exposay: set an alpha on fullscreen surfaces

This makes the desktop background actually draw when there is
a fullscreen surface and we go to exposay.

desktop-shell/exposay.c

@@ -286,6 +286,8 @@ exposay_layout(struct desktop_shell *shell)
 		if (shell->exposay.focus_current == esurface->view)
 			highlight = esurface;
 
+		set_alpha_if_fullscreen(get_shell_surface(view->surface));
+
 		exposay_animate_in(esurface);
 
 		i++;

desktop-shell/shell.c

@@ -222,6 +222,13 @@ struct shell_seat {
 	} popup_grab;
 };
 
+void
+set_alpha_if_fullscreen(struct shell_surface *shsurf)
+{
+	if (shsurf && shsurf->state.fullscreen)
+		shsurf->fullscreen.black_view->alpha = 0.25;
+}
+
 static struct desktop_shell *
 shell_surface_get_shell(struct shell_surface *shsurf);
 

desktop-shell/shell.h

@@ -188,6 +188,9 @@ struct desktop_shell {
 	char *client;
 };
 
+void
+set_alpha_if_fullscreen(struct shell_surface *shsurf);
+
 struct weston_output *
 get_default_output(struct weston_compositor *compositor);