Add dragging window with cursor feature (#1840)

* X11 implementation.

* Introduce example.

* Wayland implementation.

* Windows implementation.

* Improve Wayland seat passing.

* MacOS implementation.

* Correct windows implementation per specification.

* Update dependency smithay-client-toolkit from branch to master.

* Fixed blocking thread in windows implementation.

* Add multi-window example.

* Move Wayland to a different PR.

* Fix CHANGELOG.

* Improve example.

Co-authored-by: Markus Røyset <maroider@protonmail.com>

* Rename `set_drag_window` to `begin_drag`.

* Improve example.

* Fix CHANGELOG.

* Fix CHANGELOG.

Co-authored-by: Markus Røyset <maroider@protonmail.com>

* Rename to `drag_window`.

* Fix typo.

* Re-introduce Wayland implementation.

* Fixing Wayland build.

* Fixing Wayland build.

* Move SCTK to 0.12.3.

Co-authored-by: Markus Røyset <maroider@protonmail.com>

src/platform_impl/linux/wayland/window/mod.rs

@@ -586,6 +586,18 @@ impl Window {
         Err(ExternalError::NotSupported(NotSupportedError::new()))
     }
 
+    #[inline]
+    pub fn drag_window(&self) -> Result<(), ExternalError> {
+        let drag_window_request = WindowRequest::DragWindow;
+        self.window_requests
+            .lock()
+            .unwrap()
+            .push(drag_window_request);
+        self.event_loop_awakener.ping();
+
+        Ok(())
+    }
+
     #[inline]
     pub fn set_ime_position(&self, position: Position) {
         let scale_factor = self.scale_factor() as f64;

src/platform_impl/linux/wayland/window/shim.rs

@@ -34,6 +34,9 @@ pub enum WindowRequest {
     /// Grab cursor.
     GrabCursor(bool),
 
+    /// Drag window.
+    DragWindow,
+
     /// Maximize the window.
     Maximize(bool),
 
@@ -268,6 +271,12 @@ impl WindowHandle {
             pointer.set_cursor(Some(cursor_icon));
         }
     }
+
+    pub fn drag_window(&self) {
+        for pointer in self.pointers.iter() {
+            pointer.drag_window(&self.window);
+        }
+    }
 }
 
 #[inline]
@@ -299,6 +308,9 @@ pub fn handle_window_requests(winit_state: &mut WinitState) {
                 WindowRequest::GrabCursor(grab) => {
                     window_handle.set_cursor_grab(grab);
                 }
+                WindowRequest::DragWindow => {
+                    window_handle.drag_window();
+                }
                 WindowRequest::Maximize(maximize) => {
                     if maximize {
                         window_handle.window.set_maximized();