This is directly connected to the objectification task mentioned below and should probably be addressed after all objects have been reviewed.
Headers should only include other headers if absolutely necessary (for derived objects for example). All functions must be properly prototyped.
Split the core into several subdirectories and build libtool convenience libraries which are then linked together to form the gimp binary.
LibGimp already has a new type GimpRGB. This should be used whereever possible. If necessary we can change this to a more generic struct later. Migrating to GimpRGB first will make this much easier.
Directly derived from GObject, should probably have a name argument.
GimpDrawable, Layer, GimpImage, GDisplay need to be redone as proper GimpObjects. Write new objects (with proper names) and port all stuff to the new objects incrementally.
Brushes, Patterns, Gradients should be derived from a GimpData object. This object has to provide hooks to generate previews.
A GimpContainer that holds GimpObject objects. Comparable to the GCimContainer, but no serialization for now. Should probably dispatch "changed" (or other) signals from its children.
This container will be used for lists of brushes, patterns, layers, channels, paths, ...
The GimpBrush object we have now is not a generic BrushProvider. We need an abstract object to derive the different kinds of brushes from (BrushPipes, parametric brushes, ...). It has to provide methods for the PaintCore to transparently select and use the brush data. Paint tools should have to care about the brush type as less as possible.
Put libgimp, libgimpui (and new libs) into their own subdirectories under a toplevel libs directory. Install all header files under $prefix/include/gimp/1.3/ and change gimptool accordingly.
Put utility functions that are also used by the core into a separate library.
Write a library with a bunch of common functions for file plug-ins to remove code duplication in these plug-ins.
Views on data stored in a GimpContainer. The objects need to provide hooks that this view can use to show data like patterns, brushes, etc. in different views (list, grid, ...)
A generic preview widget with functions like scrolling and zooming useable by effect filters. Should have adaptive supersampling, progressive display (if possible) and other neat stuff.
Add an option to the Preferences to disable tearoff menus. Some people seem to be annoyed by it and it should be trivial to make them optional.
Add a "Save a Copy as" function which works as "Save as" but leaves the image's name untouched.
It's often useful to view the image you're editing on a pure white or pure black background instead of the theme's default background.
Add a possibility to show the image fullscreen (padded with the configured canvas background color).
The pluggable color selectors need to be overhauled. Move the numerical input fields, the sliders, the "old" and "new" color buttons and a color history out of the notebook so they are always visible. Optionally allow an alpha value to be specified. Maybe reduce the size of the color area in the "GIMP" color selector.
Think about a proper way to make all menus and dialogs accesible and navigationable without using a mouse.
Move the DND functionality into LibGimp. This needs to be done differently for app and plug-ins, but should be handled transparently.
Lost of existing user interface elements can be implemented as proper widgets in libgimpui, so they are useable from everywhere.
The same english string used in different contexts may need to be translated differently in other languages. Think of a way to implement this using gettext or come up with something better.
There is a patch with a possible solution on ftp.gimp.org, but actually we'd like something cleaner if possible.