How to animate weight-painting? I want that particles would appear from one corner, and like a wave would go through all the plane using vertex density. Basically just to animate the weight-painting. Is it possible do it, or maybe there is some other ways to make similar effect?
I think you're looking for the Vertex Weight Proximity modifier. It lets you assign vertex weights based on, for example, the distance to the target object's geometry, which you can animate per usual.