[maemo-developers] Xsp pixel-doubling solutions for Nokia 770?

[From: Eero Tamminen]

Hi,

ext Siarhei Siamashka wrote:
>> Same problem as using framebuffer directly.  How user switches
>> to another application?   How to invoke power menu properly etc.
> 
> What problem with using framebuffer directly? Everything should be
> fine, you can get notifications from xserver when your window becomes
> obscured, so you can stop drawing. I suggest you to try MPlayer on
> Nokia 770 to check how it interacts with xserver. The worst thing that
> can happen is some garbage data left on screen on fast applications
> switching. That can happen because there is no support to synchronize
> access to framebuffer in a reliable way (application using framebuffer
> directly may get notification from the xserver about getting inactive
> too late and overwrite some other application window).
> 
> Adding support to xserver for proper synchronization with direct
> framebuffer access applications should be quite possible. It already
> synchronizes access to framebuffer with DSP (Xsp API for registering
> DSP area). Almost all the necessary changes will probably have to be
> added at the same places in xserver which support interaction with
> DSP.

AFAIK Xserver requests & waits DSP to stop updating the framebuffer
before proceeding.  This works with HW, but you cannot expect it to
work reliably with misc X clients as there are no guarantees about
what they do. If client is not processing X events, the response would
be waited forever and device freezes.  If X server has some timeout for
the client reply, then the server and client can be updating the
framebuffer at the same time and that was what we wanted to avoid
in the first place.


> I guess it can't be helped and I will make an example application for
> using framebuffer directly and some kind of tutorial. Don't know when
> I will have enough free time to do this though.
> 
> I'm pretty much confident that direct framebuffer access (also with
> pixel doubling support) is quite possible for SDL. I don't care much
> if you believe me or not :) Someone just needs to do the dirty work
> and implement all this stuff.

Yes, it just cannot be done safely / reliably.  But for hackers
it's enough that it works when it works I guess. :-)


	- Eero