Ubuntu
xserver-xorg-video-amdgpu package

  1. Focal (20.04)
  2. Bug #1873895
  3. Comment #29

Comment 29 for bug 1873895

Revision history for this message
TJ (tj) wrote : Re: Regression: block staircase display with side-by-side monitors

With the help and suggestions of Bluesabre on #xubuntu-devel we've tracked it down to a recent change in xfwm4 where it switched from using glx to xpresent:

https://git.xfce.org/xfce/xfwm4/commit/?id=23900123ad8418149897a094d1096d6ecb984d3c

which seems to be a bug in the driver as mentioned orginally:

https://bugzilla.xfce.org/show_bug.cgi?id=16716

=>

https://gitlab.freedesktop.org/xorg/driver/xf86-video-amdgpu/-/issues/10

It is also SPECIFIC to the resolution selected on the external HDMI display.

In our case the Lenovo E495 has eDP 1920x1080 and external HDMI are 168x1050 and are affected.

I tried with another external HDMI that is natively 1920x1200 and couldn't reproduce UNTIL I set it to use 1680x1050 instead of its preferred resolution, at which point the blocked staircase returned.

As I said above it feels like an off-by-one bug on the assumption rendering the display is split into regions (columns) and it is rendering 1920 pixels to a 1680 wide output with the pixels 1680-1919 wrapping to the next 'row'.