[Coco] RGB to XGA (Bruce Borer)

[Andrew Ayers]

Hello Bruce,

I was trying to point out that there are other GIME graphics modes which 
it can display (and they can be used, but there isn't many applications 
that do - I think the majority of apps that do are recently written 
(post-1992ish?) games); also, the 225-line mode (and the others that 
exist, I forget their values).

I was just asking if you had tested all of those with your converter, 
since you mentioned only the 192-line mode, for instance? The tweaks to 
get the higher number of lines were something that was well known "back 
in the day", so there might (or is?) more software that uses them 
(versus the alternate GIME graphics modes, which while likely known, 
were either little exploited, or not at all).

And the "256-color" artifacting mode is just something from the 
composite output that - while "sorta-kinda" was known about by some back 
then, it wasn't widely published about; I know of one publication about 
it in Hot Coco - but I've not found anything about it in the Rainbow; 
someone who worked for - I think Sundog? - supposedly knew about it, but 
for some reason, it was never known or experimented with, that I know 
of, by other users or developers (a curious tale which we'll likely 
never know the reasons why - I surmise that people were so enamored by 
the more colorful modes, and RGB output, that for some reason it never 
occurred to them to play around with the 640x192x4 color mode with the 4 
grayscales and do the same "magic" as the PMODE4 screen).

The CoCo 3 has limited SG modes; SG4 and I think SG12/24 (???) - I'm not 
sure; the former is of course fully supported, while the latter two (or 
one?), like the CoCo 2, requires some special "POKES" and such to 
access, and for speed you need to use ML. Also, unlike the CoCo 2 VDG 
modes, it can't mix text with the semigraphics.

Because you say your adapter works in WIDTH32, those modes should be ok, 
I would think - but testing them could reveal differently.

Of the links I posted to you, the 3D printed "enclosure" should be of 
interest, since it was designed for a video mod primarily, but also that 
it fits inside the recess you spoke of; in theory it could make your 
adapter a more "commercial" kind of device - but since there aren't any 
design files, you'd either have to somehow convert it back into those 
(not sure if there are any tools to go from an STL to some other 3D 
editor or CAD formats) - or re-engineer it entirely.

Ultimately, I was just wondering if you had tested all the known 
graphics modes the CoCo 3 can work in, or just a limited subset, and if 
the latter...perhaps trying those other modes and/or adapting your 
hardware and/or code to support them might be of interest to you.

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

On 12/23/25 9:26 PM, Bruce Borer wrote:
> Hi Andrew,
>     You seem to be asking about changes to the CoCo itself.  My 
> converter just displays what the CoCo3 produces, including making WIDTH 
> 80 readable on readily available monitors.
> 
> Bruce