Retain layout sizes by pixel axis

tests/layout_diagnostics.rs

@@ -75,6 +75,22 @@ fn env<T: std::str::FromStr>(name: &str, fallback: T) -> T {
         .unwrap_or(fallback)
 }
 
+#[cfg(feature = "layout-diagnostics")]
+fn trace_selected(tree: &Tree) {
+    let Ok(value) = std::env::var("IRIS_TRACE_INDEX") else {
+        return;
+    };
+    let index = value
+        .parse::<usize>()
+        .expect("IRIS_TRACE_INDEX must be a tree.ids index");
+    let id = tree.ids[index];
+    iris::core::layout_diagnostics::trace_widget(id);
+    println!("tracing tree.ids[{index}] = {id:?}");
+}
+
+#[cfg(not(feature = "layout-diagnostics"))]
+fn trace_selected(_: &Tree) {}
+
 fn warm(seed: u64, depth: usize) -> (Harness, Tree) {
     let mut harness = Harness::new(OUTPUT);
     let (root, tree) = grow(&mut harness.rsc, seed, depth, &Edits::default());
@@ -157,6 +173,7 @@ fn layout_cost() {
             "fixture: seed {seed}, depth {depth}, {} widgets",
             tree.ids.len()
         );
+        trace_selected(&tree);
         #[cfg(feature = "layout-diagnostics")]
         let _ = iris::core::layout_diagnostics::take();
         run("cold", 1, &mut harness, |_, _| {});
@@ -165,6 +182,7 @@ fn layout_cost() {
 
     if selected("repaint") {
         let (mut harness, tree) = warm(seed, depth);
+        trace_selected(&tree);
         let leaf = tree.ids[0];
         run("repaint", frames, &mut harness, move |harness, _| {
             let _ = harness.rsc.widgets_mut().get_dyn_mut(leaf);
@@ -173,6 +191,7 @@ fn layout_cost() {
 
     if selected("size") {
         let (mut harness, tree) = warm(seed, depth);
+        trace_selected(&tree);
         let sized = tree.sized[0];
         run("size", frames, &mut harness, move |harness, frame| {
             harness.rsc[sized].x = Some(Len::abs(100.0 + (frame % 2) as f32 * 40.0));
@@ -181,6 +200,7 @@ fn layout_cost() {
 
     if selected("scroll") {
         let (mut harness, tree) = warm(seed, depth);
+        trace_selected(&tree);
         let scroll = tree.scrolls[0];
         run("scroll", frames, &mut harness, move |harness, frame| {
             harness.rsc[scroll].scroll(if frame % 2 == 0 { 12.0 } else { -12.0 });
@@ -189,8 +209,9 @@ fn layout_cost() {
 
     if selected("resize") {
         let (mut harness, tree) = warm(seed, depth);
+        trace_selected(&tree);
         run("resize", frames, &mut harness, |harness, frame| {
-            harness.resize((OUTPUT.0 - (frame % 2) as f32 * 8.0, OUTPUT.1));
+            harness.resize((OUTPUT.0 - ((frame + 1) % 2) as f32 * 8.0, OUTPUT.1));
         });
         drop(tree);
     }