237015dc69
Fixes: > [2636/2644] Generating devel-docs/g-ir-docs/g-ir-Gimp-python-cache with a custom command > file:///builds/GNOME/gimp/_build-x64/meson-private/dist-build/devel-docs/g-ir-docs/pages/python/Gimp-3.0/Gimp.ColorArray.page:22: parser error : EntityRef: expecting ';' > NULL);</p> <p>GeglColors **colors;</p> <p>g_object_get (obj, "colors", &colors > ^ |
||
|---|---|---|
| .. | ||
| GIMP3-plug-in-porting-guide | ||
| g-ir-docs | ||
| reference | ||
| GIMP3-API-Changes.txt | ||
| README.md | ||
| c.vim | ||
| contexts.txt | ||
| gimp-module-dependencies.svg | ||
| gitlab-mr.md | ||
| icons.md | ||
| includes.txt | ||
| interpreters.txt | ||
| meson.build | ||
| os-support.txt | ||
| parasites.txt | ||
| tagging.txt | ||
| ui-framework.txt | ||
| undo.txt | ||
README.md
| title |
|---|
| Developers documentation |
This manual holds information that you will find useful if you develop a GIMP plug-in or want to contribute to the GIMP core.
People only interested into plug-ins can probably read just the Plug-in development section. If you wish to contribute to all parts of GIMP, the whole documentation is of interest.
[TOC]
Plug-in development
Concepts
Basics
Plug-ins in GIMP are executables which GIMP can call upon certain conditions. Since they are separate executables, it means that they are run as their own process, making the plug-in infrastructure very robust. No plug-in should ever crash GIMP, even with the worst bugs. If such thing happens, you can consider this a core bug.
On the other hand, a plug-in can mess your opened files, so a badly developed plug-in could still leave your opened images in an undesirable state. If this happens, you'd be advised to close and reopen the file (provided you saved recently).
Another downside of plug-ins is that GIMP currently doesn't have any sandboxing ability. Since we explained that plug-ins are run by GIMP as independant processes, it also means they have the same rights as your GIMP process. Therefore be careful that you trust the source of your plug-ins. You should never run shady plug-ins from untrusted sources.
GIMP comes itself with a lot of plug-ins. Actually nearly all file format support is implemented as a plug-in (XCF support being the exception: the only format implemented as core code). This makes it a very good base to study plug-in development.
Procedural DataBase (PDB)
Obviously since plug-ins are separate processes, they need a way to communicate with GIMP. This is the Procedural Database role, also known as PDB.
The PDB is our protocol allowing plug-ins to request or send information from or to the main GIMP process.
Not only this, but every plug-in has the ability to register one or several procedures itself, which means that any plug-in can call features brought by other plug-ins through the PDB.
libgimp and libgimpui
The GIMP project provides plug-in developers with the libgimp library.
This is the main library which any plug-in needs. All the core PDB
procedures have a wrapper in libgimp so you actually nearly never need
to call PDB procedures explicitly (exception being when you call
procedures registered by other plug-ins; these won't have a wrapper).
The libgimpui library is an optional one which provides various
graphical interface utility functions, based on the GIMP toolkit
(GTK). Of course, it means that linking to this library is not
mandatory (unlike libgimp). Some cases where you would not do this
are: because you don't need any graphical interface (e.g. a plug-in
doing something directly without dialog, or even a plug-in meant to be
run on non-GUI servers); because you want to use pure GTK directly
without going through libgimpui facility; because you want to make
your GUI with another toolkit…
The whole C reference documentation for both these libraries can be
generated in the main GIMP build with the -Dgi-docgen=enabled meson
option (you need to have the gi-docgen tools installed).
See the API documentation
Programming Languages
While C is our main language, and the one libgimp and libgimpui are
provided in, these 2 libraries are also introspected thanks to the
GObject-Introspection (GI)
project. It means you can in fact create plug-ins with absolutely any
language with a GI binding
though of course it may not always be as easy as the theory goes.
The GIMP project explicitly tests the following languages and even provides a test plug-in as a case study:
- C (not a binding)
- Python 3 (binding)
- Lua (binding)
- Vala (binding)
- Javascript (binding, not supported on Windows for the time being)
One of the big advantage of these automatic bindings is that they are full-featured since they don't require manual tweaking. Therefore any function in the C library should have an equivalent in any of the bindings.
TODO: binding reference documentation.
Note: several GObject-Introspection's Scheme bindings exist though
we haven't tested them. Nevertheless, GIMP also provides historically
the "script-fu" interface, based on an integrated Scheme implementation.
It is different from the other bindings (even from any GI Scheme
binding) and doesn't use libgimp. Please see the Script-fu
development section.
Tutorials
TODO: at least in C and in one of the officially supported binding (ideally even in all of them).
Porting from GIMP 2 plug-ins
Take a look at our porting guide.
Debugging
GIMP provides an infrastructure to help debugging plug-ins.
You are invited to read the dedicated documentation.
Script-fu development
Script-fu is its own thing as it is a way to run Scheme script with
GIMP. It is itself implemented as an always-running plug-in with its own
Scheme mini-interpreter and therefore Script-fu scripts do not use
libgimp or libgimpui. They interface with the PDB through the
Script-fu plug-in.
TODO: Tutorials
Porting from GIMP 2 scripts
Take a look at our ScriptFu porting guide
TODO: GEGL operation development
Custom data
This section list all types of data usable to enhance GIMP functionalities. If you are interested to contribute default data to GIMP, be aware that we are looking for a very good base set, not an unfinite number of data for all possible usage (even the less common ones).
Furthermore we only accept data on Libre licenses:
Of course you are free to share data usable by GIMP on any license you want on your own. Providing them as third-party GIMP extensions is probably the best idea.
Brushes
GIMP currently supports the following brush formats:
- GIMP Brush (GBR): format to store pixmap brushes
- GIMP Brush Pipe (GIH): format to store a series of pixmap brushes
- GIMP Generated Brush (VBR): format of "generated" brushes
- GIMP Brush Pixmap (GPB): OBSOLETE format to store pixel brushes
- MyPaint brushes v1 (MYB)
- Photoshop ABR Brush
- Paint Shop Pro JBR Brush
We do fully support the GIMP formats obviously, as well as MyPaint
brushes, since we use the official libmypaint library. We are not sure
how well we support other third-party formats, especially if they had
recent versions.
If you are interested in brushes from a developer perspective, you are welcome to read specifications of GIMP formats: GBR, GIH, VBR or the obsolete GPB.
If you want to contribute brushes to the official GIMP, be aware we would only accept brushes in non-obsolete GIMP formats. All these formats can be generated by GIMP itself from images.
If you want to contribute MyPaint brushes, we recommend to propose them to the MyPaint-brushes data project, which is also used by GIMP for its default MyPaint brush set.
Otherwise, you are welcome to provide brush set in any format as third-party extensions.
Dynamics
GIMP supports the GIMP Paint Dynamics format which can be generated from within GIMP.
Patterns
GIMP supports the GIMP Pattern format (PAT, whose specification is available for developers).
This format can be exported by GIMP itself.
Alternatively GIMP supports patterns from GdkPixbuf (TODO: get more
information?).
Palettes
GIMP supports the GIMP Palette format which can be generated from within GIMP.
Gradients
GIMP supports the GIMP Gradient format (GGR, whose specification is available for developers) which can be generated from within GIMP.
Alternatively GIMP supports the SVG Gradient format.
Themes
GTK3 uses CSS themes. Don't be fooled though. It's not real CSS in that it doesn't have all the features of real web CSS, and since it's for desktop applications, some things are necessarily different. What it means is mostly that it "looks similar" enough that people used to web styling should not be too disorientated.
You can start by looking at the official documentation for theme migration (from GTK+2 to 3), which gives a good overview, though it's far from being perfect unfortunately.
Another good idea would be to look at existing well maintained GTK3 themes to get inspiration and see how things work.
Finally you can look at our existing themes, like the System
theme.
Note though that this System theme is pretty bare, and that's its goal
(try to theme as few as possible over whatever is the current real
GTK system theme).
As a last trick for theme makers, we recommend to work with the
GtkInspector tool, which allows you to test CSS rules live in the CSS
tab. You can run the GtkInspector by going to the File > Debug menu
and selecting Start GtkInspector menu item.
It also allows you to find the name of a widget to use in your CSS rules. To do so:
- Start the
GtkInspector; - go on the "Objects" tab;
- click the "target" 🞋 icon on the headerbar's top-left, then pick in GIMP interface the widget you are interested to style;
- the widget name will be displayed on the top of the information area of the dialog.
- Feel free to browse the various sections to see the class hierachy, CSS nodes and so on.
- The second top-left button (just next to the target icon) allows you to switch between the details of the selected widget and the widget hierarchy (container widgets containing other widgets), which is also very useful information.
Additionally you can quickly switch between the light and dark variant of a same theme by going to "Visual" tab and switching the "Dark Variant" button ON or OFF.
Icon themes
Icon sets (a.k.a. "icon themes") have been separated from themes since GIMP 2.10 so you can have any icon theme with any theme.
We currently only support 2 such icon themes — Symbolic and Color — and we keep around the Legacy icons.
We don't want too many alternative designs as official icon themes (people are welcome to publish their favorite designs as third-party icons) though we would welcome special-purpose icon themes (e.g. high contrast).
We also welcome design updates as a whole (anyone willing to work on this should discuss with us and propose something) and obviously fixes on existing icons or adding missing icons while keeping consistent styling.
See the dedicated icons documentation for more technical information.
TODO: Tool presets
TODO: GIMP extensions (.gex)
Continuous Integration
For most of its continuous integration (macOS excepted), GIMP project uses Gitlab CI. We recommend looking the file .gitlab-ci.yml which is the startup script.
The main URL for our CI system is build.gimp.org which redirects to Gitlab pipelines page.
Note that it is important to keep working CI jobs for a healthy code source. Therefore when you push some code which breaks the CI (you should receive a notification email when you do so), you are expected to look at the failed jobs' logs, try and understand the issue(s) and fix them (or ask for help). Don't just shrug this because it works locally (the point of the CI is to build in more conditions than developers usually do locally).
Of course, sometimes CI failures are out of our control, for instance when downloaded dependencies have issues, or because of runner issues. You should still check that these were reported and that packagers/maintainers of these parts are aware and working on a fix.
Automatic pipelines
At each commit pushed to the repository, several pipelines are currently running, such as:
- Debian testing builds
- Windows builds (cross compiled).
Additionally, we test build with alternative tools or options (e.g. with
Clang instead of gcc compiler) or jobs which may take much longer,
such as package creation as scheduled pipelines (once every few days).
The above listing is not necessarily exhaustive nor is it meant to be. Only the .gitlab-ci.yml script is meant to be authoritative. The top comment in this file should stay as exhaustive as possible.
Manual pipelines
It is possible to trigger pipelines manually, for instance with specific jobs, if you have the "Developer" Gitlab role:
- go to the Pipelines page.
- Hit the "Run pipeline" button.
- Choose the branch or tag you wish to build.
- Add relevant variables. A list of variables named
GIMP_CI_*are available (just set them to any value) and will trigger specific job lists. These variables are listed in the top comment of .gitlab-ci.yml.
Merge request pipelines
Special pipelines happen for merge request code. For instance, these also include a (non-perfect) code style check.
Additionally you can trigger Windows installer or flatpack standalone packages to be generated with the MR code as explained in gitlab-mr.md.
Release pipeline
Special pipelines happen when pushing git tags. These should be tested
before a release to avoid unexpected release-time issues, as explained
in our release procedure.
Exception: macOS
As an exception, macOS is currently built with the Circle-CI service.
The whole CI scripts and documentation can be found in the dedicated
gimp-macos-build
repository.
Eventually we want to move this pipeline to Gitlab as well.
Core development
When writing code, any core developer is expected to follow:
- GIMP's coding style;
- the directory structure
- our header file inclusion policy
GIMP's developer site contain various valuable resources.
Finally the debugging-tips file contain many very useful tricks to help you debugging in various common cases.
Newcomers
If this is your first time contributing to GIMP, you might be interested by build instructions.
You might also like to read these instructions on the process of submitting patches.
TODO: Core Contributors
Directory structure of GIMP source tree
GIMP source tree can be divided into the main application, libraries, plug-ins, data files and some stuff that don't fit into these categories. Here are the top-level directories:
| Folder | Description |
|---|---|
| app/ | Source code of the main GIMP application |
| app-tools/ | Source code of distributed tools |
| build/ | Scripts for creating binary packages |
| cursors/ | Bitmaps used to construct cursors |
| data/ | Data files: brushes, gradients, patterns, images… |
| desktop/ | Desktop integration files |
| devel-docs/ | Developers documentation |
| docs/ | Users documentation |
| etc/ | Configuration files installed with GIMP |
| extensions/ | Source code of extensions |
| icons/ | Official icon themes |
| libgimp/ | Library for plug-ins (core does not link against) |
| libgimpbase/ | Basic functions shared by core and plug-ins |
| libgimpcolor/ | Color-related functions shared by core and plug-ins |
| libgimpconfig/ | Config functions shared by core and plug-ins |
| libgimpmath/ | Mathematic operations useful for core and plug-ins |
| libgimpmodule/ | Abstracts dynamic loading of modules (used to implement loadable color selectors and display filters) |
| libgimpthumb/ | Thumbnail functions shared by core and plug-ins |
| libgimpwidgets/ | User interface elements (widgets) and utility functions shared by core and plug-ins |
| menus/ | XML/XSL files used to generate menus |
| modules/ | Color selectors and display filters loadable at run-time |
| pdb/ | Scripts for PDB source code generation |
| plug-ins/ | Source code for plug-ins distributed with GIMP |
| po/ | Translations of strings used in the core application |
| po-libgimp/ | Translations of strings used in libgimp |
| po-plug-ins/ | Translations of strings used in C plug-ins |
| po-python/ | Translations of strings used in Python plug-ins |
| po-script-fu/ | Translations of strings used in Script-Fu scripts |
| po-tags/ | Translations of strings used in tags |
| po-tips/ | Translations of strings used in tips |
| po-windows-installer/ | Translations of strings used in the Windows installer |
| themes/ | Official themes |
| tools/ | Source code for non-distributed GIMP-related tools |
| .gitlab/ | Gitlab-related templates or scripts |
The source code of the main GIMP application is found in the app/ directory:
| Folder | Description |
|---|---|
| app/actions/ | Code of actions (GimpAction* defined in app/widgets/) (depends: GTK) |
| app/config/ | Config files handling: GimpConfig interface and GimpRc object (depends: GObject) |
| app/core/ | Core of GIMP core (depends: GObject) |
| app/dialogs/ | Dialog widgets (depends: GTK) |
| app/display/ | Handles displays (e.g. image windows) (depends: GTK) |
| app/file/ | File handling routines in core (depends: GIO) |
| app/file-data/ | GIMP file formats (gbr, gex, gih, pat) support (depends: GIO) |
| app/gegl/ | Wrapper code for babl and GEGL API (depends: babl, GEGL) |
| app/gui/ | Code that puts the user interface together (depends: GTK) |
| app/menus/ | Code for menus (depends: GTK) |
| app/operations/ | Custom GEGL operations (depends: GEGL) |
| app/paint/ | Paint core that provides different ways to paint strokes (depends: GEGL) |
| app/pdb/ | Core side of the Procedural Database, exposes internal functionality |
| app/plug-in/ | Plug-in handling in core |
| app/propgui/ | Property widgets generated from config properties (depends: GTK) |
| app/tests/ | Core unit testing framework |
| app/text/ | Text handling in core |
| app/tools/ | User interface part of the tools. Actual tool functionality is in core |
| app/vectors/ | Vectors framework in core |
| app/widgets/ | Collection of widgets used in the application GUI |
| app/xcf/ | XCF file handling in core |
Auto-generated Files
Please notice that some files in the source are generated from other
sources. All those files have a short notice about being generated
somewhere at the top. Among them are the files ending in pdb.[ch] in
the libgimp/ directory and the files ending in cmds.c in the
app/pdb/ subdirectory. Those are generated from the respective .pdb
files in pdb/groups.
Other files are:
AUTHORSfromauthors.xml
You should also check out gimp-module-dependencies.svg. TODO: this SVG file is interesting yet very outdated. It should not be considered as some kind dependency rule and should be updated.
Advanced concepts
XCF
The XCF format is the core image format of GIMP, which mirrors
features made available in GIMP. More than an image format, you may
consider it as a work or project format, as it is not made for finale
presentation of an artwork but for the work-in-progress processus.
Developers are welcome to read the specifications of XCF.
Locks
Items in an image can be locked in various ways to prevent different types of edits.
This is further explained in the specifications of locks.
UI Framework
GIMP has an evolved GUI framework, with a toolbox, dockables, menus…
This document describing how the GIMP UI framework functions and how it is implemented might be of interest.
Contexts
GIMP uses a lot a concept of "contexts". We recommend reading more about how GimpContexts are used in GIMP.
Undo
GIMP undo system can be challenging at times. This quick overview of the undo system can be of interest as a first introduction.
Parasites
GIMP has a concept of "parasite" data which basically correspond to persistent or semi-persistent data which can be attached to images or items (layers, channels, paths) within an image. These parasites are saved in the XCF format.
Parasites can also be attached globally to the GIMP session.
Parasite contents is format-free and you can use any parasite name, nevertheless GIMP itself uses parasite so you should read the descriptions of known parasites.
Metadata
GIMP supports Exif, IPTC and XMP metadata as well as various image format-specific metadata. The topic is quite huge and complex, if not overwhelming.
This old document might be of interest (or maybe not, it has not been recently reviewed and might be widely outdated; in any case, it is not a complete document at all as we definitely do a lot more nowadays). TODO: review this document and delete or update it depending of whether it still makes sense.
Tagging
Various data in GIMP can be tagged across sessions.
This document on how resource tagging in GIMP works may be of interest.