Algodoo

Great Scene

Lags a bit and you can't drag the circle around. I guess it's somewhat useful but I wouldn't use it because it would lag scenes.

It's weird it lags for you, perhaps it's because of my massive reserve of fast access RAM, because this thing does lots of RAM I/O, though, this method does allow for you to only update values when you need to, so if you were using this for a spring, hinge or fixate creation, it should be far less taxing, and much friendlier. Depending on the speed your computer can save one undo step then undo it, this should run faster than normal beacons.

If I can get it to work without creating and undoing an undo step, then it shouldn't have any lag and you should be able to use drags. I may not think of how to get it to work without creating and undoing an undo step for a while, but at the moment, it is probably the easiest way to capture the geometry and entity IDs without having the user do anything.