theme: Don't give login-dialog another background-color

Its parent `lockDialogGroup` has exactly the same background-color
set in the same file. Giving them both the same wasted render time on
overdraw, and caused multi-layer blending artifacts (slight flickering
of the grey background) when the login dialog fades in/out.

While the flicker can also be fixed using `set_offscreen_redirect`,
there's no point adding that overhead when the extra layer doesn't need
to be painted. Removing it halves the average render time of the login
animation.

Closes: https://bugs.launchpad.net/bugs/2036388
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3207>

diff --git a/data/theme/gnome-shell-sass/widgets/_login-lock.scss b/data/theme/gnome-shell-sass/widgets/_login-lock.scss
index ae3fc7d8d3da2ab1c3d357d1ffd74f8f7f92363b..87ed1cad9952f615503aca7246d3dec003de1ca7 100644 (file)
--- a/data/theme/gnome-shell-sass/widgets/_login-lock.scss
+++ b/data/theme/gnome-shell-sass/widgets/_login-lock.scss
@@ -21,8 +21,6 @@ $_gdm_dialog_width: 25em;
 // GDM Login Dialog
 // uses dark grey system styles
 .login-dialog {
-  background-color: $_gdm_bg;
-
   .login-dialog-prompt-entry {
     @extend %system_entry;
   }