6 Mar
2015
6 Mar
'15
10:33 a.m.
On Mar 6, 2015, at 1:07 AM, tony duell <ard at
p850ug1.demon.co.uk> wrote:
It?s interesting to compare with the PLATO terminals. The first plasma panel terminal
(?PLATO IV?, ?Magnavox?) is from the early 1970, all hardwired logic. It does line
drawing in hardware, essentially the Bresenham algorithm. It doesn?t have area fill.
The ?PLATO V? terminal is a 1976 successor, using an 8080 with some hardware assist (the
Bresenham per-pixel step is in hardware, but the full line loop is in software). That one
initially did not have area fill but a somewhat later successor added that, in software.
So, high end feature, I suppose; PLATO terminals were used in fair numbers but were not
mainstream graphics terminals.
paul
...
One of the full-width cards is something like 'area fill'. So it does that in
hardware too?
Yes, probably, it is not that big trick (in theory). Example Amiga's custom chipsets
was capable for area fill (line
mode), and btw, prototype of that custom chip set was made from TTL
chips:http://www.floodgap.com/retrobits
/ckb/secret/cbm-lorraine-portrait.jpg
Sure. My guess is that the line drawing on this terminal is going to be similar to that
on the HP2623. A simple
state machine where the main CPU (in the HP a Z80, in the Sigma a 6800) calculates
various parameters and
the state machine goes along setting pixels. The area fill board is perhaps 50 or so TTL
ICs. Not complex
really. But I think it is a high-end feature for a 1970s terminal.