[mutter] background: Make the final monitor texture RGB instead of RGBA

[Marge Bot <marge-bot src gnome org>]

commit 93e938e22fa2cf1c13c3abde49e174f31b3c5f0f
Author: Daniel van Vugt <daniel van vugt canonical com>
Date:   Fri Jan 8 15:59:21 2021 +0800

    background: Make the final monitor texture RGB instead of RGBA
    
    The monitor texture is the final background image. It doesn't need to
    have any alpha channel. Cross-fades (which is the process of rendering
    *into* the monitor texture) still work just fine.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1665>

 src/compositor/meta-background.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/compositor/meta-background.c b/src/compositor/meta-background.c
index 1a677fe187..c0d8d335d0 100644
--- a/src/compositor/meta-background.c
+++ b/src/compositor/meta-background.c
@@ -820,7 +820,7 @@ meta_background_get_texture (MetaBackground         *self,
 
           monitor->texture = meta_create_texture (texture_width,
                                                   texture_height,
-                                                  COGL_TEXTURE_COMPONENTS_RGBA,
+                                                  COGL_TEXTURE_COMPONENTS_RGB,
                                                   META_TEXTURE_FLAGS_NONE);
           offscreen = cogl_offscreen_new_with_texture (monitor->texture);
           monitor->fbo = COGL_FRAMEBUFFER (offscreen);