✨ Add font family preview in typography selector (#10411)

Co-authored-by: alonso.torres <alonso.torres@kaleidos.net>

frontend/package.json

@@ -15,6 +15,7 @@
   },
   "scripts": {
     "build:app:assets": "node ./scripts/build-app-assets.js",
+    "build:fonts-preview": "node ./scripts/build-fonts-preview.js",
     "build:storybook": "pnpm run build:storybook:assets && pnpm run build:storybook:cljs && storybook build",
     "build:storybook:assets": "node ./scripts/build-storybook-assets.js",
     "build:storybook:cljs": "clojure -M:dev:shadow-cljs compile storybook",

frontend/scripts/_helpers.js

@@ -15,6 +15,8 @@ import pLimit from "p-limit";
 import ppt from "pretty-time";
 import wpool from "workerpool";
 
+import { buildFontsPreviewSprite } from "./build-fonts-preview.js";
+
 function getCoreCount() {
   return os.cpus().length;
 }
@@ -48,8 +50,9 @@ async function findFiles(basePath, predicate, options = {}) {
   return files;
 }
 
-function syncDirs(originPath, destPath) {
+function syncDirs(originPath, destPath, excludes = []) {
-  const command = `rsync -ar --delete ${originPath} ${destPath}`;
+  const excludeArgs = excludes.map((p) => `--exclude=${p}`).join(" ");
+  const command = `rsync -ar --delete ${excludeArgs} ${originPath} ${destPath}`;
 
   return new Promise((resolve, reject) => {
     proc.exec(command, (cause, stdout) => {
@@ -540,6 +543,36 @@ export async function compileSvgSprites() {
   }
 }
 
+export async function compileFontsPreviewSprite() {
+  const start = process.hrtime();
+  log.info("init: compile fonts preview sprite");
+  let error = false;
+  let result;
+
+  try {
+    result = await buildFontsPreviewSprite();
+  } catch (cause) {
+    error = cause;
+  }
+
+  const end = process.hrtime(start);
+
+  if (error) {
+    log.error("error: compile fonts preview sprite", `(${ppt(end)})`);
+    console.error(error);
+  } else if (result.skipped) {
+    log.info(
+      "done: compile fonts preview sprite (up-to-date, skipped)",
+      `(${ppt(end)})`,
+    );
+  } else {
+    log.info(
+      `done: compile fonts preview sprite (${result.ok} ok, ${result.failed} fallback)`,
+      `(${ppt(end)})`,
+    );
+  }
+}
+
 export async function compileTemplates() {
   const start = process.hrtime();
   let error = false;
@@ -584,7 +617,11 @@ export async function copyAssets() {
   log.info("init: copy assets");
 
   await syncDirs("resources/images/", "resources/public/images/");
-  await syncDirs("resources/fonts/", "resources/public/fonts/");
+  // The font preview sprite is generated into public/fonts/ (not committed), so
+  // exclude it from --delete to keep it across builds (see compileFontsPreviewSprite).
+  await syncDirs("resources/fonts/", "resources/public/fonts/", [
+    "fonts-preview-sprite.svg",
+  ]);
 
   const end = process.hrtime(start);
   log.info("done: copy assets", `(${ppt(end)})`);

frontend/scripts/build-app-assets.js

@@ -3,6 +3,7 @@ import * as h from "./_helpers.js";
 await h.ensureDirectories();
 await h.compileStyles();
 await h.copyAssets();
+await h.compileFontsPreviewSprite();
 await h.copyWasmPlayground();
 await h.compileSvgSprites();
 await h.compileTranslations();

frontend/scripts/build-fonts-preview.js

@@ -0,0 +1,384 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+//
+// Copyright (c) KALEIDOS INC Sucursal en España SL
+
+// Builds one SVG sprite previewing every catalog (built-in + Google) font name,
+// outlined in its own typeface, so the picker loads it once instead of one
+// request per font. Custom uploads aren't baked in and use the runtime fallback.
+//
+// Part of the asset build (compileFontsPreviewSprite in _helpers.js):
+// regenerates only when missing or older than the gfonts catalog. Run directly
+// to force a rebuild. See the technical-guide doc for the full design.
+
+import { createHash } from "node:crypto";
+import fs from "node:fs/promises";
+import os from "node:os";
+import ph from "node:path";
+import url from "node:url";
+
+import opentype from "opentype.js";
+
+// Coordinates are emitted in CSS px (1 user unit == 1px), so the UI sizes rows
+// without per-font metrics. Each name is laid out on its baseline then fitted
+// into a fixed BOX_HEIGHT box (see buildSymbol). See the technical-guide doc.
+const FONT_SIZE = 18; // visual cap/x-height target, matches the label typography
+const BOX_HEIGHT = 28; // display box height in px; keep in sync with the scss
+const VPAD = 1; // px of breathing room top/bottom before a name is scaled to fit
+// Decimals of precision. 1 (≈0.1px grid) keeps glyphs smooth; 0 makes them
+// wobbly. Sprite is ~2.3MB gzip at 1 with the relative encoding (serializePath).
+const PATH_PRECISION = 1;
+
+const CACHE_DIR = ph.join(os.tmpdir(), "penpot-fonts-preview-cache");
+const CONCURRENCY = 24;
+// Written straight to the served dir (like the SVG sprite), and excluded from
+// copyAssets' `rsync --delete` so it survives builds — see the doc / _helpers.js.
+export const OUTPUT = "resources/public/fonts/fonts-preview-sprite.svg";
+
+// Color fonts (COLR/SVG glyph tables) make opentype.js take a browser-only
+// DOMParser path that rejects a promise and crashes Node. We only need vector
+// outlines, so swallow those rejections and the COLR warning during generation
+// (restored afterwards so other build steps are unaffected).
+function installFontParsingGuards() {
+  const onRejection = () => {};
+  process.on("unhandledRejection", onRejection);
+
+  const origWarn = console.warn;
+  console.warn = (msg, ...rest) => {
+    if (typeof msg === "string" && msg.includes("COLR")) return;
+    origWarn(msg, ...rest);
+  };
+
+  return () => {
+    process.off("unhandledRejection", onRejection);
+    console.warn = origWarn;
+  };
+}
+
+// Mirror of cuerdas.core/slug as used by the `parse-gfont` macro in
+// src/app/main/fonts.clj so that ids match `(str "gfont-" (str/slug family))`.
+function slug(value) {
+  return value
+    .normalize("NFKD")
+    .replace(/[̀-ͯ]/g, "")
+    .toLowerCase()
+    .replace(/[^a-z0-9]+/g, "-")
+    .replace(/^-+|-+$/g, "");
+}
+
+async function findGfontsJson() {
+  const dir = "resources/fonts";
+  const entries = await fs.readdir(dir);
+  const matches = entries.filter((f) => /^gfonts\..*\.json$/.test(f)).sort();
+  if (matches.length === 0) {
+    throw new Error(`no gfonts.*.json found in ${dir}`);
+  }
+  return ph.join(dir, matches[matches.length - 1]);
+}
+
+async function readCatalog() {
+  const builtin = [
+    {
+      id: "sourcesanspro",
+      name: "Source Sans Pro",
+      source: {
+        type: "file",
+        path: "resources/fonts/sourcesanspro-regular.ttf",
+      },
+    },
+  ];
+
+  const gfontsPath = await findGfontsJson();
+  const raw = JSON.parse(await fs.readFile(gfontsPath, "utf-8"));
+  const google = (raw.items || []).map((item) => {
+    const family = item.family;
+    // Prefer the "menu" subset: a tiny TTF Google ships containing exactly the
+    // glyphs needed to render the family name in a font picker.
+    const url =
+      item.menu ||
+      (item.files && (item.files.regular || Object.values(item.files)[0]));
+    return {
+      id: `gfont-${slug(family)}`,
+      name: family,
+      source: { type: "url", url },
+    };
+  });
+
+  return [...builtin, ...google];
+}
+
+async function fetchWithCache(url) {
+  const key = createHash("sha1").update(url).digest("hex") + ".ttf";
+  const cached = ph.join(CACHE_DIR, key);
+  try {
+    return await fs.readFile(cached);
+  } catch {
+    // not cached yet
+  }
+
+  let lastErr;
+  for (let attempt = 0; attempt < 3; attempt++) {
+    try {
+      const res = await fetch(url);
+      if (!res.ok) throw new Error(`HTTP ${res.status}`);
+      const buf = Buffer.from(await res.arrayBuffer());
+      await fs.writeFile(cached, buf);
+      return buf;
+    } catch (err) {
+      lastErr = err;
+    }
+  }
+  throw lastErr;
+}
+
+async function loadFontBuffer(source) {
+  if (source.type === "file") return fs.readFile(source.path);
+  if (!source.url) throw new Error("missing font url");
+  return fetchWithCache(source.url);
+}
+
+// Lay the name out glyph-by-glyph with sanitized advances, NOT via
+// `font.getPath`: some menu subsets have a broken kern/NaN advance that emits
+// `NaN` into the path, which makes browsers stop parsing mid-path (only the
+// first glyph renders). Baseline at y=0; buildSymbol re-centers afterwards.
+// `hasTofu` flags glyphs the subset lacks (.notdef → "tofu" boxes), dropping the
+// font to the runtime fallback.
+function renderName(font, text) {
+  const scale = FONT_SIZE / font.unitsPerEm;
+  const path = new opentype.Path();
+  let x = 0;
+  let hasTofu = false;
+  for (const ch of text) {
+    const glyph = font.charToGlyph(ch);
+    if (glyph.index === 0 && ch.trim() !== "") hasTofu = true;
+    path.extend(glyph.getPath(x, 0, FONT_SIZE));
+    const advance = glyph.advanceWidth;
+    x += (Number.isFinite(advance) ? advance : font.unitsPerEm * 0.5) * scale;
+  }
+  return { path, hasTofu };
+}
+
+// Round to PATH_PRECISION decimals (normalizing -0). Done BEFORE deltas are
+// taken (serializePath) so the relative encoding never drifts.
+function roundGrid(value) {
+  return Number(value.toFixed(PATH_PRECISION)) + 0;
+}
+
+// Format an (already-rounded) number compactly: drop the integer "0" from
+// "0.x"/"-0.x" to save bytes (".x"/"-.x" are valid SVG numbers).
+function fmt(n) {
+  let s = n.toString();
+  if (s.startsWith("0.")) s = s.slice(1);
+  else if (s.startsWith("-0.")) s = "-" + s.slice(2);
+  return s;
+}
+
+// Serialize paths ourselves (opentype's `toPathData` separates numbers with
+// spaces only — ambiguous enough that browsers bail mid-path). Format: comma
+// WITHIN a pair, space BETWEEN pairs. Commands are RELATIVE (lowercase m/l/q/c)
+// for much smaller, better-compressing output (~6.2MB → ~2.3MB gzip), with no
+// geometry change. Curve control points are relative to the pen before the
+// command, and `z` returns the pen to the subpath start — both tracked below.
+// Coordinates are baked through the affine fit (scale `s`, translate tx/ty).
+function serializePath(commands, s, tx, ty) {
+  const ax = (v) => roundGrid(v * s + tx);
+  const ay = (v) => roundGrid(v * s + ty);
+  let out = "";
+  // px/py: current pen (rounded, absolute). sx/sy: start of the current subpath,
+  // which the pen snaps back to on `z`.
+  let px = 0,
+    py = 0,
+    sx = 0,
+    sy = 0;
+  // Re-round the delta: subtracting two grid values reintroduces float noise
+  // (13.5 - 10.9 === 2.6000000000000014). Drift-free, since the pen tracks the
+  // exact rounded absolute (x/y), not the emitted delta.
+  const d = (to, from) => fmt(roundGrid(to - from));
+  for (const c of commands) {
+    switch (c.type) {
+      case "M": {
+        const x = ax(c.x),
+          y = ay(c.y);
+        out += `m${d(x, px)},${d(y, py)}`;
+        px = sx = x;
+        py = sy = y;
+        break;
+      }
+      case "L": {
+        const x = ax(c.x),
+          y = ay(c.y);
+        out += `l${d(x, px)},${d(y, py)}`;
+        px = x;
+        py = y;
+        break;
+      }
+      case "Q": {
+        const x1 = ax(c.x1),
+          y1 = ay(c.y1),
+          x = ax(c.x),
+          y = ay(c.y);
+        out += `q${d(x1, px)},${d(y1, py)} ${d(x, px)},${d(y, py)}`;
+        px = x;
+        py = y;
+        break;
+      }
+      case "C": {
+        const x1 = ax(c.x1),
+          y1 = ay(c.y1),
+          x2 = ax(c.x2),
+          y2 = ay(c.y2),
+          x = ax(c.x),
+          y = ay(c.y);
+        out +=
+          `c${d(x1, px)},${d(y1, py)} ` +
+          `${d(x2, px)},${d(y2, py)} ${d(x, px)},${d(y, py)}`;
+        px = x;
+        py = y;
+        break;
+      }
+      case "Z":
+        out += "z";
+        px = sx;
+        py = sy;
+        break;
+    }
+  }
+  return out;
+}
+
+function buildSymbol({ id, name }, buffer) {
+  const ab = buffer.buffer.slice(
+    buffer.byteOffset,
+    buffer.byteOffset + buffer.byteLength,
+  );
+  const font = opentype.parse(ab);
+  // Drop the SVG color-glyph table to force outline rendering (see above).
+  font.tables.svg = undefined;
+
+  const { path, hasTofu } = renderName(font, name);
+  // Drop fonts whose name needs glyphs the subset lacks — they would render as
+  // .notdef boxes; the runtime fallback loads the real font instead.
+  if (hasTofu) throw new Error("missing glyphs (tofu)");
+
+  const bb = path.getBoundingBox();
+  if (!Number.isFinite(bb.x1) || bb.x2 <= bb.x1) throw new Error("empty path");
+
+  // Fit into BOX_HEIGHT, centered by bounding box so tall ascenders/descenders
+  // aren't clipped; names taller than the box are scaled down. Left-aligned at 0.
+  const usable = BOX_HEIGHT - 2 * VPAD;
+  const height = bb.y2 - bb.y1;
+  const s = height > usable ? usable / height : 1;
+  const tx = -bb.x1 * s;
+  const ty = BOX_HEIGHT / 2 - ((bb.y1 + bb.y2) / 2) * s;
+
+  const d = serializePath(path.commands, s, tx, ty);
+  if (!d || d.length === 0) throw new Error("empty path");
+  // A stray NaN (non-finite outline point) would truncate the glyph in the
+  // browser; drop the font so it cleanly falls back to the runtime loader.
+  if (d.includes("NaN")) throw new Error("non-finite path");
+  // No `fill`: the UI's <use> provides `currentColor` so it follows the theme.
+  return `<g id="font-preview-${id}"><path d="${d}"/></g>`;
+}
+
+async function mapLimit(items, limit, fn) {
+  const results = new Array(items.length);
+  let cursor = 0;
+  async function worker() {
+    while (cursor < items.length) {
+      const index = cursor++;
+      results[index] = await fn(items[index], index);
+    }
+  }
+  await Promise.all(
+    Array.from({ length: Math.min(limit, items.length) }, worker),
+  );
+  return results;
+}
+
+// True when the sprite exists and is at least as new as the gfonts catalog, so
+// the build can skip the expensive, network-bound regeneration.
+export async function isSpriteUpToDate(outputPath = OUTPUT) {
+  try {
+    const gfontsPath = await findGfontsJson();
+    const [outStat, gfontsStat] = await Promise.all([
+      fs.stat(outputPath),
+      fs.stat(gfontsPath),
+    ]);
+    return outStat.mtimeMs >= gfontsStat.mtimeMs;
+  } catch {
+    // output missing (or no catalog) → not up to date
+    return false;
+  }
+}
+
+// Regenerate the sprite into `outputPath`. Skips (returns `{ skipped: true }`)
+// when the output is already up to date, unless `force` is set. On a real
+// rebuild it returns `{ skipped:false, ok, failed, bytes }`.
+export async function buildFontsPreviewSprite({
+  outputPath = OUTPUT,
+  force = false,
+} = {}) {
+  if (!force && (await isSpriteUpToDate(outputPath))) {
+    return { skipped: true };
+  }
+
+  const restoreGuards = installFontParsingGuards();
+  try {
+    await fs.mkdir(CACHE_DIR, { recursive: true });
+
+    const catalog = await readCatalog();
+    console.log(`building font preview sprite for ${catalog.length} fonts…`);
+
+    let ok = 0;
+    const failed = [];
+    const symbols = await mapLimit(catalog, CONCURRENCY, async (font) => {
+      try {
+        const buffer = await loadFontBuffer(font.source);
+        const symbol = buildSymbol(font, buffer);
+        ok++;
+        if (ok % 200 === 0) console.log(`  …${ok}/${catalog.length}`);
+        return symbol;
+      } catch (err) {
+        failed.push({ id: font.id, reason: err.message });
+        return null;
+      }
+    });
+
+    const body = symbols.filter(Boolean).join("");
+    const sprite =
+      `<svg xmlns="http://www.w3.org/2000/svg" style="display:none" aria-hidden="true">` +
+      body +
+      `</svg>\n`;
+
+    await fs.mkdir(ph.dirname(outputPath), { recursive: true });
+    await fs.writeFile(outputPath, sprite);
+
+    if (failed.length) {
+      console.log(
+        `font preview sprite: ${failed.length} fonts will use the runtime fallback:`,
+      );
+      for (const f of failed.slice(0, 40))
+        console.log(`  - ${f.id}: ${f.reason}`);
+      if (failed.length > 40) console.log(`  …and ${failed.length - 40} more`);
+    }
+
+    return { skipped: false, ok, failed: failed.length, bytes: sprite.length };
+  } finally {
+    restoreGuards();
+  }
+}
+
+// When invoked directly (`node scripts/build-fonts-preview.js`), force a full
+// rebuild regardless of the up-to-date check.
+const isDirectRun =
+  process.argv[1] &&
+  import.meta.url === url.pathToFileURL(process.argv[1]).href;
+
+if (isDirectRun) {
+  const res = await buildFontsPreviewSprite({ force: true });
+  const mb = (res.bytes / 1024 / 1024).toFixed(1);
+  console.log(
+    `done: ${res.ok} ok, ${res.failed} failed → ${OUTPUT} (${mb} MB, served gzipped)`,
+  );
+}

frontend/scripts/watch.js

@@ -63,6 +63,7 @@ async function compileSass(path) {
 await h.ensureDirectories();
 await compileSassAll();
 await h.copyAssets();
+await h.compileFontsPreviewSprite();
 await h.copyWasmPlayground();
 await h.compileTranslations();
 await h.compileSvgSprites();

frontend/src/app/config.cljs

@@ -196,6 +196,11 @@
       (get :path)
       (str "?version=" version-tag)))
 
+(def fonts-preview-sprite-uri
+  (-> public-uri
+      (u/join "fonts/fonts-preview-sprite.svg")
+      (str)))
+
 (defn external-feature-flag
   [flag value]
   (let [f (obj/get global "externalFeatureFlag")]

frontend/src/app/main/fonts.cljs

@@ -108,6 +108,108 @@
 ;; only know if the font is needed or not
 (defonce ^:dynamic loaded-hints (l/atom #{}))
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; PREVIEW SPRITE
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; A prebuilt SVG sprite (generated by scripts/build-fonts-preview.js) holds every
+;; built-in + Google font name outlined in its own typeface, so the picker can
+;; preview the whole catalog with no per-font requests. Fonts not in it (custom
+;; uploads, ones that fail to bake) use the runtime fallback.
+;;
+;; The sprite is heavy (~2000 nodes), so we DON'T keep it in the DOM: the fetched
+;; markup is cached here as a string (`:svg`) and the nodes are materialized only
+;; while the picker is open (attach/detach below). `:ids` are the font ids it
+;; covers, so the UI can pick sprite vs fallback.
+(defonce preview-sprite (l/atom {:status :idle :ids #{} :svg nil}))
+
+;; Id prefix shared with the generator and the UI's `<use href>`; referenced here
+;; rather than re-declared so the contract stays in one place.
+(def preview-sprite-prefix "font-preview-")
+
+(defn- collect-preview-ids
+  "Set of font ids present in the sprite, read from the injected `container`
+  element's `<g id=\"font-preview-…\">` groups (prefix stripped)."
+  [^js container]
+  (let [nodes (dom/query-all container (dm/str "g[id^=\"" preview-sprite-prefix "\"]"))
+        plen  (count preview-sprite-prefix)]
+    (persistent!
+     (reduce (fn [acc node]
+               (conj! acc (subs (dom/get-attribute node "id") plen)))
+             (transient #{})
+             (array-seq nodes)))))
+
+(defn- reset-preview-sprite-error!
+  []
+  ;; :error → the UI shows plain names (no previews, no per-font load storm); a
+  ;; later `prefetch-preview-sprite!` call can retry.
+  (reset! preview-sprite {:status :error :ids #{} :svg nil}))
+
+(defn- parse-sprite-svg
+  "Parse the cached sprite markup as SVG (not HTML, so no innerHTML injection
+  surface). Returns the root `<svg>` element, or nil if it isn't valid SVG."
+  [text]
+  (let [doc  (.parseFromString (js/DOMParser.) text "image/svg+xml")
+        root (.-documentElement doc)]
+    ;; A malformed document yields a <parsererror> root instead of <svg>.
+    (when (and (= "svg" (.-tagName ^js root))
+               (nil? (dom/query doc "parsererror")))
+      root)))
+
+(defn prefetch-preview-sprite!
+  "Fetch the font-preview sprite markup and cache it in memory (no DOM yet — see
+  `attach-preview-sprite!`). Idempotent: fetches only when nothing is cached yet
+  (`:idle`) or a previous attempt failed (`:error`); no-op while `:loading` or
+  `:ready`."
+  []
+  (when (and (globals/browser?)
+             (contains? #{:idle :error} (:status @preview-sprite)))
+    (swap! preview-sprite assoc :status :loading)
+    (->> (http/send! {:method :get
+                      :uri cf/fonts-preview-sprite-uri
+                      :response-type :text
+                      :mode :cors})
+         (rx/subs!
+          (fn [response]
+            ;; http/send! doesn't reject on non-2xx; guard so an error body isn't
+            ;; cached as the sprite.
+            (if (http/success? response)
+              (swap! preview-sprite assoc :status :ready :svg (:body response))
+              (do
+                (log/wrn :hint "cannot load font preview sprite" :status (:status response))
+                (reset-preview-sprite-error!))))
+          (fn [cause]
+            (log/wrn :hint "cannot load font preview sprite" :cause cause)
+            (reset-preview-sprite-error!))))))
+
+(defn attach-preview-sprite!
+  "Materialize the cached sprite into the DOM (hidden) so rows can reference its
+  glyph groups via `<use>`, and record the covered font ids. Returns the injected
+  node (pass it to `detach-preview-sprite!` on close), or nil if not ready / the
+  markup is invalid. Parsing happens here, not on prefetch, so the cost is paid
+  only while the picker is open."
+  []
+  (let [{:keys [status svg]} @preview-sprite]
+    (when (and (globals/browser?) (= :ready status) (some? svg))
+      (if-let [node (some-> (parse-sprite-svg svg) (dom/import-node))]
+        ;; The node already carries display:none + aria-hidden from the generator.
+        (do
+          (dom/set-attribute! node "id" "font-preview-sprite")
+          (when-let [body-el (unchecked-get globals/document "body")]
+            (dom/append-child! body-el node))
+          (swap! preview-sprite assoc :ids (collect-preview-ids node))
+          node)
+        (do
+          (log/wrn :hint "cannot parse font preview sprite")
+          (reset-preview-sprite-error!)
+          nil)))))
+
+(defn detach-preview-sprite!
+  "Remove the sprite node injected by `attach-preview-sprite!` from the DOM. The
+  cached markup and `:ids` stay, so reopening re-attaches without a refetch."
+  [node]
+  (dom/remove! node))
+
 (defn- add-font-css!
   "Creates a style element and attaches it to the dom."
   [id css]
@@ -158,7 +260,7 @@
 
 (defmethod load-font :google
   [{:keys [id ::on-loaded] :as font}]
-  (when (exists? js/window)
+  (when (globals/browser?)
     (log/dbg :hint "load-font" :font-id id :backend "google")
     (let [url (generate-gfonts-url font)]
       (->> (fetch-gfont-css url)
@@ -200,7 +302,7 @@
 
 (defmethod load-font :custom
   [{:keys [id ::on-loaded] :as font}]
-  (when (exists? js/window)
+  (when (globals/browser?)
     (log/dbg :hint "load-font" :font-id id :backend "custom")
     (let [css (generate-custom-font-css font)]
       (add-font-css! id css)
@@ -215,7 +317,7 @@
   ([font-id] (ensure-loaded! font-id nil))
   ([font-id variant-id]
    (log/dbg :action "try-ensure-loaded!" :font-id font-id :variant-id variant-id)
-   (if-not (exists? js/window)
+   (if-not (globals/browser?)
      ;; If we are in the worker environment, we just mark it as loaded
      ;; without really loading it.
      (do

frontend/src/app/main/ui/workspace.cljs

@@ -8,12 +8,14 @@
   (:require-macros [app.main.style :as stl])
   (:require
    [app.common.data.macros :as dm]
+   [app.config :as cf]
    [app.main.data.common :as dcm]
    [app.main.data.helpers :as dsh]
    [app.main.data.persistence :as dps]
    [app.main.data.plugins :as dpl]
    [app.main.data.workspace :as dw]
    [app.main.features :as features]
+   [app.main.fonts :as fonts]
    [app.main.refs :as refs]
    [app.main.router :as-alias rt]
    [app.main.store :as st]
@@ -230,6 +232,13 @@
       (st/emit! (dps/initialize-persistence)
                 (dpl/update-plugins-permissions-peek)))
 
+    ;; FLAG :font-preview — prefetch the preview sprite markup on workspace mount
+    ;; (kept in memory, not the DOM) so the typography selector renders previews on
+    ;; open with no network wait. Remove the flag check to drop the feature.
+    (mf/with-effect []
+      (when (contains? cf/flags :font-preview)
+        (fonts/prefetch-preview-sprite!)))
+
     ;; Setting the layout preset by its name
     (mf/with-effect [layout-name]
       (st/emit! (dw/initialize-workspace-layout layout-name)))

frontend/src/app/main/ui/workspace/sidebar/options/menus/typography.cljs

@@ -12,6 +12,7 @@
    [app.common.data.macros :as dm]
    [app.common.exceptions :as ex]
    [app.common.types.text :as txt]
+   [app.config :as cf]
    [app.main.constants :refer [max-input-length]]
    [app.main.data.common :as dcm]
    [app.main.data.fonts :as fts]
@@ -39,6 +40,7 @@
    [app.util.timers :as tm]
    [cuerdas.core :as str]
    [goog.events :as events]
+   [promesa.core :as p]
    [rumext.v2 :as mf]))
 
 (defn- attr->string [value]
@@ -63,11 +65,73 @@
       (or next (peek fonts)))
     current))
 
+(defn- use-font-lazy-load
+  "Lazily loads `font-id` for the fallback preview when `fallback?`, on idle so
+  fast scrolling over recycled virtualized rows doesn't storm requests (cancelled
+  if the row is reused first). Returns whether the font face is loaded yet."
+  [font-id fallback?]
+  (let [loaded? (mf/use-state #(and fallback? (contains? @fonts/loaded font-id)))]
+    (mf/use-effect
+     (mf/deps font-id fallback?)
+     (fn []
+       (let [already? (and fallback? (contains? @fonts/loaded font-id))]
+         (reset! loaded? already?)
+         (if (and fallback? (not already?))
+           (let [cancelled? (volatile! false)
+                 task (tm/schedule-on-idle
+                       (fn []
+                         (-> (fonts/ensure-loaded! font-id)
+                             (p/then (fn [_]
+                                       (when-not @cancelled?
+                                         (reset! loaded? true))))
+                             (p/catch (fn [_] nil)))))]
+             (fn []
+               (vreset! cancelled? true)
+               (tm/dispose! task)))
+           (constantly nil)))))
+    @loaded?))
+
+;; --- FEATURE: font preview (flag :font-preview) ------------------------------
+;; font-item-preview* and use-font-lazy-load are the whole feature. They are only
+;; rendered/called behind the `:font-preview` flag check in font-item* below, so
+;; their hooks never run when the flag is off. To remove the flag, inline
+;; font-item-preview* into font-item* and drop the plain-name branch.
+
+(mf/defc font-item-preview*
+  "Row content with previews: a vector preview from the shared sprite for catalog
+  fonts, or the font's own name lazily loaded for custom fonts the sprite doesn't
+  cover."
+  {::mf/wrap [mf/memo]}
+  [{:keys [font]}]
+  (let [font-id    (:id font)
+        sprite     (mf/deref fonts/preview-sprite)
+        in-sprite? (contains? (:ids sprite) font-id)
+
+        ;; Fallback is ONLY for custom fonts: ones the (ready) sprite doesn't
+        ;; cover. If the sprite isn't ready (loading/error) we show the plain name
+        ;; rather than runtime-loading the whole catalog.
+        fallback?  (and (= :ready (:status sprite))
+                        (not in-sprite?))
+        loaded?    (use-font-lazy-load font-id fallback?)]
+    (if in-sprite?
+      ;; `fill: currentColor` (scss) makes the sprite glyph follow the row color.
+      [:svg {:class (stl/css :font-item-preview)
+             :role "img"
+             :aria-label (:name font)}
+       [:use {:href (dm/str "#" fonts/preview-sprite-prefix font-id)}]]
+      [:span {:class (stl/css :font-item-label)
+              :style (when loaded?
+                       #js {:fontFamily (dm/str "\"" (:family font) "\", sans-serif")})}
+       (:name font)])))
+
 (mf/defc font-item*
   {::mf/wrap [mf/memo]}
   [{:keys [font is-current on-click style]}]
   (let [item-ref (mf/use-ref)
-        on-click (mf/use-fn (mf/deps font) #(on-click font))]
+        on-click (mf/use-fn (mf/deps font) #(on-click font))
+        ;; FLAG :font-preview — gates the feature markup AND its row styling
+        ;; (.font-item-preview-on in the scss). Remove this and its two uses below.
+        preview? (contains? cf/flags :font-preview)]
 
     (mf/use-effect
      (mf/deps is-current)
@@ -82,8 +146,11 @@
            :ref item-ref
            :on-click on-click}
      [:div {:class  (stl/css-case :font-item true
+                                  :font-item-preview-on preview?
                                   :selected is-current)}
-      [:span {:class (stl/css :font-item-label)} (:name font)]
+      (if preview?
+        [:> font-item-preview* {:font font}]
+        [:span {:class (stl/css :font-item-label)} (:name font)])
       (when is-current
         [:> icon* {:icon-id i/tick
                    :size "s"}])]]))
@@ -115,6 +182,8 @@
         fonts        (mf/with-memo [state fonts]
                        (filter-fonts state fonts))
 
+        sprite-status (:status (mf/deref fonts/preview-sprite))
+
         recent-fonts (mf/deref refs/recent-fonts)
         recent-fonts (mf/with-memo [state recent-fonts]
                        (filter-fonts state recent-fonts))
@@ -165,6 +234,16 @@
       (let [key (events/listen js/document "keydown" on-key-down)]
         #(events/unlistenByKey key)))
 
+    ;; FLAG :font-preview — materialize the preview sprite into the DOM only while
+    ;; the picker is open (markup is prefetched on workspace load), removing it on
+    ;; close so its ~2000 nodes aren't kept around idle. Remove the flag clause to
+    ;; drop the feature.
+    (mf/with-effect [sprite-status]
+      (when (and (contains? cf/flags :font-preview)
+                 (= :ready sprite-status))
+        (let [node (fonts/attach-preview-sprite!)]
+          #(fonts/detach-preview-sprite! node))))
+
     (mf/with-effect [@selected]
       (when-let [inst (mf/ref-val flist)]
         (when-let [index (:index @selected)]

frontend/src/app/main/ui/workspace/sidebar/options/menus/typography.scss

@@ -11,6 +11,10 @@
 @use "ds/mixins.scss" as *;
 @use "ds/_utils.scss" as *;
 
+// Must match BOX_HEIGHT in scripts/build-fonts-preview.js (the sprite bakes each
+// font name into that box at 1 unit == 1px).
+$font-preview-box-height: 28px;
+
 .typography-entry {
   --actions-visibility: hidden;
   --typography-entry-background-color: var(--color-background-tertiary);
@@ -392,6 +396,31 @@
   min-inline-size: 0;
 }
 
+// --- FLAG :font-preview row styling. Only applied when font-item* adds the
+// .font-item-preview-on modifier; remove this whole block with the flag so rows
+// render exactly as before.
+.font-item-preview-on {
+  // Center & clip so a previewed font's own metrics never grow/overflow the row.
+  align-items: center;
+  overflow: hidden;
+
+  // Match the label size to the vector previews.
+  .font-item-label {
+    @include t.use-typography("body-medium");
+
+    line-height: 1.2;
+  }
+}
+
+// `currentColor` makes the glyph fill follow the row text color (theme + selected).
+.font-item-preview {
+  flex-grow: 1;
+  min-inline-size: 0;
+  inline-size: 100%;
+  block-size: $font-preview-box-height;
+  fill: currentcolor;
+}
+
 .font-selector-dropdown-full-size {
   block-size: var(--sidebar-element-options-height);
   display: grid;

frontend/src/app/util/dom.cljs

@@ -361,6 +361,13 @@
     (.appendChild ^js el child))
   el)
 
+(defn import-node
+  "Import `node` (e.g. parsed in another document) into the current document so
+  it can be inserted. Deep clone unless `deep?` is false."
+  ([^js node] (import-node node true))
+  ([^js node deep?]
+   (.importNode globals/document node deep?)))
+
 (defn insert-after!
   [^js el ^js ref child]
   (when (and (some? el) (some? ref))

frontend/src/app/util/globals.js

@@ -22,6 +22,13 @@ goog.scope(function () {
 
   self.global = globalThis;
 
+  // Whether we are running in a real browser (has a window), as opposed to a
+  // worker or the test environment, where the objects below are mocked.
+  // Exposed to ClojureScript as `globals/browser?`.
+  self.browser_QMARK_ = function () {
+    return typeof goog.global.window !== "undefined";
+  };
+
   function createMockedEventEmitter(k) {
     /* Allow mocked objects to be event emitters, so other modules
      * may subscribe to them.