[Coco] hardware scrolling

[Simon Jonassen]

Hey Nick....

Actually i "Think" - this is untested as of yet.....

If you were to scroll the 42byte window (mine is centered for effect) to
it's limit, then you should just be able to do a page swap without having to
copy anything at all.....

This is "theoretical" ... You might have to play about with lines, values
etc to get the 512byte boundaries to coincide at the right points in
time....

Also note that my last demo with the full 42 byte (336 pix) picture has the
bitmap placed at a "funky" location.....

The code tells the vdg to start looking at $400, but the bitmap is actually
placed at $4a8.....

If my theory is correct then you should be able to scroll more than the 10
bytes that 42byte mode gives you via some careful tomfoolery - i have yet to
prove it though !!!

/Simon :-)



 

-----Oprindelig meddelelse-----
Fra: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com] På
vegne af Nick Marentes
Sendt: 28. oktober 2013 10:19
Til: CoCoList
Emne: [Coco] hardware scrolling

So, in order to create an endless scroll, like Super Mario or Scramble, you
would need to scroll the 42 byte window till it reaches its limit then you
would have to do a software copy of the region back and repeat the scroll.

You would need to draw the new graphics just off screen from the incoming
edge.

If I'm reading this right, the bottleneck will be the block copy to achieve
the loopback.

You are playing with the restriction of 64K. Unless you allocate more RAM
for video display to scroll across into (reposition the start of screen).
Maybe move across to a 2nd 6K page, copying the disappearing edge back to
the start point so when you reach the end point, you can shift the entire
screen back to the start and repeat the process.

... That's if I'm understanding your technique right.

Since you can do split screen, you won't have to copy the entire screen but
a smaller band across the screen. This buys you cycles.

Have you explored your technique in a semigraphics mode?

Nick



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