Add WindowHandle widget

masonry/src/widget/mod.rs

@@ -31,6 +31,7 @@ mod split;
 mod textbox;
 mod variable_label;
 mod widget_arena;
+mod window_handle;
 
 pub use self::image::Image;
 pub use align::Align;
@@ -52,6 +53,7 @@ pub use variable_label::VariableLabel;
 pub use widget_mut::WidgetMut;
 pub use widget_pod::WidgetPod;
 pub use widget_ref::WidgetRef;
+pub use window_handle::WindowHandle;
 
 pub(crate) use widget_arena::WidgetArena;
 pub(crate) use widget_state::WidgetState;

masonry/src/widget/window_handle.rs

@@ -0,0 +1,147 @@
+// Copyright 2024 the Xilem Authors and the Druid Authors
+// SPDX-License-Identifier: Apache-2.0
+
+//! A titlebar area widget.
+
+use accesskit::{NodeBuilder, Role};
+use dpi::LogicalPosition;
+use smallvec::{smallvec, SmallVec};
+use tracing::{trace_span, Span};
+use vello::kurbo::Point;
+use vello::Scene;
+
+use crate::event::PointerButton;
+use crate::widget::{WidgetMut, WidgetPod};
+use crate::{
+    AccessCtx, AccessEvent, BoxConstraints, EventCtx, LayoutCtx, LifeCycleCtx, PaintCtx,
+    PointerEvent, Size, StatusChange, TextEvent, Widget, WidgetId,
+};
+
+// TODO: Maybe make this configurable somehow
+const DRAG_THRESHOLD_SQUARED: f64 = 8.0;
+
+/// A titlebar area widget.
+///
+/// A draggable area that allows moving the window, useful to create a custom titlebar widget.
+/// The child can be used to include typical titlebar elements, such as the window title and buttons.
+///
+/// Note that this widget does not set a fixed size, background color or accessibility role.
+/// It's not intended as a complete titlebar solution. To achieve this, you should create a custom
+/// widget that handles sizing, styling and accessibility, then wrap it with the `WindowHandle`.
+///
+/// This widget is inspired by the [GtkWindowHandle](https://docs.gtk.org/gtk4/class.WindowHandle.html) from GTK.
+pub struct WindowHandle<W: Widget> {
+    child: Option<WidgetPod<W>>,
+    pointer_down_pos: Option<LogicalPosition<f64>>,
+}
+
+// --- MARK: BUILDERS ---
+impl<W: Widget> WindowHandle<W> {
+    pub fn new(child: W) -> Self {
+        Self {
+            child: Some(WidgetPod::new(child)),
+            pointer_down_pos: None,
+        }
+    }
+
+    pub fn empty() -> Self {
+        Self {
+            child: None,
+            pointer_down_pos: None,
+        }
+    }
+}
+
+// --- MARK: WIDGETMUT ---
+impl<W: Widget> WidgetMut<'_, WindowHandle<W>> {
+    pub fn set_child(&mut self, child: W) {
+        if let Some(child) = self.widget.child.take() {
+            self.ctx.remove_child(child);
+        }
+        self.widget.child = Some(WidgetPod::new(child));
+        self.ctx.children_changed();
+        self.ctx.request_layout();
+    }
+
+    pub fn remove_child(&mut self) {
+        if let Some(child) = self.widget.child.take() {
+            self.ctx.remove_child(child);
+        }
+    }
+}
+
+// --- MARK: IMPL WIDGET ---
+impl<W: Widget> Widget for WindowHandle<W> {
+    fn on_pointer_event(&mut self, ctx: &mut EventCtx, event: &PointerEvent) {
+        match event {
+            PointerEvent::PointerDown(button, state) => {
+                if !ctx.is_disabled() {
+                    // TODO: Add double click to maximize
+                    match button {
+                        PointerButton::Primary => self.pointer_down_pos = Some(state.position),
+                        PointerButton::Secondary => ctx.show_window_menu(state.position),
+                        _ => (),
+                    }
+                }
+            }
+            PointerEvent::PointerMove(state) => {
+                if let Some(last_pos) = self.pointer_down_pos {
+                    let distance_squared = (state.position.x - last_pos.x).powi(2)
+                        + (state.position.y - last_pos.y).powi(2);
+
+                    if distance_squared >= DRAG_THRESHOLD_SQUARED {
+                        ctx.drag_window();
+                        self.pointer_down_pos = None;
+                    }
+                }
+            }
+            PointerEvent::PointerLeave(_) | PointerEvent::PointerUp(_, _) => {
+                self.pointer_down_pos = None;
+            }
+            _ => (),
+        }
+    }
+
+    fn on_text_event(&mut self, _ctx: &mut EventCtx, _event: &TextEvent) {}
+
+    fn on_access_event(&mut self, _ctx: &mut EventCtx, _event: &AccessEvent) {}
+
+    fn on_status_change(&mut self, _ctx: &mut LifeCycleCtx, _event: &StatusChange) {}
+
+    fn register_children(&mut self, ctx: &mut crate::RegisterCtx) {
+        if let Some(ref mut child) = self.child {
+            ctx.register_child(child);
+        }
+    }
+
+    fn layout(&mut self, ctx: &mut LayoutCtx, bc: &BoxConstraints) -> Size {
+        match self.child.as_mut() {
+            Some(child) => {
+                let size = ctx.run_layout(child, bc);
+                ctx.place_child(child, Point::ORIGIN);
+                bc.constrain(size)
+            }
+            None => bc.max(),
+        }
+    }
+
+    fn paint(&mut self, _ctx: &mut PaintCtx, _scene: &mut Scene) {}
+
+    fn accessibility_role(&self) -> Role {
+        Role::GenericContainer
+    }
+
+    fn accessibility(&mut self, _ctx: &mut AccessCtx, _node: &mut NodeBuilder) {}
+
+    fn children_ids(&self) -> SmallVec<[WidgetId; 16]> {
+        if let Some(child) = &self.child {
+            smallvec![child.id()]
+        } else {
+            SmallVec::new()
+        }
+    }
+
+    fn make_trace_span(&self) -> Span {
+        trace_span!("WindowHandle")
+    }
+}