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

[From: Tapani Pälli]

Hello;

ext Siarhei Siamashka wrote:
> 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.
>
>   
This is what I've heard from our kernel team members, maybe they could
share some more light to this. AFAIK the hardware itself does not offer
sync.

>>> 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
>   
Hmm, but how do you know when to start drawing?

> 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).
>   


// Tapani Pälli

-- 
Software Engineer
Open Source Software Operations