Have you tried setting x=0 to the CENTER of the screen, rather than the
left?
If you do that, you can use mirrored PF quite easily. This might raise
other
issues though....
It's mostly a matter of mental visualization.
I "think" in terms of a coordinate space where 0,0 is at the top left of the
screen and the scanline counter incrementing downward. It's been confusing
as it is dealing with this decrementing scanline counter. I hate that, but
it seems to be the standard way to do it on the 2600, having all the data
upside down, probably because BNE is a quicker way to end a loop than
testing for a given maximum value.
BTW, for those in the know, with rotating sprite games like Combat and
Indy500, how many of the 16 frames of sprite rotation animation are stored
in ROM? You could get by with only storing 5 frames for 1/4 of the
rotation, and then using the sprite flip register for the other half, and
scanning in reverse to flip it vertically. I'm assuming that these games
store 9 frames in order to simplify the kernel, only taking advantage of the
sprite flip.
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