These 3 toggles represent Land Rock and Water.
If only Land is active, then it wont paint on rocks or the water. great for painting plants that you dont want to accidentally place in the water or on top of rock.
If only Rock is active, It wont paint on land or the water, so you can paint ferns on top of rocks for example.
water does not let me drop things into the water. I must also select one of the other icons.,