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Bill246

PM Collisions in Advan Basic

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I've been working with Advan Basic for a few months and really enjoy it. The commands for player-missile graphics are much easier to use and faster than those in Atari Basic. One part I can't figure out is collision detection. The Advan Basic manual says the command T%=COLL(2%,16%) returns an integer whose value depends on whether or not player 2 has collided with other players. This sort of works for me, but I still stuck on getting it to work properly. What should the value of T% be if there is a collision? If I PEEK location 53260, which I think is the collision status of player 0, it returns 12. I want to do an IF statement where IF T% is the value of a collision, then do something. What number should I look for?

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There's bitsettings that would reflect what the GTIA collision registers return.

 

So player collisions are bit 3 for Player 3, bit 2 for Player 2 etc.

Of course a player can't collide with itself so it's associated value never gets set.

 

Generally you'd look for a nonzero value then take further action. Use an AND operation to filter the bits out further to see what other objects are involved.

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Without trying Advan BASIC yet, I must say that whichever method you use to check for collisions, You must be sure that the screen frame was completely drawed, or the collision registers won't be modified. I usually clear the collision registers at the very beginning of a new frame, then wait for a complete redraw of the frame, probably using WAIT statement with a value of 0 or 1 as the argument, or by waiting for the value change of memory address 20 (RTCLOK).

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