User interfaces should always be able to lead, follow, or get out of the way.

Animation should never delay interaction, and it should never interfere with gestures and mouse-ahead (or whatever the input device is).

The user should never have to wait for animation to finish before they're able to do something, and the interface should never be disabled during animation, or ever ignore the user's input under any circumstances.

User input should always pre-empt and interrupt feedback and animation.

The interface should always support quick gestures (mousing ahead, touching ahead, or whatever), without ever requiring the user to pause and wait, or focus their attention on the screen to watch the animation play out before they know it's safe to make the next move.

I developed a gestural pie menu tabbed window manager for the NeWS window system in 1990, which supported mousing ahead, suppressing the pie menu display and pop-up animation until you stopped moving, showing light weight feedback on the overlay plane, and executing commands instantly without any animation or even popping up the menu, when you make a smooth quick gesture without hesitating.

NeWS Tab Window Demo:
https://www.youtube.com/watch?v=tMcmQk-q0k4

Transcript of the relevant part of the demo:

Now you can press the right button to pop up a pie menu on the tab or on the frame itself. And that has commonly used commands like front and back in mnemonic directions. Back is down, and front is up.

When you make a menu selection by mousing ahead, it doesn't display the menu.

As long as you're moving, it suppresses the menu display.

And it gives you feedback on the overlay plane of the slice that you're in, and the label of that slice, so you can actually see what you're going to get before you choose it without even seeing the menu itself.

And when you wait, it pops up the menu once you stop moving.

So if you waste some time by just waiting around, it will waste a bit more time by giving you some stupid animation.

And this is meant to be negative reinforcement, to encourage you to mouse ahead.

The sub-menu pops up. This is "move to" which is unconstrained move.

You can always get that from the tab by mousing left and right.

That's an easy gesture. Just quickly...

Or mouse there and wait. There it is. It pops up the one you're at first.

This is constrained horizontal move.

And this is constrained vertical move.

So constrained horizontal... We'll wait.

Constrained vertical...

So, I mean, once you're there, and you know what you want, why wait?

This is "beam me up": put it in the next layout position. To tidy the windows.

So, if you've clicked the menu up and haven't moved, it will just spin it, because it's confused, and doesn't know what you're going to do.

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In other words: As it pops up and scales up the round menu, it also tilts it along the axis perpendicular to the direction of movement to reinforce the selected direction, or spins around the center if you haven't moved to show no direction is selected.

And you only ever see any animation if you actually stop moving -- once you make a selection, the command always executes or the submenu always activates immediately.

You can mouse ahead smoothly through multiple levels of sub-menus, without popping any of them up or seeing any animation, as long as you never hesitate.

By "lead, follow, or get out of the way", I mean that pie menus can lead novice users by giving them feedback and animation when they pause, follow intermediate users who move in the right direction then pause for the feedback to make sure they got it right, and get out of the way of expert users who know the right direction and can quickly articulate gestures without pausing or waiting for feedback.

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Here's another demo showing pie menus, mouse ahead gestures, and display pre-emption in SimCity:

X11 SimCity Demo:
https://www.youtube.com/watch?v=Jvi98wVUmQA

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And here's a really old demo from June 1986 of the "uwm" window manager for the X10 window system, that I hacked to support pie menus with mouse-ahead and display pre-emption.

X10 Pie Menu Window Manager:
https://www.youtube.com/watch?v=IJhvB6kwmog

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More info here:

The Design and Implementation of Pie Menus -- Dr. Dobb's Journal, Dec. 1991:
http://www.donhopkins.com/drupal/node/98