Re: [stella] bipolar joustpong

[Glenn Saunders <mos6507@xxxxxxxxxxx>]

Thinking on my feet here, if you use a regular playfield, rather than a 
symmetric playfield, you could use a single byte per playfield row and only 
use one half of the byte for each side.  For PF0 on the left you don't have 
to mask anything because the register only uses the left 4 bits, but for 
PF2 you will need to mask the left half first and then store it.

Your playfield bitmap would therefore be only 4 bits wide on either side 
but you'd be able to have smaller blocks that aren't as tall because you 
are only using as many bytes as you want rows.  20 rows should be more than 
enough and yield somewhat square looking blocks.  If you wanted more 
separation you can force a blank line between rows like Surround.

The logic to do this wouldn't take much CPU.  You'd be indexing forward on 
a single zero-page address and taking care of both sides at once.  You'd 
still have to blank out PF0 and PF2 so they don't repeat, of course.  If 
you really started to run out of space you could interlace either side so 
that for any one line you will draw the left or the right half, but not both.

There should also be enough CPU time to do some color cycling also ala 
Warlords.

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