[mutter] background: Mipmap wallpaper when shrinking

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 8e9184b62e05e60b20fcaa7ed68714c226c24a40
Author: Daniel van Vugt <daniel van vugt canonical com>
Date:   Thu Nov 15 15:39:34 2018 +0800

    background: Mipmap wallpaper when shrinking
    
    So as to minimize jaggies for wallpaper that is >= double the resolution
    of the screen.
    
    Closes: https://gitlab.gnome.org/GNOME/gnome-shell/issues/254

 src/compositor/meta-background.c | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/src/compositor/meta-background.c b/src/compositor/meta-background.c
index 0fb20d569..4670409aa 100644
--- a/src/compositor/meta-background.c
+++ b/src/compositor/meta-background.c
@@ -629,6 +629,11 @@ create_pipeline (PipelineType type)
       cogl_pipeline_set_blend (templates[type], blend_strings[type], NULL);
     }
 
+  cogl_pipeline_set_layer_filters (templates[type],
+                                   0,
+                                   COGL_PIPELINE_FILTER_LINEAR_MIPMAP_NEAREST,
+                                   COGL_PIPELINE_FILTER_LINEAR);
+
   return cogl_pipeline_copy (templates[type]);
 }