Quick fix for tearing on GNOME (< 3.30):

Open looking glass pressing ALT+F2 then lg
Type:
Meta.disable_unredirect_for_screen(global.screen);

For GNOME >=3.30

Open looking glass pressing ALT+F2 then lg
Type:
Meta.disable_unredirect_for_display(global.display);

From source code `

This will fix screen tearing at the cost of performance/heat!