Webcam support in Squeak (for VOLPC)

[Bert Freudenberg]

On Mar 7, 2007, at 18:32 , Dan Williams wrote:

> On Tue, 2007-03-06 at 17:14 -0700, Jonathan Corbet wrote:
>> If there's any way you could get Squeak to work with
>> rgb565 and cut out both conversions, I suspect you would be a lot
>> happier.
>
> Yes, format conversions really hurt.  Thou Shalt Not Format Convert.
> While the machine does have MMX, which helps somewhat, it's not a  
> magic
> bullet.  First, the GPU can only accelerate blends to the framebuffer
> when the src is the same format as the dest.  The GPU can accelerate
> format conversions, but the pipe back to main memory is really slow.
> Therefore, it's not a win to do hardware-accelerated format  
> conversions
> in GPU memory unless you're going to blit them directly to the
> framebuffer using GPU acceleration too.

So if I hand a 555 to X to be drawn on the screen, the GPU would  
accelerate it?

>   This means that all format
> conversions are best done on the Geode itself, which isn't going to be
> fast because it's a software format conversion.
>
> If you send X a pixmap that's not in the native framebuffer format
> (which happens to be 565 right now) then X will have to format convert
> that to 565 for you, which ends up being really slow, especially for
> large pixmaps.

Why doesn't it use the GPU? Provided I'm drawing to the display, that  
is.

> The moral of the story is, don't format convert, and
> keep everything you want to be fast in native framebuffer (ie 565)
> format.

What about switching to 555 in general? Seems a much more logical  
format.

- Bert -