Skip unchanged shell snapshots and share broadcast construction

compositor/src/state.rs

@@ -180,6 +180,7 @@ pub struct Ferese {
         >,
     >,
     pub(crate) shell_snapshot_serial: u32,
+    pub(crate) last_shell_snapshot: Option<crate::shell_control::ShellSnapshot>,
     pub(crate) overview: crate::overview::OverviewState,
     next_window_id: u64,
     next_output_id: u64,
@@ -651,6 +652,7 @@ impl Ferese {
             pending_screencopies: Vec::new(),
             shell_resources: Vec::new(),
             shell_snapshot_serial: 0,
+            last_shell_snapshot: None,
             overview: crate::overview::OverviewState::with_font_family(config.overview_font_family),
             next_window_id: 1,
             next_output_id: 1,