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

[From: Daniel Stone]

On Wed, May 02, 2007 at 01:01:00PM -0700, ext Arnim Sauerbier wrote:
> Siarhei Siamashka wrote:
> > This is what works for MPlayer on Nokia 770. It creates x11 window just
> > to reserve some screen space and prevent other applications from using 
> > it. After that, it renders data directly to framebuffer and uses x11 for
> > input. It is not very clean, but it works. And it works fast. The same trick
> > can be probably done for SDL.
> 
> Indeed SDL is the 'gaming api' in-use for games that run acceptably on tablets, and Xrandr would
> be the natural choice for changing screen resolution. While that would be fast and simple, it
> doesn't look good. See
> 
> http://pupnik.de/ScalersExult.png
> 
> As the screenshots show, a Scale2x or 2xSai scaler yields much more readable text (view on the
> tablet to get a good idea of this). 

I assume your 'xrandr' screenshot is taken on the desktop?  RandR
doesn't imply a specific scaling algorithm.  Indeed, my plan was to just
expose 800x480 and 400x240, and use the exact same pixel doubling in
Hailstorm to achieve the latter.

> While I appreciate that the folks at Nokia are looking into solutions aimed at future Xomap and
> tablet releases, my interest is directed toward improvements that can apply to current N770 and
> N800 tablets.

I don't see the conflict between working on new Xomap versions and
improving the N800.

> To this end, my hope would be for a fast Implementation of SDL's HWSURFACE that would allow the
> SDL app to use an internal high quality scaler or 800x480 native resolutions.

I don't see the point in doing pixel doubling in software.  Thus, what
we have is restricted to the hardware.  Not only would the expansion
take CPU time, but you then have to send the entire expanded screen over
RFBI, which sucks.

> If the memcpy on 770 is something like 190MB/s, pushing 800x480 at 30fps would use only 12 percent
> of that bandwidth

It's not about memcpy.  I think the _maximum theoretical_ rate of screen
updates is 28fps, due to the limited bandwidth between OMAP dispc and
Hailstorm.  You cannot push pixels any faster than this, even if you
try, and even if you optimise SDL to death.

Cheers,
Daniel
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