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Dead list?
Posted:
Dec 23, 1999 10:41 PM


Here's a really nasty problem I've been trying to figure out. I'm writing a topdown spaceship game, and I'm getting stumped with the collision detection. The problem is that the "game cycle" is 60 frames per second. Unfortunately, in 1/60th of a second, ships can move FAST. What I want to be able to do is, given the start position, a vector (the direction and speed the ship is going), and a radius for two ships, determine if and where they intersect. The method I'm currently using is "find the distance between the two locations, if it's less than firstradius+secondradius then they just hit each other". This won't work for very high speeds  the ships could pass straight through each other and out the other side in the time of one tick.
Just to give an idea of the things that may happen . . .
Two ships, traveling at huge speeds, missing each other by a very small distance One ship traveling at huge speeds hitting a ship at a virtual standstill Two ships racing towards each other at huge speeds Here's a nasty one: two ships in formation, one directly behind the other, traveling at high speed And a similar case where the rear ship is traveling fast enough to hit and pass through the front ship . . .
Now, if this isn't hard enough . . .
Make an option for the circles to be empty. (These circles represent the ships' shields, btw). One ship could conceivably drop its shields, the second ship flys in, and the first ship raises its shield again. We assume the second ship is much smaller, so it *can* fit in the space between the larger ship and its shields. They will not intersect (unless one makes a course correction and the other one doesn't, of course.)
Now, if this isn't hard enough . . .
The circles should be somewhat deformable. Nothing major  I'd be inputting a "height", a "width", and an "angle", and then doing whatever calculations would be necessary to make this into more useful data for the game. A long sleek ship is NOT going to have a shield shaped like a perfect circle. Everything mentioned above will still apply.
Now, if this isn't hard enough . . .
Add arbitrary polygons, quite possibly concave (something has to happen when the shields get blown away, right? at the moment the ship explodes when the shield goes down.) Once again, everything above applies, except these shapes would be solid (though a toggle would be nice).
Now, if this isn't hard enough . . .
I also will need the ability for laser weapon intersection. I'd need to get back a list of what it hits in what order. Actually, I need this for all the ships (so they only hit the first target and then bounce). Naturally, this would just be a line. This one actually shouldn't be too hard, especially considering that only the laser entity needs to get an "intersection" message.
And that's the problem. Hopefully, it won't get much harder :)
Hope someone can help,
Thanks,
Zorba



