perf(studio): stop font list work from landing in drag frames

packages/studio/src/components/editor/overlayFrameLoop.test.ts

@@ -3,8 +3,10 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import {
   IDLE_POLL_MS,
+  IDLE_SLICE_MS,
   requestOverlayFrames,
   resetOverlayFrameLoopForTests,
+  runWhenInputIdle,
   subscribeOverlayFrame,
 } from "./overlayFrameLoop";
 import { usePlayerStore } from "../../player/store/playerStore";
@@ -71,6 +73,31 @@ describe("overlay frame loop", () => {
     expect(runs).toBeGreaterThan(0);
   });
 
+  it("runs idle work in capped slices, only while no input arrives", () => {
+    const budgets: number[] = [];
+    requestOverlayFrames();
+    runWhenInputIdle((timeLeft) => {
+      budgets.push(timeLeft());
+      return budgets.length === 3;
+    });
+    vi.advanceTimersByTime(300);
+    expect(budgets).toEqual([]);
+    vi.advanceTimersByTime(200);
+    expect(budgets).toHaveLength(3);
+    expect(Math.max(...budgets)).toBeLessThanOrEqual(IDLE_SLICE_MS);
+
+    // Input during a slice holds the next one until the loop has been idle again.
+    const slices: number[] = [];
+    runWhenInputIdle(() => {
+      slices.push(performance.now());
+      if (slices.length === 1) requestOverlayFrames();
+      return slices.length === 2;
+    });
+    vi.advanceTimersByTime(1000);
+    expect(slices).toHaveLength(2);
+    expect(slices[1] - slices[0]).toBeGreaterThanOrEqual(400);
+  });
+
   it("runs every subscriber on one frame, not one frame each", () => {
     const calls: string[] = [];
     subscribeOverlayFrame(() => calls.push("a"));

packages/studio/src/components/editor/overlayFrameLoop.ts

@@ -143,6 +143,27 @@ function schedule(): void {
   }, IDLE_POLL_MS);
 }
 
+/** Longest idle slice, so input that arrives during one waits at most this long for its frame. */
+export const IDLE_SLICE_MS = 3;
+
+/**
+ * Runs `step` in idle slices once no input has woken the loop for AWAKE_MS, so it never shares a gesture's
+ * frames. `step` works while `timeLeft()` is positive and returns true when it has finished.
+ */
+export function runWhenInputIdle(step: (timeLeft: () => number) => boolean): void {
+  const wait = awakeUntil - performance.now();
+  if (wait > 0) {
+    setTimeout(() => runWhenInputIdle(step), wait);
+    return;
+  }
+  const idle = window.requestIdleCallback ?? ((callback: () => void) => setTimeout(callback, 0));
+  idle(() => {
+    const end = performance.now() + IDLE_SLICE_MS;
+    if (performance.now() < awakeUntil || !step(() => end - performance.now()))
+      runWhenInputIdle(step);
+  });
+}
+
 /** Something moved, or might have. Run frames at full rate for a moment. */
 export function requestOverlayFrames(): void {
   awakeUntil = performance.now() + AWAKE_MS;

packages/studio/src/components/editor/propertyPanelFont.test.tsx

@@ -8,7 +8,11 @@ import { sortFontOptions } from "./propertyPanelHelpers";
 
 vi.mock("./propertyPanelHelpers", async (importOriginal) => {
   const actual = await importOriginal<typeof import("./propertyPanelHelpers")>();
-  return { ...actual, sortFontOptions: vi.fn(actual.sortFontOptions) };
+  return {
+    ...actual,
+    sortFontOptions: vi.fn(actual.sortFontOptions),
+    uniqueFontFamilies: vi.fn(actual.uniqueFontFamilies),
+  };
 });
 
 (globalThis as unknown as { IS_REACT_ACT_ENVIRONMENT: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
@@ -56,13 +60,14 @@ describe("FontFamilyField font list", () => {
       root.render(<FontFamilyField flat value={value} importedFonts={[]} onCommit={vi.fn()} />);
     try {
       await act(async () => render("Arial"));
-      // The font lists arrive and the value changes while the dropdown is closed, as during a drag.
+      // The value changes while the dropdown is closed, as during a drag.
       await act(async () => render("Georgia"));
       expect(sortFontOptions).not.toHaveBeenCalled();
 
       const trigger = host.querySelector<HTMLButtonElement>('[data-flat-font-trigger="true"]');
       await act(async () => trigger?.click());
-      expect(sortFontOptions).toHaveBeenCalledTimes(1);
+      await act(async () => new Promise((resolve) => setTimeout(resolve, 10)));
+      expect(sortFontOptions).toHaveBeenCalled();
       expect(host.textContent).toContain("Roboto Slab");
       expect(document.head.querySelector('link[href*="fonts.googleapis.com"]')).toBeNull();
     } finally {
@@ -71,3 +76,75 @@ describe("FontFamilyField font list", () => {
     }
   });
 });
+
+describe("FontFamilyField session font lists", () => {
+  const fresh = async () => {
+    vi.resetModules();
+    const { FontFamilyField } = await import("./propertyPanelFont");
+    const { uniqueFontFamilies } = await import("./propertyPanelHelpers");
+    const loop = await import("./overlayFrameLoop");
+    vi.mocked(uniqueFontFamilies).mockClear();
+    const host = document.createElement("div");
+    document.body.append(host);
+    const root = createRoot(host);
+    const render = (value: string) =>
+      root.render(<FontFamilyField flat value={value} importedFonts={[]} onCommit={vi.fn()} />);
+    const toggle = () =>
+      host.querySelector<HTMLButtonElement>('[data-flat-font-trigger="true"]')?.click();
+    const done = () => {
+      act(() => root.unmount());
+      host.remove();
+      loop.resetOverlayFrameLoopForTests();
+    };
+    return { uniqueFontFamilies, loop, host, render, toggle, done };
+  };
+
+  it("does no list work in a drag's frames when the lists land mid-drag", async () => {
+    vi.useFakeTimers({ toFake: ["setTimeout", "clearTimeout", "performance", "Date"] });
+    const raf = window.requestAnimationFrame;
+    window.requestAnimationFrame = (() => 0) as typeof window.requestAnimationFrame;
+    const lists = vi.mocked(fetch).getMockImplementation()!;
+    vi.mocked(fetch).mockImplementation(async (url) => {
+      await new Promise((resolve) => setTimeout(resolve, 200));
+      return lists(url);
+    });
+    const t = await fresh();
+    const stopLoop = t.loop.subscribeOverlayFrame(() => undefined);
+    try {
+      await act(async () => t.render("Georgia"));
+      for (let elapsed = 0; elapsed < 600; elapsed += 16) {
+        window.dispatchEvent(new Event("pointermove"));
+        await act(async () => vi.advanceTimersByTimeAsync(16));
+      }
+      expect(fetch).toHaveBeenCalledTimes(2);
+      expect(t.uniqueFontFamilies).not.toHaveBeenCalled();
+
+      await act(async () => vi.advanceTimersByTimeAsync(500));
+      expect(t.uniqueFontFamilies).toHaveBeenCalledTimes(1);
+      await act(async () => t.toggle());
+      expect(t.host.textContent).toContain("Roboto Slab");
+    } finally {
+      stopLoop();
+      t.done();
+      window.requestAnimationFrame = raf;
+      vi.useRealTimers();
+    }
+  });
+
+  it("retries a failed list fetch when the picker opens", async () => {
+    vi.mocked(fetch).mockRejectedValueOnce(new Error("offline"));
+    const t = await fresh();
+    try {
+      await act(async () => t.render("Georgia"));
+      await act(async () => new Promise((resolve) => setTimeout(resolve, 10)));
+      expect(t.uniqueFontFamilies).not.toHaveBeenCalled();
+
+      await act(async () => t.toggle());
+      await act(async () => new Promise((resolve) => setTimeout(resolve, 10)));
+      expect(fetch).toHaveBeenCalledTimes(4);
+      expect(t.host.textContent).toContain("Roboto Slab");
+    } finally {
+      t.done();
+    }
+  });
+});

packages/studio/src/components/editor/propertyPanelFont.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useMemo, useRef, useState } from "react";
+import { useEffect, useMemo, useRef, useState, useSyncExternalStore } from "react";
 import {
   googleFontStylesheetUrl,
   POPULAR_GOOGLE_FONT_FAMILIES,
@@ -19,6 +19,7 @@ import {
   type LocalFontData,
 } from "./propertyPanelHelpers";
 import { useTrackDesignInput } from "../../contexts/DesignPanelInputContext";
+import { runWhenInputIdle } from "./overlayFrameLoop";
 
 /* ------------------------------------------------------------------ */
 /*  Font helper functions                                              */
@@ -117,6 +118,62 @@ function loadImportedFontStylesheet(asset: ImportedFontAsset): void {
   document.head.appendChild(style);
 }
 
+type FontLists = {
+  loaded: boolean;
+  google: readonly string[];
+  googleKeys: ReadonlySet<string>;
+  installed: string[];
+};
+
+let fontLists: FontLists = {
+  loaded: false,
+  google: POPULAR_GOOGLE_FONT_FAMILIES,
+  googleKeys: new Set(POPULAR_GOOGLE_FONT_FAMILIES.map((f) => f.toLowerCase())),
+  installed: [],
+};
+let fontListsRequest: Promise<void> | null = null;
+const fontListListeners = new Set<() => void>();
+
+async function fetchFontList(url: string): Promise<string[]> {
+  const data = (await (await fetch(url)).json()) as { fonts?: unknown };
+  if (!Array.isArray(data.fonts)) throw new Error(`${url} returned no font list`);
+  return data.fonts as string[];
+}
+
+function loadFontLists(): void {
+  if (fontLists.loaded) return;
+  fontListsRequest ??= Promise.all([
+    fetchFontList("/api/fonts"),
+    fetchFontList("/api/fonts/google"),
+  ])
+    .then(([installed, google]) => {
+      const names = google.concat(POPULAR_GOOGLE_FONT_FAMILIES);
+      const families: string[] = [];
+      const googleKeys = new Set<string>();
+      let next = 0;
+      runWhenInputIdle((timeLeft) => {
+        while (next < names.length && timeLeft() > 0) {
+          const batch = names.slice(next, next + 200);
+          next += batch.length;
+          families.push(...uniqueFontFamilies(batch, googleKeys));
+        }
+        if (next < names.length) return false;
+        fontLists = { loaded: true, google: families, googleKeys, installed };
+        for (const listener of fontListListeners) listener();
+        return true;
+      });
+    })
+    .catch(() => {
+      fontListsRequest = null;
+    });
+}
+
+function subscribeFontLists(listener: () => void): () => void {
+  fontListListeners.add(listener);
+  loadFontLists();
+  return () => fontListListeners.delete(listener);
+}
+
 /* ------------------------------------------------------------------ */
 /*  FontFamilyField                                                    */
 /* ------------------------------------------------------------------ */
@@ -146,9 +203,8 @@ export function FontFamilyField({
   const [activeIndex, setActiveIndex] = useState(-1);
   const [localFonts, setLocalFonts] = useState<string[]>([]);
   const [localFontData, setLocalFontData] = useState<LocalFontData[]>([]);
-  const [googleFonts, setGoogleFonts] = useState<string[]>(() => [...POPULAR_GOOGLE_FONT_FAMILIES]);
+  const lists = useSyncExternalStore(subscribeFontLists, () => fontLists);
   const [loadingLocalFonts, setLoadingLocalFonts] = useState(false);
-  const [loadingGoogleFonts, setLoadingGoogleFonts] = useState(false);
   const [importingFonts, setImportingFonts] = useState(false);
   const [fontNotice, setFontNotice] = useState<string | null>(null);
   const canQueryLocalFonts =
@@ -175,46 +231,18 @@ export function FontFamilyField({
   }, [open]);
 
   useEffect(() => {
-    let cancelled = false;
-    void fetch("/api/fonts")
-      .then((r) => (r.ok ? r.json() : null))
-      .then((data: { fonts?: string[] } | null) => {
-        if (cancelled || !Array.isArray(data?.fonts)) return;
-        setLocalFonts((cur) => uniqueFontFamilies([...cur, ...data.fonts!]));
-      })
-      .catch(() => undefined);
-    return () => {
-      cancelled = true;
-    };
-  }, []);
-
-  useEffect(() => {
-    let cancelled = false;
-    setLoadingGoogleFonts(true);
-    void fetch("/api/fonts/google")
-      .then((r) => (r.ok ? r.json() : null))
-      .then((data: { fonts?: string[] } | null) => {
-        if (cancelled || !Array.isArray(data?.fonts)) return;
-        setGoogleFonts(uniqueFontFamilies([...data.fonts!, ...POPULAR_GOOGLE_FONT_FAMILIES]));
-      })
-      .catch(() => undefined)
-      .finally(() => {
-        if (!cancelled) setLoadingGoogleFonts(false);
-      });
-    return () => {
-      cancelled = true;
-    };
-  }, []);
+    if (open) loadFontLists();
+  }, [open]);
 
   useEffect(() => {
-    if (googleFonts.some((f) => f.toLowerCase() === currentFamily.toLowerCase())) {
+    if (lists.googleKeys.has(currentFamily.toLowerCase())) {
       loadGoogleFontStylesheet(currentFamily);
     }
     const imported = importedFonts.find(
       (f) => f.family.toLowerCase() === currentFamily.toLowerCase(),
     );
     if (imported) loadImportedFontStylesheet(imported);
-  }, [currentFamily, googleFonts, importedFonts]);
+  }, [currentFamily, lists, importedFonts]);
 
   const loadBrowserLocalFonts = async () => {
     if (!canQueryLocalFonts || !window.queryLocalFonts) {
@@ -278,24 +306,19 @@ export function FontFamilyField({
   const options = useMemo(() => {
     if (!open) return [];
     const documentFonts = collectDocumentFontFamilies();
-    const googleSet = new Set(googleFonts.map((f) => f.toLowerCase()));
-    const taggedLocal = localFonts.map(
-      (family): FontOption => ({
-        family,
-        source: googleSet.has(family.toLowerCase()) ? "Google" : "Local",
-      }),
-    );
     return sortFontOptions(
       uniqueFontOptions([
         { family: currentFamily, source: "Current" },
         ...documentFonts.map((f): FontOption => ({ family: f, source: "Document" })),
         ...projectFontAssets,
-        ...googleFonts.map((f): FontOption => ({ family: f, source: "Google" })),
-        ...taggedLocal,
+        ...lists.google.map((f): FontOption => ({ family: f, source: "Google" })),
+        ...[...lists.installed, ...localFonts].map(
+          (f): FontOption => ({ family: f, source: "Local" }),
+        ),
         ...DEFAULT_FONT_FAMILIES.map((f): FontOption => ({ family: f, source: "System" })),
       ]),
     );
-  }, [open, currentFamily, googleFonts, localFonts, projectFontAssets]);
+  }, [open, currentFamily, lists, localFonts, projectFontAssets]);
 
   const filteredOptions = useMemo(() => {
     const matches = options.filter((o) => fontMatchesQuery(o.family, query));
@@ -392,7 +415,7 @@ export function FontFamilyField({
           type="text"
           value={query}
           disabled={disabled}
-          placeholder={loadingGoogleFonts ? "Loading Google Fonts..." : "Search fonts"}
+          placeholder={lists.loaded ? "Search fonts" : "Loading Google Fonts..."}
           onChange={(e) => {
             setQuery(e.target.value);
             setActiveIndex(-1);

packages/studio/src/components/editor/propertyPanelHelpers.ts

@@ -124,8 +124,7 @@ export function localFontSortScore(font: LocalFontData): number {
   return 3;
 }
 
-export function uniqueFontFamilies(values: string[]): string[] {
-  const seen = new Set<string>();
+export function uniqueFontFamilies(values: string[], seen = new Set<string>()): string[] {
   return values.reduce<string[]>((result, value) => {
     const family = value.trim();
     if (!family) return result;