Created attachment 59289 [details]
Patch to keep brightness choosen by user when unplugged

Version:           unspecified (using KDE 4.6.2) 
OS:                Linux

I've been using the laptop in the dark and on batteries. I've noticed this unexpected behavior where while loosing charge the brightness sometimes would jump up.

Imagine you unplug the laptop and are in a dark room. With brightness at 100 you pretty much lit the room so lets reduce the brightness to 0 (or some low level). When the battery charge reaches the low level (25% by default for me) the brightness suddenly jumps to 40%.

This happens whenever the brightness specified in the profile is higher than the confortable brightness for the moment because powerdevil always sets the specified value and ignores the user choice.

It would be nice if powedevil, since it is supposed to help saver power, only lowered the brightness when unplugged. IF the user chooses to be even lower then accept that.

Reproducible: Always

Steps to Reproduce:
1. Plug laptop to AC
2. Reduce brightness to 0
3. Unplug laptop from AC

Actual Results:  
1. Brightness = 100
2. Brightness = 0
3. Brightness = 60 (for example)

Expected Results:  
1. Brightness = 100
2. Brightness = 0
3. Brightness = 0

The attached patch has the 4.6 branch as target. In it I try to check the current brightness and only change the value if it is higher than requested in the profile. The plugged state is also checked so that when the user plugs the laptop brightness goes up.

Now the only tricky case is when the user has the laptop unplugged and manually changes the profile. In that case brightness only goes down an never up. At least for me, I hardly ever change the profiles manually. Once I had a "Presentation" profile but brightness is not that important.