How to update a mesh collider?

Hello,

I'm developing a video game student project.
A feature consists to move a bridge like Tacoma bridge

I move the mesh with bones, so the mesh moves correctly, but the mesh collider is not updated.
My case : http://www.vimeo.com/7163412

The bridges has a mesh collider and the cubes have got box colliders. The mesh collider of the bridge has got less than 255 faces.

Do you know how I could do this?

 

Hi - welcome to the forum!

If you are using a boned animation created in a 3D application, the MeshCollider will not be updated as the animation plays, it will just stay in the initial position. However, you can update the collider if you are animating the mesh from a script with the Mesh API - you just need to assign the mesh to the sharedMesh property of the MeshCollider each frame.

 

I tested to assign sharedMesh collider in Update:

Code (csharp):

1. function Update ()
2. {
3.     if(Input.GetButton ("Fire1"))
4.     {
5.         //init:
6.         //get the bone
7.         var bone2 = transform.Find("bone02");
8.         //initial force
9.         var upForce = Time.deltaTime * 10;
10.         var rotForce = Time.deltaTime * 40;
11.         //input
12.         var inputH = Input.GetAxis("Horizontal2");
13.         var inputV = Input.GetAxis("Vertical1");
14.        
15.         //move the bone
16.         bone2.transform.Rotate(Vector3.right*inputH*rotForce);
17.         bone2.transform.Rotate(Vector3.forward*inputV*upForce);
18.     }
19. }
20.  
21. function LateUpdate ()
22. {
23.     //update the mesh collider
24.     var skinnedMeshRenderer = GetComponent (SkinnedMeshRenderer);
25.     collider.sharedMesh = skinnedMeshRenderer.sharedMesh;
26. }

But nothing better, mesh collier is alway initial mesh pattern. Did I a mistake?

 

I'd be interested in the answer to this, as I don't understand why mesh colliders can't be updated. If I have a tank whose turret I want to rotate via a named bone, then it sounds like I need to manually deal with updating the mesh, or do away with it and use primitives instead.

 

Mesh colliders need serious pre-processing to function, and are not suitable for updating in real-time. You can't get the updated mesh from a skinned mesh renderer for technical reasons that I forget exactly, but even if you could, it would still be very slow to compute the mesh collider. Something like a tank is trivial to do using primitive colliders, and that's definitely the way to go.

--Eric

 

not sure if you still on this. there seems to be some change with unity 3.0 Previously
GetComponent<MeshCollider>().sharedMesh = meshFilter.mesh;

would work but in unity3 u need to null the mesh before assigning a new one.

GetComponent<MeshCollider>().sharedMesh = null;
GetComponent<MeshCollider>().sharedMesh = meshFilter.mesh;

 

did you resolve?

I couldn't resolve!!
http://forum.unity3d.com/threads/110128-How-to-modify-a-collider-according-to-a-bone

 

pkamat, thank you! I was pulling my hair out (and I don't have much left!)

 

Thank you so much!! I've been working on this for a whole day!

 

Thanks for saving me a few hours of frustration!

 

Worked for me too!

thanks

 

Thanks you a lot. I lost a morning for that fix.

It's solved it but it's kind of weird though to null the mesh before re-assigning it.

 

WOOHOO thanks!!! great tip!

 

pkamat, thank you very much!

 

Yep, I can confirm that this does indeed force the mesh collider to update...

But I can also confirm that, in my case at least, the result really is too slow (as Eric5h5 predicted). I've got dynamic terrain sculpting, but I certainly can't call this on every frame while the terrain changes.

Hmm, but maybe I don't need to... I may be able to call it only on mouse-up, at least for this particular case. Or, failing that, I'll have to walk the mesh myself, find the closest few vertices, and interpolate, but... ugh. That gets ugly fast.

 

I know you posted this years but I didn't find anything else that answered my question and I hope you (or someone else who knows the answer) will still read this: If updating a MeshCollider is so costly, what alternatives and workarounds are there?

In my case I'm working on a relatively simple "toon style" ocean (think Zelda:Wind Waker). I think I won't need very realistic and detailed wave forms so I'll try to go with just some sinus vertex deformations (probably with some perlin noise added on top) that I'll apply on a plane. But of course I'd also like to have the waves interacting with ships and such and I don't see how I'd do this without constantly updating the MeshCollider.

Thank you very much for any pointers you can give me!

Edit: I assume if the water isn't too stormy and sluggish enough it'd suffice to update the MeshCollider only every few frames but I'd still be quiet often i assume and hopefully there's a better way..

 

I think your best bet is to only calculate wave height where/when you need it, instead of calculating it across the entire mesh. It's frustrating that updating colliders is so slooooow, because it's the obvious and easiest way to do it. So for example with a boat object you need to build a function that will calculate the wave height at the boat's position, and then perform an offset to simulate buoyancy.

This is what I do in Suimono, and it works really well, but I still wish I could have just used the original collider. It would have saved me months of work and frustration. I know Unity 5 has an improved physics system but I haven't tested if mesh collider updates work any faster.

 

Thanks heaps ... I was soo stuck (still relevant with Unity 5)!

 

A small syntax error with all my respect:

GetComponent<MeshCollider>().sharedMesh = null;
GetComponent<MeshCollider>().sharedMesh = GetComponent<MeshFilter>().mesh;

 

OMG THANKYOU!!!

 

pkamat, this was REALLY helpful! Thanks!

 

I was wondering why I could not get a mesh collider to update and it was the same thing - set to null first.
Surely this is a bug!
I guess it checks if same mesh as before passed in but should check if the data within is same too...

 

Am on Unity 5.5 right now and I did not have to set it to null before (will do anyway just to be sure). Either way this is terribly cryptic.

 

thanks a lot
just it would be interesting to know this updating can or should be improved... is it a slow process? I would like to start and I have a basic idea using colliders, and I need to update frequently

 

Now it does not work in Unity 5.6.1. Any idea how to do this?

 

trying to update the mesh collider, using Unity version 2017.4.15f1.
the indicated scripting is not working for me, although my coding might be incorrect.

i have imported a .fbx animated file from Blender, trying to animate the Mesh Collider by updating the shape in response to the changing shape of the object. The object (simple cube) was animated via shape keys in Blender.

i tried writing this script and applying the script to the cube object in the hierarchy window.

public class ObjectMeshToPhysicsSurface : MonoBehaviour {

Mesh m;
MeshCollider mc;
MeshFilter mf;

// Use this for initialization
void Start () {

Debug.Log ("Object mesh script is active.");

mf = GetComponent<MeshFilter> ();

m = mf.mesh;
mc = GetComponent<MeshCollider> ();

m.RecalculateBounds ();

}

// Update is called once per frame
void Update () {

m.RecalculateBounds ();
mc.sharedMesh = null;
mc.sharedMesh = m;


}
}

 

Shape keys? Is that like blend shapes?

If so, then I don't think that'll work with a MeshCollider. You would have to use BakeMesh to get a snapshot of the current shape of the mesh, taking into account all the blend weights and bone positions, and then set that as the mesh collider mesh.

Keep in mind that mesh colliders are very expensive and have some serious limitations — if you can get by with some combination of more primitive colliders, it's almost always better to do that.

 

Thank you, i must say cheers for mentioning BakeMesh, that is so directly applicable, used for getting a snapshot of a SkinnedMeshRenderer's mesh.

if it were at all possible to update the shape of the MeshCollider.sharedMesh, using the Update() function to apply the current state of the object's mesh, then that would possibly be the most appropriate and desirably "accurate" solution. Hopefully BakeMesh is going to capture the information required. I should go try that now.

the vertex count of the object required to update in a working version of this script would, at a guess, be somewhere between 300 - 500 vertices, with simple vertex colours applied to the faces.

Not much else going on in the scene, one or two more objects that do not update their mesh colliders. So maybe it is possible. If the framerate maintains 30 per second or higher, that is acceptable.

re/ simpler workarounds ... yes, currently working on a combination of more primitive colliders, and they might be somehow better for a couple of reasons.

 

yes, blend shapes with morph targets.
the resulting animated object (fbx) imports to Unity with an associated Skinned Mesh Renderer component.

attached a MeshCollider and MeshFilter manually via Unity. Not sure if the MeshFilter is useful in this scenario.

currently this code seems to apply the MeshCollider although does not update the MeshCollider shape (or maybe it is updating the mesh very slowly).


public class ObjectMeshToPhysicsSurface : MonoBehaviour {

public SkinnedMeshRenderer skinnedMeshRenderer;
public Mesh bakedMesh;
private MeshCollider meshCollider;

private void Start() {

skinnedMeshRenderer = GetComponent<SkinnedMeshRenderer> ();
meshCollider = GetComponent<MeshCollider> ();
}

private void FixedUpdate()
{
skinnedMeshRenderer.BakeMesh(bakedMesh);
meshCollider.sharedMesh = bakedMesh;
}
}

 

I tried many ways and this one worked for me

neme "self" - is the object on which the mesh is being changed

 

It works !! Thanks a Ton dude !!!!

 

im new in unity,
I never saw that editor, how do you do it and in what section or with what package?

 

Visual scripting : Bolt

 

Thanks...you saved my day...

 

Hi do you have the equivalent Visual Scripting Graph to update for the Mesh Render?