How to make a fill algorithm like paper.io

I made a grid and ı can drawing a frame with my character but ı need the fill my frame like this:

I paint the ground if ı touch ground. They are a seperate object.I instantantiate it in a array.

 

Sorry but I am not sure what your asking here, can you explain in more detail / more clearly?

 

sounds like he wants similar flood fill system like in the old Qix game.

one old topic,
https://forum.unity.com/threads/qix-game-logic.452628/

i once tried quickly to do it myself also, but failed (this code picks wrong area to fill)
https://unitycoder.com/blog/2012/10/22/qix-prototype/

 

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