Now that we are adding more pie menus, we could make some small but effective improvements to them.
First, the wedge could be highlighted as you rollover it, to make it clearer how big the area is, like so:
Holding, Then Releasing Key Should Always Dismiss Pie
There's a slight quirk in the way we handle input: Normally, if you hold a key to invoke a pie menu and then let go, the pie menu is dismissed. This works if you move your cursor to an item, or to an empty area. But, if you don't move the cursor at all, this doesn't work. This makes the behaviour inconsistent, and makes the pies 'stick' in an annoying way if you regret opening one.
Letter Input While Pie is Active
While number input works reasonably well, in Blender we also use letters to invoke options in menus. For pies, letters work better, because the order makes less direct sense. There's nothing intuitive that says left=1, right=2, and so on. We should enable letter input to activate pie options. This way, user can press Z, S to activate Solid Mode.
These three changes should make pie menus more delightful to use.