Objects fall through ConcaveMeshShape

[andreasdr]

HI,

sometimes in like 2/8 cases objects fall through ConcaveMeshShape.
In my case the bounding volumes are just BoxShapes.

I have an example video where you can see the issue:

• https://www.youtube.com/watch?v=hCFecUVEDQs&feature=youtu.be

I can provide another video if interested.

Many thanx and

Best regards
Andreas

[DanielChappuis]

When you create the TriangleVertexArray for your concave mesh, are you using the constructor to specify your surface normals or are you letting ReactPhysics3D compute the normals ?

[andreasdr]

Hi,

I am not passing triangle/surface normals.

I also see ConvexMeshes falling through BoxShapes.

Its not super urgent. I will review my ConvexMeshShape generation again. And I will make a video to demonstrate the issues soon.

Best regards
Andreas

[DanielChappuis]

ConvexMesh and BoxShape use the same algorithm to collide against a ConcaveMeshShape. Therefore, it makes sense that you observe issues with both objects if something is wrong.

Are you able to produce a simple piece of code with a very simple ConcaveMeshShape and a BoxShape falling througth it ? It would be very helpful for debugging.

[andreasdr]

Ill do. Give me 1, max 2 days.

[DanielChappuis]

Great. Thanks a lot for your help !

[andreasdr]

I need some more time but will provide a test soon.

[andreasdr]

Hi,

I have created a test that shows the issue. I am not sure if this covers all issues I have seen. But its a issue still. Hope you do not mind that its written in TDME2.
Just checkout TDME2 and switch to reactphysics3d-current branch.

You can build with "make clean && make -jHARDWARETHREADS mains"
You can issue the test from TDME2 folder with "./bin/tdme/tests/PhysicsTest4"

See:

• https://github.com/andreasdr/tdme2/blob/reactphysics3d-current/src/tdme/tests/PhysicsTest4.cpp

Please keep me updated!

Best regards
Andreas

[DanielChappuis]

Hello,

After investigation, I think that in your example this is due to the fact that ReactPhysics3D uses discrete collision detection. What we observe is tunneling of shapes inside each other. In a given frame t the box is above the terrain and in the next frame t+1 the box is already bellow the terrain but there was no frame where the box was colliding with the terrain and therefore the collision has been missed.

I have plan to add continuous collision detection in the future but probably not in the next release. The idea is to compute when the two shapes will collide so that we don't miss the collision.

What you might try is to make sure that the collision shapes are not too small and also that their velocities when they collide to each other are not too large so that we do not miss the collision.

[andreasdr]

Hi,

What you might try is to make sure that the collision shapes are not too small and also that their velocities when they collide to each other are not too large so that we do not miss the collision.

If its just that we will find a work around! I will check that.

Thank you.

Best regards
Andreas

[andreasdr]

But no. To be honest I do not think so. In my physics tests 1-3 you can see the issue as well with larger objects and moving more slowly. Maybe I can provide a test with bigger bounding volumes?

I will double check.

[DanielChappuis]

Ok I will check your physics test 1-3

[andreasdr]

Just move the boxes or convex meshes in PhysicsTest1+3. The issue I mean happens from time to time.
E.g. a convex mesh sinks into ground and gets pushed 250ms later out of it. This is only looking strange. Sometimes it falls through too. I can try to set up a test with larger BVs.

Many thanx.

Best regards
Andreas

[DanielChappuis]

Can I ask you some questions about your physics tests in the "reactphysics3d-current" branch ?

When I run the PhysicsTest1, almost immediately, all the objects disappear. Are all the objects are falling through the ground ?

In the PhysicsTest2, I see boxes falling through boxes. Do you also have this behavior on your side ?

In the PhysicsTest3. Do you know why the objects have very strange behavior ? I mean jumping around everywhere ?