Add passthrough code

masonry/src/render_root.rs

@@ -4,10 +4,11 @@
 use std::collections::{HashMap, VecDeque};
 
 use accesskit::{ActionRequest, TreeUpdate};
+use dpi::PhysicalPosition;
 use parley::fontique::{self, Collection, CollectionOptions};
 use parley::{FontContext, LayoutContext};
 use tracing::{info_span, warn};
-use vello::kurbo::{self, Rect};
+use vello::kurbo::{self, Rect, Vec2};
 use vello::Scene;
 
 #[cfg(not(target_arch = "wasm32"))]
@@ -325,6 +326,28 @@ impl RenderRoot {
         self.cursor_icon
     }
 
+    pub fn is_passthrough(&self, pos: PhysicalPosition<f64>) -> bool {
+        let pos = Vec2::new(pos.x, pos.y) / self.scale_factor;
+
+        let mut target_id = self
+            .get_root_widget()
+            .find_widget_at_pos(pos.to_point())
+            .map(|widget| widget.id());
+
+        while let Some(widget_id) = target_id {
+            let parent_id = self.widget_arena.parent_of(widget_id);
+            let widget = self.widget_arena.get_widget(widget_id);
+
+            if !widget.item.is_passthrough() {
+                return false;
+            }
+
+            target_id = parent_id;
+        }
+
+        true
+    }
+
     // --- MARK: ACCESS WIDGETS---
     /// Get a [`WidgetRef`] to the root widget.
     pub fn get_root_widget(&self) -> WidgetRef<dyn Widget> {

masonry/src/testing/helper_widgets.rs

@@ -378,6 +378,10 @@ impl<S: 'static> Widget for ModularWidget<S> {
         self.accepts_text_input
     }
 
+    fn is_passthrough(&self) -> bool {
+        false
+    }
+
     fn make_trace_span(&self) -> tracing::Span {
         trace_span!("ModularWidget")
     }
@@ -578,6 +582,10 @@ impl<W: Widget> Widget for Recorder<W> {
         self.child.accepts_text_input()
     }
 
+    fn is_passthrough(&self) -> bool {
+        self.child.is_passthrough()
+    }
+
     fn make_trace_span(&self) -> tracing::Span {
         self.child.make_trace_span()
     }

masonry/src/widget/flex.rs

@@ -1202,6 +1202,10 @@ impl Widget for Flex {
             .collect()
     }
 
+    fn is_passthrough(&self) -> bool {
+        true
+    }
+
     fn make_trace_span(&self) -> Span {
         trace_span!("Flex")
     }

masonry/src/widget/grid.rs

@@ -311,6 +311,10 @@ impl Widget for Grid {
             .collect()
     }
 
+    fn is_passthrough(&self) -> bool {
+        true
+    }
+
     fn make_trace_span(&self) -> Span {
         trace_span!("Grid")
     }

masonry/src/widget/sized_box.rs

@@ -401,6 +401,10 @@ impl Widget for SizedBox {
         }
     }
 
+    fn is_passthrough(&self) -> bool {
+        self.background.is_none()
+    }
+
     fn make_trace_span(&self) -> Span {
         trace_span!("SizedBox")
     }

masonry/src/widget/widget.rs

@@ -199,6 +199,13 @@ pub trait Widget: AsAny {
         false
     }
 
+    /// Whether this widgets obstructs pointer events for something behind the window.
+    ///
+    /// Somewhat experimental.
+    fn is_passthrough(&self) -> bool {
+        false
+    }
+
     // TODO - Write a generic default implementation once
     // `const std::any::type_name` is stable.
     // See https://github.com/rust-lang/rust/issues/63084
@@ -467,6 +474,10 @@ impl Widget for Box<dyn Widget> {
         self.deref().accepts_text_input()
     }
 
+    fn is_passthrough(&self) -> bool {
+        self.deref().is_passthrough()
+    }
+
     fn make_trace_span(&self) -> Span {
         self.deref().make_trace_span()
     }