[Coco] sideborder

[Ciaran Anscomb]

"Simon Jonassen" wrote:
> Hey guys
> 
> Would some tell me this is a glitch in xroar !
> 
> I just broke through the sideborder on a coco2.... showing pixels in the
> right hand border !!!!
> 
> tried it on the real coco2... also showing signs of different colors in 
> the
> side border... (blue, yellow etc), but very flicker prone....
> 
> screen dump of xroar can be found at
> http://www.roust-it.dk/coco/overscancoco2.jpg
> 
> please pinch my arm and tell me i'm asleep !

The only way you should see anything like that in XRoar is by switching
to a 16-byte mode when the scanline started off in a 32-byte mode.
The VDG doesn't account for it, and ends up generating a longer scanline.
This is "sort of" emulated in XRoar - but not very well at the moment.

Unfortunately that will be unstable on a real machine - the video
timings are suddenly not something a real display can cope with!
Here, I've seen some interesting effects if you just do it for one line
though - subsequent lines sort of curve back in to their right position.
Whether that can be used as an effect though, I don't know - it almost
certainly varies by display...

Of course, if you've found another way to get XRoar to corrupt the
display, please let me know, it's probably a bug!

..ciaran