newton collision materials

[JernejL]

I know this was discussed a long time ago, that in newton 2.0 there is a way to attach materials directly to the collisions and build a compound with collision pieces of different materials.

I just came in situation when i need a compound collision box made of two pieces and 2 different materials, where one specific material would not collide with another particular material, but i cannot find out how to assign a material to collision directly, there is no "NewtonCollisionSetMaterialGroupID" or anything similar, so how does it work?

[Julio Jerez]

it uses the Shape ID,
the advance material in the wiki tutorial show how to dod it.

[JernejL]

I was looking at that, and i couldn't see it be used, so shapeid is effectively the newton material number?

Also: how do i get a collision shapeid? is it the "int m_collisionUserID;" in the newtoncollisiongetinfo structure?

[JernejL]

Ok, i tried and set the groupid to my a material i created earlier, i tried this on NewtonCreateConvexHull but the created objects don't behave as if they had the proper material, should this work like this or did i do something wrong?

[Julio Jerez]

Basically you need to implement a Material manager the unify shape and sub shape.
the shape ID was added to solb ther problem of determine what subshape was colliding with another subshape.

give me a day only I am done with the memory manager thing, and i will explain how to do it.
do you have the facility to compile C++ program?

[JernejL]

No i don't have any c++ tools.

I looked at the tutorial more in-depth now, i think i understand how it's supposed to work, i am supposed to use NewtonMaterialGetBodyCollisionID to get the GroupID, which i can then process.
And because i only need to make the specific collision parts non-collideable this shouldn't be hard to implement.

But i would suggest renaming the shapeid to CollisionID, this way it would clear up a lot of things.

[JernejL]

Awesome, i got it to function and it works PERFECT for my needs but i have a few suggestions:

- Rename shapeid parameters to CollisionID, this way it would clear up a lot of misunderstanding of what is used for what purpose.

- Add a function like NewtonMaterialUseGroup(const contactJoint: PNewtonJoint; materialgroupid1, materialgroupid2: integer)
This could be used inside a material callback to instead of overwriting values with several NewtonMaterialSetDefaultSoftness, NewtonMaterialSetDefaultElasticity, etc.. functions could just apply parameters of a particular existing created material pair, this can be useful when you don't want to implement a completely new material system, but just want to apply ordinary newton materials to separate pieces of a compound collision.

I still have that question: how do i get a collision's shapeid outside of collision callback? is it the "int m_collisionUserID;" in the NewtonCollisionGetInfo structure?

[Julio Jerez]

I still have that question: how do i get a collision's shapeid outside of collision callback? is it the "int m_collisionUserID;" in the NewtonCollisionGetInfo structure?

This is correct, but you can also call
unsigned NewtonCollisionGetUserID(const NewtonCollision* collision)

[JernejL]

At least it works good, althru it's a mess

The same parameter is called UserID twice (NewtonCollisionGetUserID, m_collisionUserID)
"shapeid": once (newtoncreate calls), and CollisionID 1 times in NewtonMaterialGetBodyCollisionID

Should be unified to use 1 single name (i would suggest CollisionID), no wonder i had trouble figuring it out :S

[Julio Jerez]

where should it be renamed?

[JernejL]

NewtonCollisionGetUserID -> NewtonCollisionGetCollisionID
collision info record - m_collisionUserID -> m_UserCollisionID
And all the newtoncreatexx calls - shapeid rename to -> CollisionID

[Aphex]

Hmm. Makes more sense to me the way it is.