Hi there!
Last time in this series *g* I was wondering why David Crane stored the
horizontal coordinates in Outlaw in reversed order, or better why he was
counting left to right from 160 to zero. I think I know the answer now:
He has to both _move_ a bullet (missile) and trace it's position.
Assuming he wants this bullet to move 4 pixel to the right.
He continues like this:
LDA #$FC ; A-> -4!
ADC verpos ; verpos = verpos-4
It moves right, so he subtracts 4 pixel following his reversed logic
here.
ATTENTION: Now, to actually move the bullet, he does just:
ASL
ASL
ASL
ASL ; A-> C0
STA HMM0,X ; Move bullet 4 pixel to the right.
Cool, or? I think that's how horizontal movement was _supposed_ to work
:-)
Did per chance anyone else notice other examples of reverse horizontal
position tracing in original '78 or older games?
Greetings,
Manuel
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