feat: Implement smooth resizing on X11 with _NET_WM_SYNC_REQUEST

Without smooth resizing, the window will appear to jitter when it is being
resized. This is because X11 completes the resize before the client gets a
chance to draw a new frame.

This is fixed by using the "sync" extension to ensure that the resize of the
X11 window is synchronized with the server.

Closes #2153

src/platform_impl/linux/x11/event_processor.rs

@@ -13,6 +13,7 @@ use x11_dl::xlib::{
     XDestroyWindowEvent, XEvent, XExposeEvent, XKeyEvent, XMapEvent, XPropertyEvent,
     XReparentEvent, XSelectionEvent, XVisibilityEvent, XkbAnyEvent, XkbStateRec,
 };
+use x11rb::protocol::sync::{ConnectionExt, Int64};
 use x11rb::protocol::xinput;
 use x11rb::protocol::xkb::ID as XkbId;
 use x11rb::protocol::xproto::{self, ConnectionExt as _, ModMask};
@@ -429,6 +430,31 @@ impl EventProcessor {
             return;
         }
 
+        if xev.data.get_long(0) as xproto::Atom == wt.net_wm_sync_request {
+            let sync_counter_id = match self
+                .with_window(xev.window as xproto::Window, |window| window.sync_counter_id())
+            {
+                Some(Some(sync_counter_id)) => sync_counter_id.get(),
+                _ => return,
+            };
+
+            #[cfg(target_pointer_width = "32")]
+            let (lo, hi) =
+                (bytemuck::cast::<c_long, u32>(xev.data.get_long(2)), xev.data.get_long(3));
+
+            #[cfg(not(target_pointer_width = "32"))]
+            let (lo, hi) = (
+                (xev.data.get_long(2) & 0xffffffff) as u32,
+                bytemuck::cast::<u32, i32>((xev.data.get_long(3) & 0xffffffff) as u32),
+            );
+
+            wt.xconn
+                .xcb_connection()
+                .sync_set_counter(sync_counter_id, Int64 { lo, hi })
+                .expect_then_ignore_error("Failed to set XSync counter.");
+            return;
+        }
+
         if xev.message_type == atoms[XdndEnter] as c_ulong {
             let source_window = xev.data.get_long(0) as xproto::Window;
             let flags = xev.data.get_long(1);