[ODE] Two Dimensions?

Chunky Kibbles chunky at icculus.org
Thu Aug 4 18:11:58 MST 2005

On Thu, Aug 04, 2005 at 01:16:03PM -0600, Megan Fox wrote:
> Er, option 2 has a number of problems, doesn't it?
> Off the top of my head:
> - So you have a 2D pile of boxes in your 2D platformer, and set of an
> explosion force.  Friction, collisions, and unexpected numerical
> inaccuracies push some of these boxes off the plane of your 2D game. 
> Now your 2D-moving character never hits the boxes, but since you just
> ignore that extra axis, it LOOKS like he should.

I mitigated that specific problem by using Torque's collision detection.
That way, contact joints always get created and point in the right
direction. I update object on-screen to reflect their flattened
dimension in ODE, then ask torque to do collisions.

> - 2D ragdolls.  These guys would flop aroun in all manner of improper
> ways with proper limits to a 2D plane.

Well, in the specific case of ragdolls, I didn't do any. But there's no
reason to stop you also using joints that *do* limit DoFs if you need

> - Friction forces against an angled surface.  Go back to the box pile,
> where boxes have fallen slightly off your plane, at an angle to your
> 2D gameplay plane.  Friction forces acting against your hero push him
> off the plane of your 2D game as he runs into the box and pushes
> around it... now EVERYTHING is skewed off from him.

Again. Mostly, by using a different collision detection system that
correctly points normals in the right direction.

> How'd you solve these problems?

A lot of wishing really hard, using a different collision detection
library, and experimentally finding that stuff works itself out.

Gary (-;

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