Comment 3 for bug 1548236

> Implementing barriers in mir will take scene state outside of the shell, confusing responsibilities.
That's not entirely true.

Mir already has (partially implemented?) input regions where the mouse cursor varies between regions of a surface. I'm not sure it's fully implemented yet, but the initial goal there is to have the Mir server change your cursor for you automatically based on the input regions (widgets) you have defined. All normal toolkit functionality. And we could easily extent that to include motion limitations too. Certainly we will need to look into this area anyway to implement grabs for gaming in future.

So considering that Unity8 is just a client of USC, it seems quite simple and reasonable that in future Unity8 (like any Mir client) would just define regions of unusual pointer behaviour. It's not confusing responsibilities as much as simply using the Mir client API that should exist in future.