How do I replace the geometry property of a Mesh?

Questions
,
1

I have an object that contains a list of balls (spheres). I want to add the ability to interactively change the ball radii.

Here is the method I added to do it:

replaceGeometry () {

    for (let mesh of this.balls) {

        // discard current geometry, an instance of a SphereBufferGeometry
        mesh.geometry.dispose();

        // replace with clone of a SphereBufferGeometry with a changed radius
        mesh.geometry = Globals.sceneManager.ballGeometry.clone();
    }

}

I added a helper function to the object that is called in the render loop:

renderLoopHelper () {

if (this.balls) {
    for (let mesh of this.balls) {
        mesh.geometry.attributes.position.needsUpdate = true;
        mesh.geometry.attributes.normal.needsUpdate = true;
        mesh.geometry.attributes.uv.needsUpdate = true;
    }
}

}

When I call replaceGeometry the spheres disappear. What am I missing?

2

Don’t. Use mesh.scale instead. :slight_smile:

3

If you wanna replace geometry tho, use geometry.copy(otherGeometry)

4

So don’t discard, just replace?

5

Hmmm … Hacking it up now.

6

Im not sure if it is necessary to dispose the geometry if you copy a new one. But if you really just wanna scale it use Mesh.scale.set(x, y, z).

7

Weird. Now, all I’m doing is scaling the meshes … and they just vanish. Poof! I don’t get it.

I am doing - essentially - exactly the same thing as example webgl_geometry_extrude_splines.html in setScale().

8

If you scale your meshes this way Mesh.scale(x, y, z), it’s wrong. Set scaling of meshes like that Mesh.scale.set(x, y, z), or Mesh.scale.setScalar(n) if you want to scale them uniformly.

2 Likes
9

Still no joy. Here is the code:

scaleRadius(scaleFactor) {
    for (let mesh of this.balls) {
        mesh.scale.setScalar(scaleFactor);
    }
}

Pretty simple. But the balls vanish when I can the method on the scale vector. Are there no other method calls I need to make? Maybe within the renderloop? Maybe mesh matrices that need to be poked? As a sanity check, when I comment out the scaling call the balls do not vanish, so it is clearly to do with the scaling. Frustrating.

10

Any chance to provide a fiddle or a pen (jsfiddle, codepen), that shows the problem?

11

Solved. The bug was actually nothing to do with the above code. When I construct the set of spheres I was calling geometry.translate(..) to position them in the scene rather then mesh.position.set(...). I suspect mixing geometry matrix methods and mesh matrix methods is not the way to go. Anyway, solved. Thanks for the assist y’all.

1 Like
12

Ah… That means the scaling applied to the offsets too. I am happy that you solved it.

It is generally discouraged to do a lot of geometry manipulation in animation. Modifying geometry will require moving much more data to the GPU than changing a transform.

13

Yep. It is also a lesson to - in general - prefer working at the highest level API available - mesh - rather then hacking at a lower level - geometry.

14

Well… If you are creating many simple objects, like in the “bird” flock examples, you may be better off modifying a geometry instead, because the many draw calls build a huge overhead.