BackgroundBlurEffect: fix for libmutter15+

[garaevdi]

While mutter and gnome-shell devs are phasing out Clutter.get_default_backend (), it's still there. Getting context through the actor isn't working because there isn't any assigned actor, so the whole thing just crashes. Gnome-shell exposes global stage and gets context from there, but this solution would require to re-engineer WindowManagerGala to be a singleton. Another solution is to pass context directly to the effect. Both options are out of scope for me because I'm not very familiar with the codebase.

Backtrace without this patch

Thread 1 "gala" received signal SIGSEGV, Segmentation fault.
clutter_actor_get_context (actor=0x0) at ../clutter/clutter/clutter-actor.c:12720
12720	  return actor->priv->context;
Missing rpms, try: dnf --enablerepo='*debug*' install wingpanel-debuginfo-8.0.4-1.fc43.x86_64
#0  clutter_actor_get_context (actor=0x0) at ../clutter/clutter/clutter-actor.c:12720
#1  0x000055555555ddde in gala_background_blur_effect_constructor (type=<optimized out>, n_construct_properties=<optimized out>, construct_properties=<optimized out>) at ../src/BackgroundBlurEffect.vala:43
#2  0x00007ffff7eb2362 in g_object_new_with_custom_constructor (class=class@entry=0x5555576a05d0, params=params@entry=0x7fffffffd0c0, n_params=n_params@entry=3) at ../gobject/gobject.c:2585
#3  0x00007ffff7eb4603 in g_object_new_internal (class=0x5555576a05d0, params=0x7fffffffd0c0, n_params=3) at ../gobject/gobject.c:2663
#4  g_object_new_valist (object_type=<optimized out>, first_property_name=first_property_name@entry=0x5555555e5b9f "blur-radius", var_args=var_args@entry=0x7fffffffd390) at ../gobject/gobject.c:3003
#5  0x00007ffff7eb4e7f in g_object_new (object_type=<optimized out>, first_property_name=first_property_name@entry=0x5555555e5b9f "blur-radius") at ../gobject/gobject.c:2479
#6  0x00005555555c7209 in gala_background_blur_effect_construct (object_type=<optimized out>, blur_radius=40, clip_radius=9, monitor_scale=1) at ../src/BackgroundBlurEffect.vala:38
#7  gala_background_blur_effect_new (blur_radius=40, clip_radius=9, monitor_scale=1) at ../src/BackgroundBlurEffect.vala:37
#8  gala_window_switcher_constructor (type=<optimized out>, n_construct_properties=<optimized out>, construct_properties=<optimized out>) at ../src/Widgets/WindowSwitcher/WindowSwitcher.vala:107
#9  0x00007ffff7eb2362 in g_object_new_with_custom_constructor (class=class@entry=0x5555576afaf0, params=params@entry=0x7fffffffd730, n_params=n_params@entry=1) at ../gobject/gobject.c:2585
#10 0x00007ffff7eb4603 in g_object_new_internal (class=0x5555576afaf0, params=0x7fffffffd730, n_params=1) at ../gobject/gobject.c:2663
#11 g_object_new_valist (object_type=<optimized out>, first_property_name=first_property_name@entry=0x5555555e5f71 "wm", var_args=var_args@entry=0x7fffffffda00) at ../gobject/gobject.c:3003
#12 0x00007ffff7eb4e7f in g_object_new (object_type=<optimized out>, first_property_name=first_property_name@entry=0x5555555e5f71 "wm") at ../gobject/gobject.c:2479
#13 0x0000555555584ae0 in gala_window_switcher_construct (object_type=<optimized out>, wm=0x5555576124a0) at ../src/Widgets/WindowSwitcher/WindowSwitcher.vala:54
#14 gala_window_switcher_new (wm=0x5555576124a0) at ../src/Widgets/WindowSwitcher/WindowSwitcher.vala:53
#15 gala_window_manager_gala_show_stage (self=0x5555576124a0) at ../src/WindowManager.vala:280
#16 gala_window_manager_gala_real_start (base=0x5555576124a0) at ../src/WindowManager.vala:139
#17 0x00007ffff6aa2cd3 in meta_plugin_manager_start (plugin_mgr=0x55555761d830) at ../src/compositor/meta-plugin-manager.c:165
#18 meta_compositor_manage (compositor=<optimized out>, plugin_options=0x0, error=<optimized out>) at ../src/compositor/compositor.c:311
#19 meta_display_new (context=<optimized out>, plugin_options=0x0, error=<optimized out>) at ../src/core/display.c:1067
#20 0x00007ffff6aaa1dc in meta_context_start (context=<optimized out>, error=error@entry=0x7fffffffdde8) at /usr/include/glib-2.0/glib/gmem.h:245
#21 0x0000555555571d41 in gala_main (args=<optimized out>, args_length1=<optimized out>) at ../src/Main.vala:78
#22 0x00007ffff63f15b5 in __libc_start_call_main (main=main@entry=0x55555555c260 <main>, argc=argc@entry=2, argv=argv@entry=0x7fffffffe248) at ../sysdeps/nptl/libc_start_call_main.h:58
#23 0x00007ffff63f1668 in __libc_start_main_impl (main=0x55555555c260 <main>, argc=2, argv=0x7fffffffe248, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fffffffe238) at ../csu/libc-start.c:360
#24 0x000055555555c2a5 in _start ()

[leolost2605]

Thank you! I think with this Gala is finally usable at least on mutter 48 right?

Just for future reference ig we should do the setup in the set_actor virtual 🤷