This code looks effective, but the following technique will make it
difficult to add players, unless you want your players to only be
positionable every 8 scanlines or so, as Centipede and both versions
of Frogger do.
> LDY #$08 ;how many scanlines is each block?
> LDX #$17 ;number of blocks of data. LDY * LDX = 192!
>
>load LDA playf0,X ;load in the data for playfield 1
> STA PF0
> LDA playf1,X ;load in the data for playfield 2
> STA PF1
> LDA playf2,X ;load in the data for playfield 3
> STA PF2
>
>grfx STA WSYNC ;draw the scanline
> DEY ;decrease the block number
> BEQ block ;if it's zero it's time for a new block
> JMP grfx ;if not then repeat the previous scanline
et cetera.
Instead of spitting out eight WSYNCs, you could use that time to position
or draw a sprite. Perhaps there isn't time to do both if you want the
full eight scanlines.
Crackers has sort of taken care of a concept I was going to write about:
multi-scanline scanning loops. His takes 8 scanlines to do not really
that much, but it would have been incredibly useful if, say, he were
writing a Pac-Man game and he used the 4th and 5th scanlines to place and
remove a row of dots from the playfield.
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