Simultaneous Update on Debian / Stretch Seems To Fix Wayland Bug, But An Effect Breaks.

This morning was one, on which most of my computers are receiving major system updates.

On the computer that acts as my Web-server, which I name ‘Phoenix’, this updated my Debian / Jessie version from 8.9 to 8.10.

On the computer which I most-recently installed, which I name ‘Plato’, this updated my Debian / Stretch version from 9.2 to 9.3 .

On both computers, this included a kernel-update. Additionally, it included an update, to the client-side X-server libraries. This posting has to do with the computer named ‘Plato’, which has kernel version ‘4.9.0-4-amd64′ now.

Previously I had blogged, that the computer named ‘Plato’ was suffering from a mysterious bug in its ‘Wayland’ compositor. If the compositing became suspended for any reason, after resuming, black rectangles would appear on the screen, as newly-opened windows faded in and out. This used to happen regardless of whether OpenGL 2 or OpenGL 3 compositing was being used.

Well since the update today, I tested the key-combination <Shift>+<Alt>+F12 again, which does the equivalent of sending the command to the compositor, to suspend. Apparently, the behavior of this key-combination has been changed since Debian / Jessie, so that instead of toggling, the compositing suspends for several seconds, and then automatically resumes. This would be useless as a user-feature, but can help with testing, because presumably, what an OpenGL application is supposed to do, is resend the signal every second or so, to make sure that compositing stays off.

To my pleasant surprise, I found that after compositing resumes, I no longer get black rectangles on the screen! :-)

  1. One small drawback which remains though, is that after compositing is resumed, the fade-in of newly-opened windows is not as smooth as it was, before compositing was suspended. And it did seem before, like this fade-in effect was triggering the black rectangles.
  2. Whenever a new window is created or made to disappear, this is briefly preceded by a black rectangle, which has the exact geometry of the window being created or destroyed. This can appear as a ‘flashing’ effect, and does get irritating after a while.

The only way to repair (1) and (2) above remains, to reboot the computer.

Note: In order to improve the stability, of the compositing, I have gone into System Settings -> Desktop Behavior -> Desktop Effects , and deselected the “Fade” effect, that causes windows to fade-in and fade-out. And doing so has also, not brought back the black rectangles.

Dirk

 

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