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2010-08-19 14:16

MisterMSK
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Registered: Jul 2009
Posts: 37

Koala Screen Swapping

Hi All,

I saw a Max Headroom demo (if you could call it that) when I was a child. It was blue and basically moved his head from side to side. It look like three different pictures. Anyway, I was curious of how to change a picture on the fly. Do I just move the image in memory down to $2000 and re-run the view code or is there a different way I am missing?

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2010-08-24 21:06

JCB
Account closed

Registered: Jun 2002
Posts: 241

Sorry about that, I'd not thought about just loading in raw koa files so they will overlap (or at least copying the screen ram to $4400 will overwrite the end of the other). I usually save everything out in parts so I can just shove things where I want them rather than 1 file.

Aaaanyway, to alleviate that problem just use $800 and $4800 for the two screen colour ram areas.

So you load one koa to $2000, the other to $6000, copy the koa+$1f40 to $800 and $4800 respectively, leave the bit data where it is and then the $d800 ram should be safe and not overwritten by anything..

After that you don't need to keep looping round and moving the $0800/$4800 ram just the $d800 from koa+$2328 and change the bank and you should be sorted.

So you should have code that looks like this...

Copy colour data for both pictures
Copy initial pictures $d800 ram
Set bitmap mode, bank, $d018 etc for 1st picture

Loop:
Wait on raster
copy other pictures $d800 ram
switch banks
Loop

*edit*
Doesn't really matter where you choose for the "screen" ram, as long as it's in the same bank, on an allowable boundary/start address etc. You can move it to just before the pixel data which makes it all a bit tidier (and one of the reasons I usually split things like koa files into their 3 sections)

2010-08-26 14:10

iAN CooG

Registered: May 2002
Posts: 3142

Lincoln Memorial - Day & Nite
source posted for those who want to learn by example.
The pics are not in koala but for convenience already split in bitmap, screenmap and colormap, the splits have been obtained by saving vice snapshots while viewing the images and then using Vice Snapshot Grabber 4.0

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