Web: the status bar shows measured render and UI times instead of 0.0 ms

In the web build, now_ms() in crates/ui-egui/src/lib.rs returned 0.0.
The status bar read "render 0.0 ms · ui 0.0 ms" however long a frame
took, and the Layers panel's budget of 8 ms for the row thumbnails it
renders in a frame never ran out, so only its limit of 16 thumbnails
applied.

now_ms() now returns the milliseconds since its first call, read from
the browser's performance.now() through web-time, which the build
already has through eframe. The desktop clock is unchanged. In Chrome,
after a pan frame of 750 ms over a document of 50,000 paths, the status
bar now reads "render 750.7 ms". The Layers panel now renders the
thumbnails of 24 groups of 2,000 paths one per frame, where main
rendered nine of them in one frame of 217 ms. The canvas has no render
worker in the web build, so it still renders on the UI thread and draws
the same pixels.

Docs: docs/target-app-parity.md.

Cargo.lock

@@ -4976,6 +4976,7 @@ dependencies = [
  "vectorcraft-three-d",
  "vectorcraft-tools",
  "wat",
+ "web-time",
 ]
 
 [[package]]

crates/ui-egui/Cargo.toml

@@ -33,6 +33,11 @@ serde = { workspace = true }
 serde_json = { workspace = true }
 log = { workspace = true }
 
+[target.'cfg(target_arch = "wasm32")'.dependencies]
+# `now_ms` (src/lib.rs) reads the page's `performance.now()` with this crate in the web build. It is
+# MIT OR Apache-2.0 and already in the build through eframe.
+web-time = "1"
+
 [dev-dependencies]
 egui_kittest = { workspace = true, features = ["wgpu", "snapshot"] }
 vectorcraft-testkit = { workspace = true }

crates/ui-egui/src/lib.rs

@@ -964,6 +964,8 @@ impl VectorcraftApp {
     }
 }
 
+/// Returns the milliseconds since the Unix epoch, or in the web build the milliseconds since the
+/// first call, read from the page's `performance.now()`.
 pub fn now_ms() -> f64 {
     #[cfg(not(target_arch = "wasm32"))]
     {
@@ -972,7 +974,10 @@ pub fn now_ms() -> f64 {
     }
     #[cfg(target_arch = "wasm32")]
     {
-        0.0
+        use std::sync::LazyLock;
+        use web_time::Instant;
+        static START: LazyLock<Instant> = LazyLock::new(Instant::now);
+        START.elapsed().as_secs_f64() * 1000.0
     }
 }
 

docs/target-app-parity.md

@@ -546,6 +546,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   The Pathfinder panel, Offset Path, Clean Up, Divide Objects Below, Make and Release Blend, Envelope Distort's Make and Release, Repeat (Radial, Grid, Mirror and Release), Vector Halftone, New and Redefine Symbol, Delete Symbol, erasing with the Symbol Sprayer, Rasterize, Convert to Artboards, Flatten Transparency, Clear Guides, Shape Builder, Live Paint, Release Image Trace, Make and Release Opacity Mask, Delete with direct-selected anchor points, Remove Anchor Points, Cut Path, and the Shaper, Knife, Eraser, Path Eraser, Line Cut, Rectangle Cut, Mirror & Cut and Blob Brush tools add and remove objects in one pass over each layer or group they change, and Outline Stroke and Expand write each new object in the place of the object it replaces (#1429).
   Type › Show Hidden Characters keeps the marks it places on each text object from one frame to the next. The canvas lays a text object out again when an edit changes it or its threaded story, or when the last frame that showed the marks did not draw it, and it lays out all type in view again when the fonts or the hyphenation exceptions change. With 1,000 two-line labels in view, drawing the marks takes 0.8 ms per frame in a release build instead of 19.7 ms.
   Delete, Cut, Group, Ungroup, Make and Release Compound Path, Make Clipping Mask, Send to Current Layer, Duplicate, Copy in the Move, Rotate, Scale, Reflect and Shear dialogs, Transform Each with Copy and each move of an Alt-drag take time in proportion to the size of the document (#1429).
+  In the web build the status bar's render and UI times are measured with the browser's `performance.now()`, and the Layers panel stops rendering row thumbnails in a frame once they have taken 8 ms.
   An Alt-drag with the Selection, Direct Selection, Group Selection, Rotate, Scale, Reflect or Shear tool copies the selection on its first move, and the moves after it transform those copies; the previews of the Move, Rotate, Scale, Reflect and Shear dialogs with Copy and Preview on copy the selection once in the same way (#1429).
   When the desktop app opens a document on a thread of its own (#1245), that thread also reads the document's linked files and lays out its type, and the UI thread only adds the finished document: in release builds, the step left on the UI thread takes 0.02 ms instead of 1.04 s for a document with 12 linked 3000 × 2000 TIFFs, and it takes 0.1 ms instead of 0.85 s for one with 300 Auto Size area type objects, every second one in three columns.
   The Layers panel's Delete Selection, Duplicate Selection, Collect in New Layer, Merge Selected, Flatten Artwork, Release to Layers (Sequence) and row drags also take time in proportion to the size of the document, and so do Cut Artboard and Duplicate Artboard with their art and each move of an Alt-drag of one artboard with the Artboard tool while Move/Copy Artwork with Artboard is on (#1429).