[Coco] RGB to XGA (Bruce Borer)

[Bruce Borer]

Hi Andrew,
    This is more information than I was aware the CoCo3 could produce
My converter supports WIDTH 32, 40 and 80 because by supporting
WIDTH 80 the others are a subset.
   Tell me more how the CoCo3 can produce 225 lines and I will work on
supporting it.  May be supporting 400 pixels by 225 lines then all other
modes would be a subset.  I believe the current hardware (video RAM)
can support it and the software can easily be changed to also support
the extra lines.

    Where can I get information on 225 lines of video from the CoCo3?

Bruce

On Wed, Dec 24, 2025 at 12:37 AM Andrew Ayers <keeper63 at cox.net> wrote:

> 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
>