So i've seen this done in "Lumber Tycoon 2",When you chop down a tree wherever your mouse has pointed it basically "negates".
So how is that done?
I think the Lumber Tycoon instead of unioning I think what it does is seperates from the mouse hit. So what it does is it fines the mouse hit then subtracts the thing then creates 2 parts 1 the size of the bottom and 1 the size of the top.