Add background handling

This does not work as expected. I think the problem is on the wlc side.
Please review, @Cloudef. To reproduce the issues:

1. Run sway
2. Open terminal in sway
3. Run swaybg

swaybg will create a surface and ask to have it set as the background,
but wlc_handle_from_wl_surface_resource will return 0. If the swaybg
surface is a shell surface, then it works - but wlc complains about the
pointer type and segfaults as soon as the pre-render hook tries to draw
the background.

1 files changed, 13 insertions, 0 deletions

diff --git a/include/extensions.h b/include/extensions.h
index e122c59a..3e2d1cde 100644
--- a/include/extensions.h
+++ b/include/extensions.h
@@ -1,6 +1,19 @@
 #ifndef _SWAY_EXTENSIONS_H
 #define _SWAY_EXTENSIONS_H
 
+#include "list.h"
+
+struct background_config {
+        wlc_handle output;
+        wlc_handle surface;
+};
+
+struct desktop_shell_state {
+        list_t *backgrounds;
+};
+
+extern struct desktop_shell_state desktop_shell;
+
 void register_extensions(void);
 
 #endif