server/osd_window: update window margin when parameters change

This ensures the window margin is always correct. This also fixes an
annoying issue where the monitor scale factor is not always correct (it
never changes back to scale 1 if it was scale 2 at some point) by
transforming the monitor height into window coordinates manually.

Fixes #101.

src/server/osd_window.rs

@@ -56,16 +56,34 @@ impl SwayosdWindow {
 
 		window.set_child(Some(&container));
 
+        let update_margins = |window: &gtk::ApplicationWindow, monitor: &gdk::Monitor| {
+            // Monitor scale factor is not always correct
+            // Transform monitor height into coordinate system of window
+            let mon_height = monitor.geometry().height() * monitor.scale_factor() / window.scale_factor();
+            // Calculate new margin
+            let bottom = mon_height - window.allocated_height();
+            let margin = (bottom as f32 * get_top_margin()).round() as i32;
+            window.set_margin(gtk_layer_shell::Edge::Top, margin);
+        };
+
 		// Set the window margin
-		window.connect_realize(clone!(
-			#[strong]
-			monitor,
-			move |win| {
-				let bottom = monitor.geometry().height() - win.allocated_height();
-				let margin = (bottom as f32 * get_top_margin()).round() as i32;
-				win.set_margin(gtk_layer_shell::Edge::Top, margin);
-			}
-		));
+        update_margins(&window, monitor);
+        // Ensure window margin is updated when necessary
+        window.connect_scale_factor_notify(clone!(
+            #[weak]
+            monitor,
+            move |window| update_margins(window, &monitor)
+        ));
+        monitor.connect_scale_factor_notify(clone!(
+            #[weak]
+            window,
+            move |monitor| update_margins(&window, monitor)
+        ));
+        monitor.connect_geometry_notify(clone!(
+            #[weak]
+            window,
+            move |monitor| update_margins(&window, monitor)
+        ));
 
 		Self {
 			window,