implement resize increments under wayland

winit-core/src/window.rs

@@ -834,7 +834,7 @@ pub trait Window: AsAny + Send + Sync + fmt::Debug {
     ///
     /// ## Platform-specific
     ///
-    /// - **iOS / Android / Web / Wayland / Orbital:** Always returns [`None`].
+    /// - **iOS / Android / Web / Orbital:** Always returns [`None`].
     fn surface_resize_increments(&self) -> Option<PhysicalSize<u32>>;
 
     /// Sets resize increments of the surface.
@@ -846,7 +846,6 @@ pub trait Window: AsAny + Send + Sync + fmt::Debug {
     ///
     /// - **macOS:** Increments are converted to logical size and then macOS rounds them to whole
     ///   numbers.
-    /// - **Wayland:** Not implemented.
     /// - **iOS / Android / Web / Orbital:** Unsupported.
     fn set_surface_resize_increments(&self, increments: Option<Size>);
 

winit-wayland/src/window/mod.rs

@@ -171,6 +171,12 @@ impl Window {
             Cursor::Custom(cursor) => window_state.set_custom_cursor(cursor),
         }
 
+        // Apply resize increments.
+        if let Some(increments) = attributes.surface_resize_increments {
+            let increments = increments.to_logical(window_state.scale_factor());
+            window_state.set_resize_increments(Some(increments));
+        }
+
         // Activate the window when the token is passed.
         if let (Some(xdg_activation), Some(token)) = (xdg_activation.as_ref(), activation_token) {
             xdg_activation.activate(token.into_raw(), &surface);
@@ -370,11 +376,18 @@ impl CoreWindow for Window {
     }
 
     fn surface_resize_increments(&self) -> Option<PhysicalSize<u32>> {
-        None
+        let window_state = self.window_state.lock().unwrap();
+        let scale_factor = window_state.scale_factor();
+        window_state
+            .resize_increments()
+            .map(|size| super::logical_to_physical_rounded(size, scale_factor))
     }
 
-    fn set_surface_resize_increments(&self, _increments: Option<Size>) {
-        warn!("`set_surface_resize_increments` is not implemented for Wayland");
+    fn set_surface_resize_increments(&self, increments: Option<Size>) {
+        let mut window_state = self.window_state.lock().unwrap();
+        let scale_factor = window_state.scale_factor();
+        let increments = increments.map(|size| size.to_logical(scale_factor));
+        window_state.set_resize_increments(increments);
     }
 
     fn set_title(&self, title: &str) {

winit-wayland/src/window/state.rs

@@ -140,6 +140,7 @@ pub struct WindowState {
     /// Min size.
     min_surface_size: LogicalSize<u32>,
     max_surface_size: Option<LogicalSize<u32>>,
+    resize_increments: Option<LogicalSize<u32>>,
 
     /// The size of the window when no states were applied to it. The primary use for it
     /// is to fallback to original window size, before it was maximized, if the compositor
@@ -223,6 +224,7 @@ impl WindowState {
             last_configure: None,
             max_surface_size: None,
             min_surface_size: MIN_WINDOW_SIZE,
+            resize_increments: None,
             pointer_constraints,
             pointers: Default::default(),
             queue_handle: queue_handle.clone(),
@@ -361,6 +363,36 @@ impl WindowState {
                 .unwrap_or(new_size.height);
         }
 
+        // Apply size increments.
+        // We only apply increments if:
+        // 1. The compositor let us decide the size (constrain == true).
+        // 2. OR we are strictly resizing interactively (is_resizing), in which case we want to snap the mouse position.
+        // We do NOT apply increments if we are maximizing, fullscreening, or tiling (where checks below handle it),
+        // or if the compositor simply told us to be a specific size without resizing (e.g. corner snap).
+        if (constrain || configure.is_resizing())
+            && !configure.is_maximized()
+            && !configure.is_fullscreen()
+            && !configure.is_tiled()
+        {
+            if let Some(increments) = self.resize_increments {
+                // We use min size as a base size for the increments, similar to how X11 does it.
+                //
+                // This ensures that we can always reach the min size and the increments are calculated
+                // from it.
+                let (delta_width, delta_height) = (
+                    new_size.width.saturating_sub(self.min_surface_size.width),
+                    new_size.height.saturating_sub(self.min_surface_size.height),
+                );
+
+                let width = self.min_surface_size.width
+                    + (delta_width / increments.width) * increments.width;
+                let height = self.min_surface_size.height
+                    + (delta_height / increments.height) * increments.height;
+
+                new_size = (width, height).into();
+            }
+        }
+
         let new_state = configure.state;
         let old_state = self.last_configure.as_ref().map(|configure| configure.state);
 
@@ -749,6 +781,18 @@ impl WindowState {
         self.selected_cursor = SelectedCursor::Custom(cursor);
     }
 
+    /// Set the resize increments of the window.
+    pub fn set_resize_increments(&mut self, increments: Option<LogicalSize<u32>>) {
+        self.resize_increments = increments;
+        // NOTE: We don't update the window size here, because it will be done on the next resize
+        // or configure event.
+    }
+
+    /// Get the resize increments of the window.
+    pub fn resize_increments(&self) -> Option<LogicalSize<u32>> {
+        self.resize_increments
+    }
+
     fn apply_custom_cursor(&self, cursor: &CustomCursor) {
         self.apply_on_pointer(|pointer, data| {
             let surface = pointer.surface();