Split Layout::find_id, renaming to probe, try_probe

crates/kas-core/src/core/layout.rs

@@ -42,7 +42,7 @@ use kas_macros::autoimpl;
 ///     cached by `size_rules`.
 /// 4.  The widget is updated again after any data change (see [`ConfigCx::update`]).
 /// 5.  The widget is ready for event-handling and drawing ([`Events`],
-///     [`Self::find_id`], [`Self::draw`]).
+///     [`Self::try_probe`], [`Self::draw`]).
 ///
 /// Widgets are responsible for ensuring that their children may observe this
 /// lifecycle. Usually this simply involves inclusion of the child in layout
@@ -176,7 +176,7 @@ pub trait Layout {
     /// Required: [`Self::size_rules`] is called for both axes before this
     /// method is called, and that this method has been called *after* the last
     /// call to [`Self::size_rules`] *before* any of the following methods:
-    /// [`Layout::find_id`], [`Layout::draw`], [`Events::handle_event`].
+    /// [`Layout::try_probe`], [`Layout::draw`], [`Events::handle_event`].
     ///
     /// Default implementation when not using the `layout` property: set `rect`
     /// field of `widget_core!()` to the input `rect`.
@@ -216,7 +216,7 @@ pub trait Layout {
     /// *and* child widgets need to implement this.
     /// Such widgets must also implement [`Events::handle_scroll`].
     ///
-    /// Affects event handling via [`Layout::find_id`] and affects the positioning
+    /// Affects event handling via [`Layout::probe`] and affects the positioning
     /// of pop-up menus. [`Layout::draw`] must be implemented directly using
     /// [`DrawCx::with_clip_region`] to offset contents.
     ///
@@ -226,59 +226,65 @@ pub trait Layout {
         Offset::ZERO
     }
 
-    /// Translate a coordinate to an [`Id`]
+    /// Probe a coordinate for a widget's [`Id`]
     ///
-    /// This method is used to determine which widget reacts to the mouse cursor
-    /// or a touch event. The result affects mouse-hover highlighting, event
-    /// handling by the target, and potentially also event handling by other
-    /// widgets (e.g. a `Label` widget will not handle touch events, but if it
-    /// is contained by a `ScrollRegion`, that widget may capture these via
-    /// [`Events::handle_event`] to implement touch scrolling).
+    /// Returns the [`Id`] of the lowest descendant (leaf-most element of the
+    /// widget tree) occupying `coord` (exceptions possible; see below).
+    ///
+    /// The callee may assume that it occupies `coord`.
+    /// Callers should prefer to call [`Tile::try_probe`] instead.
+    ///
+    /// This method is used to determine which widget reacts to the mouse and
+    /// touch events at the given coordinates. The widget identified by this
+    /// method may be highlighted (if hovered by the mouse) and may respond to
+    /// click/touch events. Unhandled click/touch events are passed to the
+    /// parent widget and so on up the widget tree.
     ///
     /// The result is usually the widget which draws at the given `coord`, but
     /// does not have to be. For example, a `Button` widget will return its own
     /// `id` for coordinates drawn by internal content, while the `CheckButton`
     /// widget uses an internal component for event handling and thus reports
     /// this component's `id` even over its own area.
     ///
+    /// ### Call order
+    ///
     /// It is expected that [`Layout::set_rect`] is called before this method,
     /// but failure to do so should not cause a fatal error.
     ///
-    /// The default implementation suffices for widgets without children as well
-    /// as widgets using the `layout` property of [`#[widget]`](crate::widget).
-    /// Custom implementations may be required if:
-    ///
-    /// -   A custom [`Layout`] implementation is used
-    /// -   Event stealing or donation is desired (but note that
-    ///     `layout = button: ..;` does this already)
+    /// ### Default implementation
     ///
-    /// When writing a custom implementation:
-    ///
-    /// -   Widgets should test `self.rect().contains(coord)`, returning `None`
-    ///     if this test is `false`; otherwise, they should always return *some*
-    ///     [`Id`], either a childs or their own.
-    /// -   If the Widget uses a translated coordinate space (i.e.
-    ///     `self.translation() != Offset::ZERO`) then pass
-    ///     `coord + self.translation()` to children.
-    ///
-    /// The default implementation is non-trivial:
+    /// The default macro-generated implementation considers all children of the
+    /// `layout` property and of [`#[widget]`](crate::widget) fields:
     /// ```ignore
-    /// if !self.rect().contains(coord) {
-    ///     return None;
-    /// }
     /// let coord = coord + self.translation();
     /// for child in ITER_OVER_CHILDREN {
-    ///     if let Some(id) = child.find_id(coord) {
+    ///     if let Some(id) = child.try_probe(coord) {
     ///         return Some(id);
     ///     }
     /// }
-    /// Some(self.id())
+    /// self.id()
     /// ```
-    fn find_id(&mut self, coord: Coord) -> Option<Id> {
+    fn probe(&mut self, coord: Coord) -> Id {
         let _ = coord;
         unimplemented!() // make rustdoc show that this is a provided method
     }
 
+    /// Probe a coordinate for a widget's [`Id`]
+    ///
+    /// Returns the [`Id`] of the lowest descendant (leaf-most element of the
+    /// widget tree) occupying `coord`, if any.
+    ///
+    /// This method returns `None` if `!self.rect().contains(coord)`, otherwise
+    /// returning the result of [`Layout::probe`].
+    ///
+    /// ### Call order
+    ///
+    /// It is expected that [`Tile::set_rect`] is called before this method,
+    /// but failure to do so should not cause a fatal error.
+    fn try_probe(&mut self, coord: Coord) -> Option<Id> {
+        self.rect().contains(coord).then(|| self.probe(coord))
+    }
+
     /// Draw a widget and its children
     ///
     /// This method is invoked each frame to draw visible widgets. It should

crates/kas-core/src/core/node.rs

@@ -28,7 +28,7 @@ trait NodeT {
     fn set_rect(&mut self, cx: &mut ConfigCx, rect: Rect, hints: AlignHints);
 
     fn nav_next(&self, reverse: bool, from: Option<usize>) -> Option<usize>;
-    fn find_id(&mut self, coord: Coord) -> Option<Id>;
+    fn try_probe(&mut self, coord: Coord) -> Option<Id>;
     fn _draw(&mut self, draw: DrawCx);
 
     fn _configure(&mut self, cx: &mut ConfigCx, id: Id);
@@ -80,8 +80,8 @@ impl<'a, T> NodeT for (&'a mut dyn Widget<Data = T>, &'a T) {
     fn nav_next(&self, reverse: bool, from: Option<usize>) -> Option<usize> {
         self.0.nav_next(reverse, from)
     }
-    fn find_id(&mut self, coord: Coord) -> Option<Id> {
-        self.0.find_id(coord)
+    fn try_probe(&mut self, coord: Coord) -> Option<Id> {
+        self.0.try_probe(coord)
     }
     fn _draw(&mut self, mut draw: DrawCx) {
         draw.recurse(&mut self.0);
@@ -303,8 +303,8 @@ impl<'a> Node<'a> {
     }
 
     /// Translate a coordinate to an [`Id`]
-    pub(crate) fn find_id(&mut self, coord: Coord) -> Option<Id> {
-        self.0.find_id(coord)
+    pub(crate) fn try_probe(&mut self, coord: Coord) -> Option<Id> {
+        self.0.try_probe(coord)
     }
 
     cfg_if::cfg_if! {

crates/kas-core/src/core/widget.rs

@@ -31,7 +31,7 @@ use kas_macros::autoimpl;
 ///     cached by `size_rules`.
 /// 4.  The widget is updated again after any data change (see [`ConfigCx::update`]).
 /// 5.  The widget is ready for event-handling and drawing
-///     ([`Events::handle_event`], [`Layout::find_id`], [`Layout::draw`]).
+///     ([`Events::handle_event`], [`Layout::try_probe`], [`Layout::draw`]).
 ///
 /// Widgets are responsible for ensuring that their children may observe this
 /// lifecycle. Usually this simply involves inclusion of the child in layout
@@ -256,7 +256,7 @@ pub enum NavAdvance {
 ///     cached by `size_rules`.
 /// 4.  The widget is updated again after any data change (see [`ConfigCx::update`]).
 /// 5.  The widget is ready for event-handling and drawing
-///     ([`Events::handle_event`], [`Layout::find_id`], [`Layout::draw`]).
+///     ([`Events::handle_event`], [`Layout::try_probe`], [`Layout::draw`]).
 ///
 /// Widgets are responsible for ensuring that their children may observe this
 /// lifecycle. Usually this simply involves inclusion of the child in layout
@@ -310,7 +310,7 @@ pub enum NavAdvance {
 /// -   **Layout** is specified either via [layout syntax](macros::widget#layout-1)
 ///     or via implementation of at least [`Layout::size_rules`] and
 ///     [`Layout::draw`] (optionally also `set_rect`, `nav_next`, `translation`
-///     and `find_id`).
+///     and `probe`).
 ///-    **Event handling** is optional, implemented through [`Events`].
 ///
 /// For examples, check the source code of widgets in the widgets library

crates/kas-core/src/event/cx/cx_pub.rs

@@ -717,7 +717,7 @@ impl<'a> EventCx<'a> {
     ///
     /// When calling this method, be aware that some widgets use an inner
     /// component to handle events, thus calling with the outer widget's `id`
-    /// may not have the desired effect. [`Layout::find_id`] and
+    /// may not have the desired effect. [`Layout::try_probe`] and
     /// [`EventState::next_nav_focus`] are usually able to find the appropriate
     /// event-handling target.
     pub fn send_command(&mut self, id: Id, cmd: Command) {

crates/kas-core/src/event/cx/platform.rs

@@ -266,11 +266,11 @@ impl EventState {
                 cx.action.remove(Action::REGION_MOVED);
 
                 // Update hovered widget
-                let hover = win.find_id(data, cx.last_mouse_coord);
+                let hover = win.try_probe(data, cx.last_mouse_coord);
                 cx.set_hover(win.as_node(data), hover);
 
                 for grab in cx.touch_grab.iter_mut() {
-                    grab.cur_id = win.find_id(data, grab.coord);
+                    grab.cur_id = win.try_probe(data, grab.coord);
                 }
             }
         });
@@ -408,7 +408,7 @@ impl<'a> EventCx<'a> {
                 let coord = position.cast_approx();
 
                 // Update hovered win
-                let id = win.find_id(data, coord);
+                let id = win.try_probe(data, coord);
                 self.set_hover(win.as_node(data), id.clone());
 
                 if let Some(grab) = self.state.mouse_grab.as_mut() {
@@ -527,7 +527,7 @@ impl<'a> EventCx<'a> {
                 let coord = touch.location.cast_approx();
                 match touch.phase {
                     TouchPhase::Started => {
-                        let start_id = win.find_id(data, coord);
+                        let start_id = win.try_probe(data, coord);
                         if let Some(id) = start_id.as_ref() {
                             if self.config.event().touch_nav_focus() {
                                 if let Some(id) =
@@ -547,7 +547,7 @@ impl<'a> EventCx<'a> {
                         }
                     }
                     TouchPhase::Moved => {
-                        let cur_id = win.find_id(data, coord);
+                        let cur_id = win.try_probe(data, coord);
 
                         let mut redraw = false;
                         let mut pan_grab = None;

crates/kas-core/src/event/events.rs

@@ -152,7 +152,7 @@ pub enum Event {
     /// Motion events for the grabbed mouse pointer or touched finger are sent.
     ///
     /// If `cur_id` is `None`, no widget was found at the coordinate (either
-    /// outside the window or [`crate::Layout::find_id`] failed).
+    /// outside the window or [`crate::Layout::try_probe`] failed).
     PressMove { press: Press, delta: Offset },
     /// End of a click/touch press
     ///
@@ -168,7 +168,7 @@ pub enum Event {
     /// sent.
     ///
     /// If `cur_id` is `None`, no widget was found at the coordinate (either
-    /// outside the window or [`crate::Layout::find_id`] failed).
+    /// outside the window or [`crate::Layout::try_probe`] failed).
     PressEnd { press: Press, success: bool },
     /// Update from a timer
     ///

crates/kas-core/src/event/mod.rs

@@ -16,7 +16,7 @@
 //!
 //! 1.  Determine the target's [`Id`]. For example, this may be
 //!     the [`nav_focus`](EventState::nav_focus) or may be determined from
-//!     from mouse/touch coordinates by calling [`find_id`](crate::Layout::find_id).
+//!     from mouse/touch coordinates by calling [`try_probe`](crate::Layout::try_probe).
 //! 2.  If the target is [disabled](EventState::is_disabled), then find the
 //!     top-most ancestor which is disabled and make that the target, but
 //!     inhibit calling of [`Events::handle_event`] on this widget (but still