Hey @James_Wang, thanks for the question.
It looks like you’re using the code shared in Cesium weather effects
As I understand it this code relies on the time between frames, the dt, to be defined to give meaningful positions to the particles. I think the updateCallback is getting called it’s just not returning values that produce the smoke you want.
You can try enabling the clock/animations on the viewer and see if this fixes it.
const viewer = new Cesium.Viewer("cesiumContainer", {
shouldAnimate: true,
});
If you have another limitation that prevents you from enabling animations then you may have to come up with a different way to calculate the new particle positions that accounts for when dt = 0