How to optimize a scene with 10k mesh instances?

[Evgeni_Popov]

@Stephen

1. How do you properly implement an octree for static meshes and does it even make sense in a case like this where it’s one open field?

An octree is useful only if your geometry is at least moderately complex and span a large area in your scene. If all / most of your meshes are always visible it is of no use, and the additional time to traverse the tree will actually make your fps worse, as you could see.

@Stephen

2. Should these functions be run on the mesh after you load it in or on each instance of it after you created it? e.g. mesh.material.freeze(); mesh.freezeWorldMatrix();

You can call mesh.material.freeze() right away, even if the mesh is not loaded yet. The system will really freeze the material only after it has been fully generated (meaning when the underlying effect has been correctly created).

If you freeze the active meshes, call the function by passing it true:

scene.freezeActiveMeshes(true);

That way, computeWorldMatrix won’t be called on any mesh without you having to call mesh.freezeWorldMatrix on all meshes beforehand (also, small performance gain as you will avoid a loop on all meshes inside scene._evaluateActiveMeshes).

By doing so, if you want to update a mesh afterward, just update the position/rotation/scale properties and call mesh.computeWorldMatrix, no need to call unfreezeWorldMatrix / freezeWorldMatrix before/after.

@Stephen

3. When I create instances of a mesh does the performance decrease exponentially the more instances I have? (For example would a scene with 10k cubes run smoother than a scene with 10k cubes that have a bevel and a few more vertices?)

I don’t think so, as it is still a single draw call to the GPU. So it all depends on the GPU, you could double your instances for free if the GPU is fast enough to process the rendering in parallel to the javascript code needed to handle a frame. You will have to perform testing to know for sure, however.

@Stephen

4. Do you guys think it’s even possible to get a scene with this many mesh instances to run on ~60 on mobile or is that a pipe dream?

No idea as I don’t know mobile dev. If freezing all meshes + all materials, the javascript code load is reduced to a minimum, so much of the time will be passed on the rendering GPU side.

Note that _evaluateActiveMeshes is called in the course of renderFromCamera, so the timing of both functions are linked.