[OLPC-Games] GTK+ video target for SDL, first attempt.

[Ryan C. Gordon]

> Tell me everything you know; I'll be starting work in this area in a few
> days.

- Get the source from Subversion:

      svn co http://svn.libsdl.org/branches/SDL-1.2-olpc

- Build it with GTK+ support:

      ./autogen.sh
      ./configure --enable-video-gtk
      make && sudo make install

- export SDL_VIDEODRIVER=gtk

- Run SDL apps.   :)    The best bet is to go through everything in the 
test directory:

     cd SDL-1.2-olpc/test
     ./configure
     make
     ./testalpha


The code in question is in SDL-1.2-olpc/src/video/gtk ... it's fairly 
straightforward, since I started from the "dummy" driver which is mostly 
empty. 9/10ths of the work is going through the code in src/video/x11 
and making the GTK target functionally equivalent...mostly that's a 
matter of finding the GDK equivalent of a given Xlib call, and trimming 
X11 cruft for various extensions and buggy X servers, etc.

There is a lot of functionality that's missing right now. Here's my 
probably-incomplete list:

- No mousegrab support (probably not necessary with Sugar).
- No fullscreen support (not sure how this pans out in Sugar).
- No ability to change fullscreen resolutions (again, not needed in Sugar?)
- No palette support at the moment (may not be an issue, I think this is 
just for actual 8-bit visuals, not the shadow surface, which SDL can 
convert when blitting to the screen.)
- Keyboard input needs to be hooked up. This will need a lookup table 
and the appropriate GTK+ signals wired up, where it gets converted 
through the lookup table and pushed into the SDL event queue. Writing 
this will be a little tedious, but probably not difficult.
- There are a bunch of FIXME comments where I'm not sure about how 
refcounting is handled in GTK for various APIs...you can probably clean 
these up with a little research, otherwise we are likely leaking a few 
bytes of memory here and there.
- We're using _gdk_windowing_get_bits_for_depth(), which is not a public 
GDK entry point...this will probably cease working if GTK+ is ever 
rebuilt with GCC's -fvisibility=hidden, so a better solution is needed here.
- The background color property of the window probably needs to be set 
to black by default (compare x11 and gtk target with 
SDL-1.2-olpc/test/testoverlay.c).
- These patches should be applied:
    Remove polling from SDL_WaitEvent() (this will need further patches 
to the GTK video target):
       http://bugzilla.libsdl.org/show_bug.cgi?id=323
    Remove extra memset from audio callback (saves CPU cycles, not 
required):
       http://bugzilla.libsdl.org/show_bug.cgi?id=416

Things like joysticks and audio output and threads and such should Just 
Work as-is on the laptops, really this is strictly about gluing SDL to GTK+.

If you make progress, I'll get you write access to the Subversion repo. 
Patches committed to Subversion email me a copy of the patch, and since 
it's on a branch, I don't care what you break, so you can commit without 
going through me first and I'll comment if I see an issue.

And, of course, if you have any questions, don't hesitate to ask. If I 
do any work on it, I'll let you know, too, so we don't step on each 
other's toes.

Thanks,
--ryan.