Collision detection optimisation?

[AndyH]

Hi

I remember a while ago (back in MMF1.5) it was mentioned that using fine collision is a little faster than not using it (ie: using box collision instead). Is this correct and still the case?

I'm wondering in what order of speed (quickest first) the following types of collisions would be:

Fine collision against fine collision
Fine collision against box collision
Box collision against box collision

I'm not experiencing any speed issues, but as my game gets bigger I think I might benefit from keeping things like this as efficient as possible.

[xyzzy]

i think box collisions are the fastest, since you could just compare boundaries and not individual pixels

[AndyH]

Well that's what I thought originally, but I'm sure someone (was it Yves) said that fine collisions were actually a little faster? But that is why I'm asking now so I can be sure

[Yves]

Did I say that? I think box collisions are faster (as the fine collisions are detected only if a box collision occurs).

[Sphax]

I think Box collisions are faster too because a collision mask is created for fine collisions and this creation can take some time on some objects.

Fine collision against fine collision : 2 collision masks are created and tested => slowest
Fine collision against box collision : 1 collision mask is created and tested
Box collision against box collision : 0 collision mask is created and tested => fastest

I work on some objects and they are faster if "fine collision detection" is disabled.

The speed difference should be more visible for very big objects.

[AndyH]

Thanks all. Yes, that's what I thought and makes sense. I think it was about the speed difference of fine to box collisions v fine to fine back in MMF1.0, so a little longer ago, if I remember correctly.