* = not done
/ = work in progress
? = should it be done?

See the HACKING file for KWin details. The composite-related sources are mostly
composite.cpp and scene_opengl.cpp (TODO: add comments and general overview).

Sources:

- glcompmgr : http://lists.freedesktop.org/archives/xorg/2006-July/017006.html ,
              http://www.mail-archive.com/compiz%40lists.freedesktop.org/msg00023.html
    - simple and easy to understand
    - works even without texture_from_pixmap extension
    - claims to support several different gfx cards
- compiz : git clone git://anongit.freedesktop.org/git/xorg/app/compiz
    - the ultimate <whatever>
    - glxcompmgr : git clone git://anongit.freedesktop.org/git/xorg/app/glxcompgr
        - a rather old version of compiz, but also simpler and as such simpler
            to understand
- libcm (metacity) : cvs -d :pserver:anonymous@anoncvs.gnome.org:/cvs/gnome co libcm
    - no idea about it

TODO:

* Check/make it work with other gfx cards
    - I've tested only with nvidia with the 9625 beta drivers so far
    * latest stable nvidia drivers don't quite work, the COPY_BUFFERS
        or REFRESH_DRAWABLES workaround from glcompmgr should take care of that
        - the COPY_BUFFERS hack, if I'm getting it right, just creates a copy
            of the X Pixmap first, so just always using ALPHA_CLEAR_COPY hack
            in KWin should do the same
    - I have absolutely no idea about other gfx cards, needs to be tested
        * ati
        * intel
        * who knows what else

? Xgl support
    - Compiz itself doesn't work when compiled with the libGL from nvidia,
        it ships its own and links against it
    ? might be worth trying to use that libGL as well
    - it may be just because of the special libGL, but when testing with Xgl
        it even seemed non-conformant - none of the provided configs had
        GLX_RENDER_TYPE with GLX_RGBA_BIT even though required by GLX
        and other funny things. Indeed, it may be just me being still pretty
        clueless about these things.
    * is there a good reason to support Xgl? With the 9625 nvidia drivers
        it seems to work fine without them
        
? AIGLX support
    - no idea about this at all
    * find out if it works

* XComposite overlay window
    - X.Org 7.1 and newer have XComposite extension version 0.3, which allows
        creating an overlay window to paint to instead of painting to the root window
    - I still run older X.Org here
    - the code in glcompmgr for this is in HAVE_OVERLAYS, stealing primarily from
        here should be better since it's simpler and the code so far has been
        modelled more after glcompmgr
    - the code in compiz for this is in USE_COW
    * use double-buffering with the overlay window - kwin already has code
        for double-buffered destination drawable, but I haven't been able to test it

* when relying on extensions, detect that they are available
    - some of the glcompmgr code probably depends on OpenGL/GLX extensions that may
        not be always available, probably the same with compiz
    * find out which code relies on extensions and add checks

? alpha clear hack
    * find out if it affects performance
    * if yes, try to find a better way of solving the problem

/ design framework for graphical effects
    - modelling it after compiz seems to make a lot of sense

* make paintSimpleScreen() clip non-visible parts
    - clip parts of lower windows by parts of windows above them, so that those parts
        don't need to be painted
    - similarly like in scene_xrender.cpp