Slow rendering with DRI3, intel and rotate monitor in webki2gtk
Submitted by Jan Burgmeier
Assigned to Xorg Project Team
Created attachment 141251 XOrg log
I'am experincing very slow rendering in webki2gtk on webpages using accelerated rendering. For example while using LIBGL_DEBUG=verbose mini-browser I can see that for https://www.webkitgtk.org/ no GL is loaded and it is fast and for https://www.google.com GL is loaded and typing text in the textfield is very slow. The slow rendering only occurs if one monitor in a two monitor setup is rotated. As soon as the rotation is unset the slowdown is gone, no restart of mini-browser needed. If mini-browser is started with LIBGL_DRI3_DISABLE=true the slowdown is also gone.
The intel DDX driver or modesetting on radeon does not have this problem.
I found bug #85064 but in the webkit2gtk version I use this should already be fixed.
Environment: Kernel: 4.14.39 Mesa: 18.1.6 and git master XOrg: 1.20.1 Webkit2gtk: 2.20.2 Screen: Dual monitor one rotated
Attachment 141251, "XOrg log":