Collision Against Uniform Grid (Voxel) Without Creating Mesh

[Julio Jerez]

Ok here is a patch or a mesh as defined by the collision system. The mesh do no have to be a triangular, it only nee to be made of convex faces

triangleMesh1.png (15.44 KiB) Viewed 4824 times

I0, i1, i2, i3 are the indices to the vertices of the face indices
M0, in the material assigned that the center face
N is the index to the face normal
N0, N1, N2, N3 are the normal of the adjacent face that share the respective edge to the center face, I call it the edge adjacent normal
A Is the length of the of the larger diagonal of the face, rounded up to the nearest integer.

when a face does no have adjacent face at an edge, the that edge adjacent normal is set to N, the same face normal.

for a voxel data all this values can be synthesized on the flight in the callback from lookup tables based on the cell number.
That's how the terrain collision does it .

[PJani]

Oh now i understand it thnx for the img

Hmm you think the vertexes could be generated on the fly? What about large objects? Then i need to load more vertexes. I am looking performance wise.

[Julio Jerez]

Ok the user mesh collision is back working now.

[Layla]

Thanks for getting them working again. I can take a shot at it now. I may need some help but the general idea is to not store an actual mesh for the whole level but generate a small set of faces on the fly in the callback to collide against?

[PJani]

Yep...also it might be a good idea to use somekind of caching because newton would use same chunk of faces few times before you might need to generate new set of faces.

[Julio Jerez]

you can implement the caching yes, in my view caching provides very little gain on performances, at the expense of lots of memory and complex algorithm.
I would go for the simplicity first and use that as control test, then implement caching and compared to the non cached .

Remember collection the face is usually the fastest part of the collision, each time a body move, contact have to be recalculated, and that cost a lot more than getting the faces.

[Layla]

I can work around it but just a heads up that scaled collision shapes don't collide against user meshes. You can replicate it in the ConvexCast demo by replacing the scene collision with the infinite plane. There's only a small area the falling box can collide with, throw it out a bit and it goes straight through the floor. So I guess the collision is working but scaling isn't being taken into account somewhere in the user mesh.

[Julio Jerez]

you can always keep the scale and bake the scale on the user mesh.

But I believe it should work.
Anyway I will verify tonight, I am late for work now.

[Layla]

Sure. Just pointing out the problem if you wanted to fix it.

[Julio Jerez]

what are you scaling, the user mesh of the colliding shape?

They both be should be working, but I will verify tonight.

[Layla]

The colliding shape. Just replace the floor of convex shapes with the infinite plane in the ConvexCast demo to replicate it.

[Julio Jerez]

Ha thanks, I will try that and see what's wrong.

assuming not scaling, do you think the user mesh could work for you?

[Layla]

It's hard to say right now. It's going to take me a while to get it working because I'm not too good at maths. It does seem like the best way to go about this though, my only worry is that it may be slow to create all the faces for a very large object that touches a lot of the level. My game wont need that though so it shouldn't be a problem.

[Julio Jerez]

the scale bug is fixed.

build a path of quad for can no be any slower than, you buildh when you cnnage the model. The engioen doe shat for terrain highfield and that is no a factor at all.

But in any case you are the only one who knows what is best for your game.

[Layla]

Sorry it took so long, I was working on other things but I managed to get this working. Generating a patch of faces in a user collision is by far the best solution I've tried so far. I haven't even merged faces together yet and it's faster than anything I've tried before, has very little memory usage and I don't need to edit the collision when geometry is added to the map - it just works.