README for Prisma VNC client

This is the source for a VNC client for Minix 2.0.2 running on an
ISICAD Prisma model 700 with a 33249 or 33500 Video Buffer board.
It is based on the VNC X client version 3.3.2.

This is a snapshot release, it works but is unusably slow. I am making
it available in the hope that it may encourage someone to port it to
i386 Minix.

The Makefiles are written for GCC running as a cross-compiler on my
NetBSD system.


What is VNC
-----------
VNC stands for Virtual Network Computing, it is based on the concept
of a remote framebuffer and allows the VNC client to display the screen
of a system running the VNC server. Clients and servers have been written
for X/Unix, Windows 3.1/95/NT, Macintosh, Amiga and others. More details
can be found on the VNC web site:

    http://www.uk.research.att.com/vnc/


VNC on the Prisma
-----------------
The Prisma port is based on the X client. To minimise the number of 
changes in the core code (so that it will be easier to upgrade when
a new X client is released), I have used dummy structures and functions
in place of the missing X headers and libraries. The network code has
been modified to use the Minix interface and a simple mouse driver has
been added to work with a standard two-button serial mouse.

Most of the effort has gone into the display interface but the
results to date are disappointing. The Prisma's video buffer is not
memory mapped, instead it is only accessible through a series of
control registers. The board does have hardware assist for line
drawing but has no block fill or move capability. Pixels can only
be written or read in vertical groups of four and the order in which
they appear varies with both the x and y coordinates!

Information on programming the video buffer is scant so most of the
details have been deduced by looking at how the monitor ROM does it.
I have spent a lot of time trying to improve the performance by
moving some of the loops into optimised assembler code but although
this has helped, the overall performace is still unusable. It may be
that there are better ways of driving the display but I haven't
found them yet :-(

I am unlikely to do much more work on the client unless I can think of
some radical way to improve the display driver, but having got this
far I am seriously considering trying to port a full X server instead
to see if that could be made to perform any better :-)


George Harvey
fr30@dial.pipex.com
29th May 1999