Re: ISA Vector card already done...

At the risk of sounding like a bone head, I'll ask this question,
because now I'm really curious as to what's going on ..

Zonn wrote:
>
> Now to do this digitally you must be able to move the trace along the same path
> the charging capacitor takes. So you must now divide that trace up into as
> small as pieces needed to create the appearance of a smooth line using digital
> jumps. 1024 positions across a 19" monitor is the minimum that looks decent.
> Even at a 1024 positions you can still see the "pixels" that make up the line if
> you look carefully.
>
> Now in order to draw the lines fast enough to keep up with the number of times
> the lines must be drawn in a second, to fool the eye into thinking they're
> always there, we must draw them pretty fast. How fast depends on the spec of
> the monitor. And for our purpose, how fast the original hardware drew them
> since we must keep up with it.
>
> What it gets down to, is for us to draw a line digitally from one side of the
> screen to the other we have to update the DAC 1024 times, in the same amount of
> time the game has to update the DAC once (assuming the trace is already on one
> side of the screen). So now we're already 1024 times faster than the
> Cinematronics (worst case). The DAC will have to be updated at a 6mhz rate to
> keep up. And this is exactly what the original Asteroids (which is digital)
> does. It used parallel input DACs so that all 20 data lines were loaded in one
> 6mhz clock pulse (10 X data lines, and 10 Y).

>From which it sounds like you are saying that if I wanted to draw a
vector from point (0,x) to (1023,x), the DVG must output 1024 values?
I.e., this is what you mean when you said "update the DAC 1024 times"
... [to draw a full width line]

I thought the whole point of a vector display is that you truly can just
output end points, which are the absolute values of the coordinates that
you are trying to draw.

An experiment that I've done, that I've mentioned here, was that I
hooked up the output of my sound card to the X and Y input of my scope.
I input the vertices of a 3D cube to a program of mine that then
performed 3D rotational transforms to it on demand (when I hit certain
keys for instance). The program output a stereo 16 bit 44.1K wave file
with the left channel holding X data and the right channel holding Y
data. This small program drew my rotating cube perfectly. But the
point is that I never output anything BUT the endpoints of my vectors,
and thus the vectors were perfectly smooth.

Are you saying that the Atari games do output a unique analog value for
each pixel along the line of a vector? (And therefore, not just
endpoints?) If that's the case, then what you described above makes
sense to me if the purpose of this card were to be able to run a vector
game emulator on the PC with a vector display ... but I thought this
project of Clay's was more for "new" vector game development. In which
case, why would you choose to draw vectors as you've outlined above,
when you can just output end points?

I certainly look forward to hearing the explanation. I love the topic
since I've been interested in a project like this since I started with
the hobby 3 years ago.

Joel-
Received on Wed Mar 25 14:33:28 1998