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 -
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