improv: PreOperation for tracking children in selections

core/src/widget/operation.rs

@@ -78,6 +78,9 @@ pub trait Operation<T = ()>: Send {
 
     /// Track the active window id being processed if relevant to the operation
     fn set_window_id(&mut self, _id: window::Id) {}
+
+    /// Used to mark the beginning of operations for a widget and its children
+    fn pre_operation(&mut self, _id: Option<&Id>) {}
 }
 
 impl<T, O> Operation<O> for Box<T>
@@ -147,6 +150,10 @@ where
     fn set_window_id(&mut self, id: window::Id) {
         self.as_mut().set_window_id(id);
     }
+
+    fn pre_operation(&mut self, id: Option<&Id>) {
+        self.as_mut().pre_operation(id);
+    }
 }
 
 /// The result of an [`Operation`].
@@ -251,6 +258,10 @@ where
             Outcome::None
         }
 
+        fn pre_operation(&mut self, id: Option<&Id>) {
+            self.operation.pre_operation(id);
+        }
+
         fn set_window_id(&mut self, id: window::Id) {
             self.operation.set_window_id(id);
         }
@@ -352,6 +363,10 @@ where
                 ) {
                     self.operation.custom(id, bounds, state);
                 }
+
+                fn pre_operation(&mut self, id: Option<&Id>) {
+                    self.operation.pre_operation(id);
+                }
             }
 
             self.operation.traverse(&mut |operation| {
@@ -425,6 +440,10 @@ where
         fn set_window_id(&mut self, id: window::Id) {
             self.operation.set_window_id(id);
         }
+
+        fn pre_operation(&mut self, id: Option<&Id>) {
+            self.operation.pre_operation(id);
+        }
     }
 
     Map {
@@ -534,6 +553,10 @@ where
         fn set_window_id(&mut self, id: window::Id) {
             self.operation.set_window_id(id);
         }
+
+        fn pre_operation(&mut self, id: Option<&Id>) {
+            self.operation.pre_operation(id);
+        }
     }
 
     Chain {
@@ -586,6 +609,10 @@ pub fn scoped<T: 'static>(
             }
         }
 
+        fn pre_operation(&mut self, id: Option<&Id>) {
+            self.operation.pre_operation(id);
+        }
+
         fn set_window_id(&mut self, id: window::Id) {
             self.operation.set_window_id(id);
         }

selector/src/find.rs

@@ -285,4 +285,8 @@ where
     fn set_window_id(&mut self, id: window::Id) {
         self.strategy.set_window_id(id);
     }
+
+    fn pre_operation(&mut self, id: Option<&Id>) {
+        self.strategy.feed(Candidate::PreOperation { id });
+    }
 }

selector/src/lib.rs

@@ -193,6 +193,8 @@ pub fn focus() -> impl Selector<Output = (bool, Target, window::Id)> {
                 ))
             } else if matches!(candidate, Candidate::Scrollable { .. }) {
                 Some((false, Target::from(candidate), self.cur_window_id))
+            } else if matches!(candidate, Candidate::PreOperation { .. }) {
+                Some((false, Target::from(candidate), self.cur_window_id))
             } else {
                 None
             }

selector/src/target.rs

@@ -42,6 +42,9 @@ pub enum Target {
         bounds: Rectangle,
         visible_bounds: Option<Rectangle>,
     },
+    PreOperation {
+        id: Option<Id>,
+    },
 }
 
 impl Target {
@@ -54,6 +57,7 @@ impl Target {
             | Target::TextInput { bounds, .. }
             | Target::Text { bounds, .. }
             | Target::Custom { bounds, .. } => *bounds,
+            Target::PreOperation { .. } => Rectangle::default(),
         }
     }
 
@@ -66,6 +70,7 @@ impl Target {
             | Target::TextInput { visible_bounds, .. }
             | Target::Text { visible_bounds, .. }
             | Target::Custom { visible_bounds, .. } => *visible_bounds,
+            Target::PreOperation { .. } => None,
         }
     }
 }
@@ -138,6 +143,9 @@ impl From<Candidate<'_>> for Target {
                 bounds,
                 visible_bounds,
             },
+            Candidate::PreOperation { id } => {
+                Self::PreOperation { id: id.cloned() }
+            }
         }
     }
 }
@@ -195,6 +203,8 @@ pub enum Candidate<'a> {
         visible_bounds: Option<Rectangle>,
         state: &'a dyn Any,
     },
+    /// Used to mark the beginning of operations for a widget and its children
+    PreOperation { id: Option<&'a Id> },
 }
 
 impl<'a> Candidate<'a> {
@@ -206,7 +216,8 @@ impl<'a> Candidate<'a> {
             | Candidate::Scrollable { id, .. }
             | Candidate::TextInput { id, .. }
             | Candidate::Text { id, .. }
-            | Candidate::Custom { id, .. } => *id,
+            | Candidate::Custom { id, .. }
+            | Candidate::PreOperation { id } => *id,
         }
     }
 
@@ -219,6 +230,7 @@ impl<'a> Candidate<'a> {
             | Candidate::TextInput { bounds, .. }
             | Candidate::Text { bounds, .. }
             | Candidate::Custom { bounds, .. } => *bounds,
+            Candidate::PreOperation { .. } => Rectangle::default(),
         }
     }
 
@@ -231,6 +243,7 @@ impl<'a> Candidate<'a> {
             | Candidate::TextInput { visible_bounds, .. }
             | Candidate::Text { visible_bounds, .. }
             | Candidate::Custom { visible_bounds, .. } => *visible_bounds,
+            Candidate::PreOperation { .. } => None,
         }
     }
 }

widget/src/scrollable.rs

@@ -676,6 +676,8 @@ where
         let translation =
             state.translation(self.direction, bounds, content_bounds);
 
+        operation.pre_operation(Some(&self.id));
+
         operation.traverse(&mut |operation| {
             self.content.as_widget_mut().operate(
                 &mut tree.children[0],