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/changelog/unreleased.md

@@ -57,6 +57,7 @@ changelog entry.
   to send specific data to be processed on the main thread.
 - Changed `EventLoopProxy::send_event` to `EventLoopProxy::wake_up`, it now
   only wakes up the loop.
+- On X11, implement smooth resizing through the sync extension API.
 - `ApplicationHandler::create|destroy_surfaces()` was split off from
   `ApplicationHandler::resumed/suspended()`.
 

src/platform_impl/linux/x11/atoms.rs

@@ -48,6 +48,8 @@ atom_manager! {
     _NET_WM_NAME,
     _NET_WM_PID,
     _NET_WM_PING,
+    _NET_WM_SYNC_REQUEST,
+    _NET_WM_SYNC_REQUEST_COUNTER,
     _NET_WM_STATE,
     _NET_WM_STATE_ABOVE,
     _NET_WM_STATE_BELOW,

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);

src/platform_impl/linux/x11/mod.rs

@@ -127,6 +127,7 @@ pub struct ActiveEventLoop {
     xconn: Arc<XConnection>,
     wm_delete_window: xproto::Atom,
     net_wm_ping: xproto::Atom,
+    net_wm_sync_request: xproto::Atom,
     ime_sender: ImeSender,
     control_flow: Cell<ControlFlow>,
     exit: Cell<Option<i32>>,
@@ -167,6 +168,7 @@ impl EventLoop {
 
         let wm_delete_window = atoms[WM_DELETE_WINDOW];
         let net_wm_ping = atoms[_NET_WM_PING];
+        let net_wm_sync_request = atoms[_NET_WM_SYNC_REQUEST];
 
         let dnd = Dnd::new(Arc::clone(&xconn))
             .expect("Failed to call XInternAtoms when initializing drag and drop");
@@ -292,6 +294,7 @@ impl EventLoop {
             xconn,
             wm_delete_window,
             net_wm_ping,
+            net_wm_sync_request,
             redraw_sender: WakeSender {
                 sender: redraw_sender, // not used again so no clone
                 waker: waker.clone(),

src/platform_impl/linux/x11/window.rs

@@ -1,14 +1,16 @@
 use std::ffi::CString;
 use std::mem::replace;
+use std::num::NonZeroU32;
 use std::os::raw::*;
 use std::path::Path;
 use std::sync::{Arc, Mutex, MutexGuard};
 use std::{cmp, env};
 
 use tracing::{debug, info, warn};
-use x11rb::connection::Connection;
+use x11rb::connection::{Connection, RequestConnection};
 use x11rb::properties::{WmHints, WmSizeHints, WmSizeHintsSpecification};
 use x11rb::protocol::shape::SK;
+use x11rb::protocol::sync::{ConnectionExt as _, Int64};
 use x11rb::protocol::xfixes::{ConnectionExt, RegionWrapper};
 use x11rb::protocol::xproto::{self, ConnectionExt as _, Rectangle};
 use x11rb::protocol::{randr, xinput};
@@ -116,6 +118,7 @@ pub struct UnownedWindow {
     root: xproto::Window,               // never changes
     #[allow(dead_code)]
     screen_id: i32, // never changes
+    sync_counter_id: Option<NonZeroU32>, // never changes
     selected_cursor: Mutex<SelectedCursor>,
     cursor_grabbed_mode: Mutex<CursorGrabMode>,
     #[allow(clippy::mutex_atomic)]
@@ -338,6 +341,7 @@ impl UnownedWindow {
             visual,
             root,
             screen_id,
+            sync_counter_id: None,
             selected_cursor: Default::default(),
             cursor_grabbed_mode: Mutex::new(CursorGrabMode::None),
             cursor_visible: Mutex::new(true),
@@ -468,21 +472,44 @@ impl UnownedWindow {
                 leap!(window.set_icon_inner(icon.inner)).ignore_error();
             }
 
-            // Opt into handling window close
+            // Opt into handling window close and resize synchronization
             let result = xconn.xcb_connection().change_property(
                 xproto::PropMode::REPLACE,
                 window.xwindow,
                 atoms[WM_PROTOCOLS],
                 xproto::AtomEnum::ATOM,
                 32,
-                2,
+                3,
                 bytemuck::cast_slice::<xproto::Atom, u8>(&[
                     atoms[WM_DELETE_WINDOW],
                     atoms[_NET_WM_PING],
+                    atoms[_NET_WM_SYNC_REQUEST],
                 ]),
             );
             leap!(result).ignore_error();
 
+            // Create a sync request counter
+            if leap!(xconn.xcb_connection().extension_information("SYNC")).is_some() {
+                let sync_counter_id = leap!(xconn.xcb_connection().generate_id());
+                window.sync_counter_id = NonZeroU32::new(sync_counter_id);
+
+                leap!(xconn
+                    .xcb_connection()
+                    .sync_create_counter(sync_counter_id, Int64::default()))
+                .ignore_error();
+
+                let result = xconn.xcb_connection().change_property(
+                    xproto::PropMode::REPLACE,
+                    window.xwindow,
+                    atoms[_NET_WM_SYNC_REQUEST_COUNTER],
+                    xproto::AtomEnum::CARDINAL,
+                    32,
+                    1,
+                    bytemuck::cast_slice::<u32, u8>(&[sync_counter_id]),
+                );
+                leap!(result).ignore_error();
+            }
+
             // Set visibility (map window)
             if window_attrs.visible {
                 leap!(xconn.xcb_connection().map_window(window.xwindow)).ignore_error();
@@ -1813,6 +1840,10 @@ impl UnownedWindow {
         WindowId(self.xwindow as _)
     }
 
+    pub(super) fn sync_counter_id(&self) -> Option<NonZeroU32> {
+        self.sync_counter_id
+    }
+
     #[inline]
     pub fn request_redraw(&self) {
         self.redraw_sender.send(WindowId(self.xwindow as _));