perf(ribbon): build only selected density after measuring

benches/ribbon_layout_benchmark.rs

@@ -0,0 +1,80 @@
+//! End-to-end ribbon view construction and layout benchmark.
+//!
+//! Unlike the broader performance bench's widget-construction-only metric, this
+//! carries Iced's widget-tree cache across frames and runs layout at a fixed size.
+
+use std::hint::black_box;
+use std::time::Instant;
+
+use OpenCADStudio::ui::ribbon::{LayerInfo, Ribbon};
+use iced::{Color, Size};
+use iced_test::runtime::user_interface::{Cache, UserInterface};
+
+fn main() {
+    let mut ribbon = Ribbon::new();
+    ribbon.set_styles(
+        vec!["Standard".into(), "Title".into(), "Annotative".into()],
+        "Standard",
+        vec!["Standard".into()],
+        "Standard",
+        vec!["Standard".into()],
+        "Standard",
+        vec!["Standard".into()],
+        "Standard",
+    );
+    ribbon.set_layers(
+        ["0", "DRAWING", "DIMENSIONS", "ANNOTATIONS"]
+            .into_iter()
+            .map(|name| LayerInfo {
+                name: name.into(),
+                color: Color::TRANSPARENT,
+                visible: true,
+                frozen: false,
+                locked: false,
+                vp_frozen: None,
+            })
+            .collect(),
+        "0",
+    );
+
+    let mut renderer = iced_test::futures::futures::executor::block_on(
+        <iced::Renderer as iced_test::core::renderer::Headless>::new(
+            iced_test::core::renderer::Settings::default(),
+            None,
+        ),
+    )
+    .expect("headless renderer");
+    let mut cache = Cache::default();
+    let bounds = Size::new(1600.0, 180.0);
+
+    let frame = |cache, renderer: &mut iced::Renderer| {
+        let ui = UserInterface::build(
+            ribbon.view(false, false, 0, 0, false, None),
+            bounds,
+            cache,
+            renderer,
+        );
+        black_box(ui.into_cache())
+    };
+
+    for _ in 0..10 {
+        cache = frame(cache, &mut renderer);
+    }
+
+    let iterations = 100;
+    let runs = 7;
+    let mut samples = Vec::with_capacity(runs);
+    for _ in 0..runs {
+        let start = Instant::now();
+        for _ in 0..iterations {
+            cache = frame(cache, &mut renderer);
+        }
+        samples.push(start.elapsed().as_secs_f64() * 1_000_000.0 / iterations as f64);
+    }
+    samples.sort_by(f64::total_cmp);
+    println!(
+        "ribbon view + Iced layout (cached steady state): median {:.1} µs/frame; samples {:?}",
+        samples[runs / 2],
+        samples
+    );
+}