[ODE] contact points

Lewis Foster doof205 at gmail.com
Wed Apr 11 11:16:39 MST 2007

Hi all, i'm playing around with convex hull's at the minute and what i've
got so far seems to be generating the correct contact normal and so i've
moved on to creating the contact points.

The problem i'm having is that the contact points are either doing nothing,
or if anything they are pulling one object into the other, so you would
think the normal was inverted. However the normal should be able to be in
either direction, so long as you have the correct ordering of g1 and g2.

Picture this, box1 is dropping onto box2 which is resting on the floor. The
normal correctly points from box1 toward box2, downwards.

Cycling through the points of box2, two points are correctly identified as
being behind the plane of box1 and so are added to the contact array. The
depth is correctly identified and is positive.

Why then would box1 continue downwards into box2? It seems that as box2 is
unable to move in the direction of the normal (due to the floor) it remains
where it is and box1 simply continues to fall through....obviously the
collision detection side of things doesn't need to know if there is an
immovable object resisting one objects motion. In this case, how does the
collision detection, or ODE, know to invert the normal and make the
collision points act in the opposite direction on the other object, that is
free to move?

I hope that makes sense. Any help would be greatly appreciated...I wonder if
i'll finish this before Erwin finishes the bullet integration...my work will
be obsolete otherwise.


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