[Coco] hardware scrolling

[Nick Marentes]

 > Regarding the "yawn, had all allready been there..." which came up here
recently:


It's certainly not a yawn. What Simon has done is a major accomplishment 
in pushing the 6847 VDG beyond what the designers had intended.

It has been done before is what I meant. Let me clarify...

Games with horizontal/vertical scrolling have been done before on the 
CoCo1/2... albeit in software. My point is about the end result. A pmode 
4/3 screen only takes up 6K so, as a game developer, one needs to weigh 
up the advantages between trying to use the hardware versus doing it in 
software.

On the CoCo3, a 16 colour screen takes up 32K, so a hardware technique 
may be the faster option over software.

Each has advantages and depending on the game, one may suit the other 
better. When we're only playing with 6K a software scroll is not taxing 
past the impossible. It's made even easier when, as with most games, you 
actually don't have to scroll the entire screen, leaving some areas 
static for score displays etc.

Compare these advantages with Simon's hardware scroll. Are the 
advantages that much better when you take in to account the routine 
required to pull it off?

Maybe? Maybe not? Simon knows the routines better so he may say yes. It 
does depend on the application and this is where the programmer must 
decide which way is best for the desired application.

Certainly, a "tech demo" is best done with hardware because the "tech 
demo" is actually highlighting the hardware capabilities.

Look at the Amiga's famous bouncing ball demo. A spinning ball bouncing 
around the screen. It was wow in 1985 but soon after, people were 
writing software derivatives achieving the same and more with software. 
But that wasn't the point of the demo. The demo was almost completely 
run by manipulating the hardware registers. The ball spun due to palette 
animation and the bounce using the vertical and horizontal hardware 
registers. The ball overlay was a feature of the Amiga's dual pane 
bitplanes. Very few cpu cycles were used to achieve this entire effect.

So, in summary, what Simon has discovered and created is great, 
fantastic, mindblowing when you consider that he is manipulating the 
hardware. Not understanding this achievement, from a software 
perspective it appears like "I've seen it all before".

So Simon, don't hold back. Go ahead and demonstrate this discovery of 
yours in a mind-blowing demo. Just make sure you highlight that this is 
not software but utilizing untapped hardware feature.

Nick