Tuesday, July 15, 2008

Having a play.....

Okay, so I'm not doing my mini-game thing, I've been playing with my Super CPU instead. One question thats always got me thinking is what can you do with a superCPU that you can't do with a stock C64 (3D aside...).

Well, heres one: full screen overscan bitmap scrolling. Not using expanded sprites or anything, but using the full bitmap screen AND sprites in the side border. Now... I thought you might actually manage to do that with delayed DMA etc. but drawing into a full screen height would be virtually impossible surely, particually since you have to scroll through 4 sprites.

Well... okay... you COULD kinda do it... kindof... Imagine this...

FULL screen bitmap, delayed DMA scrolls that - great. Now how about the edges? Well, you need sprites there of course. BUT that means you've to smooth scroll through 4 sprites (2 on each side). Well no. Sprites can move in pixels after all, so just move in bytes and move the sprites in pixels to sumulate a normal scroll.

This still means you have to redraw the sprites though, and thats 4 sprites, (say) 189 pixels each. Quite a bit.... well...no...

IF you used another extra sprite on each side, then you can scroll the sprites and bring on new empty ones each frame too, then your only drawing 2 colums or sprites 189 pixels high over 8 frames (along with the bitmap) - which is perfectly doable.

Could make for a pretty cool C64 demo - standard MCM res, full screen/overscan scroller...neat. Course... since you can't change the colours very well in sprites, you'd have to pick 3 normal colours (sades of blue etc)... but still. You could also use character maps of course, which would make scrolling them much easier and would mean you didn't have to use delayed dma, as long as you double buffered the character map.

So the outcome.....A cool demo on a normal 64, and I still need to find an impossible task for the SuperCPU. It's pretty amazing what a stock machine can do if you poke it a little....


(and before you ask...no I have actually written it all, I've just been playing and know HOW to write it....)

8 comments:

TMR said...

This is pretty much the problem i had when i was loaned a SuperCPU; apart from 3D (which i don't personally like anyway) i couldn't think of anything to do that wouldn't be at least possible on a machine with a RAM expansion...

simon said...

What about a 'bullet-hell' scrolling shooter in full bitmap mode, with all the bullets being plotted on the bitmap, and sprites being used only for the player+enemies?

Mike said...

I still think a full parallax scroller would be cool...

You could do that on a stock C64 anyway... Im also doing something similar on Xeo3 but in character mode.. The baddie bullets are already masked.

Vladimir Janković said...

Parallax scroller like Flimbos quest but in full screen bitmap mcm mode with black monochrome hard sprites overlayed on top in some places... :)

And plus software sprites ofcourse :)

simon said...

...but I mean, like, 100 enemy bullets on screen, Dodonpachi style, with smooth 50 f.p.s.movement.

actually, the bullets would probably have to move at a lower framerate, otherwise they'd move too quickly.

but yes, some parallax scrolling wouldn't go astray either! :D

Anonymous said...

Hi Mike,

You've had my suggestion already of a Lemmings type thing with full screen scroll and lots of Lemmings.

I remember speaking to Russ Micheals once and he was pondering whether or not an REU or RAMLink would be quick enough for interlaced animations. I guess someone would have done it though if it was possible.

Anyway, I await your outcomes :-) keep experimenting.

T.M.R said...

An REU could do interlaced animations no problem... getting the data into it to play them back at a speed that couldn't be measureed in geological time is a different matter! =-)

Mike said...

I do actually have one of them.. a proper C= 17??-somthing, and the animation demo was painful to say the least!

An MMC loader+REU would be more interesting...