------------------------------
                   GNU Image Manipulation Program
                         Development Branch
                   ------------------------------

This is the unstable branch of GIMP.


Overview of Changes from GIMP 2.10.x to GIMP 2.99.2
===================================================

Core:

  - Improved "space invasion".
  - New extension format support (.gex a.k.a. GIMP Extension) which is
    an archive containing various supported data. So far, it can
    package: brushes, MyPaint brushes, dynamics, patterns, gradients,
    palettes, tool presets, plug-ins, splash images and themes.
  - New extension manager allowing to enable, disable or uninstall
    installed extensions, with a dialog available in `Edit > Manage
    Extensions`.
  - Multi selection of layers now possible. Various tools and features
    are now multi-selection aware.
  - XCF format bumped to version 14 with awareness of multiple layer
    selection.
  - All code is year-2038-safe with deprecated time API replaced.
  - "Alpha to Selection" various actions warn when the result selection
    is empty.

User Interface:

  - Whole interface ported to GTK+3.
  - Proper HiDPI support, which will follow the system's scale factor
    for all widgets. This is a core toolkit support, unlike the basic
    better-than-nothing hacks from GIMP 2.10.x.
  - GTK+3 CSS-like support. All themes for former versions are therefore
    not working anymore.
  - GTK+3 themes have the concept of "dark variant", so a same theme may
    propose both a light and a dark versions. Preference for dark
    variants can now be checked in `Preferences > Themes > Use dark
    theme variant if available` checkbox, allowing for instance to use
    your system theme in its light variant everywhere except in GIMP.
    This option is checked by default as graphics software are often
    prefered in dark modes.
  - Symbolic icon themes are now recolored automatically according to
    the theme colors (no theme and icon theme tweaking anymore to end up
    with dark on dark or light on light interfaces), except for color
    elements whose SVG style is marked as "!important".
  - Image display rendered faster with a render cache that keeps the
    result of scaling, color management, display filters and shell mask
    (for tools like fuzzy select).
  - Shift-click on layer GimpContainerTreeView (typically the Layers
    dockable) allows to expand/collapse all item groups but the clicked
    one.

Devices:

  - Device hotplug supported. In particular, you don't need to have your
    tablets and other devices plugged before you start GIMP anymore, and
    enabling your devices in the "Configure Input Devices" dialog is not
    needed anymore. Tablets will work out-of-the box.

Plug-ins:

  - Major rewrite of the API. So GIMP 2.10.x plug-ins and below must be
    ported to the new API.
  - Various objects are now proper GObject in the plug-in API, and not
    just ID integers.
  - The API is GObject Introspected, which means plug-ins can be written
    in various non-C languages. So far the following languages have been
    tested and work well: Python 3, Lua and Javascript (Note: Python 2
    is also still working, but considering that this language is
    end-of-life since 2020, we don't really care).
  - Every introspected binding which we test comes with a "Goat
    Exercise", which is a demo plug-in popping a dialog and showing its
    own source code. It processes a simple "gegl:invert" operation on a
    drawable. All "Goat Exercises" must do the same thing in the same
    way, simply in their respective languages, as documentation code for
    a language binding.
  - Plug-ins must be installed in their own subdirectory in
    `$XDG_CONFIG_HOME/GIMP/2.99/plug-ins/`, thus preventing data mess
    (with plug-ins coming with data and installing it all in the root
    plug-ins/ directory) and DLL hell. The main plug-in executable must
    be named the same as the directory (possibly with an added
    extension).
    E.g.: `plug-ins/my-cool-plug-in/my-cool-plug-in.py`

Documentation:

  - `devel-docs/xcf.txt` updated to handle XCF 14.

Build:

  - New meson build system. Still deemed "experimental" for the time
    being. Packagers are recommended to continue using the autotools
    build system in order to avoid specific bugs.
  - Continuous integration in Gitlab with:
    - an autotools build with GCC on a Debian/testing runner
    - a meson build with GCC on a Debian/testing runner
    - a meson build with Clang on a Debian/testing runner
    - a meson cross-build with Mingw-w64 for Windows 32-bit
    - a meson cross-build with Mingw-w64 for Windows 64-bit
    - static code analysis with cppcheck

Known blocker issues:

  - GTK+3 port is functional but not complete as some deprecated APIs
    are still being used.
  - Space invasion is still a work-in-progress.
  - Plug-ins API update is still a work-in-progress.
  - GIMP extensions are still a work-in-progress.
  - Multiple layer selection is still work-in-progress. Some issues are
    expected, and possibly even some crashes in code paths which were
    not updated yet.
  - No custom theme yet, in particular we want a neutral gray theme with
    light/dark variants, and likely a middle-gray theme too.