[maemo-developers] SDL, tearing, X overhead and direct framebuffer gfx

[From: Siarhei Siamashka]

On Feb 17, 2008 9:56 PM, Tobias Oberstein <tobias.oberstein at gmail.com> wrote:

[...]

> I've read a lot of bits on the web 'bout mplayer, vsync, omapfb etc.
> and tried to assemble a minimal example of using direct framebuffer
> access for gfx output.
>
> Q: I can't get the tearing away (only fixed at certain line positions).
> What am I doing wrong?

Transfer framebuffer->videoram must be fast enough to complete for the
period of two LCD refresh cycles, also see
http://lists.maemo.org/pipermail//maemo-developers/2007-March/009202.html
Using smaller source rectangle in the framebuffer will reduce data
transfer time and the tearing line at the bottom will disappear (using
'new' screen update ioctl which was introduced in N800 kernel, this
rectangle can be upscaled to fullscreen). You can calculate the
resolution which can be used without tearing either theoretically or
in an experimental way.

> I wondered if there would be any plans to make SDL run directly on
> framebuffer .. if not, I'd maybe give it a try.
>
> Q: Where can I find the sources to the OS2008 SDL?

AFAIK, SDL is used pretty much unmodified. My guess is that you can
get it here: http://repository.maemo.org/pool/chinook/free/source/

As for some practical solution on N800/N810, I think it makes sense
tweaking xserver to add support rgb color format in Xv and tweaking
SDL to use Xv for the emulation of setting arbitrary screen
resolutions (setting low resolution will eliminate tearing and will be
useful for games).

For those interested in the topic, documentation for the Epson LCD
controller used in N8x0 (S1D13745) is available here:
http://vdc.epson.com/index.php?option=com_docman&task=cat_view&gid=38&Itemid=40