Popup anchor system refinement (#4646)

Implement possibility to change the anchor properties of a popup on wayland and imitate the behaviour for other platforms which do not support such anchoring system

winit-appkit/Cargo.toml

@@ -111,7 +111,12 @@ objc2-foundation = { workspace = true, features = [
     "NSThread",
     "NSValue",
 ] }
-winit-common = { workspace = true, features = ["core-foundation", "event-handler", "foundation"] }
+winit-common = { workspace = true, features = [
+    "core-foundation",
+    "event-handler",
+    "foundation",
+    "positioner",
+] }
 
 [dev-dependencies]
 winit.workspace = true

winit-appkit/src/monitor.rs

@@ -6,7 +6,7 @@ use std::ptr::NonNull;
 use std::{fmt, ptr};
 
 use dispatch2::run_on_main;
-use dpi::{LogicalPosition, PhysicalPosition, PhysicalSize};
+use dpi::{LogicalPosition, LogicalSize, PhysicalPosition, PhysicalSize};
 use objc2::MainThreadMarker;
 use objc2::rc::Retained;
 use objc2_app_kit::NSScreen;
@@ -171,6 +171,22 @@ impl MonitorHandle {
         })
     }
 
+    /// The monitor's work area, i.e. its bounds minus space reserved by the system for the menu
+    /// bar and the Dock (see `NSScreen.visibleFrame`). `None` if the underlying
+    /// `NSScreen` can no longer be found.
+    pub(crate) fn work_area(&self) -> Option<(PhysicalPosition<i32>, PhysicalSize<u32>)> {
+        let scale_factor = self.scale_factor();
+        run_on_main(|mtm| {
+            let visible_frame = self.ns_screen(mtm)?.visibleFrame();
+            let origin = flip_window_screen_coordinates(visible_frame);
+            let position =
+                LogicalPosition::new(origin.x, origin.y).to_physical::<i32>(scale_factor);
+            let size = LogicalSize::new(visible_frame.size.width, visible_frame.size.height)
+                .to_physical::<u32>(scale_factor);
+            Some((position, size))
+        })
+    }
+
     pub(crate) fn ns_screen(&self, mtm: MainThreadMarker) -> Option<Retained<NSScreen>> {
         let uuid = self.uuid();
         NSScreen::screens(mtm).into_iter().find(|screen| {

winit-appkit/src/window.rs

@@ -15,7 +15,7 @@ use winit_core::icon::Icon;
 use winit_core::monitor::{Fullscreen, MonitorHandle as CoreMonitorHandle};
 use winit_core::window::{
     ImeCapabilities, ImeRequest, ImeRequestError, Theme, UserAttentionType, Window as CoreWindow,
-    WindowAttributes, WindowButtons, WindowId, WindowLevel, WindowType,
+    WindowAttributes, WindowButtons, WindowId, WindowLevel, WindowPositioner, WindowType,
 };
 
 use super::event_loop::ActiveEventLoop;
@@ -26,7 +26,6 @@ pub(crate) struct Window {
     window: MainThreadBound<Retained<NSWindow>>,
     /// The window only keeps a weak reference to this, so we must keep it around here.
     delegate: MainThreadBound<Retained<WindowDelegate>>,
-    window_type: WindowType,
 }
 
 impl Window {
@@ -35,15 +34,22 @@ impl Window {
         attributes: WindowAttributes,
     ) -> Result<Self, RequestError> {
         let mtm = window_target.mtm;
-        let window_type = attributes.window_type;
         let delegate =
             autoreleasepool(|_| WindowDelegate::new(&window_target.app_state, attributes, mtm))?;
         window_target.app_state.register_window(&delegate, mtm);
-        Ok(Window {
+        let window = Window {
             window: MainThreadBound::new(delegate.window().retain(), mtm),
             delegate: MainThreadBound::new(delegate, mtm),
-            window_type,
-        })
+        };
+        window.reposition();
+        Ok(window)
+    }
+
+    /// Recomputes this window's position (and, if constrained, its size) from its positioner
+    /// state, using [`winit_common::positioner::place_window`], and applies the result. No-op if
+    /// this window isn't anchored, or if it has no parent.
+    fn reposition(&self) {
+        self.maybe_wait_on_main(|delegate| delegate.reposition());
     }
 
     pub(crate) fn maybe_wait_on_main<R: Send>(
@@ -99,7 +105,15 @@ impl rwh_06::HasWindowHandle for Window {
 
 impl CoreWindow for Window {
     fn window_type(&self) -> WindowType {
-        self.window_type
+        self.maybe_wait_on_main(|delegate| delegate.window_type())
+    }
+
+    fn positioner(&self) -> WindowPositioner {
+        self.maybe_wait_on_main(|delegate| delegate.popup_positioner())
+    }
+
+    fn set_positioner(&self, positioner: WindowPositioner) {
+        self.maybe_wait_on_main(|delegate| delegate.set_popup_positioner(positioner));
     }
 
     fn id(&self) -> winit_core::window::WindowId {

winit-appkit/src/window_delegate.rs

@@ -44,6 +44,7 @@ use objc2_foundation::{
 };
 use tracing::{debug_span, trace, warn};
 use winit_common::core_foundation::MainRunLoop;
+use winit_common::positioner::place_window;
 use winit_core::cursor::Cursor;
 use winit_core::data_transfer::DataTransferId;
 use winit_core::error::{NotSupportedError, RequestError};
@@ -52,7 +53,8 @@ use winit_core::icon::Icon;
 use winit_core::monitor::{Fullscreen, MonitorHandle as CoreMonitorHandle, MonitorHandleProvider};
 use winit_core::window::{
     CursorGrabMode, ImeCapabilities, ImeRequest, ImeRequestError, ResizeDirection, Theme,
-    UserAttentionType, WindowAttributes, WindowButtons, WindowId, WindowLevel, WindowType,
+    UserAttentionType, WindowAttributes, WindowButtons, WindowId, WindowLevel, WindowPositioner,
+    WindowType,
 };
 
 use super::app_state::AppState;
@@ -112,7 +114,16 @@ pub(crate) struct State {
     is_simple_fullscreen: Cell<bool>,
     saved_style: Cell<Option<NSWindowStyleMask>>,
     is_borderless_game: Cell<bool>,
-    is_popup: Cell<bool>,
+    /// The window's role, used for creation/role behavior (decorations, activation/keyboard-grab
+    /// default, initial placement). Does *not* determine whether the window is anchor-positioned
+    /// -- see `anchored`.
+    window_type: WindowType,
+    /// Whether this window is positioned relative to its parent using the anchor/gravity/
+    /// positioner system, either because it's a [`WindowType::Popup`] or because anchor
+    /// attributes were set on a [`WindowType::Window`]. Gates the parent-relative coordinate
+    /// frame used when applying anchor/gravity/positioner-offset changes.
+    anchored: bool,
+    positioner: RefCell<WindowPositioner>,
 }
 
 define_class!(
@@ -149,6 +160,9 @@ define_class!(
             let _entered = debug_span!("windowDidResize:").entered();
             // NOTE: WindowEvent::SurfaceResized is reported using NSViewFrameDidChangeNotification.
             self.emit_move_event();
+            // `windowDidMove:` isn't triggered when a move is part of a resize (e.g. dragging the
+            // top or left edge), so anchored children need repositioning here too.
+            self.reposition_child_windows();
         }
 
         #[unsafe(method(windowWillStartLiveResize:))]
@@ -170,6 +184,7 @@ define_class!(
         fn window_did_move(&self, _: Option<&AnyObject>) {
             let _entered = debug_span!("windowDidMove:").entered();
             self.emit_move_event();
+            self.reposition_child_windows();
         }
 
         #[unsafe(method(windowDidChangeBackingProperties:))]
@@ -657,7 +672,7 @@ fn new_window(
     app_state: &Rc<AppState>,
     attrs: &WindowAttributes,
     macos_attrs: &WindowAttributesMacOS,
-    is_popup: bool,
+    anchored: bool,
     mtm: MainThreadMarker,
 ) -> Option<Retained<NSWindow>> {
     autoreleasepool(|_| {
@@ -685,10 +700,12 @@ fn new_window(
                     None => NSSize::new(800.0, 600.0),
                 };
                 let position = match attrs.position {
-                    // A popup's position is parent-relative; it's applied in `WindowDelegate::new`
-                    // (after the delegate exists) via the shared translation in
-                    // `set_outer_position`.
-                    _ if is_popup => NSPoint::new(0.0, 0.0),
+                    // An anchored window's position is parent-relative; it's applied in
+                    // `WindowDelegate::new` (after the delegate exists) via the shared
+                    // translation in `set_outer_position`. A parentless anchored window can't be
+                    // positioned that way, so it falls through to the same handling as a
+                    // non-anchored window below.
+                    _ if anchored && attrs.parent_window().is_some() => NSPoint::new(0.0, 0.0),
                     Some(position) => {
                         let position = position.to_logical(scale_factor);
                         flip_window_screen_coordinates(NSRect::new(
@@ -839,8 +856,8 @@ fn new_window(
                 window.collectionBehavior() | NSWindowCollectionBehavior::FullScreenAuxiliary,
             );
         }
-        // Popups are positioned relative to their parent in `WindowDelegate::new`.
-        if attrs.position.is_none() && !is_popup {
+        // Center window if the position is not set or it doesn't have any parent
+        if attrs.position.is_none() && !(anchored && attrs.parent_window().is_some()) {
             window.center();
         }
 
@@ -904,7 +921,9 @@ impl WindowDelegate {
             .and_then(|attrs| attrs.cast::<WindowAttributesMacOS>().ok())
             .unwrap_or_default();
 
-        let is_popup = matches!(attrs.window_type(), WindowType::Popup);
+        let window_type = attrs.window_type();
+        let is_popup = matches!(window_type, WindowType::Popup);
+        let anchored = is_popup || attrs.positioner.is_some();
         if is_popup {
             // A popup is an undecorated, non-activating panel with no titlebar buttons. Model it
             // as such so it flows through the existing borderless + panel paths in `new_window`
@@ -918,7 +937,7 @@ impl WindowDelegate {
             }
         }
 
-        let window = new_window(app_state, &attrs, &macos_attrs, is_popup, mtm)
+        let window = new_window(app_state, &attrs, &macos_attrs, anchored, mtm)
             .ok_or_else(|| os_error!("couldn't create `NSWindow`"))?;
 
         match attrs.parent_window() {
@@ -979,7 +998,9 @@ impl WindowDelegate {
             is_simple_fullscreen: Cell::new(false),
             saved_style: Cell::new(None),
             is_borderless_game: Cell::new(macos_attrs.borderless_game),
-            is_popup: Cell::new(is_popup),
+            window_type,
+            anchored,
+            positioner: RefCell::new(attrs.positioner.unwrap_or_default()),
         });
         let delegate: Retained<WindowDelegate> = unsafe { msg_send![super(delegate), init] };
 
@@ -1026,10 +1047,10 @@ impl WindowDelegate {
 
         delegate.set_window_level(attrs.window_level);
 
-        // The popup position is relative to the parent window, and the parent is only
-        // attached above, so apply the (translated) position now. Default to the parent's
+        // An anchored window's position is relative to the parent window, and the parent is
+        // only attached above, so apply the (translated) position now. Default to the parent's
         // content top-left when no position was given.
-        if is_popup {
+        if anchored {
             let position = attrs.position.unwrap_or_else(|| LogicalPosition::new(0.0, 0.0).into());
             delegate.set_outer_position(position);
         }
@@ -1189,8 +1210,8 @@ impl WindowDelegate {
 
     pub fn outer_position(&self) -> Result<PhysicalPosition<i32>, RequestError> {
         let position = flip_window_screen_coordinates(self.window().frame());
-        let position =
-            self.translate_popup_position_to_parent(LogicalPosition::new(position.x, position.y));
+        let position = self
+            .translate_anchored_position_to_parent(LogicalPosition::new(position.x, position.y));
         Ok(position.to_physical(self.scale_factor()))
     }
 
@@ -1215,7 +1236,7 @@ impl WindowDelegate {
 
     pub fn set_outer_position(&self, position: Position) {
         let position = position.to_logical(self.scale_factor());
-        let position = self.translate_popup_position(position);
+        let position = self.translate_anchored_position(position);
         let point = flip_window_screen_coordinates(NSRect::new(
             NSPoint::new(position.x, position.y),
             self.window().frame().size,
@@ -1223,11 +1244,11 @@ impl WindowDelegate {
         self.window().setFrameOrigin(point);
     }
 
-    /// Popups receive their position relative to the top-left of the parent window's
+    /// Anchored windows receive their position relative to the top-left of the parent window's
     /// content area (matching the Win32 and Wayland backends). macOS positions windows
     /// in global screen coordinates, so add the parent content area's origin.
-    fn translate_popup_position(&self, position: LogicalPosition<f64>) -> LogicalPosition<f64> {
-        if !self.ivars().is_popup.get() {
+    fn translate_anchored_position(&self, position: LogicalPosition<f64>) -> LogicalPosition<f64> {
+        if !self.ivars().anchored {
             return position;
         }
         let Some(parent) = self.window().parentWindow() else {
@@ -1238,15 +1259,15 @@ impl WindowDelegate {
         LogicalPosition::new(parent_origin.x + position.x, parent_origin.y + position.y)
     }
 
-    /// Inverse of [`Self::translate_popup_position`]. Popups report their position
+    /// Inverse of [`Self::translate_anchored_position`]. Anchored windows report their position
     /// relative to the top-left of the parent window's content area (matching the
     /// Win32 and Wayland backends), so subtract the parent content area's origin from
-    /// the global screen coordinates. Non-popup windows are returned unchanged.
-    fn translate_popup_position_to_parent(
+    /// the global screen coordinates. Non-anchored windows are returned unchanged.
+    fn translate_anchored_position_to_parent(
         &self,
         position: LogicalPosition<f64>,
     ) -> LogicalPosition<f64> {
-        if !self.ivars().is_popup.get() {
+        if !self.ivars().anchored {
             return position;
         }
         let Some(parent) = self.window().parentWindow() else {
@@ -1257,6 +1278,95 @@ impl WindowDelegate {
         LogicalPosition::new(position.x - parent_origin.x, position.y - parent_origin.y)
     }
 
+    /// The parent window's content area origin, in global (Winit, top-left/y-down) screen
+    /// coordinates. `None` if this window isn't anchored, or it has no parent.
+    pub fn parent_content_origin(&self) -> Option<LogicalPosition<f64>> {
+        if !self.ivars().anchored {
+            return None;
+        }
+        let parent = self.window().parentWindow()?;
+        let origin = flip_window_screen_coordinates(parent.contentRectForFrameRect(parent.frame()));
+        Some(LogicalPosition::new(origin.x, origin.y))
+    }
+
+    pub fn window_type(&self) -> WindowType {
+        self.ivars().window_type
+    }
+
+    pub fn popup_positioner(&self) -> WindowPositioner {
+        *self.ivars().positioner.borrow()
+    }
+
+    pub fn set_popup_positioner(&self, positioner: WindowPositioner) {
+        *self.ivars().positioner.borrow_mut() = positioner;
+        self.reposition();
+    }
+
+    /// Recomputes this window's position (and, if constrained, its size) from its positioner
+    /// state, using [`winit_common::positioner::place_window`], and applies the result. No-op if
+    /// this window isn't anchored. If it has no parent, the positioner is resolved relative to
+    /// the screen instead of the parent's content area.
+    pub(crate) fn reposition(&self) {
+        if !self.ivars().anchored {
+            return;
+        }
+
+        let positioner = *self.ivars().positioner.borrow();
+
+        let parent_origin = self.parent_content_origin().unwrap_or_default();
+
+        let Some(monitor) = self.current_monitor() else { return };
+        // Clip to the monitor's work area rather than its full bounds, so anchored popups don't
+        // get placed underneath the menu bar or the Dock.
+        let Some((work_area_position, work_area_size)) = monitor.work_area() else { return };
+
+        let scale_factor = self.scale_factor();
+
+        // The anchor rect's position is relative to the parent's content area, and
+        // `set_outer_position` re-adds the parent's screen origin for anchored windows (see
+        // `translate_anchored_position`). To stay in the same coordinate space, the clip region
+        // also needs to be expressed relative to the parent's content area.
+        let work_area_position = work_area_position.to_logical::<f64>(scale_factor);
+        let clip_position = LogicalPosition::new(
+            work_area_position.x - parent_origin.x,
+            work_area_position.y - parent_origin.y,
+        );
+        let clip_size = work_area_size.to_logical::<f64>(scale_factor);
+
+        let current_outer_size = self.outer_size().to_logical::<f64>(scale_factor);
+
+        let (origin, new_outer_size) =
+            place_window(&positioner, scale_factor, current_outer_size, (clip_position, clip_size));
+
+        self.set_outer_position(Position::Logical(origin));
+        if new_outer_size != current_outer_size {
+            // `place_window` positions the window by its outer/frame corner, so it operates on
+            // the outer size; convert back to the surface (content) size that
+            // `request_surface_size` expects, via AppKit's frame/content rect conversion.
+            let frame = NSRect::new(
+                NSPoint::new(0.0, 0.0),
+                NSSize::new(new_outer_size.width, new_outer_size.height),
+            );
+            let content_size = self.window().contentRectForFrameRect(frame).size;
+            let content_size = LogicalSize::new(content_size.width, content_size.height);
+            let _ = self.request_surface_size(Size::Logical(content_size));
+        }
+    }
+
+    /// Repositions any anchored children owned by this window. AppKit's `addChildWindow:ordered:`
+    /// only manages ordering and visibility for child windows -- it doesn't keep their position
+    /// in sync with the parent -- so this has to be done manually whenever this window moves.
+    fn reposition_child_windows(&self) {
+        let Some(children) = self.window().childWindows() else { return };
+        for child in children.iter() {
+            let Some(child_delegate) = child.delegate() else { continue };
+            let Ok(child_delegate) = child_delegate.downcast::<WindowDelegate>() else { continue };
+            if child_delegate.ivars().anchored {
+                child_delegate.reposition();
+            }
+        }
+    }
+
     #[inline]
     pub fn surface_size(&self) -> PhysicalSize<u32> {
         self.view().surface_size()

winit-common/Cargo.toml

@@ -12,6 +12,9 @@ version.workspace = true
 # Event Handler
 event-handler = []
 
+# Positioner
+positioner = ["dep:dpi"]
+
 # XKB
 wayland = ["dep:memmap2"]
 x11 = ["xkbcommon-dl?/x11", "dep:x11-dl"]
@@ -24,6 +27,7 @@ core-foundation = ["dep:block2", "dep:objc2", "dep:objc2-core-foundation"]
 foundation = ["dep:block2", "dep:objc2", "dep:objc2-foundation"]
 
 [dependencies]
+dpi = { workspace = true, optional = true }
 smol_str = { workspace = true, optional = true }
 tracing.workspace = true
 winit-core.workspace = true

winit-common/src/lib.rs

@@ -8,5 +8,7 @@ pub mod core_foundation;
 pub mod event_handler;
 #[cfg(feature = "foundation")]
 pub mod foundation;
+#[cfg(feature = "positioner")]
+pub mod positioner;
 #[cfg(feature = "xkb")]
 pub mod xkb;

winit-common/src/positioner.rs

@@ -0,0 +1,523 @@
+//! The `xdg_positioner`-style algorithm ([`place_window`]) that resolves a [`WindowPositioner`]
+//! into a concrete position and size.
+//!
+//! This is only needed by backends (such as Win32 and AppKit) that have no native equivalent of
+//! Wayland's `xdg_positioner` and therefore need to compute the popup placement themselves; it's
+//! not part of winit's public API.
+
+use dpi::{LogicalPosition, LogicalSize};
+use winit_core::window::{
+    WindowAnchor, WindowConstraintAdjustment, WindowGravity, WindowPositioner,
+};
+
+/// Returns, as fractions of the anchor rectangle's width/height, the point within that rectangle
+/// that the popup is anchored to (0.0 = left/top edge, 0.5 = center, 1.0 = right/bottom edge).
+/// Mirrors the Wayland `xdg_positioner` anchor semantics.
+fn anchor_fraction(anchor: WindowAnchor) -> (f64, f64) {
+    match anchor {
+        WindowAnchor::Center => (0.5, 0.5),
+        WindowAnchor::Top => (0.5, 0.0),
+        WindowAnchor::Bottom => (0.5, 1.0),
+        WindowAnchor::Left => (0.0, 0.5),
+        WindowAnchor::Right => (1.0, 0.5),
+        WindowAnchor::TopLeft => (0.0, 0.0),
+        WindowAnchor::BottomLeft => (0.0, 1.0),
+        WindowAnchor::TopRight => (1.0, 0.0),
+        WindowAnchor::BottomRight => (1.0, 1.0),
+        // `WindowAnchor` is `#[non_exhaustive]`; fall back to `Center` for variants added after
+        // this crate was built against an older `winit-core`.
+        _ => (0.5, 0.5),
+    }
+}
+
+/// Returns, as fractions of the popup's own width/height, the offset from the anchor point to
+/// the popup's origin (top-left corner). For example a gravity of `BottomRight` places the
+/// popup's top-left corner at the anchor point, so the popup grows down and to the right.
+fn gravity_fraction(gravity: WindowGravity) -> (f64, f64) {
+    match gravity {
+        WindowGravity::Center => (-0.5, -0.5),
+        WindowGravity::Top => (-0.5, -1.0),
+        WindowGravity::Bottom => (-0.5, 0.0),
+        WindowGravity::Left => (-1.0, -0.5),
+        WindowGravity::Right => (0.0, -0.5),
+        WindowGravity::TopLeft => (-1.0, -1.0),
+        WindowGravity::BottomLeft => (-1.0, 0.0),
+        WindowGravity::TopRight => (0.0, -1.0),
+        WindowGravity::BottomRight => (0.0, 0.0),
+        // `WindowGravity` is `#[non_exhaustive]`; fall back to `Center` for variants added after
+        // this crate was built against an older `winit-core`.
+        _ => (-0.5, -0.5),
+    }
+}
+
+/// Adjusts a single axis of the popup's placement to stay within `[clip_min, clip_max]`, applying
+/// `flip`/`slide`/`resize` in the order the `xdg_positioner` protocol suggests: flip, then slide,
+/// then resize. `flipped_origin` is the alternate origin obtained by mirroring both the anchor
+/// edge and the gravity on this axis; it is only used when `flip` is set and it actually results
+/// in a better fit than the original origin.
+fn constrain_axis(
+    origin: f64,
+    extent: f64,
+    (clip_min, clip_max): (f64, f64),
+    flipped_origin: f64,
+    (flip, slide, resize): (bool, bool, bool),
+) -> (f64, f64) {
+    let fits = |o: f64| o >= clip_min && o + extent <= clip_max;
+
+    let mut origin = origin;
+    if !fits(origin) && flip && fits(flipped_origin) {
+        origin = flipped_origin;
+    }
+
+    if !fits(origin) && slide {
+        // `extent` may exceed the clip size, in which case `clip_max - extent` would be less
+        // than `clip_min`; `.max(clip_min)` keeps the clamp range valid in that case.
+        let slide_max = (clip_max - extent).max(clip_min);
+        origin = origin.clamp(clip_min, slide_max);
+    }
+
+    let mut extent = extent;
+    if resize && !fits(origin) {
+        let clamped_origin = origin.max(clip_min);
+        // Intersect with the clip rectangle on both ends, not just `clip_max`: if only the
+        // leading edge overflows (`origin < clip_min`) while the trailing edge already fits,
+        // this must shrink down to the original trailing edge rather than growing all the way
+        // out to `clip_max`.
+        extent = (clip_max.min(origin + extent) - clamped_origin).max(0.0);
+        origin = clamped_origin;
+    }
+
+    (origin, extent)
+}
+
+/// Finds a placement for a window of `window_size`, anchored per `positioner` (whose
+/// [`anchor_rect`](WindowPositioner::anchor_rect) and
+/// [`offset`](WindowPositioner::offset) are converted to logical
+/// coordinates using `scale_factor`, then interpreted in the same coordinate space as `clip`), and
+/// constrained to stay within the `clip` rectangle according to
+/// [`constraint_adjustment`](WindowPositioner::constraint_adjustment).
+///
+/// This mirrors the Wayland `xdg_positioner` placement algorithm used natively on Wayland, for
+/// backends (such as Win32 and AppKit) that have no equivalent native concept and therefore need
+/// to compute the popup position themselves: `anchor` selects a point on the anchor rectangle,
+/// `gravity` decides which corner/edge of the popup is placed at that point, and if the resulting
+/// rectangle doesn't fit inside the clip rectangle, `constraint_adjustment`'s flags decide whether
+/// (and how) the popup is moved (slide), mirrored to the other side of the anchor point (flip),
+/// or shrunk (resize) to fit. Axes are adjusted independently. If none of the flags are set for an
+/// axis, that axis is left as computed even if it doesn't fit, matching the protocol's "none"
+/// behavior.
+pub fn place_window(
+    positioner: &WindowPositioner,
+    scale_factor: f64,
+    window_size: LogicalSize<f64>,
+    (clip_position, clip_size): (LogicalPosition<f64>, LogicalSize<f64>),
+) -> (LogicalPosition<f64>, LogicalSize<f64>) {
+    let anchor = positioner.anchor;
+    let gravity = positioner.gravity;
+    let constraint_adjustment = positioner.constraint_adjustment;
+    let (anchor_position, anchor_size) = positioner.anchor_rect;
+    let anchor_position = anchor_position.to_logical::<f64>(scale_factor);
+    let anchor_size = anchor_size.to_logical::<f64>(scale_factor);
+    let offset = positioner.offset.to_logical::<f64>(scale_factor);
+
+    let (anchor_fx, anchor_fy) = anchor_fraction(anchor);
+    let (gravity_fx, gravity_fy) = gravity_fraction(gravity);
+
+    let anchor_point_x = anchor_position.x + anchor_size.width * anchor_fx;
+    let anchor_point_y = anchor_position.y + anchor_size.height * anchor_fy;
+
+    let origin_x = anchor_point_x + window_size.width * gravity_fx + offset.x;
+    let origin_y = anchor_point_y + window_size.height * gravity_fy + offset.y;
+
+    // Flipping mirrors both the anchor edge and the gravity on that axis, effectively placing the
+    // popup on the opposite side of the anchor rectangle.
+    let flipped_anchor_point_x = anchor_position.x + anchor_size.width * (1.0 - anchor_fx);
+    let flipped_anchor_point_y = anchor_position.y + anchor_size.height * (1.0 - anchor_fy);
+    let flipped_x = flipped_anchor_point_x + window_size.width * (-1.0 - gravity_fx) + offset.x;
+    let flipped_y = flipped_anchor_point_y + window_size.height * (-1.0 - gravity_fy) + offset.y;
+
+    let clip_min_x = clip_position.x;
+    let clip_max_x = clip_position.x + clip_size.width;
+    let clip_min_y = clip_position.y;
+    let clip_max_y = clip_position.y + clip_size.height;
+
+    let (x, width) = constrain_axis(
+        origin_x,
+        window_size.width,
+        (clip_min_x, clip_max_x),
+        flipped_x,
+        (
+            constraint_adjustment.contains(WindowConstraintAdjustment::FLIP_X),
+            constraint_adjustment.contains(WindowConstraintAdjustment::SLIDE_X),
+            constraint_adjustment.contains(WindowConstraintAdjustment::RESIZE_X),
+        ),
+    );
+    let (y, height) = constrain_axis(
+        origin_y,
+        window_size.height,
+        (clip_min_y, clip_max_y),
+        flipped_y,
+        (
+            constraint_adjustment.contains(WindowConstraintAdjustment::FLIP_Y),
+            constraint_adjustment.contains(WindowConstraintAdjustment::SLIDE_Y),
+            constraint_adjustment.contains(WindowConstraintAdjustment::RESIZE_Y),
+        ),
+    );
+
+    (LogicalPosition::new(x, y), LogicalSize::new(width, height))
+}
+
+#[cfg(test)]
+mod tests {
+    use dpi::{Position, Size};
+
+    use super::*;
+
+    const GRID_COLS: usize = 60;
+    const GRID_ROWS: usize = 24;
+    const DRAW: bool = false;
+
+    /// Prints an ASCII rendering of the clip region (`.`), the anchor rect (`A`), and the
+    /// resulting popup rect (`P`, `X` where it overlaps the anchor) for a quick visual sanity
+    /// check. Run with `cargo test -p winit-common positioner -- --nocapture` to see it.
+    // `println!` (rather than `tracing`) is intentional: this is only meant to be read directly
+    // via `--nocapture`, which doesn't require a tracing subscriber to be installed.
+    #[allow(clippy::disallowed_macros)]
+    fn draw(
+        label: &str,
+        clip: (LogicalPosition<f64>, LogicalSize<f64>),
+        anchor: (LogicalPosition<f64>, LogicalSize<f64>),
+        popup: (LogicalPosition<f64>, LogicalSize<f64>),
+    ) {
+        if !DRAW {
+            return;
+        }
+
+        let (clip_position, clip_size) = clip;
+        let (anchor_position, anchor_size) = anchor;
+        let (popup_position, popup_size) = popup;
+        let has_clip = clip_size.width > 0.0 && clip_size.height > 0.0;
+
+        // Bounding box covering everything we're about to draw, plus a small margin.
+        let mut min_x = anchor_position.x.min(popup_position.x);
+        let mut min_y = anchor_position.y.min(popup_position.y);
+        let mut max_x =
+            (anchor_position.x + anchor_size.width).max(popup_position.x + popup_size.width);
+        let mut max_y =
+            (anchor_position.y + anchor_size.height).max(popup_position.y + popup_size.height);
+        if has_clip {
+            min_x = min_x.min(clip_position.x);
+            min_y = min_y.min(clip_position.y);
+            max_x = max_x.max(clip_position.x + clip_size.width);
+            max_y = max_y.max(clip_position.y + clip_size.height);
+        }
+        let margin_x = ((max_x - min_x) * 0.1).max(1.0);
+        let margin_y = ((max_y - min_y) * 0.1).max(1.0);
+        min_x -= margin_x;
+        min_y -= margin_y;
+        max_x += margin_x;
+        max_y += margin_y;
+
+        // Terminal characters are roughly twice as tall as they are wide, so use half the
+        // vertical scale to keep the rendered rectangles' proportions roughly correct.
+        let scale =
+            (GRID_COLS as f64 / (max_x - min_x)).min(2.0 * GRID_ROWS as f64 / (max_y - min_y));
+
+        let mut grid = vec![vec![' '; GRID_COLS]; GRID_ROWS];
+        let mut plot = |position: LogicalPosition<f64>, size: LogicalSize<f64>, ch: char| {
+            let x0 = ((position.x - min_x) * scale).round() as isize;
+            let y0 = ((position.y - min_y) * scale / 2.0).round() as isize;
+            let x1 = ((position.x + size.width - min_x) * scale).round() as isize;
+            let y1 = ((position.y + size.height - min_y) * scale / 2.0).round() as isize;
+            for y in y0.max(0)..y1.min(GRID_ROWS as isize) {
+                for x in x0.max(0)..x1.min(GRID_COLS as isize) {
+                    let cell = &mut grid[y as usize][x as usize];
+                    *cell = if *cell == ' ' || *cell == ch { ch } else { 'X' };
+                }
+            }
+        };
+
+        if has_clip {
+            plot(clip_position, clip_size, '.');
+        }
+        plot(anchor_position, anchor_size, 'A');
+        plot(popup_position, popup_size, 'P');
+
+        println!("--- {label} (A = anchor, P = popup, X = overlap, . = clip region) ---");
+        for row in grid {
+            println!("{}", row.into_iter().collect::<String>());
+        }
+    }
+
+    /// A 20x10 anchor rect at (100, 100), popup size 40x30, no constraints applied
+    /// (unclipped).
+    #[test]
+    fn test_place_popup_gravity() {
+        let anchor_position = LogicalPosition::new(100., 100.);
+        let anchor_size = LogicalSize::new(20., 10.);
+        let popup_size = LogicalSize::new(40., 30.);
+        let clip_position = LogicalPosition::new(0., 0.);
+        let clip_size = LogicalSize::new(0., 0.);
+        let offset = Position::Logical(LogicalPosition::new(0., 0.));
+
+        let place = |anchor: WindowAnchor, gravity: WindowGravity| {
+            let positioner = WindowPositioner::new(
+                anchor,
+                (Position::Logical(anchor_position), Size::Logical(anchor_size)),
+                offset,
+                gravity,
+                WindowConstraintAdjustment::empty(),
+            );
+            place_window(&positioner, 1.0, popup_size, (clip_position, clip_size))
+        };
+
+        // BottomRight gravity anchored to the anchor's bottom-right corner: the popup's top-left
+        // corner sits exactly at the anchor rect's bottom-right corner.
+        let (origin, size) = place(WindowAnchor::BottomRight, WindowGravity::BottomRight);
+        draw(
+            "gravity: BottomRight anchor + BottomRight gravity",
+            (clip_position, clip_size),
+            (anchor_position, anchor_size),
+            (origin, size),
+        );
+        assert_eq!(origin, LogicalPosition::new(120., 110.));
+        assert_eq!(size, popup_size);
+
+        // TopLeft gravity anchored to the anchor's top-left corner: the popup's bottom-right
+        // corner sits exactly at the anchor rect's top-left corner, so the popup extends
+        // up-left.
+        let (origin, size) = place(WindowAnchor::TopLeft, WindowGravity::TopLeft);
+        draw(
+            "gravity: TopLeft anchor + TopLeft gravity",
+            (clip_position, clip_size),
+            (anchor_position, anchor_size),
+            (origin, size),
+        );
+        assert_eq!(origin, LogicalPosition::new(100. - 40., 100. - 30.));
+
+        // Bottom anchor + Bottom gravity: horizontally centered on the anchor, growing downward
+        // from its bottom edge.
+        let (origin, size) = place(WindowAnchor::Bottom, WindowGravity::Bottom);
+        draw(
+            "gravity: Bottom anchor + Bottom gravity",
+            (clip_position, clip_size),
+            (anchor_position, anchor_size),
+            (origin, size),
+        );
+        assert_eq!(
+            origin,
+            LogicalPosition::new(100. + anchor_size.width / 2. - popup_size.width / 2., 110.)
+        );
+
+        // Center anchor + Center gravity centers the popup exactly on the anchor rect's center.
+        let (origin, size) = place(WindowAnchor::Center, WindowGravity::Center);
+        draw(
+            "gravity: Center anchor + Center gravity",
+            (clip_position, clip_size),
+            (anchor_position, anchor_size),
+            (origin, size),
+        );
+        let anchor_center =
+            LogicalPosition::new(100. + anchor_size.width / 2., 100. + anchor_size.height / 2.);
+        assert_eq!(
+            origin,
+            LogicalPosition::new(
+                anchor_center.x - popup_size.width / 2.,
+                anchor_center.y - popup_size.height / 2.
+            )
+        );
+    }
+
+    /// Place the Anchor so that the popup will go outside of the right side of the clip rectangle
+    /// Because of FLIP_X the popup will be flipped on the left side of the anchor rectangle
+    #[test]
+    fn test_place_popup_flip() {
+        // Anchor rect hugging the right edge of a 300x300 clip region; with BottomRight gravity
+        // the popup would overflow past the right edge, so flipping should place it to the left
+        // instead.
+        let clip_position = LogicalPosition::new(0., 0.);
+        let clip_size = LogicalSize::new(300., 300.);
+        let anchor_position = LogicalPosition::new(280., 100.);
+        let anchor_size = LogicalSize::new(10., 10.);
+        let popup_size = LogicalSize::new(50., 50.);
+
+        let flip_only = WindowConstraintAdjustment::FLIP_X | WindowConstraintAdjustment::FLIP_Y;
+        let offset = Position::Logical(LogicalPosition::new(0., 0.));
+
+        // Without flipping the popup would start at x=290 and end at x=340, past the clip's
+        // right edge (300); flipping mirrors both anchor edge and gravity, so it should end up
+        // entirely to the left of the anchor rect instead, fully inside the clip region.
+        let positioner = WindowPositioner::new(
+            WindowAnchor::TopRight,
+            (Position::Logical(anchor_position), Size::Logical(anchor_size)),
+            offset,
+            WindowGravity::BottomRight,
+            flip_only,
+        );
+        let (origin, size) = place_window(&positioner, 1.0, popup_size, (clip_position, clip_size));
+        draw("flip", (clip_position, clip_size), (anchor_position, anchor_size), (origin, size));
+        assert!(origin.x >= 0. && origin.x + size.width <= 300.);
+        assert_eq!(size, popup_size);
+        // Flipped horizontally: popup's right edge lands on the anchor rect's left edge
+        // (x=280).
+        assert_eq!(origin.x, 280. - popup_size.width);
+        // Not flipped vertically: still grows down from the anchor's top edge.
+        assert_eq!(origin.y, 100.);
+    }
+
+    /// Anchor near the bottom-right corner of the clip region; sliding (without flipping)
+    /// should shift the popup back into view while keeping its size and general placement
+    /// direction.
+    #[test]
+    fn test_place_popup_slide() {
+        let clip_position = LogicalPosition::new(0., 0.);
+        let clip_size = LogicalSize::new(300., 300.);
+        let anchor_position = LogicalPosition::new(280., 280.);
+        let popup_size = LogicalSize::new(50., 50.);
+
+        let slide_only = WindowConstraintAdjustment::SLIDE_X | WindowConstraintAdjustment::SLIDE_Y;
+        let offset = Position::Logical(LogicalPosition::new(0., 0.));
+
+        let positioner = WindowPositioner::new(
+            WindowAnchor::BottomRight,
+            (Position::Logical(anchor_position), Size::Logical(LogicalSize::new(0., 0.))),
+            offset,
+            WindowGravity::BottomRight,
+            slide_only,
+        );
+        let (origin, size) = place_window(&positioner, 1.0, popup_size, (clip_position, clip_size));
+        draw(
+            "slide",
+            (clip_position, clip_size),
+            (anchor_position, LogicalSize::new(0., 0.)),
+            (origin, size),
+        );
+        assert_eq!(size, popup_size);
+        assert_eq!(origin, LogicalPosition::new(250., 250.));
+    }
+
+    /// Popup larger than the clip region on both axes; with only `resize` enabled it should
+    /// be shrunk (and clamped) to exactly fill the clip region rather than sliding or
+    /// flipping.
+    #[test]
+    fn test_place_popup_resize() {
+        let clip_position = LogicalPosition::new(0., 0.);
+        let clip_size = LogicalSize::new(300., 300.);
+        let anchor_position = LogicalPosition::new(0., 0.);
+        let popup_size = LogicalSize::new(500., 500.);
+
+        let resize_only =
+            WindowConstraintAdjustment::RESIZE_X | WindowConstraintAdjustment::RESIZE_Y;
+        let offset = Position::Logical(LogicalPosition::new(0., 0.));
+
+        let positioner = WindowPositioner::new(
+            WindowAnchor::TopLeft,
+            (Position::Logical(anchor_position), Size::Logical(LogicalSize::new(0., 0.))),
+            offset,
+            WindowGravity::BottomRight,
+            resize_only,
+        );
+        let (origin, size) = place_window(&positioner, 1.0, popup_size, (clip_position, clip_size));
+        draw(
+            "resize",
+            (clip_position, clip_size),
+            (anchor_position, LogicalSize::new(0., 0.)),
+            (origin, size),
+        );
+        assert_eq!(origin, clip_position);
+        assert_eq!(size, clip_size);
+    }
+
+    /// Popup that only overflows the clip region on its leading edge (its trailing edge
+    /// already fits comfortably). With only `resize` enabled, it should shrink down to the
+    /// intersection with the clip region -- i.e. stay anchored to its original trailing edge --
+    /// rather than growing all the way out to the far side of the clip region.
+    #[test]
+    fn test_place_popup_resize_leading_edge_only() {
+        let clip_position = LogicalPosition::new(0., 0.);
+        let clip_size = LogicalSize::new(300., 300.);
+        // TopLeft anchor + BottomRight gravity places the popup's origin exactly at the anchor
+        // position, so this popup starts at x=-20 (off the left edge) and ends at x=30 (well
+        // within the clip region).
+        let anchor_position = LogicalPosition::new(-20., 0.);
+        let popup_size = LogicalSize::new(50., 50.);
+
+        let resize_only = WindowConstraintAdjustment::RESIZE_X;
+        let offset = Position::Logical(LogicalPosition::new(0., 0.));
+
+        let positioner = WindowPositioner::new(
+            WindowAnchor::TopLeft,
+            (Position::Logical(anchor_position), Size::Logical(LogicalSize::new(0., 0.))),
+            offset,
+            WindowGravity::BottomRight,
+            resize_only,
+        );
+        let (origin, size) = place_window(&positioner, 1.0, popup_size, (clip_position, clip_size));
+        draw(
+            "resize (leading edge only)",
+            (clip_position, clip_size),
+            (anchor_position, LogicalSize::new(0., 0.)),
+            (origin, size),
+        );
+        assert_eq!(origin, LogicalPosition::new(0., 0.));
+        // Trailing edge (originally at x=30) must stay put -- the popup should shrink to width
+        // 30, not grow out to the clip region's full width of 300.
+        assert_eq!(size, LogicalSize::new(30., 50.));
+    }
+
+    /// With no constraint-adjustment flags set, an overflowing popup is left exactly where
+    /// the anchor/gravity math puts it, matching the `xdg_positioner` "none" behavior.
+    #[test]
+    fn test_place_popup_no_adjustment() {
+        let clip_position = LogicalPosition::new(0., 0.);
+        let clip_size = LogicalSize::new(100., 100.);
+        let anchor_position = LogicalPosition::new(90., 90.);
+        let popup_size = LogicalSize::new(50., 50.);
+        let offset = Position::Logical(LogicalPosition::new(0., 0.));
+
+        let positioner = WindowPositioner::new(
+            WindowAnchor::TopLeft,
+            (Position::Logical(anchor_position), Size::Logical(LogicalSize::new(0., 0.))),
+            offset,
+            WindowGravity::BottomRight,
+            WindowConstraintAdjustment::empty(),
+        );
+        let (origin, size) = place_window(&positioner, 1.0, popup_size, (clip_position, clip_size));
+        draw(
+            "no adjustment",
+            (clip_position, clip_size),
+            (anchor_position, LogicalSize::new(0., 0.)),
+            (origin, size),
+        );
+        assert_eq!(origin, anchor_position);
+        assert_eq!(size, popup_size);
+    }
+
+    /// Sanity check: when the popup already fits, none of the adjustment flags should move
+    /// or resize it, regardless of which are enabled.
+    #[test]
+    fn test_place_popup_all_adjustment_no_op_when_fits() {
+        let clip_position = LogicalPosition::new(0., 0.);
+        let clip_size = LogicalSize::new(300., 300.);
+        let anchor_position = LogicalPosition::new(100., 100.);
+        let popup_size = LogicalSize::new(50., 50.);
+        let offset = Position::Logical(LogicalPosition::new(0., 0.));
+
+        let positioner = WindowPositioner::new(
+            WindowAnchor::TopLeft,
+            (Position::Logical(anchor_position), Size::Logical(LogicalSize::new(0., 0.))),
+            offset,
+            WindowGravity::BottomRight,
+            WindowConstraintAdjustment::all(),
+        );
+        let (origin, size) = place_window(&positioner, 1.0, popup_size, (clip_position, clip_size));
+        draw(
+            "all adjustment, already fits",
+            (clip_position, clip_size),
+            (anchor_position, LogicalSize::new(0., 0.)),
+            (origin, size),
+        );
+        assert_eq!(origin, anchor_position);
+        assert_eq!(size, popup_size);
+    }
+}

winit-core/src/window.rs

@@ -1,4 +1,6 @@
 //! The [`Window`] trait and associated types.
+mod positioner;
+
 use std::any::Any;
 use std::fmt;
 
@@ -7,6 +9,7 @@ use cursor_icon::CursorIcon;
 use dpi::{
     LogicalPosition, LogicalSize, PhysicalInsets, PhysicalPosition, PhysicalSize, Position, Size,
 };
+pub use positioner::{WindowAnchor, WindowConstraintAdjustment, WindowGravity};
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 
@@ -57,6 +60,9 @@ pub enum WindowType {
     /// tooltip. Requires a parent set via [`WindowAttributes::with_parent_window`], and its
     /// position is interpreted relative to that parent.
     ///
+    /// The anchor/gravity/positioning system described on [`WindowAttributes::with_positioner`]
+    /// can be used to position the popup or window in a more advanced way
+    ///
     /// ## Platform-specific
     ///
     /// - **macOS:** A borderless, non-activating child window. The system does *not* draw rounded
@@ -66,6 +72,71 @@ pub enum WindowType {
     Popup,
 }
 
+/// The positioner state backing a window's anchor-based placement.
+///
+/// Set at window creation via [`WindowAttributes::with_positioner`], and read/mutated at runtime
+/// through [`Window::positioner`]/[`Window::set_positioner`]. See those methods for
+/// platform-specific behavior, and [`WindowPositioner::default`] for the values used when
+/// [`WindowAttributes::with_positioner`] is never called.
+///
+/// The structure is based on the wayland structure. For more information see the wayland
+/// documentation [XDG Positioner](https://wayland.app/protocols/xdg-shell#xdg_positioner)
+#[non_exhaustive]
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub struct WindowPositioner {
+    /// The edge or corner of the anchor rect used to position the window relative to it.
+    ///
+    /// Combined with [`gravity`](Self::gravity), this controls which corner/edge of the anchor
+    /// rectangle the window is pinned to. Defaults to [`WindowAnchor::Center`].
+    pub anchor: WindowAnchor,
+    /// The anchor rectangle the window is positioned relative to.
+    ///
+    /// The [`Position`] is the top-left corner of the rectangle relative to the parent window's
+    /// content area, and the [`Size`] its dimensions. Defaults to a `1x1` rectangle at the
+    /// content origin. Passing a [`WindowPositioner`] to [`WindowAttributes::with_positioner`]
+    /// overrides the position value set with [`WindowAttributes::with_position`].
+    pub anchor_rect: (Position, Size),
+    /// The window's position relative to the anchor rect. Defaults to no offset.
+    pub offset: Position,
+    /// The direction the window surface extends away from the anchor point.
+    ///
+    /// Combined with [`anchor`](Self::anchor), this determines the final position of the window
+    /// relative to its anchor rectangle. Defaults to [`WindowGravity::Center`].
+    pub gravity: WindowGravity,
+    /// How the window should be repositioned when it would be constrained.
+    ///
+    /// The flags in [`WindowConstraintAdjustment`] can be combined to allow sliding, flipping,
+    /// and/or resizing the window independently on each axis. Defaults to no adjustment.
+    pub constraint_adjustment: WindowConstraintAdjustment,
+}
+
+impl WindowPositioner {
+    pub fn new(
+        anchor: WindowAnchor,
+        anchor_rect: (Position, Size),
+        offset: Position,
+        gravity: WindowGravity,
+        constraint_adjustment: WindowConstraintAdjustment,
+    ) -> Self {
+        WindowPositioner { anchor, anchor_rect, offset, gravity, constraint_adjustment }
+    }
+}
+
+impl Default for WindowPositioner {
+    fn default() -> Self {
+        Self {
+            anchor: WindowAnchor::default(),
+            anchor_rect: (
+                Position::Logical(LogicalPosition::new(0.0, 0.0)),
+                Size::Logical(LogicalSize::new(1.0, 1.0)),
+            ),
+            offset: Position::Logical(LogicalPosition::new(0.0, 0.0)),
+            gravity: WindowGravity::default(),
+            constraint_adjustment: WindowConstraintAdjustment::empty(),
+        }
+    }
+}
+
 /// Attributes used when creating a window.
 #[derive(Debug)]
 #[non_exhaustive]
@@ -105,6 +176,8 @@ pub struct WindowAttributes {
     pub fullscreen: Option<Fullscreen>,
     pub platform: Option<Box<dyn PlatformWindowAttributes>>,
     pub window_type: WindowType,
+    /// See [`WindowAttributes::with_positioner`].
+    pub positioner: Option<WindowPositioner>,
 }
 
 impl WindowAttributes {
@@ -438,6 +511,27 @@ impl WindowAttributes {
     pub fn window_type(&self) -> WindowType {
         self.window_type
     }
+
+    /// Sets the positioner used to place the window relative to its anchor rect.
+    ///
+    /// See [`WindowPositioner`] and its fields for what each part of the positioner controls and
+    /// its default when left as `None`.
+    ///
+    /// ## Platform-specific
+    ///
+    /// - **Wayland:** Only takes effect when the window is a [`WindowType::Popup`], since the
+    ///   Wayland positioner is part of the `xdg_popup` protocol role.
+    /// - **macOS, Windows:** Works for both [`WindowType::Window`] and [`WindowType::Popup`]. A
+    ///   [`WindowType::Popup`] always requires a parent window to be set via
+    ///   [`with_parent_window`](Self::with_parent_window). A [`WindowType::Window`] without a
+    ///   parent is positioned relative to the screen's available space instead of the parent's
+    ///   content area.
+    /// - **X11, Web, Android, iOS, Orbital:** No effect.
+    #[inline]
+    pub fn with_positioner(mut self, positioner: WindowPositioner) -> Self {
+        self.positioner = Some(positioner);
+        self
+    }
 }
 
 impl Clone for WindowAttributes {
@@ -466,6 +560,7 @@ impl Clone for WindowAttributes {
             fullscreen: self.fullscreen.clone(),
             platform: self.platform.as_ref().map(|platform| platform.box_clone()),
             window_type: self.window_type,
+            positioner: self.positioner,
         }
     }
 }
@@ -497,6 +592,7 @@ impl Default for WindowAttributes {
             cursor: Cursor::default(),
             blur: Default::default(),
             window_type: Default::default(),
+            positioner: Default::default(),
         }
     }
 }
@@ -541,6 +637,31 @@ pub trait Window: Any + Send + Sync + fmt::Debug {
     /// Returns the window type of this window
     fn window_type(&self) -> WindowType;
 
+    /// Returns the positioner used to place this window relative to its anchor rect.
+    ///
+    /// Returns [`WindowPositioner::default`] if this window doesn't use anchor positioning, see
+    /// [`WindowAttributes::with_positioner`].
+    ///
+    /// ## Platform-specific
+    ///
+    /// - **Wayland:** Always [`WindowPositioner::default`] unless the window is a
+    ///   [`WindowType::Popup`], since the Wayland positioner is part of the `xdg_popup` protocol
+    ///   role.
+    fn positioner(&self) -> WindowPositioner {
+        WindowPositioner::default()
+    }
+
+    /// Sets the positioner used to place this window relative to its anchor rect.
+    ///
+    /// No-op if this window doesn't use anchor positioning, see
+    /// [`WindowAttributes::with_positioner`].
+    ///
+    /// ## Platform-specific
+    ///
+    /// - **Wayland:** No-op unless the window is a [`WindowType::Popup`], since the Wayland
+    ///   positioner is part of the `xdg_popup` protocol role.
+    fn set_positioner(&self, _positioner: WindowPositioner) {}
+
     /// Returns an identifier unique to the window.
     fn id(&self) -> WindowId;
 

winit-core/src/window/positioner.rs

@@ -0,0 +1,54 @@
+//! Anchor-based window placement: the types describing a placement request.
+//!
+//! The `xdg_positioner`-style algorithm that resolves these into a concrete position and size
+//! lives in `winit-common`, since it's only needed by backends without a native equivalent of
+//! Wayland's `xdg_positioner` (such as Win32 and AppKit) and isn't part of winit's public API.
+
+/// Anchor rect within the parent surface
+/// See: https://wayland.app/protocols/xdg-shell#xdg_positioner:request:set_anchor_rect
+#[derive(Debug, Clone, Copy, Default, PartialEq)]
+#[non_exhaustive]
+pub enum WindowAnchor {
+    #[default]
+    Center,
+    Top,
+    Bottom,
+    Left,
+    Right,
+    TopLeft,
+    BottomLeft,
+    TopRight,
+    BottomRight,
+}
+
+/// Defines in what direction a surface should be positioned
+/// See: https://wayland.app/protocols/xdg-shell#xdg_positioner:request:set_gravity
+#[derive(Debug, Clone, Copy, Default, PartialEq)]
+#[non_exhaustive]
+pub enum WindowGravity {
+    #[default]
+    Center,
+    Top,
+    Bottom,
+    Left,
+    Right,
+    TopLeft,
+    BottomLeft,
+    TopRight,
+    BottomRight,
+}
+
+bitflags::bitflags! {
+    /// Specify how the window should be positioned if the originally intended position caused the
+    /// surface to be constrained See: https://wayland.app/protocols/xdg-shell#xdg_positioner:request:set_constraint_adjustment
+    /// For all other platforms than wayland the behaviour is simulated on the winit side
+    #[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Hash)]
+    pub struct WindowConstraintAdjustment: u32 {
+        const SLIDE_X = 1 << 0;
+        const SLIDE_Y = 1 << 1;
+        const FLIP_X = 1 << 2;
+        const FLIP_Y = 1 << 3;
+        const RESIZE_X = 1 << 4;
+        const RESIZE_Y = 1 << 5;
+    }
+}

winit-wayland/src/lib.rs

@@ -22,7 +22,7 @@ use std::ffi::c_void;
 use std::hash::BuildHasher;
 use std::ptr::NonNull;
 
-use dpi::{LogicalSize, PhysicalSize, Position, Size};
+use dpi::{LogicalSize, PhysicalSize};
 use sctk::reexports::client::Proxy;
 use sctk::reexports::client::backend::ObjectId;
 use sctk::reexports::client::protocol::wl_surface::WlSurface;
@@ -98,120 +98,6 @@ impl WindowExtWayland for dyn CoreWindow + '_ {
     }
 }
 
-/// Additional methods on [`Popup`] that are specific to Wayland.
-pub trait PopupExtWayland {
-    fn anchor_rect(&self) -> Option<(impl Into<Position>, impl Into<Size>)>;
-
-    /// Sets the anchor edge of the parent surface the popup is positioned relative to.
-    ///
-    /// See [`PopupAnchor`] for the available edges and corners.
-    fn set_anchor(&self, anchor: PopupAnchor);
-
-    /// Sets the anchor rectangle within the parent surface the popup is positioned relative to.
-    ///
-    /// `position` is the top-left corner of the rectangle relative to the parent window's content
-    /// area, and `size` its dimensions.
-    fn set_anchor_rect(&self, position: impl Into<Position>, size: impl Into<Size>);
-
-    /// Sets how the compositor should reposition the popup when it would be constrained by screen
-    /// edges.
-    ///
-    /// See [`PopupConstraintAdjustment`] for the available adjustment flags.
-    fn set_constraint_adjustment(&self, constraint_adjustment: PopupConstraintAdjustment);
-
-    /// Sets the direction the popup surface extends from the anchor point.
-    ///
-    /// See [`PopupGravity`] for the available directions.
-    fn set_gravity(&self, gravity: PopupGravity);
-
-    /// Set the popup position relative to the anchor rect
-    fn set_positioner_offset(&self, position: impl Into<Position>);
-}
-
-impl PopupExtWayland for dyn CoreWindow + '_ {
-    fn set_anchor(&self, anchor: PopupAnchor) {
-        if let Some(popup) = self.cast_ref::<Popup>() {
-            popup.set_anchor(anchor);
-        }
-    }
-
-    fn anchor_rect(&self) -> Option<(impl Into<Position>, impl Into<Size>)> {
-        if let Some(popup) = self.cast_ref::<Popup>() { popup.anchor_rect() } else { None }
-    }
-
-    fn set_anchor_rect(&self, position: impl Into<Position>, size: impl Into<Size>) {
-        if let Some(popup) = self.cast_ref::<Popup>() {
-            popup.set_anchor_rect(position, size);
-        }
-    }
-
-    fn set_constraint_adjustment(&self, constraint_adjustment: PopupConstraintAdjustment) {
-        if let Some(popup) = self.cast_ref::<Popup>() {
-            popup.set_constraint_adjustment(constraint_adjustment);
-        }
-    }
-
-    fn set_gravity(&self, gravity: PopupGravity) {
-        if let Some(popup) = self.cast_ref::<Popup>() {
-            popup.set_gravity(gravity);
-        }
-    }
-
-    fn set_positioner_offset(&self, position: impl Into<Position>) {
-        if let Some(popup) = self.cast_ref::<Popup>() {
-            popup.set_positioner_offset(position);
-        }
-    }
-}
-
-/// Anchor rect within the parent surface
-/// See: https://wayland.app/protocols/xdg-shell#xdg_positioner:request:set_anchor_rect
-#[derive(Debug, Clone, Copy, Default, PartialEq)]
-#[non_exhaustive]
-pub enum PopupAnchor {
-    #[default]
-    None,
-    Top,
-    Bottom,
-    Left,
-    Right,
-    TopLeft,
-    BottomLeft,
-    TopRight,
-    BottomRight,
-}
-
-/// Defines in what direction a surface should be positioned
-/// See: https://wayland.app/protocols/xdg-shell#xdg_positioner:request:set_gravity
-#[derive(Debug, Clone, Copy, Default, PartialEq)]
-#[non_exhaustive]
-pub enum PopupGravity {
-    #[default]
-    None,
-    Top,
-    Bottom,
-    Left,
-    Right,
-    TopLeft,
-    BottomLeft,
-    TopRight,
-    BottomRight,
-}
-
-bitflags::bitflags! {
-    /// Specify how the window should be positioned if the originally intended position caused the
-    /// surface to be constrained See: https://wayland.app/protocols/xdg-shell#xdg_positioner:request:set_constraint_adjustment
-    #[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Hash)]
-    pub struct PopupConstraintAdjustment: u32 {
-        const SLIDE_X = 1 << 0;
-        const SLIDE_Y = 1 << 1;
-        const FLIP_X = 1 << 2;
-        const FLIP_Y = 1 << 3;
-        const RESIZE_X = 1 << 4;
-        const RESIZE_Y = 1 << 5;
-    }
-}
-
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub(crate) struct ApplicationName {
     pub(crate) general: String,
@@ -224,13 +110,6 @@ pub struct WindowAttributesWayland {
     pub(crate) name: Option<ApplicationName>,
     pub(crate) activation_token: Option<ActivationToken>,
     pub(crate) prefer_csd: bool,
-    pub(crate) anchor: Option<PopupAnchor>,
-    pub(crate) anchor_rect: Option<(Position, Size)>,
-    /// Only for Popup: The offset of the popup to the
-    /// anchor rect
-    pub(crate) positioner_offset: Option<Position>,
-    pub(crate) gravity: Option<PopupGravity>,
-    pub(crate) constraint_adjustment: Option<PopupConstraintAdjustment>,
 }
 
 impl WindowAttributesWayland {
@@ -269,63 +148,6 @@ impl WindowAttributesWayland {
         self.prefer_csd = prefer_csd;
         self
     }
-
-    /// Sets the edge or corner of the anchor rectangle the popup is attached to.
-    ///
-    /// Combined with [`with_gravity`](Self::with_gravity), this controls which corner/edge of the
-    /// anchor rectangle the popup is pinned to. Has no effect unless the window is created as a
-    /// [`Popup`](winit_core::window::WindowType::Popup).
-    #[inline]
-    pub fn with_anchor(mut self, anchor: PopupAnchor) -> Self {
-        self.anchor = Some(anchor);
-        self
-    }
-
-    /// Set the anchor rectangle the popup is positioned relative to.
-    ///
-    /// `position` is the top-left corner of the rectangle relative to the parent window's content
-    /// area, and `size` its dimensions. Defaults to a `1x1` rectangle at the content origin.
-    /// This value overwrites the position value set with `with_position` in the window attributes
-    #[inline]
-    pub fn with_anchor_rect(
-        mut self,
-        position: impl Into<Position>,
-        size: impl Into<Size>,
-    ) -> Self {
-        self.anchor_rect = Some((position.into(), size.into()));
-        self
-    }
-
-    /// Set the popup position relative to the anchor rect
-    pub fn with_positioner_offset(mut self, position: impl Into<Position>) -> Self {
-        self.positioner_offset = Some(position.into());
-        self
-    }
-
-    /// Sets how the compositor should reposition the popup when it would be constrained.
-    ///
-    /// The flags in [`PopupConstraintAdjustment`] can be combined to allow sliding, flipping,
-    /// and/or resizing the popup independently on each axis. Has no effect unless the window is
-    /// created as a [`Popup`](winit_core::window::WindowType::Popup).
-    #[inline]
-    pub fn with_constraint_adjustment(
-        mut self,
-        constraint_adjustment: PopupConstraintAdjustment,
-    ) -> Self {
-        self.constraint_adjustment = Some(constraint_adjustment);
-        self
-    }
-
-    /// Sets the direction the popup surface extends away from the anchor point.
-    ///
-    /// Combined with [`with_anchor`](Self::with_anchor), this determines the final position of the
-    /// popup relative to its anchor rectangle. Has no effect unless the window is created as a
-    /// [`Popup`](winit_core::window::WindowType::Popup).
-    #[inline]
-    pub fn with_gravity(mut self, gravity: PopupGravity) -> Self {
-        self.gravity = Some(gravity);
-        self
-    }
 }
 
 impl PlatformWindowAttributes for WindowAttributesWayland {
@@ -381,64 +203,3 @@ fn image_to_buffer(
 
     Ok(buffer)
 }
-
-impl From<PopupGravity> for wayland_protocols::xdg::shell::client::xdg_positioner::Gravity {
-    fn from(value: PopupGravity) -> Self {
-        use wayland_protocols::xdg::shell::client::xdg_positioner::Gravity;
-        match value {
-            PopupGravity::None => Gravity::None,
-            PopupGravity::Top => Gravity::Top,
-            PopupGravity::Bottom => Gravity::Bottom,
-            PopupGravity::Left => Gravity::Left,
-            PopupGravity::Right => Gravity::Right,
-            PopupGravity::TopLeft => Gravity::TopLeft,
-            PopupGravity::BottomLeft => Gravity::BottomLeft,
-            PopupGravity::TopRight => Gravity::TopRight,
-            PopupGravity::BottomRight => Gravity::BottomRight,
-        }
-    }
-}
-
-impl From<PopupAnchor> for wayland_protocols::xdg::shell::client::xdg_positioner::Anchor {
-    fn from(value: PopupAnchor) -> Self {
-        use wayland_protocols::xdg::shell::client::xdg_positioner::Anchor;
-        match value {
-            PopupAnchor::None => Anchor::None,
-            PopupAnchor::Top => Anchor::Top,
-            PopupAnchor::Bottom => Anchor::Bottom,
-            PopupAnchor::Left => Anchor::Left,
-            PopupAnchor::Right => Anchor::Right,
-            PopupAnchor::TopLeft => Anchor::TopLeft,
-            PopupAnchor::BottomLeft => Anchor::BottomLeft,
-            PopupAnchor::TopRight => Anchor::TopRight,
-            PopupAnchor::BottomRight => Anchor::BottomRight,
-        }
-    }
-}
-
-impl From<PopupConstraintAdjustment>
-    for wayland_protocols::xdg::shell::client::xdg_positioner::ConstraintAdjustment
-{
-    fn from(value: PopupConstraintAdjustment) -> Self {
-        use wayland_protocols::xdg::shell::client::xdg_positioner::ConstraintAdjustment;
-
-        const _: () = {
-            assert!(
-                PopupConstraintAdjustment::SLIDE_X.bits() == ConstraintAdjustment::SlideX.bits()
-            );
-            assert!(
-                PopupConstraintAdjustment::SLIDE_Y.bits() == ConstraintAdjustment::SlideY.bits()
-            );
-            assert!(PopupConstraintAdjustment::FLIP_X.bits() == ConstraintAdjustment::FlipX.bits());
-            assert!(PopupConstraintAdjustment::FLIP_Y.bits() == ConstraintAdjustment::FlipY.bits());
-            assert!(
-                PopupConstraintAdjustment::RESIZE_X.bits() == ConstraintAdjustment::ResizeX.bits()
-            );
-            assert!(
-                PopupConstraintAdjustment::RESIZE_Y.bits() == ConstraintAdjustment::ResizeY.bits()
-            );
-        };
-
-        ConstraintAdjustment::from_bits_retain(value.bits())
-    }
-}

winit-wayland/src/popup.rs

@@ -18,16 +18,16 @@ use winit_core::event::{Ime, WindowEvent};
 use winit_core::monitor::{Fullscreen, MonitorHandle as CoreMonitorHandle};
 use winit_core::window::{
     CursorGrabMode, ImeCapabilities, ImeRequest, ImeRequestError, ResizeDirection, Theme,
-    UserAttentionType, Window as CoreWindow, WindowAttributes, WindowButtons, WindowId,
-    WindowLevel,
+    UserAttentionType, Window as CoreWindow, WindowAnchor, WindowAttributes, WindowButtons,
+    WindowConstraintAdjustment, WindowGravity, WindowId, WindowLevel, WindowPositioner,
 };
 
 use super::ActiveEventLoop;
 use super::output::MonitorHandle;
+use crate::WindowAttributesWayland;
 use crate::window::Handles;
 use crate::window::handles::WindowRequests;
 use crate::window::state::{WindowState, WindowType};
-use crate::{PopupExtWayland, WindowAttributesWayland};
 
 #[derive(Debug)]
 pub struct Popup {
@@ -66,27 +66,21 @@ impl Popup {
                 .xdg_activation
                 .as_ref()
                 .map(|activation_state| activation_state.global().clone());
-            let positioner = XdgPositioner::new(&state.xdg_shell)
+            let xdg_positioner = XdgPositioner::new(&state.xdg_shell)
                 .map_err(|_| error("Failed to create positioner"))?;
             let parent_window_id =
                 WindowId::from_raw(parent_window_handle.surface.as_ptr() as usize);
             let (popup, popup_state) = if let Some(parent_window_state) =
                 state.windows.borrow().get(&parent_window_id)
             {
-                let wayland_attributes = attributes
-                    .platform
-                    .as_ref()
-                    .and_then(|p| p.cast_ref::<WindowAttributesWayland>())
-                    .cloned()
-                    .unwrap_or_default();
-                let WindowAttributesWayland {
-                    gravity,
+                let WindowPositioner {
                     anchor,
                     anchor_rect,
+                    offset: positioner_offset,
+                    gravity,
                     constraint_adjustment,
-                    positioner_offset,
                     ..
-                } = wayland_attributes;
+                } = attributes.positioner.unwrap_or_default();
                 let grab_keyboard = attributes.active;
 
                 let mut parent_window_state = parent_window_state.lock().unwrap();
@@ -107,48 +101,51 @@ impl Popup {
                 // This is important for client side decorations
                 let geometry_origin = parent_window_state.content_surface_origin();
                 let anchor_position = LogicalPosition::new(-geometry_origin.x, -geometry_origin.y);
-                positioner.set_anchor(anchor.unwrap_or(crate::PopupAnchor::TopLeft).into());
-                positioner.set_gravity(gravity.unwrap_or(crate::PopupGravity::BottomRight).into());
-                constraint_adjustment
-                    .inspect(|c| positioner.set_constraint_adjustment((*c).into()));
-                let (anchor_rect_position, anchor_rect_size) = match anchor_rect {
-                    Some((position, size)) => (
-                        position.to_logical::<i32>(scale_factor),
-                        size.to_logical::<i32>(scale_factor),
-                    ),
-                    None => {
-                        // anchor rect was not specified use attributes.position
-                        let pos: LogicalPosition<i32> = attributes
-                            .position
-                            .map(|position| position.to_logical(scale_factor))
-                            .unwrap_or_default();
-                        (pos, LogicalSize::new(1, 1))
-                    },
+                if xdg_positioner.version() >= 3 {
+                    xdg_positioner.set_reactive();
+                }
+                xdg_positioner.set_anchor(from_anchor(anchor));
+                xdg_positioner.set_gravity(from_gravity(gravity));
+                xdg_positioner
+                    .set_constraint_adjustment(from_constraint_adjustment(constraint_adjustment));
+
+                let (anchor_rect_position, anchor_rect_size) = if attributes.positioner.is_some() {
+                    let size = anchor_rect.1.to_logical::<i32>(scale_factor);
+                    (
+                        anchor_rect.0.to_logical::<i32>(scale_factor),
+                        LogicalSize::new(size.width.max(1), size.height.max(1)),
+                    )
+                } else {
+                    // anchor rect was not specified use attributes.position
+                    let pos: LogicalPosition<i32> = attributes
+                        .position
+                        .map(|position| position.to_logical(scale_factor))
+                        .unwrap_or_default();
+                    (pos, LogicalSize::new(1, 1))
                 };
+
                 let anchor_rect = (
                     LogicalPosition::new(
                         anchor_rect_position.x + anchor_position.x,
                         anchor_rect_position.y + anchor_position.y,
                     ),
-                    LogicalSize::new(anchor_rect_size.width.max(1), anchor_rect_size.height.max(1)),
+                    anchor_rect_size,
                 );
-                positioner.set_anchor_rect(
+                xdg_positioner.set_anchor_rect(
                     anchor_rect.0.x,
                     anchor_rect.0.y,
                     anchor_rect.1.width,
                     anchor_rect.1.height,
                 );
-                positioner_offset.inspect(|o| {
-                    let o = o.to_logical(scale_factor);
-                    positioner.set_offset(o.x, o.y);
-                });
-                positioner.set_size(size.width, size.height);
+                let offset: LogicalPosition<i32> = positioner_offset.to_logical(scale_factor);
+                xdg_positioner.set_offset(offset.x, offset.y);
+                xdg_positioner.set_size(size.width, size.height);
 
                 let parent_surface = parent_window_state.window.xdg_surface();
                 let surface = state.compositor_state.create_surface(&queue_handle);
                 let popup = SctkPopup::from_surface(
                     Some(parent_surface),
-                    &positioner,
+                    &xdg_positioner,
                     &queue_handle,
                     surface.clone(),
                     &state.xdg_shell,
@@ -163,10 +160,16 @@ impl Popup {
                     size.into(),
                     WindowType::Popup {
                         popup: popup.clone(),
-                        positioner,
+                        xdg_positioner,
                         last_configure: None,
-                        anchor_rect,
                         parent_origin: geometry_origin,
+                        positioner: WindowPositioner::new(
+                            anchor,
+                            (anchor_rect_position.into(), anchor_rect_size.into()),
+                            positioner_offset,
+                            gravity,
+                            constraint_adjustment,
+                        ),
                     },
                     attributes.preferred_theme,
                     false,
@@ -288,6 +291,53 @@ impl CoreWindow for Popup {
         winit_core::window::WindowType::Popup
     }
 
+    fn positioner(&self) -> WindowPositioner {
+        let Some(state) = self.popup_state.upgrade() else { return WindowPositioner::default() };
+        if let WindowType::Popup { positioner, .. } = &state.lock().unwrap().window {
+            *positioner
+        } else {
+            WindowPositioner::default()
+        }
+    }
+
+    fn set_positioner(&self, new_positioner: WindowPositioner) {
+        let Some(state) = self.popup_state.upgrade() else {
+            return;
+        };
+
+        let mut state = state.lock().unwrap();
+        let scale_factor = state.scale_factor();
+
+        if let WindowType::Popup { popup, xdg_positioner, parent_origin, positioner, .. } =
+            &mut state.window
+        {
+            *positioner = new_positioner;
+
+            xdg_positioner.set_anchor(from_anchor(new_positioner.anchor));
+            xdg_positioner.set_gravity(from_gravity(new_positioner.gravity));
+            xdg_positioner.set_constraint_adjustment(from_constraint_adjustment(
+                new_positioner.constraint_adjustment,
+            ));
+
+            let (position, size) = new_positioner.anchor_rect;
+            let size: LogicalSize<i32> = size.to_logical(scale_factor);
+            let position: LogicalPosition<i32> = position.to_logical(scale_factor);
+            xdg_positioner.set_anchor_rect(
+                position.x - parent_origin.x,
+                position.y - parent_origin.y,
+                size.width.max(1),
+                size.height.max(1),
+            );
+
+            let offset: LogicalPosition<i32> = new_positioner.offset.to_logical(scale_factor);
+            xdg_positioner.set_offset(offset.x, offset.y);
+
+            if popup.xdg_popup().version() >= 3 {
+                popup.reposition(xdg_positioner, 0);
+            }
+        }
+    }
+
     fn id(&self) -> WindowId {
         self.window_id
     }
@@ -332,19 +382,22 @@ impl CoreWindow for Popup {
         let Some(s) = self.popup_state.upgrade() else { return };
         let mut state = s.lock().unwrap();
         let scale_factor = state.scale_factor();
-        if let WindowType::Popup { popup, positioner, anchor_rect, parent_origin, .. } =
+        if let WindowType::Popup { popup, xdg_positioner, positioner, parent_origin, .. } =
             &mut state.window
         {
-            let position = position.to_logical(scale_factor);
-            anchor_rect.0 = position;
-            positioner.set_anchor_rect(
-                anchor_rect.0.x - parent_origin.x,
-                anchor_rect.0.y - parent_origin.y,
-                anchor_rect.1.width,
-                anchor_rect.1.height,
+            let size = positioner.anchor_rect.1;
+            positioner.anchor_rect = (position, size);
+
+            let logical_position: LogicalPosition<i32> = position.to_logical(scale_factor);
+            let logical_size: LogicalSize<i32> = size.to_logical(scale_factor);
+            xdg_positioner.set_anchor_rect(
+                logical_position.x - parent_origin.x,
+                logical_position.y - parent_origin.y,
+                logical_size.width,
+                logical_size.height,
             );
             if popup.xdg_popup().version() >= 3 {
-                popup.reposition(positioner, 0);
+                popup.reposition(xdg_positioner, 0);
             }
         }
     }
@@ -668,80 +721,59 @@ impl rwh_06::HasDisplayHandle for Popup {
     }
 }
 
-impl PopupExtWayland for Popup {
-    fn set_anchor(&self, anchor: crate::PopupAnchor) {
-        let Some(state) = self.popup_state.upgrade() else {
-            return;
-        };
-
-        if let WindowType::Popup { popup, positioner, .. } = &state.lock().unwrap().window {
-            positioner.set_anchor(anchor.into());
-            popup.reposition(positioner, 0);
-        }
-    }
-
-    fn anchor_rect(&self) -> Option<(impl Into<Position>, impl Into<Size>)> {
-        let state = self.popup_state.upgrade()?;
-        if let WindowType::Popup { anchor_rect, .. } = &state.lock().unwrap().window {
-            Some(*anchor_rect)
-        } else {
-            None
-        }
-    }
-
-    fn set_anchor_rect(&self, position: impl Into<Position>, size: impl Into<Size>) {
-        let Some(state) = self.popup_state.upgrade() else {
-            return;
-        };
-
-        let state = state.lock().unwrap();
-        let scale_factor = state.scale_factor();
-        let size: LogicalSize<i32> = size.into().to_logical(scale_factor);
-        let position: LogicalPosition<i32> = position.into().to_logical(scale_factor);
-
-        if let WindowType::Popup { popup, positioner, parent_origin, .. } = &state.window {
-            positioner.set_anchor_rect(
-                position.x - parent_origin.x,
-                position.y - parent_origin.y,
-                size.width.max(1),
-                size.height.max(1),
-            );
-            popup.reposition(positioner, 0);
-        }
-    }
-
-    fn set_positioner_offset(&self, position: impl Into<Position>) {
-        let Some(state) = self.popup_state.upgrade() else {
-            return;
-        };
-
-        let scale_factor = state.lock().unwrap().scale_factor();
-        let position: LogicalPosition<i32> = position.into().to_logical(scale_factor);
-        if let WindowType::Popup { popup, positioner, .. } = &state.lock().unwrap().window {
-            positioner.set_offset(position.x, position.y);
-            popup.reposition(positioner, 0);
-        }
-    }
-
-    fn set_constraint_adjustment(&self, constraint_adjustment: crate::PopupConstraintAdjustment) {
-        let Some(state) = self.popup_state.upgrade() else {
-            return;
-        };
-
-        if let WindowType::Popup { popup, positioner, .. } = &state.lock().unwrap().window {
-            positioner.set_constraint_adjustment(constraint_adjustment.into());
-            popup.reposition(positioner, 0);
-        }
-    }
-
-    fn set_gravity(&self, gravity: crate::PopupGravity) {
-        let Some(state) = self.popup_state.upgrade() else {
-            return;
-        };
-
-        if let WindowType::Popup { popup, positioner, .. } = &state.lock().unwrap().window {
-            positioner.set_gravity(gravity.into());
-            popup.reposition(positioner, 0);
-        }
+fn from_gravity(
+    gravity: WindowGravity,
+) -> wayland_protocols::xdg::shell::client::xdg_positioner::Gravity {
+    use wayland_protocols::xdg::shell::client::xdg_positioner::Gravity;
+    match gravity {
+        WindowGravity::Center => Gravity::None,
+        WindowGravity::Top => Gravity::Top,
+        WindowGravity::Bottom => Gravity::Bottom,
+        WindowGravity::Left => Gravity::Left,
+        WindowGravity::Right => Gravity::Right,
+        WindowGravity::TopLeft => Gravity::TopLeft,
+        WindowGravity::BottomLeft => Gravity::BottomLeft,
+        WindowGravity::TopRight => Gravity::TopRight,
+        WindowGravity::BottomRight => Gravity::BottomRight,
+        _ => Gravity::None,
     }
 }
+
+fn from_anchor(
+    value: WindowAnchor,
+) -> wayland_protocols::xdg::shell::client::xdg_positioner::Anchor {
+    use wayland_protocols::xdg::shell::client::xdg_positioner::Anchor;
+    match value {
+        WindowAnchor::Center => Anchor::None,
+        WindowAnchor::Top => Anchor::Top,
+        WindowAnchor::Bottom => Anchor::Bottom,
+        WindowAnchor::Left => Anchor::Left,
+        WindowAnchor::Right => Anchor::Right,
+        WindowAnchor::TopLeft => Anchor::TopLeft,
+        WindowAnchor::BottomLeft => Anchor::BottomLeft,
+        WindowAnchor::TopRight => Anchor::TopRight,
+        WindowAnchor::BottomRight => Anchor::BottomRight,
+        _ => Anchor::None,
+    }
+}
+
+fn from_constraint_adjustment(
+    value: WindowConstraintAdjustment,
+) -> wayland_protocols::xdg::shell::client::xdg_positioner::ConstraintAdjustment {
+    use wayland_protocols::xdg::shell::client::xdg_positioner::ConstraintAdjustment;
+
+    const _: () = {
+        assert!(WindowConstraintAdjustment::SLIDE_X.bits() == ConstraintAdjustment::SlideX.bits());
+        assert!(WindowConstraintAdjustment::SLIDE_Y.bits() == ConstraintAdjustment::SlideY.bits());
+        assert!(WindowConstraintAdjustment::FLIP_X.bits() == ConstraintAdjustment::FlipX.bits());
+        assert!(WindowConstraintAdjustment::FLIP_Y.bits() == ConstraintAdjustment::FlipY.bits());
+        assert!(
+            WindowConstraintAdjustment::RESIZE_X.bits() == ConstraintAdjustment::ResizeX.bits()
+        );
+        assert!(
+            WindowConstraintAdjustment::RESIZE_Y.bits() == ConstraintAdjustment::ResizeY.bits()
+        );
+    };
+
+    ConstraintAdjustment::from_bits_retain(value.bits())
+}

winit-wayland/src/window/state.rs

@@ -34,6 +34,7 @@ use winit_core::cursor::{CursorIcon, CustomCursor as CoreCustomCursor};
 use winit_core::error::{NotSupportedError, RequestError};
 use winit_core::window::{
     CursorGrabMode, ImeCapabilities, ImeRequest, ImeRequestError, ResizeDirection, Theme, WindowId,
+    WindowPositioner,
 };
 
 use crate::event_loop::OwnedDisplayHandle;
@@ -64,10 +65,11 @@ pub enum WindowType {
     },
     Popup {
         popup: Popup,
-        positioner: XdgPositioner,
+        xdg_positioner: XdgPositioner,
         last_configure: Option<PopupConfigure>,
         parent_origin: LogicalPosition<i32>,
-        anchor_rect: (LogicalPosition<i32>, LogicalSize<i32>),
+
+        positioner: WindowPositioner,
     },
 }
 
@@ -844,11 +846,11 @@ impl WindowState {
                     self.resize(surface_size.to_logical(self.scale_factor()))
                 }
             },
-            WindowType::Popup { popup, positioner, .. } => {
+            WindowType::Popup { popup, xdg_positioner, .. } => {
                 let size = surface_size.to_logical(self.scale_factor());
-                positioner.set_size(size.width, size.height);
+                xdg_positioner.set_size(size.width, size.height);
                 if popup.xdg_popup().version() >= 3 {
-                    popup.reposition(positioner, 0);
+                    popup.reposition(xdg_positioner, 0);
                 }
             },
         }

winit-win32/Cargo.toml

@@ -20,6 +20,7 @@ serde = { workspace = true, optional = true }
 smol_str.workspace = true
 tracing.workspace = true
 url.workspace = true
+winit-common = { workspace = true, features = ["positioner"] }
 winit-core.workspace = true
 
 # Platform-specific

winit-win32/src/event_loop.rs

@@ -40,27 +40,28 @@ use windows_sys::Win32::UI::Input::{
     MOUSE_MOVE_RELATIVE, RAWINPUT, RIM_TYPEKEYBOARD, RIM_TYPEMOUSE,
 };
 use windows_sys::Win32::UI::WindowsAndMessaging::{
-    CREATESTRUCTW, CreateWindowExW, DefWindowProcW, DestroyWindow, DispatchMessageW, GWL_STYLE,
-    GWL_USERDATA, GetClientRect, GetCursorPos, GetMenu, HTCAPTION, HTCLIENT, LoadCursorW,
-    MINMAXINFO, MNC_CLOSE, MSG, MWMO_INPUTAVAILABLE, MsgWaitForMultipleObjectsEx,
-    NCCALCSIZE_PARAMS, PEN_FLAG_BARREL, PEN_FLAG_ERASER, PEN_MASK_PRESSURE, PEN_MASK_ROTATION,
-    PEN_MASK_TILT_X, PEN_MASK_TILT_Y, PM_REMOVE, PT_PEN, PT_TOUCH, PeekMessageW, PostMessageW,
-    QS_ALLINPUT, RI_MOUSE_HWHEEL, RI_MOUSE_WHEEL, RegisterClassExW, RegisterWindowMessageA,
-    SC_MINIMIZE, SC_RESTORE, SIZE_MAXIMIZED, SPI_GETWHEELSCROLLCHARS, SPI_GETWHEELSCROLLLINES,
-    SWP_NOACTIVATE, SWP_NOMOVE, SWP_NOSIZE, SWP_NOZORDER, SetCursor, SetWindowPos,
-    SystemParametersInfoW, TranslateMessage, WHEEL_DELTA, WINDOWPOS, WM_CAPTURECHANGED, WM_CLOSE,
-    WM_CREATE, WM_DESTROY, WM_DPICHANGED, WM_ENTERSIZEMOVE, WM_EXITSIZEMOVE, WM_GETMINMAXINFO,
-    WM_IME_COMPOSITION, WM_IME_ENDCOMPOSITION, WM_IME_SETCONTEXT, WM_IME_STARTCOMPOSITION,
-    WM_INPUT, WM_INPUTLANGCHANGE, WM_KEYDOWN, WM_KEYUP, WM_KILLFOCUS, WM_LBUTTONDOWN, WM_LBUTTONUP,
-    WM_MBUTTONDOWN, WM_MBUTTONUP, WM_MENUCHAR, WM_MOUSEHWHEEL, WM_MOUSEMOVE, WM_MOUSEWHEEL,
-    WM_NCACTIVATE, WM_NCCALCSIZE, WM_NCCREATE, WM_NCDESTROY, WM_NCLBUTTONDOWN, WM_PAINT,
-    WM_POINTERDOWN, WM_POINTERUP, WM_POINTERUPDATE, WM_RBUTTONDOWN, WM_RBUTTONUP, WM_SETCURSOR,
-    WM_SETFOCUS, WM_SETTINGCHANGE, WM_SIZE, WM_SIZING, WM_SYSCOMMAND, WM_SYSKEYDOWN, WM_SYSKEYUP,
-    WM_TOUCH, WM_WINDOWPOSCHANGED, WM_WINDOWPOSCHANGING, WM_XBUTTONDOWN, WM_XBUTTONUP, WMSZ_BOTTOM,
-    WMSZ_BOTTOMLEFT, WMSZ_BOTTOMRIGHT, WMSZ_LEFT, WMSZ_RIGHT, WMSZ_TOP, WMSZ_TOPLEFT,
-    WMSZ_TOPRIGHT, WNDCLASSEXW, WS_EX_LAYERED, WS_EX_NOACTIVATE, WS_EX_TOOLWINDOW,
-    WS_EX_TRANSPARENT, WS_OVERLAPPED, WS_POPUP, WS_VISIBLE,
+    CREATESTRUCTW, CreateWindowExW, DefWindowProcW, DestroyWindow, DispatchMessageW,
+    EnumThreadWindows, GW_OWNER, GWL_STYLE, GWL_USERDATA, GetClientRect, GetCursorPos, GetMenu,
+    GetWindow, HTCAPTION, HTCLIENT, LoadCursorW, MINMAXINFO, MNC_CLOSE, MSG, MWMO_INPUTAVAILABLE,
+    MsgWaitForMultipleObjectsEx, NCCALCSIZE_PARAMS, PEN_FLAG_BARREL, PEN_FLAG_ERASER,
+    PEN_MASK_PRESSURE, PEN_MASK_ROTATION, PEN_MASK_TILT_X, PEN_MASK_TILT_Y, PM_REMOVE, PT_PEN,
+    PT_TOUCH, PeekMessageW, PostMessageW, QS_ALLINPUT, RI_MOUSE_HWHEEL, RI_MOUSE_WHEEL,
+    RegisterClassExW, RegisterWindowMessageA, SC_MINIMIZE, SC_RESTORE, SIZE_MAXIMIZED,
+    SPI_GETWHEELSCROLLCHARS, SPI_GETWHEELSCROLLLINES, SWP_NOACTIVATE, SWP_NOMOVE, SWP_NOSIZE,
+    SWP_NOZORDER, SetCursor, SetWindowPos, SystemParametersInfoW, TranslateMessage, WHEEL_DELTA,
+    WINDOWPOS, WM_CAPTURECHANGED, WM_CLOSE, WM_CREATE, WM_DESTROY, WM_DPICHANGED, WM_ENTERSIZEMOVE,
+    WM_EXITSIZEMOVE, WM_GETMINMAXINFO, WM_IME_COMPOSITION, WM_IME_ENDCOMPOSITION,
+    WM_IME_SETCONTEXT, WM_IME_STARTCOMPOSITION, WM_INPUT, WM_INPUTLANGCHANGE, WM_KEYDOWN, WM_KEYUP,
+    WM_KILLFOCUS, WM_LBUTTONDOWN, WM_LBUTTONUP, WM_MBUTTONDOWN, WM_MBUTTONUP, WM_MENUCHAR,
+    WM_MOUSEHWHEEL, WM_MOUSEMOVE, WM_MOUSEWHEEL, WM_NCACTIVATE, WM_NCCALCSIZE, WM_NCCREATE,
+    WM_NCDESTROY, WM_NCLBUTTONDOWN, WM_PAINT, WM_POINTERDOWN, WM_POINTERUP, WM_POINTERUPDATE,
+    WM_RBUTTONDOWN, WM_RBUTTONUP, WM_SETCURSOR, WM_SETFOCUS, WM_SETTINGCHANGE, WM_SIZE, WM_SIZING,
+    WM_SYSCOMMAND, WM_SYSKEYDOWN, WM_SYSKEYUP, WM_TOUCH, WM_WINDOWPOSCHANGED, WM_WINDOWPOSCHANGING,
+    WM_XBUTTONDOWN, WM_XBUTTONUP, WMSZ_BOTTOM, WMSZ_BOTTOMLEFT, WMSZ_BOTTOMRIGHT, WMSZ_LEFT,
+    WMSZ_RIGHT, WMSZ_TOP, WMSZ_TOPLEFT, WMSZ_TOPRIGHT, WNDCLASSEXW, WS_EX_LAYERED,
+    WS_EX_NOACTIVATE, WS_EX_TOOLWINDOW, WS_EX_TRANSPARENT, WS_OVERLAPPED, WS_POPUP, WS_VISIBLE,
 };
+use windows_sys::core::BOOL;
 use winit_core::application::ApplicationHandler;
 use winit_core::cursor::{CustomCursor, CustomCursorSource};
 use winit_core::data_transfer::{
@@ -94,7 +95,7 @@ use crate::keyboard::KeyEventBuilder;
 use crate::keyboard_layout::LAYOUT_CACHE;
 use crate::monitor::{self, MonitorHandle};
 use crate::util::{WIN10_BUILD_VERSION, wrap_device_id};
-use crate::window::{InitData, Window};
+use crate::window::{self, InitData, Window};
 use crate::window_state::{CursorFlags, ImeState, WindowFlags, WindowState};
 use crate::{raw_input, util};
 
@@ -1112,6 +1113,31 @@ unsafe fn lose_active_focus(window: HWND, userdata: &WindowData) {
     userdata.send_window_event(window, Focused(false));
 }
 
+/// Repositions any anchored windows owned by `parent`. Win32 does not reposition owned windows
+/// when their owner moves (unlike Wayland subsurfaces or X11's override-redirect popups), so this
+/// has to be done manually whenever `parent` receives a `WM_WINDOWPOSCHANGED` that moved it.
+unsafe fn reposition_owned_windows(parent: HWND) {
+    unsafe extern "system" fn enum_proc(hwnd: HWND, lparam: LPARAM) -> BOOL {
+        if unsafe { GetWindow(hwnd, GW_OWNER) } != lparam as HWND {
+            return true.into(); // continue enumeration
+        }
+
+        let userdata_ptr = unsafe { util::get_window_long(hwnd, GWL_USERDATA) } as *mut WindowData;
+        if !userdata_ptr.is_null() {
+            let userdata = unsafe { &*userdata_ptr };
+            if userdata.window_state_lock().window_flags.contains(WindowFlags::ANCHORED) {
+                window::reposition_owned_popup(hwnd, &userdata.window_state);
+            }
+        }
+
+        true.into() // continue enumeration
+    }
+
+    unsafe {
+        EnumThreadWindows(GetCurrentThreadId(), Some(enum_proc), parent as LPARAM);
+    }
+}
+
 /// Any window whose callback is configured to this function will have its events propagated
 /// through the events loop of the thread the window was created in.
 // This is the callback that is called by `DispatchMessage` in the events loop.
@@ -1449,6 +1475,8 @@ unsafe fn public_window_callback_inner(
                 let physical_position =
                     unsafe { PhysicalPosition::new((*windowpos).x, (*windowpos).y) };
                 userdata.send_window_event(window, Moved(physical_position));
+
+                unsafe { reposition_owned_windows(window) };
             }
 
             // This is necessary for us to still get sent WM_SIZE.

winit-win32/src/monitor.rs

@@ -126,6 +126,16 @@ impl MonitorHandle {
         }
     }
 
+    /// The monitor's work area, i.e. its bounds minus space reserved by the system for things
+    /// like the taskbar (see `rcWork` in [`MONITORINFO`]).
+    pub(crate) fn work_area(&self) -> Option<(PhysicalPosition<i32>, PhysicalSize<u32>)> {
+        let rc_work = get_monitor_info(self.0).ok()?.monitorInfo.rcWork;
+        Some((PhysicalPosition { x: rc_work.left, y: rc_work.top }, PhysicalSize {
+            width: (rc_work.right - rc_work.left) as u32,
+            height: (rc_work.bottom - rc_work.top) as u32,
+        }))
+    }
+
     pub(crate) fn video_mode_handles(&self) -> Box<dyn Iterator<Item = VideoModeHandle>> {
         // EnumDisplaySettingsExW can return duplicate values (or some of the
         // fields are probably changing, but we aren't looking at those fields

winit-win32/src/window.rs

@@ -7,7 +7,9 @@ use std::sync::mpsc::channel;
 use std::sync::{Arc, Mutex, MutexGuard};
 use std::{io, panic, ptr};
 
-use dpi::{PhysicalInsets, PhysicalPosition, PhysicalSize, Position, Size};
+use dpi::{
+    LogicalPosition, LogicalSize, PhysicalInsets, PhysicalPosition, PhysicalSize, Position, Size,
+};
 use tracing::warn;
 use windows_sys::Win32::Foundation::{
     HWND, LPARAM, OLE_E_WRONGCOMPOBJ, POINT, POINTS, RECT, RPC_E_CHANGED_MODE, S_OK, WPARAM,
@@ -47,6 +49,7 @@ use windows_sys::Win32::UI::WindowsAndMessaging::{
     TPM_RETURNCMD, TrackPopupMenu, WDA_EXCLUDEFROMCAPTURE, WDA_NONE, WM_NCLBUTTONDOWN, WM_SETICON,
     WM_SYSCOMMAND, WNDCLASSEXW,
 };
+use winit_common::positioner::place_window;
 use winit_core::cursor::Cursor;
 use winit_core::error::{NotSupportedError, RequestError};
 use winit_core::icon::{Icon, RgbaIcon};
@@ -54,7 +57,7 @@ use winit_core::monitor::{Fullscreen, MonitorHandle as CoreMonitorHandle, Monito
 use winit_core::window::{
     CursorGrabMode, ImeCapabilities, ImeRequest, ImeRequestError, ResizeDirection, Theme,
     UserAttentionType, Window as CoreWindow, WindowAttributes, WindowButtons, WindowId,
-    WindowLevel, WindowType,
+    WindowLevel, WindowPositioner, WindowType,
 };
 
 use crate::dark_mode::try_theme;
@@ -100,9 +103,6 @@ pub struct Window {
 
     // The events loop proxy.
     thread_executor: event_loop::EventLoopThreadExecutor,
-
-    /// The type of window of this
-    window_type: WindowType,
 }
 
 impl Window {
@@ -114,37 +114,26 @@ impl Window {
         // First person to remove the need for cloning here gets a cookie!
         //
         // done. you owe me -- ossi
-        unsafe { init(w_attr, &event_loop.0) }
+        let window = unsafe { init(w_attr, &event_loop.0) }?;
+        window.reposition();
+        Ok(window)
     }
 
     fn window_state_lock(&self) -> MutexGuard<'_, WindowState> {
         self.window_state.lock().unwrap()
     }
 
-    // If we have a popup the position is relative to the parent window and not
+    // If the window is anchored the position is relative to the parent window and not
     // relative to the screen. Therefore we have to translate it from the parent
     // coordinate system to the display coordinate system
     fn translate_outer_position(&self, position: Position) -> PhysicalPosition<i32> {
-        let position = position.to_physical::<i32>(self.scale_factor());
-        let mut point = POINT { x: position.x, y: position.y };
-
-        let window_flags = self.window_state_lock().window_flags;
-        if window_flags.contains(WindowFlags::POPUP) && !window_flags.contains(WindowFlags::CHILD) {
-            let parent = unsafe { GetParent(self.hwnd()) };
-            if !parent.is_null() {
-                unsafe {
-                    ClientToScreen(parent, &mut point);
-                }
-            }
-        }
-
-        PhysicalPosition::new(point.x, point.y)
+        translate_outer_position(self.hwnd(), &self.window_state, position, self.scale_factor())
     }
 
-    // Inverse of `translate_outer_position`: if we have a popup the position is
+    // Inverse of `translate_outer_position`: if the window is anchored the position is
     // reported relative to the parent window instead of the screen. Therefore we
     // translate it from the display coordinate system back to the parent
-    // coordinate system. Non-popup windows are left in screen coordinates.
+    // coordinate system. Non-anchored windows are left in screen coordinates.
     fn translate_outer_position_to_parent(
         &self,
         position: PhysicalPosition<i32>,
@@ -152,7 +141,9 @@ impl Window {
         let mut point = POINT { x: position.x, y: position.y };
 
         let window_flags = self.window_state_lock().window_flags;
-        if window_flags.contains(WindowFlags::POPUP) && !window_flags.contains(WindowFlags::CHILD) {
+        if window_flags.contains(WindowFlags::ANCHORED)
+            && !window_flags.contains(WindowFlags::CHILD)
+        {
             let parent = unsafe { GetParent(self.hwnd()) };
             if !parent.is_null() {
                 unsafe {
@@ -164,6 +155,28 @@ impl Window {
         PhysicalPosition::new(point.x, point.y)
     }
 
+    /// Recomputes this window's position (and, if constrained, its size) from its positioner
+    /// state, using [`winit_common::positioner::place_window`], and applies the result. No-op if
+    /// this window isn't anchored. If it has no parent (which the Win32 backend never allows for
+    /// a popup, see `init`), the positioner is resolved relative to the screen's work area
+    /// instead of the parent's content area.
+    fn reposition(&self) {
+        let (anchored, positioner) = {
+            let window_state = self.window_state_lock();
+            (window_state.anchored, window_state.positioner)
+        };
+        let Some((origin, size, current_size)) =
+            compute_anchored_placement(self.hwnd(), anchored, &positioner, self.scale_factor())
+        else {
+            return;
+        };
+
+        self.set_outer_position(Position::Logical(origin));
+        if size != current_size {
+            let _ = self.request_surface_size(Size::Logical(size));
+        }
+    }
+
     /// Returns the `hwnd` of this window.
     pub fn hwnd(&self) -> HWND {
         self.window.hwnd()
@@ -463,7 +476,16 @@ impl rwh_06::HasWindowHandle for Window {
 
 impl CoreWindow for Window {
     fn window_type(&self) -> WindowType {
-        self.window_type
+        self.window_state_lock().window_type
+    }
+
+    fn positioner(&self) -> WindowPositioner {
+        self.window_state_lock().positioner
+    }
+
+    fn set_positioner(&self, positioner: WindowPositioner) {
+        self.window_state_lock().positioner = positioner;
+        self.reposition();
     }
 
     fn set_title(&self, text: &str) {
@@ -566,12 +588,7 @@ impl CoreWindow for Window {
     }
 
     fn outer_size(&self) -> PhysicalSize<u32> {
-        util::WindowArea::Outer
-            .get_rect(self.hwnd())
-            .map(|rect| {
-                PhysicalSize::new((rect.right - rect.left) as u32, (rect.bottom - rect.top) as u32)
-            })
-            .unwrap()
+        outer_size_of(self.hwnd())
     }
 
     fn request_surface_size(&self, size: Size) -> Option<PhysicalSize<u32>> {
@@ -1215,6 +1232,159 @@ impl CoreWindow for Window {
     }
 }
 
+fn outer_size_of(hwnd: HWND) -> PhysicalSize<u32> {
+    util::WindowArea::Outer
+        .get_rect(hwnd)
+        .map(|rect| {
+            PhysicalSize::new((rect.right - rect.left) as u32, (rect.bottom - rect.top) as u32)
+        })
+        .unwrap()
+}
+
+fn surface_size_of(hwnd: HWND) -> PhysicalSize<u32> {
+    util::WindowArea::Inner
+        .get_rect(hwnd)
+        .map(|rect| {
+            PhysicalSize::new((rect.right - rect.left) as u32, (rect.bottom - rect.top) as u32)
+        })
+        .unwrap()
+}
+
+// If the window is anchored the position is relative to the parent window and not relative to
+// the screen. Therefore we have to translate it from the parent coordinate system to the display
+// coordinate system. Free function so it can be used both from `Window` and from an owned
+// popup's `hwnd`/`WindowState` alone (see `reposition_owned_popup`).
+fn translate_outer_position(
+    hwnd: HWND,
+    window_state: &Mutex<WindowState>,
+    position: Position,
+    scale_factor: f64,
+) -> PhysicalPosition<i32> {
+    let position = position.to_physical::<i32>(scale_factor);
+    let mut point = POINT { x: position.x, y: position.y };
+
+    let window_flags = window_state.lock().unwrap().window_flags;
+    if window_flags.contains(WindowFlags::ANCHORED) && !window_flags.contains(WindowFlags::CHILD) {
+        let parent = unsafe { GetParent(hwnd) };
+        if !parent.is_null() {
+            unsafe {
+                ClientToScreen(parent, &mut point);
+            }
+        }
+    }
+
+    PhysicalPosition::new(point.x, point.y)
+}
+
+/// Computes an anchored window's new outer position and surface size from its positioner state,
+/// using [`winit_common::positioner::place_window`]. Returns `None` if the window isn't anchored,
+/// or its monitor's work area can't be determined.
+///
+/// On success, returns `(origin, size, current_size)`:
+/// - `origin`: the window's new outer position, in logical coordinates relative to the parent's
+///   content area, or to the screen if this window has no parent
+/// - `size`: the window's new surface size, as constrained by [`place_window`] and converted back
+///   from the outer size it operates on (see below)
+/// - `current_size`: the window's surface size *before* this placement, i.e. `hwnd`'s current
+///   surface size
+fn compute_anchored_placement(
+    hwnd: HWND,
+    anchored: bool,
+    positioner: &WindowPositioner,
+    scale_factor: f64,
+) -> Option<(LogicalPosition<f64>, LogicalSize<f64>, LogicalSize<f64>)> {
+    if !anchored {
+        return None;
+    }
+
+    let monitor = monitor::current_monitor(hwnd);
+    // Clip to the monitor's work area rather than its full bounds, so anchored popups don't get
+    // placed underneath the taskbar.
+    let (work_area_position, work_area_size) = monitor.work_area()?;
+
+    // The anchor rect's position is relative to the parent's content area (see
+    // `Popup::set_anchor_rect`), and `set_outer_position` re-adds the parent's screen origin for
+    // anchored windows (see `translate_outer_position`). To stay in the same coordinate space,
+    // the clip region also needs to be expressed relative to the parent's content area. Without a
+    // parent, both the anchor rect and `set_outer_position` operate directly in screen
+    // coordinates instead, so the origin is left at zero and the clip region stays in screen
+    // space.
+    let parent = unsafe { GetParent(hwnd) };
+    let mut parent_origin = POINT { x: 0, y: 0 };
+    if !parent.is_null() {
+        unsafe { ClientToScreen(parent, &mut parent_origin) };
+    }
+
+    let clip_position = PhysicalPosition::new(
+        work_area_position.x - parent_origin.x,
+        work_area_position.y - parent_origin.y,
+    )
+    .to_logical::<f64>(scale_factor);
+    let clip_size = work_area_size.to_logical::<f64>(scale_factor);
+
+    let current_outer_size = outer_size_of(hwnd).to_logical::<f64>(scale_factor);
+    let current_size = surface_size_of(hwnd).to_logical::<f64>(scale_factor);
+
+    let (origin, outer_size) =
+        place_window(positioner, scale_factor, current_outer_size, (clip_position, clip_size));
+
+    // The window's non-client insets (title bar, borders, ...), assumed constant regardless of
+    // the window's size, to translate `outer_size` back into a surface size.
+    let insets_width = current_outer_size.width - current_size.width;
+    let insets_height = current_outer_size.height - current_size.height;
+    let size = LogicalSize::new(
+        (outer_size.width - insets_width).max(0.0),
+        (outer_size.height - insets_height).max(0.0),
+    );
+
+    Some((origin, size, current_size))
+}
+
+/// Repositions (and, if constrained, resizes) the popup with the given `hwnd`, using its
+/// positioner state stored in `window_state`
+///
+/// This is used to reposition a window when its parent moves, since Win32 does not do so
+/// automatically for owned windows, this is only ever called from the event loop
+/// thread (from a sibling window's message procedure while handling the parent's
+/// `WM_WINDOWPOSCHANGED`), so it's safe to update the OS window and `WindowState` directly
+/// instead of going through `EventLoopThreadExecutor`
+pub(crate) fn reposition_owned_popup(hwnd: HWND, window_state: &Mutex<WindowState>) {
+    let (anchored, positioner, scale_factor) = {
+        let state = window_state.lock().unwrap();
+        (state.anchored, state.positioner, state.scale_factor)
+    };
+
+    let Some((origin, size, current_size)) =
+        compute_anchored_placement(hwnd, anchored, &positioner, scale_factor)
+    else {
+        return;
+    };
+
+    let position =
+        translate_outer_position(hwnd, window_state, Position::Logical(origin), scale_factor);
+    WindowState::set_window_flags(window_state.lock().unwrap(), hwnd, |f| {
+        f.set(WindowFlags::MAXIMIZED, false)
+    });
+    unsafe {
+        SetWindowPos(
+            hwnd,
+            ptr::null_mut(),
+            position.x,
+            position.y,
+            0,
+            0,
+            SWP_ASYNCWINDOWPOS | SWP_NOZORDER | SWP_NOSIZE | SWP_NOACTIVATE,
+        );
+        InvalidateRgn(hwnd, ptr::null_mut(), false.into());
+    }
+
+    if size != current_size {
+        let physical_size = Size::Logical(size).to_physical::<u32>(scale_factor);
+        let window_flags = window_state.lock().unwrap().window_flags;
+        window_flags.set_size(hwnd, physical_size);
+    }
+}
+
 pub(super) struct InitData<'a> {
     // inputs
     pub runner: &'a Rc<EventLoopRunner>,
@@ -1266,7 +1436,6 @@ impl InitData<'_> {
             window: SyncWindowHandle(window),
             window_state,
             thread_executor: self.runner.create_thread_executor(),
-            window_type: self.attributes.window_type,
         }
     }
 
@@ -1426,9 +1595,14 @@ unsafe fn init(
     unsafe { register_window_class(&class_name) };
 
     let is_popup = matches!(attributes.window_type, WindowType::Popup);
+    // Whether this window is positioned relative to its parent via the anchor/gravity/
+    // positioner system -- either because it's a `WindowType::Popup`, or because anchor
+    // attributes were explicitly set on a `WindowType::Window` (Windows supports both).
+    let anchored = is_popup || attributes.positioner.is_some();
     let mut window_flags = WindowFlags::empty();
     window_flags.set(WindowFlags::MARKER_DECORATIONS, attributes.decorations);
     window_flags.set(WindowFlags::POPUP, is_popup);
+    window_flags.set(WindowFlags::ANCHORED, anchored);
     window_flags.set(WindowFlags::MARKER_UNDECORATED_SHADOW, win_attributes.decoration_shadow);
     window_flags
         .set(WindowFlags::ALWAYS_ON_TOP, attributes.window_level == WindowLevel::AlwaysOnTop);

winit-win32/src/window_state.rs

@@ -20,7 +20,7 @@ use windows_sys::Win32::UI::WindowsAndMessaging::{
 use winit_core::icon::Icon;
 use winit_core::keyboard::ModifiersState;
 use winit_core::monitor::Fullscreen;
-use winit_core::window::{ImeCapabilities, Theme, WindowAttributes};
+use winit_core::window::{ImeCapabilities, Theme, WindowAttributes, WindowPositioner, WindowType};
 
 use crate::{SelectedCursor, WindowAttributesWindows, event_loop, util};
 
@@ -51,6 +51,21 @@ pub(crate) struct WindowState {
 
     pub window_flags: WindowFlags,
 
+    /// The role of this window. Governs creation/role behavior (OS window style, decorations)
+    /// only -- see `anchored` for whether this window is positioned via the anchor system.
+    pub window_type: WindowType,
+
+    /// Whether this window is positioned relative to its parent using the anchor/gravity/
+    /// positioner system, either because it's a [`WindowType::Popup`] or because anchor
+    /// attributes were set on a [`WindowType::Window`]. Stored here (rather than only on the
+    /// `Window` struct) so it stays reachable from just an `hwnd` via `GWL_USERDATA` -- e.g. to
+    /// reposition an anchored window when its parent moves.
+    pub anchored: bool,
+
+    /// The positioner state backing `anchored` placement, meaningful only when `anchored` is
+    /// `true`.
+    pub positioner: WindowPositioner,
+
     pub ime_state: ImeState,
     pub ime_capabilities: Option<ImeCapabilities>,
 
@@ -140,6 +155,12 @@ bitflags! {
 
         const CLIP_CHILDREN = 1 << 22;
 
+        /// Whether this window is positioned relative to its parent via the anchor/gravity/
+        /// positioner system. Independent of `POPUP`, which only selects the OS window style --
+        /// a `WindowType::Window` can be `ANCHORED` too. Used to pick the coordinate frame in
+        /// `translate_outer_position`/`translate_outer_position_to_parent`.
+        const ANCHORED = 1 << 23;
+
         const EXCLUSIVE_FULLSCREEN_OR_MASK = WindowFlags::ALWAYS_ON_TOP.bits();
     }
 }
@@ -186,6 +207,11 @@ impl WindowState {
             preferred_theme,
             window_flags: WindowFlags::empty(),
 
+            window_type: attributes.window_type,
+            anchored: matches!(attributes.window_type, WindowType::Popup)
+                || attributes.positioner.is_some(),
+            positioner: attributes.positioner.unwrap_or_default(),
+
             ime_state: ImeState::Disabled,
             ime_capabilities: None,
 
@@ -287,23 +313,25 @@ impl WindowFlags {
             }
         } else {
             style |= WS_CAPTION | WS_SYSMENU | WS_BORDER;
+
+            if self.contains(WindowFlags::RESIZABLE) {
+                style |= WS_SIZEBOX;
+            }
+            if self.contains(WindowFlags::MAXIMIZABLE) {
+                style |= WS_MAXIMIZEBOX;
+            }
+            if self.contains(WindowFlags::MINIMIZABLE) {
+                style |= WS_MINIMIZEBOX;
+            }
+
+            if self.contains(WindowFlags::ON_TASKBAR) {
+                style_ex |= WS_EX_APPWINDOW;
+            }
         };
 
-        if self.contains(WindowFlags::RESIZABLE) {
-            style |= WS_SIZEBOX;
-        }
-        if self.contains(WindowFlags::MAXIMIZABLE) {
-            style |= WS_MAXIMIZEBOX;
-        }
-        if self.contains(WindowFlags::MINIMIZABLE) {
-            style |= WS_MINIMIZEBOX;
-        }
         if self.contains(WindowFlags::VISIBLE) {
             style |= WS_VISIBLE;
         }
-        if self.contains(WindowFlags::ON_TASKBAR) {
-            style_ex |= WS_EX_APPWINDOW;
-        }
         if self.contains(WindowFlags::ALWAYS_ON_TOP) {
             style_ex |= WS_EX_TOPMOST;
         }

winit/examples/popup.rs

@@ -0,0 +1,214 @@
+//! This example shows the capabilities of popups
+//! Move the mouse on the window and press 'A' to create a new Popup and 'D' to delete it again.
+//! Move the Window to the border so see how the constraint adjustments behave like flipping or
+//! sliding. See `spawn_popup` and play with the various properties
+
+#[cfg(any(x11_platform, macos_platform, windows_platform, wayland_platform))]
+#[allow(deprecated)]
+fn main() -> Result<(), impl std::error::Error> {
+    use std::collections::HashMap;
+
+    use softbuffer::{Context, Surface};
+    use tracing::info;
+    use winit::application::ApplicationHandler;
+    use winit::dpi::{LogicalPosition, LogicalSize, PhysicalPosition, Position};
+    use winit::event::{ElementState, KeyEvent, WindowEvent};
+    use winit::event_loop::{ActiveEventLoop, EventLoop, OwnedDisplayHandle};
+    use winit::raw_window_handle::HasRawWindowHandle;
+    use winit::window::{Window, WindowAttributes, WindowId};
+
+    #[path = "util/fill.rs"]
+    mod fill;
+
+    #[derive(Debug)]
+    struct WindowData {
+        surface: Surface<OwnedDisplayHandle, Box<dyn Window>>,
+        color: u32,
+    }
+
+    impl WindowData {
+        fn new(context: &Context<OwnedDisplayHandle>, window: Box<dyn Window>, color: u32) -> Self {
+            let surface = Surface::new(context, window).unwrap();
+            Self { surface, color }
+        }
+    }
+
+    #[derive(Debug)]
+    struct Application {
+        parent_window_id: Option<WindowId>,
+        main_window: Option<WindowId>,
+        windows: HashMap<WindowId, WindowData>,
+        popups: Vec<WindowId>,
+        position: Option<PhysicalPosition<f64>>,
+        context: Context<OwnedDisplayHandle>,
+    }
+
+    impl ApplicationHandler for Application {
+        fn can_create_surfaces(&mut self, event_loop: &dyn ActiveEventLoop) {
+            let attributes = WindowAttributes::default()
+                .with_title("parent window")
+                .with_position(Position::Logical(LogicalPosition::new(0.0, 0.0)))
+                .with_surface_size(LogicalSize::new(600.0f32, 600.0f32))
+                .with_decorations(true);
+            let window = event_loop.create_window(attributes).unwrap();
+            self.parent_window_id = Some(window.id());
+
+            if self.main_window.is_none() {
+                self.main_window = Some(window.id());
+            }
+            self.windows.insert(window.id(), WindowData::new(&self.context, window, 0xffbbbbbb));
+        }
+
+        fn window_event(
+            &mut self,
+            event_loop: &dyn ActiveEventLoop,
+            window_id: winit::window::WindowId,
+            event: WindowEvent,
+        ) {
+            use winit::keyboard::{KeyCode, PhysicalKey};
+
+            match event {
+                WindowEvent::CloseRequested => {
+                    self.windows.remove(&window_id);
+                    self.popups.retain_mut(|id| id != &window_id);
+                    if self.windows.is_empty() {
+                        event_loop.exit();
+                    }
+                },
+                WindowEvent::PointerEntered { .. } => {
+                    // On x11, println when the cursor entered in a window even if the child window
+                    // is created by some key inputs.
+                    // the child windows are always placed at (0, 0) with size (200, 200) in the
+                    // parent window, so we also can see this log when we move
+                    // the cursor around (200, 200) in parent window.
+                    info!("cursor entered in the window {window_id:?}");
+                },
+                WindowEvent::PointerMoved { position, .. } => {
+                    let tracked = self.popups.last().copied().or(self.main_window);
+                    self.position = (tracked == Some(window_id)).then(|| {
+                        info!("Physical position: {position:?}");
+                        position
+                    });
+                },
+                WindowEvent::KeyboardInput {
+                    event:
+                        KeyEvent {
+                            state: ElementState::Released,
+                            physical_key: PhysicalKey::Code(code),
+                            ..
+                        },
+                    ..
+                } => {
+                    match code {
+                        KeyCode::KeyA => {
+                            let window_id = if let Some(popup_id) = self.popups.last() {
+                                popup_id
+                            } else {
+                                // The mainwindow must exist, otherwise the event_loop was ended
+                                &self.main_window.unwrap()
+                            };
+
+                            // Add a new Popup
+                            let child_index = self.windows.len() - 1;
+                            let child_color =
+                                0xff000000 + 3_u32.pow((child_index + 2).rem_euclid(16) as u32);
+
+                            let parent_window = self.windows.get(window_id).unwrap();
+                            let child_window = spawn_popup(
+                                parent_window.surface.window().as_ref(),
+                                event_loop,
+                                child_index,
+                                self.position,
+                            );
+                            let child_id = child_window.id();
+                            self.popups.push(child_id);
+                            self.windows.insert(
+                                child_id,
+                                WindowData::new(&self.context, child_window, child_color),
+                            );
+                        },
+                        KeyCode::KeyD => {
+                            // Delete
+                            if let Some(l) = self.popups.pop() {
+                                self.windows.remove(&l);
+                            }
+
+                            // // When deleting the first, it should not lead to a wayland protocol
+                            // // error
+                            // if let Some(l) = self.popups.first() {
+                            //     self.windows.remove(&l);
+                            // }
+                        },
+                        _ => (),
+                    }
+                },
+                WindowEvent::RedrawRequested => {
+                    if let Some(window) = self.windows.get_mut(&window_id) {
+                        if window_id == self.parent_window_id.unwrap() {
+                            fill::fill(&mut window.surface);
+                        } else {
+                            fill::fill_with_color(&mut window.surface, window.color);
+                        }
+                    }
+                },
+                _ => (),
+            }
+        }
+    }
+
+    fn spawn_popup(
+        parent: &dyn Window,
+        event_loop: &dyn ActiveEventLoop,
+        _child_count: usize,
+        position: Option<PhysicalPosition<f64>>,
+    ) -> Box<dyn Window> {
+        use winit::dpi::Size;
+        use winit::window::{
+            WindowAnchor, WindowConstraintAdjustment, WindowGravity, WindowPositioner, WindowType,
+        };
+
+        let parent = parent.raw_window_handle().unwrap();
+
+        let mut window_attributes = WindowAttributes::default()
+            .with_title("child window")
+            .with_surface_size(LogicalSize::new(300.0f32, 300.0))
+            .with_decorations(false)
+            .with_visible(true)
+            .with_active(true) // Grab keyboard
+            .with_window_type(WindowType::Popup)
+            .with_positioner(WindowPositioner::new(
+                WindowAnchor::TopLeft,
+                (
+                    Position::Physical(position.unwrap_or_default().cast()),
+                    Size::Logical(LogicalSize { width: 1., height: 1. }),
+                ),
+                Position::Logical(LogicalPosition { x: 0., y: 0. }),
+                WindowGravity::BottomRight,
+                WindowConstraintAdjustment::all(),
+            ));
+
+        // `with_parent_window` is unsafe. Parent window must be a valid window.
+        window_attributes = unsafe { window_attributes.with_parent_window(Some(parent)) };
+
+        event_loop.create_window(window_attributes).unwrap()
+    }
+
+    let event_loop = EventLoop::new().unwrap();
+    let context = Context::new(event_loop.owned_display_handle()).unwrap();
+    event_loop.run_app(Application {
+        context,
+        parent_window_id: None,
+        windows: HashMap::new(),
+        popups: Vec::default(),
+        position: Default::default(),
+        main_window: None,
+    })
+}
+
+#[cfg(not(any(x11_platform, macos_platform, windows_platform, wayland_platform)))]
+fn main() {
+    panic!(
+        "This example is supported only on wayland, x11, macOS, and Windows, with the `rwh_06` \
+         feature enabled."
+    );
+}

winit/src/changelog/unreleased.md

@@ -51,7 +51,19 @@ changelog entry.
 - On Android, added scancode conversions for more obscure key codes.
 - On Wayland, added `HoldGesture` event for multi-finger hold gestures
 - On Wayland, added ext-background-effect-v1 support.
-- On Wayland, Windows and macOS, added native popups (`WindowType::Popup`).
+- On Wayland, Windows and macOS, added native popups (`WindowType::Popup`), with
+  `WindowAttributes::with_positioner` for configuring their placement via a
+  `WindowPositioner` (grouping the anchor edge/corner, the anchor rect, the
+  gravity direction, the positioner offset and the constraint adjustment, using
+  the new `WindowAnchor`, `WindowGravity` and `WindowConstraintAdjustment`
+  types), and matching `Window::positioner`/`set_positioner` methods for
+  reading/controlling it at runtime. These work on every `Window`, popup or not;
+  use `Window::window_type` to tell whether a given window is a genuine
+  `WindowType::Popup`. On Windows and macOS, which have no native positioner
+  concept, the placement is computed by winit itself, mirroring Wayland's
+  `xdg_positioner` behavior, and it also works for a plain `WindowType::Window`
+  that has a parent; on Wayland the positioner is part of the `xdg_popup`
+  protocol, so it only applies to `WindowType::Popup`.
 - On macOS, add `WindowAttributesMacOS::with_fullscreen_auxiliary` and
   `WindowExtMacOS::set_fullscreen_auxiliary` / `WindowExtMacOS::fullscreen_auxiliary`, allowing a
   window to be shown on the same Space as a fullscreen window