values for the function. If there is only a single return value, the plugin function should return just that value. If there is more than one, the plugin function should return a tuple of results.

The final parameter to register is the plugin function itself.

After registering one or more plugin functions, you must call the main function. This will cause the plugin to start running. A GUI will be displayed when needed, and your plugin function will be called at the appropriate times.
The Procedural Database

The procedural database is a registry of things gimp and its plug-ins can do. When you install a procedure for your plugin, you are extending the procedural database.

The procedural database is self documenting, in that when you install a procedure in it, you also add documentation for it, its parameters and return values.
The Gimp-Python Model

In Gimp-Python, the procedural database is represented by the object gimp.pdb. In most of my plug-ins, I make an assignment from gimp.pdb to pdb for convenience.

You can query the procedural database with pdb's method query. Its specification is:

pdb.query(name, [blurb, [help, [author, [copyright, [date, [type]]]]]])

Each parameter is a regular expression that is checked against the corresponding field in the procedural database. The method returns a list of the names of matching procedures. If query is called without any arguments, it will return every procedure in the database.
Procedural Database Procedures

Procedures can be accessed as procedures, or by treating pdb as a mapping object. As an example, the procedure gimp_edit_fill can be accessed as either pdb.gimp_edit_fill or pdb['gimp_edit_fill']. The second form is mainly for procedures whose names are not valid Python names (eg in script-fu-…, the dashes are interpreted as minuses).

These procedure objects have a number of attribute:

proc_name

The name of the procedure.
proc_blurb

A short piece of information about the procedure.
proc_help

More detailed information about the procedure.
proc_author

The author of the procedure.
proc_copyright

The copyright holder for the procedure (usually the same as the author).
proc_date

The date when the procedure was written.
proc_type

The type of procedure. This will be one of PROC_PLUG_IN, PROC_EXTENSION or PROC_TEMPORARY.
nparams

The number of parameters the procedure takes.
nreturn_vals

The number of return values the procedure gives.
params

A description of parameters of the procedure. It takes the form of a tuple of 3-tuples, where each 3-tuple describes a parameter. The items in the 3-tuple are a parameter type (one of the PARAM_* constants), a name for the parameter, and a description of the parameter.
return_vals

A description of the return values. It takes the same form as the params attribute.

A procedure object may also be called. At this point, Gimp-Python doesn't support keyword arguments for PDB procedures. Arguments are passed to the procedure in the normal method. The return depends on the number of return values:

If there are zero return values, None is returned.

If there is only a single return value, it is returned.

If there are more return values, then they are returned as a tuple.

More Information

For more information on invoking PDB procedures, please see the example plug-ins. For information on individual procedures, please see the PDB Browser plugin (in the Xtns menu). It allows you to peruse to the database interactively.
GIMP Module Procedures

The gimp module contains a number of procedures and functions, as well as the definitions of many gimp types such as images, and the procedural database. This section explains the base level procedures.
Constructors and Object Deletion

There are a number of functions in the gimp module that are used to create the objects used to make up an image in GIMP. Here is a set of descriptions of these constructors:

gimp.Image(width, height, type)

This procedure creates an image with the given dimensions and type (type is one of RGB , GRAY or INDEXED ).
gimp.Layer(img, name, width, height, type, opacity, mode)

Create a new layer called name, with the given dimensions and type (one of the *_IMAGE constants), opacity (float between 0 and 100) and a mode (one of the *_MODE constants). The layer can then be added to the image with the img.add_layer method.
gimp.Channel(img, name, width, height, opacity, colour)

Create a new channel object with the given dimensions, opacity and colour (one of the *_CHANNEL constants). This channel can then be added to an image.
gimp.Display(img)

Create a new display window for the given image. The window will not be displayed until a call to gimp.displays_flush is made.
gimp.Parasite(name, flags, data)

Create a new parasite. The parasite can then be attached to gimp, an image or a drawable. This is only available in gimp >= 1.1

When any of these objects get removed from memory (such as when their name goes out of range), the gimp thing it represents does not get deleted with it (otherwise when your plugin finished running, it would delete all its work). In order to delete the thing the Python object represents, you should use the gimp.delete procedure. It deletes the gimp thing associated with the Python object given as a parameter. If the object is not an image, layer, channel, drawable or display gimp.delete does nothing.
Configuration Information

There are a number of functions that can be used to gather information about the environment the plugin is running in:

gimp.color_cube() or gimp.colour_cube()

Returns the current colour cube.
gimp.gamma()

Returns the current gamma correction.
gimp.install_cmap()

Returns non-zero if a colour map has been installed.
gimp.use_xshm()

Returns non-zero if GIMP is using X shared memory.
gimp.gtkrc()

Returns the file name of the GTK configuration file.

Palette Operations

These functions alter the currently selected foreground and background.

gimp.get_background()

Returns a 3-tuple containing the current background colour in RGB form.
gimp.get_foreground()

Returns a 3-tuple containing the current foreground colour in RGB form.
gimp.set_background(r, g, b)

Sets the current background colour. The three arguments can be replaced by a single 3-tuple like that returned by gimp.get_background.
gimp.set_foreground(r, g, b)

Sets the current foreground colour. Like gimp.set_background, the arguments may be replaced by a 3-tuple.

Gradient Operations

These functions perform operations on gradients:

gimp.gradients_get_active()

Returns the name of the active gradient.
gimp.gradients_set_active(name)

Sets the active gradient.
gimp.gradients_get_list()

Returns a list of the names of the available gradients.
gimp.gradients_sample_uniform(num)

Returns a list of num samples, where samples consist of 4-tuples of floats representing the red, green, blue and alpha values for the sample.
gimp.gradients_sample_custom(pos)

Similar to gimp.gradients_sample_uniform, except the samples are taken at the positions given in the list of floats pos instead of uniformly through the gradient.

PDB Registration Functions

These functions either install procedures into the PDB or alert gimp to their special use (eg as file handlers).

For simple plug-ins, you will usually only need to use register from gimpfu.

gimp.install_procedure(name, blurb, help, author, copyright, date, menu_path, image_types, type, params, ret_vals)

This procedure is used to install a procedure into the PDB. The first eight parameters are strings, type is a one of the PROC_* constants, and the last two parameters are sequences describing the parameters and return values. Their format is the same as the param and ret_vals methods or PDB procedures.
gimp.install_temp_proc(name, blurb, help, author, copyright, date, menu_path, image_types, type, params, ret_vals)

This procedure is used to install a procedure into the PDB temporarily. That is, it must be added again every time gimp is run. This procedure will be called the same way as all other procedures for a plugin.
gimp.uninstall_temp_proc(name)

This removes a temporary procedure from the PDB.
gimp.register_magic_load_handle`r(`name, extensions, prefixes, magics)

This procedure tells GIMP that the PDB procedure name can load files with extensions and prefixes (eg http:) with magic information magics.
gimp.register_load_handler(name, extensions, prefixes)

This procedure tells GIMP that the PDB procedure name can load files with extensions and prefixes (eg http:).
gimp.register_save_handler(name, extensions, prefixes)

This procedure tells GIMP that the PDB procedure name can save files with extensions and prefixes (eg http:).

Other Functions

These are the other functions in the gimp module.

gimp.main(init_func, quit_func, query_func, run_func)

This function is the one that controls the execution of a Gimp- Python plugin. It is better to not use this directly but rather subclass the plugin class, defined in the gimpplugin Module.
gimp.pdb

The procedural database object.
gimp.progress_init([label])

(Re)Initialise the progress meter with label (or the plugin name) as a label in the window.
gimp.progress_update(percent)

Set the progress meter to percent done.
gimp.image_list()

Returns a list of all the image objects.
gimp.quit()

Stops execution immediately and exits.
gimp.displays_flush()

Update all the display windows.
gimp.tile_width()

The maximum width of a tile.
gimp.tile_height()

The maximum height of a tile.
gimp.tile_cache_size(kb)

Set the size of the tile cache in kilobytes.
gimp.tile_cache_ntiles(n)

Set the size of the tile cache in tiles.
gimp.get_data(key)

Get the information associated with key. The data will be a string. This function should probably be used through the gimpshelf Module.
gimp.set_data(key, data)

Set the information in the string data with key. The data will persist for the whole gimp session. Rather than directly accessing this function, it is better to go through the gimpshelf Module.
gimp.extension_ack()

Tells gimp that the plugin has finished its work, while keeping the plugin connection open. This is used by an extension plugin to tell gimp it can continue, while leaving the plugin connection open. This is what the script-fu plugin does so that only one scheme interpreter is needed.
gimp.extension_process(timeout)

Makes the plugin check for messages from gimp. generally this is not needed, as messages are checked during most calls in the gimp module.

Parasites

In gimp >= 1.1, it is possible to attach arbitrary data to an image through the use of parasites. Parasites are simply wrappers for the data, containing its name and some flags. Parasites have the following parameters:

data

The data for the parasite — a string
flags

The flags for the parasite
is_persistent

True if this parasite is persistent
is_undoable

True if this parasite is undoable
name

The name of the parasite

Parasites also have the methods copy, is_type and has_flag.

There is a set of four functions that are used to manipulate parasites. They exist as functions in the gimp module, and methods for image and drawable objects. They are:

parasite_find(name)

find a parasite by its name.
parasite_attach(parasite)

Attach a parasite to this object.
attach_new_parasite(name, flags, data)

Create a new parasite and attach it.
parasite_detach(name)

Detach the named parasite

GIMP Objects

Gimp-Python implements a number of special object types that represent the different types of parameters you can pass to a PDB procedure. Rather than just making these place holders, I have added a number of members and methods to them that allow a lot of configurability without directly calling PDB procedures.

There are also a couple of extra objects that allow low level manipulation of images. These are tile objects (working) and pixel regions (not quite finished).
Image Object

This is the object that represents an open image. In this section, image represents a generic image object.
Image Members

image.active_channel

This is the active channel of the image. You can also assign to this member, or None if there is no active channel.
image.active_layer

This is the active layer of the image. You can also assign to this member, or None if there is no active layer.
image.base_type

This is the type of the image (eg RGB, INDEXED).
image.channels

This is a list of the channels of the image. Altering this list has no effect, and you can not assign to this member.
image.cmap

This is the colour map for the image.
image.filename

This is the filename for the image. A file load or save handler might assign to this.
image.height

This is the height of the image. You can't assign to this member.
image.floating_selection

The floating selection layer, or None if there is no floating selection.
image.layers

This is a list of the layers of the image.
image.selection

The selection mask for the image.
image.width

This is the width of the image. You can't assign to this member.

Image Methods

image.add_channel(channel, position)

Adds channel to image in position position.
image.add_layer(layer, position)

Adds layer to image in position position.
image.add_layer_mask(layer, mask)

Adds the mask mask to layer.
image.clean_all()

Unsets the dirty flag on the image.
image.disable_undo()

Disables undo for image.
image.enable_undo()

Enables undo for image. You might use these commands round a plugin, so that the plug-in's actions can be undone in a single step.
image.flatten()

Returns the resulting layer after merging all the visible layers, discarding non visible ones and stripping the alpha channel.
image.get_component_active(component)

Returns true if component (one of the *_CHANNEL constants) is active.
image.get_component_visible(component)

Returns true if component is visible.
image.set_component_active(component, active)

Sets the activeness of component.
image.set_component_visible(component, active)

Sets the visibility of component.
image.lower_channel(channel)

Lowers channel.
image.lower_layer(layer)

Lowers layer.
image.merge_visible_layers(type)

Merges the visible layers of image using the given merge type.
image.pick_correlate_layer(x, y)

Returns the layer that is visible at the point (x,y), or None if no layer matches.
image.raise_channel(channel)

Raises channel.
image.raise_layer(layer)

Raises layer.
image.remove_channel(channel)

Removes channel from image.
image.remove_layer(layer)

Removes layer from image.
image.remove_layer_mask(layer, mode)

Removes the mask from layer, with the given mode (either APPLY or DISCARD).
image.resize(width, height, x, y)

Resizes the image to size (width, height) and places the old contents at position (x,y).

Channel Objects

These objects represent a GIMP Image's colour channels. In this section, channel will refer to a generic channel object.
Channel Members

channel.colour or channel.color

The colour of the channel.
channel.height

The height of the channel.
channel.width

The width of the channel.
channel.image

The image the channel belongs to, or None if it isn't attached yet.
channel.layer

The channel's layer (??) or None if one doesn't exist.
channel.layer_mask

Non zero if the channel is a layer mask.
channel.name

The name of the channel.
channel.opacity

The opacity of the channel.
channel.show_masked

The show_masked value of the channel.
channel.visible

Non-zero if the channel is visible.

Channel Methods

channel.copy()

returns a copy of the channel.

Layer Objects

Layer objects represent the layers of a GIMP image. In this section I will refer to a generic layer called layer.
Layer Members

layer.apply_mask

The apply mask setting. (non zero if the layer mask is being composited with the layer's alpha channel).
layer.bpp

The number of bytes per pixel.
layer.edit_mask

The edit mask setting. (non zero if the mask is active, rather than the layer).
layer.height

The height of the layer.
layer.image

The image the layer is part of, or None if the layer isn't attached.
layer.is_floating_selection

Non zero if this layer is the image's floating selection.
layer.mask

The layer's mask, or None if it doesn't have one.
layer.mode

The mode of the layer.
layer.name

The name of the layer.
layer.opacity

The opacity of the layer.
layer.preserve_transparency

The layer's preserve transparency setting.

Layer Methods

layer.add_alpha()

Adds an alpha component to the layer.
layer.copy([alpha])

Creates a copy of the layer, optionally with an alpha layer.
layer.create_mask(type)

Creates a layer mask of type type.
layer.resize(w, h, x, y)

Resizes the layer to (w, h), positioning the original contents at (x,y).
layer.scale(h, w, origin)

Scales the layer to (w, h), using the specified origin (local or image).
layer.set_offsets(x, y)

Sets the offset of the layer, relative to the image's origin
layer.translate(x, y)

Moves the layer to (x, y) relative to its current position.

Drawable Objects

Both layers and channels are drawables. Hence there are a number of operations that can be performed on both objects. They also have some common attributes and methods. In the description of these attributes, I will refer to a generic drawable called drawable.
Drawable Members

drawable.bpp

The number of bytes per pixel.
drawable.is_colour or drawable.is_color or drawable.is_rgb

Non zero if the drawable is colour.
drawable.is_grey or drawable.is_gray

Non zero if the drawable is greyscale.
drawable.has_alpha

Non zero if the drawable has an alpha channel.
drawable.height

The height of the drawable.
drawable.image

The image the drawable belongs to.
drawable.is_indexed

Non zero if the drawable uses an indexed colour scheme.
drawable.mask_bounds

The bounds of the drawable's selection.
drawable.name

The name of the drawable.
drawable.offsets

The offset of the top left hand corner of the drawable.
drawable.type

The type of the drawable.
drawable.visible

Non zero if the drawable is visible.
drawable.width

The width of the drawable.

Drawable Methods

drawable.fill(fill_type)

Fills the drawable with given fill_type (one of the *_FILL constants).
drawable.flush()

Flush the changes to the drawable.
drawable.get_pixel_rgn(x, y, w, h, [dirty, [shadow])

Creates a pixel region for the drawable. It will cover the region with origin (x,y) and dimensions w x h. The dirty argument sets whether any changes to the pixel region will be reflected in the drawable (default is TRUE). The shadow argument sets whether the pixel region acts on the shadow tiles or not (default is FALSE). If you draw on the shadow tiles, you must call drawable.merge_shadow() for changes to take effect.
drawable.get_tile(shadow, row, col)

Get a tile at (row, col). Either on or off the shadow buffer.
drawable.get_tile2(shadow, x, y)

Get the tile that contains the pixel (x, y).
drawable.merge_shadow()

Merge the shadow buffer back into the drawable.
drawable.update(x, y, w, h)

Update the given portion of the drawable.

Tile Objects

Tile objects represent the way GIMP stores information. A tile is basically just a 64x64 pixel region of the drawable. The reason GIMP breaks the image into small pieces like this is so that the whole image doesn't have to be loaded into memory in order to alter one part of it. This becomes important with larger images.

In Gimp-Python, you would use Tiles if you wanted to perform some low level operation on the image, instead of using procedures in the PDB. This type of object gives a Gimp-Python plugin the power of a C plugin, rather than just the power of a Script-Fu script. Tile objects are created with either the drawable.get_tile() or drawable.get_tile2() functions. In this section, I will refer to a generic tile object named tile.
Tile Members

All tile members are read only.

tile.bpp

The number of bytes per pixel.
tile.dirty

If there have been changes to the tile since it was last flushed.
tile.drawable

The drawable that the tile is from.
tile.eheight

The actual height of the tile.
tile.ewidth

The actual width of the tile.
tile.ref_count

The reference count of the tile. (this is independent of the Python object reference count).
tile.shadow

Non zero if the tile is part of the shadow buffer.

Tile Methods

tile.flush()

Flush any changes in the tile. Note that the tile is automatically flushed when the Python object is deleted from memory.

Tile Mapping Behaviour

Tile objects also act as a mapping, or sequence. You can access the pixels in the tile in one of two ways. You can either access them with a single number, which refers to its position in the tile (eg. tile [64] refers to the first pixel in the second row of a 64x64 pixel tile). The other way is with a tuple, representing the coordinates on the tile (eg. tile [0, 1] refers to the first pixel on the second row of the tile).

The type of these subscripts is a string of length tile.bpp. When you assign to a subscript, the dirty flag is automatically set on the tile, so you don't have to explicitly set the flag, or flush the tile.
Pixel Regions

Pixel region objects give an interface for low level operations to act on large regions of an image, instead of on small 64x64 pixel tiles. In this section I will refer to a generic pixel region called pr. For an example of a pixel region's use, please see the example plugin whirlpinch.py .
Pixel Region Members

pr.drawable

The drawable this pixel region is for.
pr.bpp

The number of bytes per pixel for the drawable.
pr.rowstride

The rowstride for the pixel region.
pr.x

The x coordinate of the top left hand corner.
pr.y

The y coordinate of the top left hand corner.
pr.w

The width of the pixel region.
pr.h

The height of the pixel region.
pr.dirty

Non zero if changes to the pixel region will be reflected in the drawable.
pr.shadow

Non zero if the pixel region acts on the shadow tiles of the drawable.

Pixel Region Methods

pr.resize(x, y, w, h)

resize the pixel region so that it operates on the the region with corner (x, y) with dimensions w x h.

Pixel Region Mapping Behaviour

The pixel region acts as a mapping. The index is a 2-tuple with components that are either integers or slices. The subscripts may be read and assigned to. The type of the subscripts is a string containing the binary data of the requested region. Here is a description of the possible operations:

pr[x, y]

Get/Set the pixel at (x,y)
pr[x1:x2, y]

Get/Set the row starting at (x1, y), width x2 - x1.
pr[x, y1:y2]

Get/Set the column starting at (x, y1), height y2 - y1.
pr[x1:x2, y1:y1]

Get/Set the rectangle starting at (x1, y1), width x2 - x1 and height y2 - y1.

Support Modules

This section describes the modules that help make using the gimp module easier. These range from a set of constants to storing persistent data.
The gimpenums Module

This module contains all the constants found in the header libgimp/gimpenums.h , as well as some extra constants that are available in Script-Fu.
The gimpfu Module

This module was fully described in an earlier section. It provides an easy interface for writing plug-ins, where you do not need to worry about run_modes, GUI's and saving previous values. It is the recommended module for writing plug-ins.
The gimpplugin Module

This module provides the framework for writing GIMP plug-ins in Python. It gives more flexibility for writing plug-ins than the gimpfu module, but does not offer as many features (such as automatic GUI building).

To use this framework you subclass gimpplugin.plugin like so:

import gimpplugin
class myplugin(gimpplugin.plugin):
def init(self):
# initialisation routines
# called when gimp starts.
def quit(self):
# clean up routines
# called when gimp exits (normally).
def query(self):
# called to find what functionality the plugin provides.
gimp.install_procedure("procname", ...)
# note that this method name matches the first arg of
# gimp.install_procedure
def procname(self, arg1, ...):
# do what ever this plugin should do

The gimpshelf Module

This module gives a nicer interface to the persistent storage interface for GIMP plug-ins. Due to the complicated nature of Python objects (there is often a lot of connections between them), it can be difficult to work out what to store in GIMP's persistent storage. The python interface only allows storage of strings, so this module wraps pickle and unpickle to allow persistent storage of any python object.

Here is some examples of using this module:

>>> from gimpshelf import shelf
>>> shelf['james'] = ['forty-two', (42, 42L, 42.0)]
>>> shelf.has_key('james')
1
>>> shelf['james']
['forty-two', (42, 42L, 42.0)]

Anything you store with gimpshelf.shelf will exist until GIMP exits. This makes this interface perfect for when a plugin is executed with the run mode RUN_WITH_LAST_VALS .
Script-Fu Invocation
The Script-Fu to GIMP Python Interface

As all other plug-ins, the ones written with GIMP Python are registered in the procedural database (See Procedural Database). As such, they can be easily interfaced using Script-Fu; let's consider this GIMP Python plug-in:

#! /usr/bin/env python
from gimpfu import *

def echo(*args):
"""Print the arguments on standard output"""
print "echo:", args

register(
"console_echo", "", "", "", "", "",
"<Toolbox>/Xtns/Languages/Python-Fu/Test/_Console Echo", "",
[
(PF_STRING, "arg0", "argument 0", "test string"),
(PF_INT, "arg1", "argument 1", 100 ),
(PF_FLOAT, "arg2", "argument 2", 1.2 ),
(PF_COLOR, "arg3", "argument 3", (0, 0, 0) ),
],
[],
echo
)

main()

Using Script-Fu, one could easily invoke the correct Scheme function call: (python-fu-console-echo RUN-NONINTERACTIVE "another string" 777 3.1416 '(1 0 0)) . There are a couple of details worth mentioning:

The registered procedure name (first parameter of the register() function) is mangled: all underscores are converted to hyphens, to better match the usual Scheme syntatic style (here, console_echo becomes console-echo ). Moreover, a python-fu- prefix is automatically added; it is better not to explicitly add it ourselves, as it will makes the often useful (plug-in-script-fu- eval …) evaluation fail.

The mandatory first parameter to any pdb call (Script-Fu constant RUN-INTERACTIVE , or RUN-NONINTERACTIVE ) discriminates between user-driven or scripted calls. In the case of gimpfu-based plug-ins, it is automatically taken care of internally — interactive calls will dismiss all the remaining arguments, and an interface will be presented (when possible) to the user. The plug-in core Python function ( echo() in this case), never has to deal with it.

Script-Fu is able to process strings, integer and floats literals, and pass them as corresponding first-class objects to Python. It can also pass compound arguments such as colors as tuples in Python by expressing them as Scheme lists (in the (python-fu-console-echo …) call above, fourth argument to the pythonic echo() function will be a 3-tuple of integers representing a pure red color).

All other special purposes gimpfu parameter types (PF_FILE , etc.) can be constructed using those simple literals and list constructs, and received as appropriate objects in Python. If you need booleans, pass them as integers.

GIMP Python Invocation from the Shell

All this means that you could easily invoke a GIMP Python plug-in such as the one above directly from your shell using the (plug-in-script- fu-eval …) evaluator:

gimp --no-interface --batch '(python-fu-console-echo RUN-NONINTERACTIVE "another string" 777 3.1416 (list 1 0 0))' '(gimp-quit 1)'

The invocation here was done without an interface since this specific procedure didn't need any.

See the GIMP Script-Fu Documentation to learn more about it.
End Note

This package is not yet complete, but it has enough in it to be useful for writing plug-ins for GIMP. If you write any plug-ins that might be useful as examples, please mail me at james@daa.com.au.