perf: improve rendering performance by ~20x

1 files changed, 51 insertions, 0 deletions

diff --git a/rust/wasm/src/perf.rs b/rust/wasm/src/perf.rs
new file mode 100644
index 00000000..0c346a4d
--- /dev/null
+++ b/rust/wasm/src/perf.rs
@@ -0,0 +1,51 @@
+#![cfg(target_arch = "wasm32")]
+
+//! Per-frame profile buffer for the render pipeline.
+//!
+//! Sub-span timings are recorded into a thread-local during `renderFrame`
+//! and drained by JS via `getLastFrameProfile()`.
+
+use std::cell::RefCell;
+
+use js_sys::{Array, Object, Reflect};
+use wasm_bindgen::{JsValue, prelude::wasm_bindgen};
+
+thread_local! {
+    static LAST_FRAME_PROFILE: RefCell<Vec<(&'static str, f64)>> = const { RefCell::new(Vec::new()) };
+}
+
+pub(crate) fn now_ms() -> f64 {
+    web_sys::window()
+        .and_then(|window| window.performance())
+        .map(|performance| performance.now())
+        .unwrap_or(0.0)
+}
+
+pub(crate) fn reset() {
+    LAST_FRAME_PROFILE.with(|cell| cell.borrow_mut().clear());
+}
+
+pub(crate) fn record(name: &'static str, duration_ms: f64) {
+    LAST_FRAME_PROFILE.with(|cell| cell.borrow_mut().push((name, duration_ms)));
+}
+
+#[wasm_bindgen(js_name = getLastFrameProfile)]
+pub fn get_last_frame_profile() -> Array {
+    LAST_FRAME_PROFILE.with(|cell| {
+        let entries = cell.borrow();
+        let array = Array::new_with_length(entries.len() as u32);
+        for (index, (name, duration_ms)) in entries.iter().enumerate() {
+            let entry = Object::new();
+            Reflect::set(&entry, &JsValue::from_str("name"), &JsValue::from_str(name))
+                .expect("set name");
+            Reflect::set(
+                &entry,
+                &JsValue::from_str("durationMs"),
+                &JsValue::from_f64(*duration_ms),
+            )
+            .expect("set durationMs");
+            array.set(index as u32, entry.into());
+        }
+        array
+    })
+}