Comment 119 for bug 278471

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In , Stuff-i-need-an-email-for (stuff-i-need-an-email-for) wrote :

I've got some info on how to reproduce this bug on an affected system, some of the triggering events for the screen flickering and the pattern of the flickering.

Firstly leave the system completely alone for 45 secs. No mouse and keyboard input.
When you cause the blinking to be triggered (specific triggers given below) the first blink will happen about 1 second after the triggering event, now you should not create any further input on mouse or keyboard. There will be a second blink after 30 secs and a third at 45 secs after the trigger. These intervals are exact and repeatable at every attempt. This may be why the blinking seems random at first because some of the flickering is caused by what you did 30 and 45 seconds ago. I can't see any further blinking after 45 secs if I leave the system alone. After the 45 seconds you can use the same trigger to start the 3 blink cycle over again.

Some triggers for the initial blink I have found:
1.) Minimising a window with the minimise window composite effect enabled. Disabling this composite effect will stop the blink from happening when a window is minimised.
2.) Click and hold on a window titlebar such that the transparency effect is enabled. Simply clicking the titlebar will not trigger the blink, you have to hold until the transparency happens.

With window compositing completely disabled it is still possible to cause the blinking with these triggers in applications where there is a scrollbar:
3.) In konqueror go to a web page that is long enough to cause the scrollbar to appear and then using the scroll area of a laptop touchpad scroll all the way to the bottom of the page and keep scrolling down after the bottom of the page is hit. I can not get this to happen in the same way with a mouse scroll wheel. Nor can I cause the trigger by clicking on the scrollbar up/down buttons or by clicking in an empty area of the scrollbar. I can get it to happen with a mouse scroll wheel by rapidly wheeling down then up then down in rapid succession. This rapid up and down also works with the touchpad scroll area to trigger the blink. Holding the scrollbar button and dragging it also seems to cause the blink but I can't pinpoint the exact trigger event.

4.) Same as above but only in kickoff when you have selected a tab with lots of entries that causes a scrollbar to appear. Touchpad scroll area used to scroll down past the bottom will cause the blink.

I'm a software engineer but not a Qt/Kde or linux one so I can only be of limited help to debug further. My system is kubuntu 9.04 with kde 4.3.2 from the backport ppa but I seem to remember this annoying problem throughout kde4 release cycle. I'll provide any further info about my system on request.