XFree86

[Jeremy Chatfield]

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Hugo van der Kooij wrote:
> 
> On Thu, 2 Apr 1998, Matthew Valenta wrote:
> 
> > Hello,
> > This is actually a question only tangential to VNC, but I currently use
> > X-Free86 and remote control my Winblows box with VNC in 24 bit depth.  I'd
> > like to only use 8 bit from Windows to speed things up a bit,
> > but I can't make X-Free86 run both a 8bit and 24 bit server concurrently.
> >
> > Does anyone know how to do this?
> 
> xnest should be able to do that.

This does incur a performance penalty, though, as Xnest runs a virtual
Server using only a framebuffer (no hardware acceleration) and then
requests the output of the Server to be shown in the real Server (which
means that it avoids the hardware acceleration in the real Server).  If
you run the real Server in 24bpp, even if fully accelerated you'll be
running at about 1/4 the speed of an 8bpp only Server, or less.

There are some Servers on both PC's and workstations that support
concurrent 8bpp and 24bpp operation, if the right hardware support is
available.  They all use hardware acceleration, though the memory layout
of PC graphics boards is not designed for this use, so there is some
speed loss with PC graphics boards.  8bpp operations on an accelerated
Server for a PC with overlays are about the same performance as 16bpp
operations.  Visibly faster than using Xnest, and visibly slower than
using an 8bpp only Server.  Using hardware designed for overlay
operation would result in little measurable penalty, as is the case on
workstations that support overlays.

Overlays also have one other beneficial use, which is that the image
data in the 24bpp plane is not destroyed when you slide an 8bpp window
over the top of it.  This can considerably reduce time delays in
redrawing images and decreases Server computational and bus bandwidth
requirements (translation: your machine feels faster).

Xnest is a popular and low cost solution, and has been successfully used
with WABI for Linux, whose supported color depth is 8bpp.

The idea of using VNC's virtual X Server to create a framebuffer, to
feed the Xnest framebuffer virtual X Server which finally feeds a real
hardware implemented X Server is rather amusing... Given the network
latencies of VNC, it is probably workable, but I expect that you'll be
able to perceive a performance penalty.

Cheers, JeremyC.
-- 
Jeremy Chatfield, Xi Graphics  mailto:jdc "at" xig.com  tel:+44(0)1234.710030 
 Commercial X Products: Servers, CDE, contracts and custom development
    http://www.xig.com ftp://ftp.xig.com/ mailto:majordomo "at" xig.com
     tel:+1.303.298.7478  fax:+1.303.298.1406  mailto:info "at" xig.com
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