[Coco] Coco compatible monitors...

[Mark McDougall]

On 6/07/2011 11:13 PM, John Kent wrote:

> I'm not sure what is meant by "artifact colours" but the problem of reading,
> modifying and writing back graphics is the available memory bandwidth. You
> have to steal more cycles from the CPU to be able to read and write back the
> information. The number of colors is restricted by the way the graphic chip
> stores the graphics.

<http://en.wikipedia.org/wiki/TRS-80_Color_Computer#Artifact_colors>

If you're running your Coco implementation at native speed, there should be 
plenty of bandwidth to interleave access to video memory by a 'filter' that 
attempts to produce some form of artifacting, without having to steal CPU 
cycles.

Alternatively, you can use a line buffer and produce the effects on-the-fly 
without requiring extra bandwidth. However, indications are that adjacent 
lines combine to affect one-another, so one line wouldn't be sufficient. 
You'd have to buffer several lines.

I did see somewhere in a software emulator an approximation of the 
artifacting... from memory it used a rather complex (and large) matrix, 
though IIRC it was empirically derived rather than based on any theory of 
the cause in a real Coco.

Regards,

-- 
|              Mark McDougall                | "Electrical Engineers do it
|  <http://members.iinet.net.au/~msmcdoug>   |   with less resistance!"