[can16358p]

It does, indeed. Not like constantly recording though. I think they apply some heuristics that keep the camera on in the background (e.g if you open on story camera frequently and on the main screen, but not while at a screen when camera is not accesible). Otherwise the device would become noticeably hot, but I haven't encountered such an issue.

[redwall_hp]

The way that would make sense, for that particular example, is to start the camera up when the user begins the interaction to open it. Like how https://instant.page/ works. If it takes 200ms to get the camera running, do it while the gesture to swipe over to the camera is in progress. It will take more than 200ms for the user to physically move.

iOS has events for gesture start, in progress, finished and cancelled.