5 replies to this topic

[ynm]

Hi everyone,

I have seen the sui generis demo here, it is pretty amazing:


At 00:59 he showed the game physics rigid body collision, it seems very accurate and I wonder what techniques behind that accurate collision between complex shaped objects? Can it be implemented in large scale or does it draw heavy computing power?

Thanks

[Hodgman]

There was a recent thread about it here.

[ynm]

Thanks, I think he used some kinds of graphics based collision, there is 2D version of it, but is there a 3D version?

[Hodgman]

For 3D collisions, most physics engines like to work with convex shapes, so this presents a problem when you want to use arbitrary 3D meshes (which may be concave).
The solution is a process called "convex decomposition", which takes a concave shape and splits it up into a collection of convex ones.

Many physics engines have tools where you can provide a 3D mesh (e.g. a visual model) and have it be decomposed into a collection of convex polyhedra, which can then be used by the physics engine.
However, on most games that I've worked on, as an optimisation, the artists have always created a 2nd low-poly mesh specifically for physics, because it's wasteful to have perfect collisions
The Sui Generis guy mentioned that he wants to save as much development time as possible, so he's using the actual visual meshes instead of hand-crafting optimised collision meshes. As long as his convex-polyhedra collision code is fast, then it won't be too much of a problem for him.

Edited by Hodgman, 18 November 2012 - 09:52 PM.

[ynm]

Ah, many thanks for the explanation

Regards

[Steve_Segreto]

Sui Generis looks awesome!

Advanced Character Physics is a cool subject. Below is the link to the 2001 Jakobsen paper to get you started and then a video showing some of the concepts in action.

http://www.pagines.m...cterPhysics.pdf



I suppose the system of verlet integrated particles connected by springs described by Jakobsen could be used to describe rigid bodies as well and this might provide the collision response observed in the Sui Generis demos, but I'm just guessing. Something like one particle per model vertex and infinitely rigid springs between two vertices.

Edited by Steve_Segreto, 23 November 2012 - 01:26 AM.