I have found out the problem. I'll use my laptop as an example. It has 7 brightness levels (from 0 to 6).
The default brightness parameters are brightness_ac=100, brightness_battery=70, idle_brightness=30. Hence, if I start the system plugged, my LCD starts at level 6. Then I unplug: gnome-power-manager tries to decrease the brightness level by 30%. It computes the current level, and it is 100%, it then decreases the brightness to 70%. Since the actual levels are only 7 and truncates this value to level 4 (which correspontos to 66.66%, the first valid level smaller than 70%). Now I plug my system back. It computes the level and it is now 66.66%, it then increase it to 66.66 + 30 = 96.66%. However this value does not correspond to a discrete, it then truncates the value to the closest level which is now 5 and not 6 anymore. (Note that 5 corresponds to 83.33%, which is much smaller than 96.66%, however gpm always truncate when looking for the correct discreate level). Now I unplug the system, which is in level 83.33%. It decreases the level to 83.33 - 30 = 53.33%. The new discrete level is now 3 (and not 4 as before in the un-plugged state). The cycle goes on, loosing one level at a time. The problem is the truncation, or more precisely the weird idea of increasing or decreaseing the current level by the amount 100 - brightness_battery (in floating point). This kind of floating point computation, when translated to a very small number of discrete levels will always result in weird behavior. I am proposing a patch that use gpm brightness parameters as absolute targets. When you plug the cord it will take you LCD level to brightness_ac (or leave it alone if it was alerady there or above). When you unplug it will take the level to brightness_battery (or leave it alone if it was already there or below). It also works with the auto-dim feature. Note that my patch uses brightness_battery as a target value. Hence if you want your brightness level to be around 30% of the total level when unplugged set it to 30 (instead of the current 70, which I find odd. I can easily cahnge this). Please test the patch and say what you think. If you are too lazy to apply the patch and compile, and if you trust me, you can download a compiled package at http://www.ime.usp.br/~pjssilva/gnome-power- manager_2.22.1-1ubuntu4_i386.deb ** Attachment added: "Proposed patch. Apply it to a source after applying all Ubuntu patches." http://launchpadlibrarian.net/15490655/80-fix-backlight.patch.level-1.log -- g-p-m does not honor its configuration for LCD brightness levels after multiple unplug-replug from AC https://bugs.launchpad.net/bugs/215484 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
