🚀 go-pugleaf

> It has been my understanding that the X11/NeWS servers (version 1.0 and 2.0) 
> do not utilize accelerators, period.

Unless you've got some strange release of OpenWindows, Xnews from 2.0 uses the
LEGO for operations which it can.  The SBus doesn't run fast enough to give the
rectangle fill and copyarea rates which I've measured here.

> In a separate, but related subject, Keith Packard, in his discussion of
> Server internals at Xhibition a couple of weeks ago, indicated that he has 
> tested, and found that (almost) none of the accelerated frame buffers (Sun, 
> or otherwise) provide any usable performance improvement for GUI type drawing 
> activity.  In a nutshell, he said that the overhead of setting up the 
> accelerator pipeline, putting the instructions into the pipeline, and then 
> closing the pipeline, negated any possible advantage. 

I don't think this is a direct quote.  In particular, I know that the Sun LEGO
accelerator is capable of drawing long zero-width lines, filling solid
rectangles and copying data around on the screen faster than the completely
dumb frame buffer.  These operations are very useful for many GUI-style
activities.  However, it is also true that for short lines, or for text, the
overhead of communicating with that particular accelerator is greater than the
performance gained by using it (or at least so my measurements using the OW2.0
server show).  And the fancy polygon fill hardware doesn't match X pixelization
rules, forcing the Xnews server to render them in software.

It is also the case that the LEGO card provides slow access to the frame buffer
for the CPU, making dumb frame buffer operations slower on this card than on
the CG3 - this gives you an opportunity to choose the board which more closely
matches your application needs.  For example, if your application doesn't use
any of the accelerated operations, you'd probably be better off with the dumb
frame buffer, while applications which can take advantage of the fast
operations will see substantial performance benefits when using the more
expensive hardware.  If only Sun would allow the customer to make this choice -
I, at least, was unable to purchase a SS2 with the dumb frame buffer, except by
getting a monochrome SS2 and adding a separate CG3 (total price > SS2+LEGO).

It is also possible to build hardware which doesn't suffer from these
performance problems; simply design it carefully taking into consideration the
needs of the X server.  The new HP Snake series seems to fit in here - all of
the X performance data I could get indicates that this is one hot piece of
hardware (except that it doesn't render to VM - I don't know how it handles
pixmap rendering).

> Keith also indicated that the R5 server will be even faster than the R4
> server due, among other things, to newer, more efficient rasterization 
> algorithms, and the judicious use of assembly.

R4 is a dog.