Lots of claude-driven performance work.

lib/ui/benches/layout_bench.rs

@@ -0,0 +1,94 @@
+use criterion::{Criterion, criterion_group, criterion_main};
+use ruin_ui::{
+    Color, Element, FlexDirection, LayoutCache, TextStyle, TextSystem, UiSize,
+    layout_snapshot_with_cache,
+};
+
+fn text_style() -> TextStyle {
+    TextStyle::new(14.0, Color::rgb(0xFF, 0xFF, 0xFF))
+}
+
+fn make_column_tree(n: usize) -> Element {
+    let mut root = Element::new().direction(FlexDirection::Column);
+    for i in 0..n {
+        root = root.child(Element::text(format!("item {i}"), text_style()));
+    }
+    root
+}
+
+/// Static tree — nothing changes between frames.  After one warmup frame, all
+/// subsequent frames should be near-zero cost (all cache hits).
+fn bench_static_tree(c: &mut Criterion) {
+    let mut text_system = TextSystem::new();
+    let mut layout_cache = LayoutCache::new();
+    let root = make_column_tree(200);
+    let size = UiSize::new(400.0, 4000.0);
+
+    // Warm up cache.
+    layout_snapshot_with_cache(1, size, &root, &mut text_system, &mut layout_cache);
+
+    c.bench_function("layout_static_200_nodes", |b| {
+        let mut version = 2u64;
+        b.iter(|| {
+            version += 1;
+            layout_snapshot_with_cache(version, size, &root, &mut text_system, &mut layout_cache)
+        });
+    });
+}
+
+/// 200 nodes, one text content changes per frame — only one cache miss expected.
+fn bench_single_change(c: &mut Criterion) {
+    let mut text_system = TextSystem::new();
+    let mut layout_cache = LayoutCache::new();
+    let size = UiSize::new(400.0, 4000.0);
+
+    // Initial warmup.
+    let root = make_column_tree(200);
+    layout_snapshot_with_cache(1, size, &root, &mut text_system, &mut layout_cache);
+
+    c.bench_function("layout_single_change_200_nodes", |b| {
+        let mut counter = 0usize;
+        let mut version = 2u64;
+        b.iter(|| {
+            counter += 1;
+            version += 1;
+            let mut tree = make_column_tree(200);
+            tree.children[100] = Element::text(format!("changed {counter}"), text_style());
+            layout_snapshot_with_cache(version, size, &tree, &mut text_system, &mut layout_cache)
+        });
+    });
+}
+
+/// Scroll box with 500 items, 20 visible.  Simulates a large list.
+fn bench_scroll_list(c: &mut Criterion) {
+    let mut text_system = TextSystem::new();
+    let mut layout_cache = LayoutCache::new();
+    let item_height = 32.0;
+    let viewport_height = 640.0;
+    let n = 500;
+
+    let mut scroll_box = Element::scroll_box(0.0).width(400.0).height(viewport_height);
+    for i in 0..n {
+        scroll_box = scroll_box.child(
+            Element::new()
+                .height(item_height)
+                .child(Element::text(format!("list item {i}"), text_style())),
+        );
+    }
+    let root = Element::new().child(scroll_box);
+    let size = UiSize::new(400.0, viewport_height);
+
+    // Warm up.
+    layout_snapshot_with_cache(1, size, &root, &mut text_system, &mut layout_cache);
+
+    c.bench_function("layout_scroll_list_500_items", |b| {
+        let mut version = 2u64;
+        b.iter(|| {
+            version += 1;
+            layout_snapshot_with_cache(version, size, &root, &mut text_system, &mut layout_cache)
+        });
+    });
+}
+
+criterion_group!(benches, bench_static_tree, bench_single_change, bench_scroll_list);
+criterion_main!(benches);