[Coco] Artifacting (again)

[Robert Gault]

Ciaran Anscomb wrote:
> Robert Gault wrote:
>> [artifacting]
>> Don't get confused by the output of emulators. There is only one emulator that
>> comes close to correct artifact appearance, MESS.
>
> XRoar (no CoCo 3) does a reasonable approximation of the cross-colour.
> It uses a heuristic though, rather than calculate the actual interference
> from the harmonics of the high frequency luminance.  That's actually
> something I intend to (optionally) do properly at some point...
>
>> The Keil, and VCC emulators
>> approximate the artifact effect by using pure white, black, red, and blue but
>> these are not artifacts. As a result of this graphics on these emulators will
>> look sharper than the same screen would be on a real Coco attached to an NTSC
>> monitor.
>
> Do NTSC CoCo3s also artifact in this way, then?  For some reason
> I thought I'd read before that they provided a simple cross-colour
> "palette".  Perhaps that was someone describing another emulator and I
> got wires crossed.
>
> ..ciaran
>

The Coco3 emulates the MC6883 and MC6847 chips while in Coco 1/2 mode. Therefore 
on the PMODE4 screen, the result on an NTSC monitor is just like a real Coco 1/2.
Palette selection is possible, so you can, for example, change the four colors 
of the Coco 1/2 PMODE3 screen to any you want.

What can be done with a Coco3 is to patch commercial programs so that instead of 
using a PMODE4 screen, they use an HSCREEN at 256x192x4 resolution. This screen 
has 4 true colors and if made black, white, red, and blue through palette 
selection, you can get color on an RGB monitor that looks like the Keil and VCC 
attempts at artifact color.