Tom, could you please file a feedback report and ping us the feedback ID? We'll likely want to take a look at powerd logs.

Do you have a sense of how long your hand is covering ALS when this happens?

Over to Opal since he's been working on eve ALS levels. I'm not supportive of plumbing the fact that the user is taking a note into powerd, though.

Couldn't we just filter the ALS more aggressively? We already filter it after all... It's not like your hand will hang in front of it forever, you are going to eventually get tired :)

Currently we read ALS every second.[1] And we change brightness if it is at next step 2 times [2]

[1] http://cs/chromeos_public/src/platform2/power_manager/powerd/system/ambient_light_sensor.cc?l=35
[2] http://cs/chromeos_public/src/platform2/power_manager/powerd/policy/ambient_light_handler.cc?l=22

I think 2 seconds is a bit to low. I propose that we should change it to 10 seconds.

Also +Yung

So we'd always wait ten seconds before responding to brightness changes, regardless of how large they are? That seems like it could be problematic.

For me, I think that the 10 seconds lag between ambient and panel brightness change is acceptable.

I saw 1 user feedback handwriting make screen brightness adjust in past 90 days.
https://listnr.corp.google.com/report/85044744599

I think this is probably rare enough to be wontfix since we don't have good solution for this.

I wouldn't use feedback reports as the signal that this is rare. I think it makes the stylus writing experience clearly worse, but still possible. Just watching other people use stylus, many of them are initially puzzled at why their device is suddenly so dim while taking notes.

Could we be more gradual, or look at when/where the stylus was last used before dimming? If it's nearby the camera, that's a sign that the user's hand is likely covering the sensor rather than the room suddenly getting darker.

powerd (the thing that adjusts the backlight brightness) unfortunately doesn't know anything about stylus events (which are processed by Chrome).

I'd be okay with changes that added a D-Bus method to powerd that Chrome could call to say "stop doing ALS-triggered adjustments" and "start doing them again".

perhaps disable auto-brightness control when stylus is in use?  I think we can certainly do better.  Also should we also look at touchscreen events as well?  Probably similar issue as the stylus?

+1 for Dan's suggestion in #c11

+Adlr for his input as well.

+1 to #11.

@puthik will you take on adding that dbus method, and then we can call it from Chrome when the user is writing with stylus?

Dan owns powerd but if he didn't have time for that. I can take a look.

I'll do the powerd side of this if you find an eng owner for the Chrome work, Tom.

Please tie this in with the FR at issue 774223 for a setting to enable/disable automatic brightness adjustments. Then we can use the same mechanism to disable adjustments when the setting is disabled and when the user is using the stylus.

Thanks Dan, I'll look into these two issues together from the UI side.