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

[From: Arnim Sauerbier]

--- Daniel Stone <daniel.stone at nokia.com> wrote:

> I assume your 'xrandr' screenshot is taken on the desktop?
> RandR doesn't imply a specific scaling algorithm.

Yes. I mistakenly assumed that xrandr would imply a point-scaler algorithm.

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

There is none, but look again at the title of this thread.  :)

> I don't see the point in doing pixel doubling in software.

The point is to consider alternatives to improve performance for SDL games on the 770 (and by
extension, the 800).

> It's not about memcpy.  I think the _maximum theoretical_ rate of screen updates is 28 fps
> 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.

Thanks for that info.  I estimate my action games need roughly 20-25 FPS at 640x480 and RPGs 8-15
FPS at 800x480, so available bandwidth would be sufficient, correct?

I'd like to thank Matthew, Eero, Daniel and Tapani for sharing their ideas on the future of pixel
doubling and Xomap here, but given the status of N770 support, we in the community can not
reasonably ask or expect Nokia to implement them for IT2006. If this is correct, I respectfully
request that discussion about future Xomap releases be forked to another thread and we return here
to the question of how to improve SDL game performance on the current OS.

To review:

- When UQM updates the full 320x240 screen (as in the intro and settings menus) Xsp doubling works
as intended.  When it updates portions of the screen (main menu, combat, dialogues) doubling is
getting disabled.  I don't understand why this is happening and apparently nobody else does
either.

- UQM combat is running at 21-24 FPS in 320x240 mode and at 6-11 FPS in 640x480. Getting 640x480
up to 20+ FPS is all that's needed to make it playable.

- Given the stated goal (deliver SDL games to current tablet users) and the known constraints (Xsp
problems, no Xomap fixes for IT2006), I see three potential solutions for the community (not
Nokia):

1) find out and document how to avoid the Xsp-doubling/damage problems for SDL apps, in general
2) write a SDL putrect equivalent that can use DSP pixel doubling directly, without using Xsp
3) write a fast SDL putrect equivalent direct to framebuffer (cf mplayer) - optional SW scaling

There are a number of classic SDL games that are close to playable on the 770.  We could dive into
each one individually and look for performance gains, but speeding-up scaled SDL surfaces across
the board would yield a bigger payoff.  I have doubts whether #1 is possible and #2 would require
an intrepid coder who can venture into 'here be dragons' DSP-land.  I think #3 (basically
Siarhei's suggestion) looks like the most general and do-able route to speed up SDL games, since
he's already implemented something like this for mplayer.

Any thoughts?  (besides "sell your 6-month old 770")

Arnim

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com