[ODE] Need performance tips

[nearaz]

> flat terrain represented by a box geom (until I add support for ODE 
> planes) and 20 crates also represented by box geoms.  All the crates 

Is your terrain-box also a body?

>  performance suffers quite a bit.  I know that this is happening 
> because a lot of contact joints are being generated when the boxes 

If your terrain is also a body, then the slowdown is because the terrain and 
all the boxes on it form a single island; and thus computation time is 
roughly O(N^3), where N is proportional to the number of contact joints. You 
probably should try "stepfast" iterative solver in this case... (or read 
below).

> I though about detecting 
> that the crates have stopped moving (how can this be detected in the 
> first place?)

Yes, just disable the bodies that are "inactive" (say, moving/turning only a 
little).

> disable the crate bodies so that they don't fall through the ground, 
> they will no longer interact with whatever might happen in the world 
> (say another box falling in the pile for some reason.)

When a disabled body is joined to non-disabled body by some joint (in your 
case - contact joint), it's automatically enabled by ODE. So there's no 
problem.

>  How do games that deal with large worlds handle such problems?

It's best to not simulate motion of non-moving objects (as the terrain), so 
the big islands of connected bodies just don't form. And, as a side note, 
games rarely have "physics simulation" as it's in ODE :)



Aras Pranckevicius aka NeARAZ
http://www.gim.ktu.lt/nesnausk/nearaz/