Re: Some considerations

[email protected] wrote:

> I see your point now. Still, it might be better to keep them in
> AGP memory anyway. You have to keep copying them over the AGP bus,
> but even at extremely high drawing rates you can't be taking more
> than 100MB/sec. 

It will be way worse than that for two reasons:

1. AGP memory is either uncached or write combined, so CPU reads are 
terribly slow, just like video memory. 10-20Mb/s max is about the norm 
for most modern cards.

2. If the glyphs are color alpha bitmaps intended anti-aliased rendering, 
then will need to be blended into the AGP surface, and unless the 
hardware has the ability to draw into AGP memory (which I don't believe 
most hardware can do), then the blending would be entirely in software 
and would also be affected by the terrible read performance.

If the glyphs are just mono bitmaps for non anti-aliased text, always 
keep those in system memory. There is zero performance advantage to 
caching them in offscreen memory memory due to the high speed of writes 
to the hardware combined with the fact that the bitmaps are basically 
compressed. Each byte in the bitmap expands to 32 bytes in video memory 
for 32-bit display modes, which is a 32x compression factor. Hence if you 
can transfer data at 100Mb/s to the hardware, you would need hardware 
that can do mono expansion at a rate of more then 3.2Gb/s before it would 
be faster to store them in video memory (ie: not likely).

Then again since we are talking about a modern system, non anti-aliased 
text is probably not very interesting ;-)

Regards,

---
Kendall Bennett
Chief Executive Officer
SciTech Software, Inc.
Phone: (530) 894 8400
http://www.scitechsoft.com

~ SciTech SNAP - The future of device driver technology! ~