Simulator vs. Real device

Not really.  This isn't something you can learn in a week.

And as Travis (one of the Garmin CIQ engineers) said in the link you posted, it won't change,  If you follow the basic rule of assuming that when onUpdate() in a watch face is called the screen is blank and you have to re-draw everything, things are fine.  The only time it's vaiid to only update part of the screen is in onPartialUpdate.

As you see ate least 2 person have the same problem (but I think more than 2). So

1. documentation is silent about it

2. sim not enough reflects to device (and this bug is important - it touch the most important part of app - onUpdate). So if garmin require whole screen drawing it should simple clears it in sim (except on onPartialUpdate of course).

In my case, I found out this from my user just because I have f6.

Is it good that every new developer goes through all of this? And it's just the fault of not listening to the developers and not fixing bugs.

So what if 95% is ok as the other 5% is making a lot of trouble. But you can either accept this fact or let go and not tire yourself :)

It would be nice if Garmin would tell us which devices wipe the screen on each onUpdate and which ones don't.

You want to assume that all of them do.  You always want to redraw everything in onUpdate().  You can redraw parts of the screen with onPartialUpdate().

If you use layouts, View.onUpdate() also clears the screen, so any dc calls need to be done after the View.onUpdate() or they will be lost.

This causes an unnecessary battery drop. ️

I don’t want to draw it all over again if there are no changes.

Not really,  Most of the time onUpdate is only called once a minute.

Skip using onPartialUpdate to save battery, as that's called every second most of the time.

OK. Thank you.