[spiffyk]

> What if something is costly, that you need to compute dynamically, but not often, makes it into the frame? Do you separately now create a state flag for that one render object?

The point of immediate mode UIs is not necessarily that there is no state specific to the UI, but rather that the state is owned by user code. You can (and, in these more complex cases, should) retain state between frames. The main difference is that the state is still managed by your code, rather than the UI system ("library", whatever).