* = 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
    
- http://opengl.org - documentation - OpenGL Redbook, GLX docs, extensions docs

TODO:

* Check/make it work with other gfx cards
    - I've tested only with nvidia with the 9625 beta drivers and 8776 stable drivers so far
    - 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
    - since kompmgr has an option to make only the decoration transparent,
        it should be possible to do the same here - if the window has alpha and a decoration
        or if there should be only the decoration transparent, paint first the contents
        and then the decoration - this should make it possible to paint the decoration
        without the random alpha that is right now handled by the alpha hack

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

* update only those parts of the screen that have been changed
    - for paintSimpleScreen() - it currently sets region to the whole screen
    * instead of using glXSwapBuffers() there should be glCopyPixels() used
        - compiz has such code in evenLoop() in the if() block for COMP_SCREEN_DAMAGE_REGION_MASK
        * perhaps syncing to vblank will be needed to avoid flicker
    * XCopyArea() should not update the whole screen but only the affected areas

* sync to vblank
    - currently the compositing code is run with 20ms timer, i.e. constant 50fps
    - the GLX_SGI_video_sync extension should be used
    - compiz uses this, no idea about it though

? GL_ARB_texture_rectangle vs GL_ARB_texture_non_power_of_two
    - code currently uses GL_ARB_texture_rectangle (GL_TEXTURE_RECTANGLE_ARB), using
        normal textures when GL_ARB_texture_non_power_of_two is available should(?) be
        preferred

? in SceneOpenGL::bindTexture() with tfp_mode, with some gfx cards it seems
    to be faster to not short-circuit the texture binding when there's been
    no damage
    * confirm and try to find out when to do it and when not