Dev Mode: setting to change the post frame callback duration

[g123k]

Following the PR #1732, a timeout is set to detect if we have to relaunch the camera.
In some cases, it seems that this duration is not enough.

To find a correct value, a setting in the dev mode would be nice

[monsieurtanuki]

@g123k Beyond setting a decent minimum duration, are you sure there are no other ways to detect "the right moment"? Like somme callback, some event?

Not 100% related: would that be possible to limit the camera to the top half of the screen? I mean, not just processing rather the top part, but using a camera viewer Widget whose height is only half of the screen height? That would be less to process, and anyway the bottom half of the screen is already occupied.

[g123k]

@monsieurtanuki I don't think we can do it otherwise, unfortunately.
I have tried many ways to detect the event and that's the most accurate I've found.

For the camera, it won't change anything (or at least, only be marginal), as the stream sent from the camera is exactly the same.

[monsieurtanuki]

Maybe all these problems come from the fact that we're virtually displaying 3 pages while hiding 2 of them. Things would perhaps be easier if the scan page was a normal page users go to and go back to. Thinking out loud.

[g123k]

Actually we have "one real" visible Widget and two hidden (via an Offstage).
We can fully remove them, but will mean we will have to manage the state.

I will experiment this, as part of #1047