Re: [Algorithms] Kinematic Collision

[Mark W. <Mwa...@to...>]

The problem we've found with a single ray is unwelded geometry or cracks
in geometry - the ray can fit between them and not register a hit, and
the character falls for a frame or two (maybe longer if the player has a
very small velocity). Using multiple rays (clustered for a single
spatial query) solves this relatively easily. Then there's the situation
where the ray(s) don't collide with anything but the body object (eg.
capsule) does, like if you jump into a barrel where the rays don't touch
the bottom but the capsule sits on the rim of the barrel. As long as you
handle these cases it works pretty well - though it is pretty funny to
jump into a barrel and get "wedged" like a fat dude (the first time
anyway!) :-)

Cheers,
Mark

> -----Original Message-----
> From: Jon Watte [mailto:jw...@gm...] 
> Sent: Tuesday, 8 September 2009 3:21 AM
> To: Game Development Algorithms
> Subject: Re: [Algorithms] Kinematic Collision
> 
> 
> The simplest character I find that I can get away with in the 
> general case is the lollipop. One ray for legs, and a capsule 
> for the body. The capsule extends between the knees and the 
> top of the head, and is slightly wider than shoulders (to 
> give some space for swinging arms, etc). This is fairly cheap 
> (capsule tests are cheap, and seldom actually collide with 
> things), and nicely prevents you from penetrating things 
> you're not supposed to.
> 
> If you're really worried about sideways penetrations, or want 
> to cut a hundred more cycles from the collision test, you can 
> replace the capsule with a sphere. It won't let characters 
> get as close to things (or each other, if you test char/char), though.
> 
> Sincerely,
> 
> jw
> 
> 
> David Black wrote:
> > Figuring out what surface is fine to "be on" and how to handle 
> > surfaces you should not be in, or the penetration into either is a 
> > major pain.  In the simple cases its trivial, but in the face
> >   
> 
> -- 
> 
>   Revenge is the most pointless and damaging of human desires.
> 
> 
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