RE: Game design...

> I love that effect too, but is there really any reason that you can't
> do
> that on a color screen? I always assumed that the way they did that
> was
> to re-draw each shot several times per frame while drawing everything
> else
> only once. I also assumed that the reason they didn't do it on the
> color
> games is that they all had more going on and doing that would take too
> much time away from the other shapes and cause flickering. Could
> someone
> confirm this? Did I assume right?
>
The monochrome monitor has a lot to do with that effect. The monochrome
phosphors have a longer persistence (which leaves those glowing "trails"
on shots in Asteroids) which act as kind of an integrator to changes in
brightness. You just change the intensity between "high" and "low" and
the phosphors will "ramp" up and down to the brightness which gives the
"firey" effect.

Color monitors have a shorter persistence phosphor (usually to *defeat*
the "trails" effect) and since the color vector monitors use standard
"raster" tubes (with P22 phosphor I back then?) the trail effect isn't
as great. Now you *can* get some of the same effect with a color vector
since you're actually driving the color guns a lot "hotter" than you
would on a raster-- there's some persistance on the display, but it's
not exactly like a monochrome.

> What does Asteroids look like on a
> color monitor? I have never seen one.
>
Depends on how you hook it up. If you just connect the Z-output of
Asteroids to a color gun input on a WG the display will look "OK",
although the phosphor trails are less pronounced. You can compensate by
bumping up the output of the Z amp (or messing with the neck board
settings and/or screen drive). Running the guns hot though increases
the chance of phosphor burn-in.

If you hook up more than one color gun to the Z output (tie RGB together
for example) you'll get a lot more brightness because you've got all
guns hitting phosphors next to each other on the tube. Be careful if
you "turn up" the brightness on a monitor with a screen that has reds,
greens, and blues without any "white". White will be much brighter than
the primary colors separately.

The other "gotcha" with vector colors is that the intensity is
cumulative. On a "raster" each line of video only gets hit once per
field. On a Vector you can redraw any area as many times as you like.
So even if the color guns are at a "safe" level if you redraw the same
thing a bunch of times it can get so much energy that it'll burn-in.
(Which is why you get a lot of "TEMPEST" burn-in on monitors-- when the
logo zooms in it's a bunch of single images that eventually stack up on
top of each other. That ads to the brightness. So even if you dial in
a "safe" level for the "white" on the test screen, the "TEMPEST" logo
will still be much brighter!)

-Clay
Received on Wed May 5 15:11:06 1999