The physics engine acting on the instance is not working
The sphere can fall freely before adding an instance, but it will remain motionless after adding an instance.
sphere.thinInstanceSetBuffer("matrix", bufferMatrices);
sphere.thinInstanceSetBuffer("color", bufferColors, 4);
Hello @lxq100 , how are you doing?
My understanding is that thin instances and the physics system are not designed to be used together. Iām adding @Cedric here just to be sure. But from what I understand from those systems the physics system is not aware of the thin instances buffer system to update them directly.
What you can do is to use a Transform node that will be updated by the physics system and transfer that information manually to the thin instance system (see example bellow):
Thin instances + physics | Babylon.js Playground (babylonjs.com)
When you want to have physics on thininstances you may want to declare them as non-static per the documentation (Babylon.js docs).
Also, you can later change the position of all the instances on lines 40-46 like that.
What @riven04 says 