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

[From: Siarhei Siamashka]

On Feb 18, 2008 9:39 AM, Tapani Pälli <tapani.palli at nokia.com> wrote:
> > When using the supplied SDL library for doing timer-based frame
> > rendering, there seems to be
> > - heavy tearing
>
> Tearing unfortunately happens because there is no vsync available for
> framebuffer driver to use.

Could you please verify and confirm this information? Framebuffer
driver from OS2007 supported tearsync (via OMAPFB_FORMAT_FLAG_TEARSYNC
flag as Frantisek mentioned), and it was used at least for video.
Well, I have noticed some tearing in mplayer with OS2008 though.

> > Q: I can't get the tearing away (only fixed at certain line positions).
> > What am I doing wrong?
> >
> >
> Nothing, you cannot get away from tearing.

Still what about trying different LCD panel timings? For example,
reducing LCD refresh rate to something like 40Hz should allow 20 full
resolution fullscreen rgb updates per second with perfect tearsync. I
don't dare trying such experiments myself as I'm afraid to kill LCD
panel of my N800 :) Can any HW expert tell if it can be possible? Link
to LCD controller docs is available earlier in this thread.

On the other hand, reducing refresh rate may introduce problems for 25
and 30 fps video playback (for high resolution video only, when the
time to transfer frame data over graphics bus is larger than one LCD
refresh cycle).