DECDLD usage -good enough for minimal graphics?

[Julian Wolfe]

VT220 does not have graphics, but does have an available down-line-loadable
character set.
DECDLD is the (protocol?) that is used to transfer the custom fonts to the
terminal.  I was wondering how fast it does this  - from what I can gather,
using this method you can redefine and line up the characters so that they
form a picture, while still retaining the ROM character set.

Am I totally off base about this?


-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]
On Behalf Of Paul Koning
Sent: Monday, August 08, 2005 4:51 PM
To: cctalk at classiccmp.org
Subject: Re: DECDLD usage -good enough for minimal graphics?

>>>>> "Julian" == Julian Wolfe <Wolfe> writes:

 Julian> Hello everyone!  I was just investigating the usage of DECDLD
 Julian> for defining a small graphic screen on my PDP11 during a
 Julian> program.

 Julian> When using a VT220 at 19200 baud, how fast can a screen be
 Julian> refreshed using DECDLD graphics?  I was thinking of doing a
 Julian> multiplayer (4 player) game using this system.

If you plan the graphics properly, sure, no problem.  PLATO had
multiplayer games long ago using 1200 baud lines.  That was with a
MUCH more efficient graphics encoding, though.

Did you mean VT240?  Unless my brain is going, VT220 is text only.
VT240 supports REGIS, which is a simple graphics protocol (somewhat
verbose in its encoding as I recall).

Assuming that REGIS doesn't lose more than a factor of 16 in coding
efficiency vs. PLATO -- which should be true -- you should be able to
get a couple of refreshes per second.  There are plenty of interactive
games that can live with that.

      paul