Large force reaction when object sliding over evenly lined up, but separate objects

PhysX 3.2.1, PC SDK 64 bit

Hello.

We are experiencing an issue that is causing sliding vehicles to bump into the air on the separation between two objects.

For example, say we build a road with slabs made from rectangular PhysX box shapes. We slide a bunch of these together making sure they are perfectly aligned and most importantly at the same height so there are no bumps.

(See here: for an example with intentional spacing put in to show the slabs)

When we use impulses to slide a car over these aligned slabs of road, the car bounces and sometimes has an angular velocity imparted on it at every “joint”. Leaving a small gap, or intentionally partly overlapping the objects does not fix the issue. The only mitigation we’ve foind is to cut the slabs in the travel direction like so /-------//-------/. We are assuming the PhysX solver is somehow “seeing” the joint between the objects even though from the top surface the sliding object should not be affected.

Turning CCD on or off does not seem to affect this issue.

This issue is especially important to us because we’re using the PhysX SDK for a 3d virtual world, and people expect objects to react to surfaces how they seem them. This is preventing the creation of smooth racetracks, bridges and other surfaces that are friendly to vehicles.

I have tried adjusting the RestOffset and ContactOffset and nothing seems to make the issue better. In fact, surprisingly, increasing the rest offset seems to make it worse.

Thank you for your help.

Hello,

is it possible to post a pvd capture of the bug? With luck this will provide the information required to understand the problem better.

Thanks,

Gordon

Hi,
I’m having a similar issue. Where you able to solve this? If yes, could you please guide me how?

I would like to add that I am also seeing this and would also very much like to see a work around. This happens to me in Unity and Unreal, and this single bug has put my game on hold.

Even if someone could point me to the area of the code base that controls this would be helpful.

From trying to figure what was going on in Unity I determined that PhysX appears to send back multiple collisions when the seem between two objects is reached. I am thinking that one possible fix would be to flag the seems somehow (maybe using UV2 or UV3) so that the PhysX engine can test for the flag, and ignore the collision when it sees the flag.

My problem is trying to figure out the code base is a big learning curve, and may be over my head to be honest. A pointer to the right file to lookup would be really helpful.