How to create snow layer in top down 2D game?

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:bust_in_silhouette: Asked By Varden

I want to create a game with top down view, minimum static objects, some moving objects on map. I need layer of snow, every moving object can leave trail in it, that will fill up again in time. Objects speed depends on amount of snow under it.
I plan map size around 8000x8000 pixels.
So my question is how to implement that idea?

First my idea is:

  • use bitmap
  • every moving object will update some pixels if moving
  • once a second bitmap fills trails with some snow until its (snow) thickness is max
    I am afraid that it can work too slow if I have a lot moving objects.