Comment 25 for bug 753971

This update is particularly in response to JayTaoko's comment #21 regarding the fact that the fix was not tested on a multi-monitor setup.

The original problem was observed also when plugging in an external display to the laptops. I tested this and here are the results.

I first checked the original bug, by using the old version of Unity (3.8.10). I plug in an external screen, and when the system detects it, we observe the same garbling as originally described. This can be "cleaned up" by dragging windows around or for instance, by maximizing (F11) and then restoring a terminal window.

I then upgraded to the PPA unity (3.8.12-0ubuntu1~ppa1). I plugged in the external display. When the system detects it I see screen corruption that's different from what I originally observed :( And up to a point, it's probably worse than the original problem, as this can't be easily worked around in any way I could find.

Picture "a" shows the main display with a garbled/noisy area at the top. Notice that the top panel and Unity are correctly drawn. However, the garbling/noise completely covers any app windows that are in that region on the screen; it doesn't disappear even when dragging stuff around it.

Picture "b" shows the external display with the same noise all over. The panel is visible at the top (pic is a bit dark, check top right corner). Windows that are launched are not visible because the "noise" covers them.

If I press Super-A to launch the Unity dash, it appears correctly! see picture "c", and also notice the "black" area where the original noise/garbling used to be. However, other than the dash, that area of the screen is still "dead" and doesn't show any application windows or desktop background.

Picture "d" shows the screen incorrectly restored after I dismiss the dash; a portion of it is still visible in the "dead" portion.

During all this, the external display evolves to what's shown in picture "e". Panel still visible at the top, app windows still covered by garbly/dead portion of the screen.

The system shown here is the Inspiron 1545, however, I observed this on all 4 systems I used to validate this configuration, as mentioned on my previous report. The only difference is that the noise "pattern" in the dead area of the screen varies, on some systems it's just a dark area, on others it's a repeating pattern, and on the 1545 what appears to be random noise.