Some functions are too slow to compute on each slider increment, but one still wants to be able to move a slider and trigger a computation on release, rather than have to go to a "calculate" button each time. One implementation idea is to have three settings for auto-call: True/on-value-change, on-release, False. Whether this is done with an enum, a union of an enum/bool, or something else... 🤷
xref scikit-image/skimage-tutorials#55