When the instance count of MultiMesh is changed, strange data appears in the buffer.

[SneaK1ng]

Godot version

v4.1.dev.custom_build.c29866dbc

System information

Win10, AMD 2600, GeForce GTX 1060, Vulkan API 1.3.205

Issue description

I don’t know if it’s normal.

When I change the instance count of MultiMesh, sometimes strange data will appear in the buffer like below:

Steps to reproduce

Just change the number of instance_count several times.

Minimal reproduction project

nothing

[Calinou]

• Related to Vulkan: MultiMeshInstance3D not showing up and having culling issues depending on how fast they get created #56357.

[bitsawer]

I did some related digging during my MultiMesh bugfix and I can confirm this happening, it's pretty easy to repro. I suspect the reason might either be the semi-asynchronous nature of the buffer update or simply uninitialized data somewhere. Either way, the end result is that sometimes when resizing the buffer data in the editor, it gets filled with garbage data.