UI layout tree debug print

crates/bevy_ui/src/layout/debug.rs

@@ -0,0 +1,87 @@
+use crate::UiSurface;
+use bevy_ecs::prelude::Entity;
+use bevy_utils::HashMap;
+use std::fmt::Write;
+use taffy::prelude::Node;
+use taffy::tree::LayoutTree;
+
+/// Prints a debug representation of the computed layout of the UI layout tree for each window.
+pub fn print_ui_layout_tree(ui_surface: &UiSurface) {
+    let taffy_to_entity: HashMap<Node, Entity> = ui_surface
+        .entity_to_taffy
+        .iter()
+        .map(|(entity, node)| (*node, *entity))
+        .collect();
+    for (&entity, &node) in ui_surface.window_nodes.iter() {
+        let mut out = String::new();
+        print_node(
+            ui_surface,
+            &taffy_to_entity,
+            entity,
+            node,
+            false,
+            String::new(),
+            &mut out,
+        );
+        bevy_log::info!("Layout tree for window entity: {entity:?}\n{out}");
+    }
+}
+
+/// Recursively navigates the layout tree printing each node's information.
+fn print_node(
+    ui_surface: &UiSurface,
+    taffy_to_entity: &HashMap<Node, Entity>,
+    entity: Entity,
+    node: Node,
+    has_sibling: bool,
+    lines_string: String,
+    acc: &mut String,
+) {
+    let tree = &ui_surface.taffy;
+    let layout = tree.layout(node).unwrap();
+    let style = tree.style(node).unwrap();
+
+    let num_children = tree.child_count(node).unwrap();
+
+    let display_variant = match (num_children, style.display) {
+        (_, taffy::style::Display::None) => "NONE",
+        (0, _) => "LEAF",
+        (_, taffy::style::Display::Flex) => "FLEX",
+        (_, taffy::style::Display::Grid) => "GRID",
+    };
+
+    let fork_string = if has_sibling {
+        "├── "
+    } else {
+        "└── "
+    };
+    writeln!(
+        acc,
+        "{lines}{fork} {display} [x: {x:<4} y: {y:<4} width: {width:<4} height: {height:<4}] ({entity:?}) {measured}",
+        lines = lines_string,
+        fork = fork_string,
+        display = display_variant,
+        x = layout.location.x,
+        y = layout.location.y,
+        width = layout.size.width,
+        height = layout.size.height,
+        measured = if tree.needs_measure(node) { "measured" } else { "" }
+    ).ok();
+    let bar = if has_sibling { "│   " } else { "    " };
+    let new_string = lines_string + bar;
+
+    // Recurse into children
+    for (index, child_node) in tree.children(node).unwrap().iter().enumerate() {
+        let has_sibling = index < num_children - 1;
+        let child_entity = taffy_to_entity.get(child_node).unwrap();
+        print_node(
+            ui_surface,
+            taffy_to_entity,
+            *child_entity,
+            *child_node,
+            has_sibling,
+            new_string.clone(),
+            acc,
+        );
+    }
+}

crates/bevy_ui/src/layout/mod.rs

@@ -1,4 +1,5 @@
 mod convert;
+pub mod debug;
 
 use crate::{CalculatedSize, Node, Style, UiScale};
 use bevy_ecs::{