BoundingBox of a moving Mesh does not update properly

Help & Support
1

Hey, i have a question. Why do I need to call app.removeChild(renderer) and app.addChild(renderer) in Update everytime i change the values of my vertices to have proper BoundingBoxes. :slight_smile:.
I thought mesh.update() should do the work.

BoundingBoxTest.prototype.update = function (dt) {

this.time += dt;

this.vertexPositions[0] = 2 * Math.cos(this.time * 0.5);
this.vertexPositions[2] = 2 * Math.sin(this.time * 0.5);

this.vertexPositions[3] = 1 + 2 * Math.cos(this.time * 0.5);
this.vertexPositions[5] = 2 * Math.sin(this.time * 0.5);

this.vertexPositions[6] = 2 * Math.cos(this.time * 0.5);
this.vertexPositions[8] = 1 + 2 * Math.sin(this.time * 0.5);


// this.app.root.removeChild(this.arcEntity);

this.mesh.setPositions(this.vertexPositions);
this.mesh.update();

// this.app.root.addChild(this.arcEntity);

};

With removeChild and addChild it works fine.

2

Hi @Andrushka130,

Hmm, it maybe that the MeshInstance using that Mesh may be caching the aabb for performance reasons.

A bounding box is in world units, and even though the mesh has its own, each mesh instance based on its node/entity world position has a different bounding box.

No need to remove/add the child, you can just update the mesh instance aabb. @mvaligursky is there an official way of forcing a mesh instance to do that?

3

mesh.update() is the right way to do it and it works correctly. Try adding

console.log(mesh.aabb.center)

in the live editor of this example (e.g. add it somewhere in updateMesh function)
https://playcanvas.github.io/#/graphics/mesh-generation

You will see that the aabb center is changed every frame.

1 Like
4

agreed with Lexxik, there is no way to force is as it gets updated every frame automatically.

1 Like
5

Agreed with Lexxik, the boundingBox of the mesh is getting updated properly, but the boundingBox of the MeshInstance does not update and i think the frustum Culling of an camera is using the meshInstance BoundingBox.

I try to explain my project. I am trying to create an VR Framework for my company and i am casting an Arc out of an Controller. The arc is only displayed when i look at the ground (0,0,0) because the boundingBox of my MeshInstance of the Arc is not getting updated.

If i disable frustum Culling and render everything it works properly. But i want to enable frustum Culling of course, so if i enable frustumCulling and use removeChild and addChild the meshInstance boundingBox is getting updated and my ray is displayed properly and i have no problems.

I hope my thesis make sense :smiley: and thank you for your fast replies.

6

Yes, that makes sense. I would probably do it using a custom AABB. When you set a custom AABB on a render component, it will be assigned to the mesh instance. The default AABB would not be used. Then you could do something like:

const aabb = new pc.BoundingBox();

entity.render.customAabb = aabb;

update(dt) {
    aabb.compute(this.vertexPositions, this.vertexPositions.length / 3);
}
1 Like
7

put a breakpoint in MeshInstance.get aabb to see what happens there for your mesh. Hack something on your mesh, say mesh.hack = true; and set up conditional breakpoint for this, you should see if the world space aabb gets updated there correctly.

8

@mvaligursky do you mean the world aabb on mesh instance? I don’t think it would update, because those will both be equal after the first frame:

image

9

I found another solution:

this.meshInstance.aabb = this.mesh.aabb.clone();

this works as well. I set my meshInstance.aabb every frame

10

No it does not update correctly.

11

Perhaps you could create an issue here with a simple repro: Issues · playcanvas/engine · GitHub
and I’ll investigate / fix if needed.

1 Like
12

Created a ticket for follow up:

13

Here is another sample project, which illustrates this issue:
https://playcanvas.com/project/1147948/overview/mesh-instance-aabb-update

Yellow → Mesh aabb
Magenta → MeshInstance aabb

I also add this sample to the github issue

1 Like
14

@LucaHeft
thanks, a workaround for now is to use

this.arcEntity.setLocalPosition(this.arcEntity.getLocalPosition());

which makes the version change, forcing the update

15

@Andrushka130 - try the same workaround instead of adding / removing the entity from parent

16

And the engine fix: [Fix] World space aabb gets updated when local space aabb of mesh changes by mvaligursky · Pull Request #5726 · playcanvas/engine · GitHub
(will get released at the next engine patch release)

2 Likes
17

yes , thank you :slight_smile: