[Coco] hardware scrolling revisited...

[Nick Marentes]

Steve Bjork <6809er at ...> writes:

> 
> The Artifact mode is do to a failure NTSC Color standard to handle the 
> screen like the CoCo's 256 dot mode.  The "great and power" Woz used 
> this failure in NTSC  to create the Hi-Res Color mode of the apple II.
> 
> Tandy never know their CoCo had a four color (Black, White, Red and 
> Blue) mode based on the 256 Black and White mode till I shipped them 
> PopCorn.  It took many letters and phone calls before they believe this 
> mode worked on all CoCos.  (At the time, there was no pal version of the 
> CoCo.)  By the time I shipped Mega-Bug, the Artifact was a "Documented" 
> graphics mode and why so much design time was spent to support it in the 
> CoCo3.
> 
> Steve


I wouldn't go as far as calling artifact a "mode".

The mode was standard PMODE 4 (SCREEN 1,1).

Artifact was a failing of the NTSC standard to resolve color properly and
was used on several systems at the time such as the Apple II and even the
Atari to get more colors from it's highest res modes (It had 256 real colors
in lowest res)

PAL had this too but because of the different frequencies used, the artifact
colors came out differently. Instead of solid red and blue, PAL would show
stripes of purple and green. It was ugly.

But all was not lost for us PAL users. I found that I could achieve
artifacting in PMODE 3 (SCREEN 1,1) using horizontal striping. With this, I
was able to achieve blue and red on top of the standard buff,magenta, orange
and cyan.

Anyone who has the original CoCo1/2 version of my Donut Dilemma game and
runs it on a PAL system will see this. I later removed the striping for it
to be CoCo3 RGB compatible (where this technique didn't work).