Dennis wrote:
> Sorry for the multiple questions but I want to understand how these
> illegal opcodes work as I think they may help me...
I am always glad if I can help. :-)
> I see you are using dcp (opcode $c7, decrement and compare). What does
> this have to do with the y-register? Does dcp effect the y-register is some
> way?
No. DCP doesn't effect any registers, except the flag register. P0_Y is simply initialized with the distance from the top of the screen/kernel and decremented every second scanline. When it goes below CARHEIGHT (=8) the car is drawn. After that P0_Y is decremented below zero and the compare fails again.
> You're not updating y for each scanline, right?
Right, only every 2nd scanline (-> 2LK). All objects have a two line vertical resolution. The positioning is done with single line precision by using VDELPx (for the cars) and different kernels (for the zombies).
>Apparently, I'm the only one here that doesn't get it
Probably you are just the only one who tried and doesn't get it. ;-)
Have?fun!
Thomas
_______________________________________________________
Thomas?Jentzsch?????????|?***?Every?bit?is?sacred?!?***
tjentzsch?at?web?dot?de?|
______________________________________________________________________________
Ihre Freunde sind in Italien? Schicken Sie ihnen trotzdem eine SMS
mit WEB.DE FreeMail http://freemail.web.de/features/?mc=021172
----------------------------------------------------------------------------------------------
Archives (includes files) at http://www.biglist.com/lists/stella/archives/
Unsub & more at http://www.biglist.com/lists/stella/
