(some) OMAP hardware support for SDL
by notaz (notasas@gmail.com)


About
-----

This is a quick SDL driver to make use of some OMAP features, namely double
buffering and hardware scaler.

The backstory of this is that SDL on Pandora console was suffering from tearing
and stuttering problems because SDL default x11 driver doesn't work that well
there. Almost 6 months have passed after pandora's release, no improved
SDL versions appeared (not blaming anyone here, pandora's availability was low
and there where were several SDL improvement in the works though). This
encouraged me to create this quick version until something better appears
(if ever).

Although this was created for pandora, there is nothing preventing this to work
on other OMAP platforms as well (well, nothing intentional at least).


Usage / environment
-------------------

To enable this driver, SDL_VIDEODRIVER environment variable must be set to
"omapdss". It can be set by calling setenv() in the code, but it's better to
just set it in launcher script so that it can be changed easily without
recompiling as needed:
---
#!/bin/sh
export SDL_VIDEODRIVER=omapdss
./your_program_here
---

Other environment variables:

SDL_OMAP_LAYER_SIZE:
  Output layer size. Regardless what you set with SDL_SetVideoMode(), output
  will be scaled to this size using hardware with zero processing cost.
  Note: scaling amount range is limited to roughly 1/4x-8x. The exact range
  depends on various factors like version of the driver or OMAP hardware itself.
  Valid values:
    "WxH", for example "640x480"
    "fullscreen" to cover whole screen.

SDL_OMAP_BORDER_CUT:
  This can be used to move parts of SDL surface out of screen, in other
  words cut borders and zoom in. Format: <left>,<right>,<top>,<bottom>
  For example, "0,0,16,0" would hide top 16 lines offscreen, making 17th
  (16th if you count from 0) line the first visible.
  Note: like for layer size ranges are limited.

SDL_OMAP_VSYNC:
  Enables waiting for vertical sync on SDL_Flip() calls.
  Set to "1" to enable, "0" to disable.

SDL_OMAP_DEFAULT_MODE:
  If the app doesn't specify resolution in SDL_SetVideoMode(), then use this.
  Should be specified in "WxH" format, for example "640x480".

SDL_OMAP_FORCE_DOUBLEBUF:
  This can force double buffering to on, which can help to eliminate tearing.
  Note that if app isn't updating whole buffer each frame, it will glitch.
  This is the same as specifying SDL_DOUBLEBUF to SDL_SetVideoMode.

SDL_OMAP_NO_TS_TRANSLATE:
  Disable automatic touchscreen screen -> layer coordinate translation,
  return real screen coordinates.


Config file
-----------

Optionally a file named "omapsdl.cfg" can be created in the game's working
directory. It has lower priority than environment variables, and has these
options (only when omapdss driver is active):

# same as SDL_OMAP_VSYNC
force_vsync = 1/0

# same as SDL_OMAP_FORCE_DOUBLEBUF
force_doublebuf = 1/0

# same as SDL_OMAP_NO_TS_TRANSLATE
no_ts_translate = 1/0

# can be used to bind a key to SDL keysym, good for quick ports.
# Example:
# bind ev_home = sdlk_space
bind ev_<evdev_key> = <sdl_key>


Source
------

Available at git://notaz.gp2x.de/~notaz/sdl_omap.git