[maemo-developers] Wishlist (was:Re: N800 and USB host mode)

From: Tapani Pälli tapani.palli at nokia.com
Date: Fri Mar 9 09:46:31 EET 2007
ext Daniel Stone wrote:
> On Thu, Mar 08, 2007 at 01:06:00PM -0800, ext Daniel Amelang wrote:
>> On 3/7/07, Eero Tamminen <eero.tamminen at nokia.com> wrote:
>>> Err.  Translucency means compositing and keeping the composited items in
>>> memory.  Due to additional memory accesses needed for this, it would be
>>> slower (and take more memory) regardless of how "accelerated" it would
>>> be.
>> Keeping the composited items in memory is not necessary. After you
>> composite, you can (and often) just keep the final result around.
> The Composite extension to the X server requires a backing pixmap for
> every window, and a final pixmap which is essentially the fb.  So, while
> you're right about compositing as a concept, I think Eero's talking abou
> the possibility of using the Composite extension.

I think on Maemo platform we might be able to optimize memory usage
since only one application window is visible at time and we are not
considering to have translucent application windows. I'm currently
investigating if optimizations would be possible and we could have
something nice done with composite engine in matchbox-window-manager.
Maybe compositor could have only desktop window with it's panels and
menus, topmost application window and it's dialogs, menus etc in
memory at once?

Performance is also problematic, currently matchbox-window-manager
with composite enabled performs rather well (xcompmgr being slightly
faster though) but CPU usage is much higher meaning higher power usage.

So to sum this up, we are looking and investigating the usage of
composite management in Maemo.

>>> You can see this even on Desktop, just ask how many gamers are happy
>>> with integrated graphics cards which share memory with the rest of the
>>> system instead of having (hundreds of megs) of their own memory in which
>>> to store textures etc. and in where the operations can be done without
>>> loading the memory bus of the rest of the system (downside is that all
>>> this costs, adds to the computer power consumption & heating).  :-)
>> I don't totally agree here either. It sounds like you're saying that
>> the hardware acceleration won't get you much unless you have dedicated
>> video memory.
> He is, and I'm willing to back him up.
>> Here's a counter-example: the macbook uses an integrated graphics card
>> to do all of its fancy accelerated UI effects, including translucency.
>> Yes, the macbook is not a gaming machine, but that's not the issue,
>> here. The issue is that hardware-accelerated graphics enable advanced
>> user interfaces, even w/out dedicated video memory.
> It would be nice if we had the MacBook hardware in the N800's form
> factor, with the exact same power consumption.  Tragically, this is not
> the case, and our memory bandwidth is, shall we say, not staggeringly
> high, limited both by raw clock speed, and memory bus design.
> The MacBook has PCIE, and fast main memory, meaning that it's able to
> push textures between the GPU and main memory at a blazing fast rate.
> N800 has its own 'video memory' for the final framebuffer (so your main
> memory isn't impacted by the load of scanning out), but the rest would
> have to be done in main memory, where you're in direct contention with
> applications for the bandwidth.
> Cheers,
> Daniel
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// Tapani

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