[Coco] Breaking the Four-Color Barrier

[Andrew]

It's been a while since I last posted here; I am usually posting on the 
FB forum, so I thought I'd switch things up a bit.

Over there, I had made a post about H. Allen Curtis's "Desktop Publisher 
on a Shoestring" article (and later "follow-up") that appeared in the 
Rainbow. Consequently, I've been rummaging thru the scans I have on my 
NAS, finding interesting and old things - some of them I recall playing 
with as a kid back in the day.

As the subject of this post indicates, I found something of note, that 
shows - at least when it comes to the CoCo 3 and the Rainbow - just how 
close someone came to finding the 256-color artifacting mode of the CoCo 3.

See the Rainbow, October 1988, Page 51 "Breaking the Four-Color Barrier" 
by Rusty Cutchin

Now - I'm not wanting to rehash the whole 256 color thing, and really, 
doing artifacting isn't even mentioned; in fact, it seems like this 
article is about making colors by mixing primary colors in the 640 
(HSCREEN 4) 4-color mode on an RGB monitor.

I recall playing with this code, and finding it somewhat interesting, 
but I couldn't use it for what I wanted (namely, high-resolution solid 
3D models, via Lee Adams' books of the day), because it didn't modify 
the HPAINT routine to support the method, and I didn't have the skills 
then to do it.

Heck, today...while I would be willing to tackle it and could probably 
make the system do -something-, I really don't have the deep intimate 
knowledge of the CoCo 3's SECB in RAM to do more than break things, I 
think. I'd have to pull out the Unravelled series and pray to the gods 
for understanding. IOW, someone else here likely could mod/patch the ROM 
routines faster and better than I could.

But anyhow...this particular article does show something interesting, 
and at the same time - while it wasn't focused on it, actually doesn't 
even hint at it - I do today wonder what if someone had said "4 colors, 
4 gray levels, 640 pixels, artifacting...hmm" and tried it back then. 
Honestly, I don't know why I didn't try it, because at the time I had an 
RGB monitor and my TV hooked up to my CoCo 3. But it never occurred to me.

The past is strange that way, I guess.

Regardless, though - this technique for gaining some "colors" in that 
higher-res mode does look interesting, and I wonder how far it could be 
pushed - that is, what kind of dithering techniques or such could be 
used to make it look like many, many more colors. I know it's possible 
(Simon's PMODE 3 Torus demo shows that, I think).

Well...maybe someone can run with it. :)

Andrew L. Ayers
Glendale, Arizona
phoenixgarage.org
github.com/andrew-ayers