Fix #579: fonts activated by font services such as Adobe Fonts are listed on Windows

Font services load their fonts with GDI at run time, from files in their
own folders, without installing them: neither the font folders nor the
registry list them, so the font scan never saw them. DirectWrite's system
font collection holds them since Windows 10 1607.

- vectorcraft-text: `set_platform_font_files` lets the app name font files
  the platform knows; each scan and each check for installed fonts asks
  again and reads those outside the font folders. A file named by itself
  is read whatever its extension (font services keep fonts in files
  without one).
- The desktop app lists the local files of DirectWrite's system font
  collection on Windows (`system_fonts.rs`, through the windows crate
  already in the build), read in place.
- The check for fonts installed while the app was in the background runs
  on a thread: DirectWrite's check for updates takes about 50 ms.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Cargo.lock

@@ -4312,8 +4312,10 @@ dependencies = [
  "rfd",
  "serde_json",
  "vectorcraft-engine",
+ "vectorcraft-text",
  "vectorcraft-ui-egui",
  "webbrowser",
+ "windows",
  "winit",
  "winresource",
 ]

ROADMAP.md

@@ -4,7 +4,7 @@ VectorCraft is a clean-room, open-source, pure-Rust reimplementation of the Adob
 
 This file tracks **how far we are and what's left**. Time estimates are wall-clock hours of continuous Claude Opus 5.5 agent work (including builds and the CI gate), given both for **one agent** and for **4–6 parallel agents** on disjoint crates. They are counted from the remaining work (see [Parity estimate](#parity-estimate)), calibrated against measured throughput, and updated as work lands.
 
-_Last updated: 2026-10-09 (after placed documents (File › Place of a `.vectorcraft` file, linked), M4.14–M4.98, M8.1–M8.20, M14.4–M14.7, the MCP prompts, resource templates, completions and logging, the 2026-10-07 issue fixes, the Layers panel rework and the 2026-10-08 community contributions: Pen and shape-tool modifiers, path editing, Layers, Artboards, Swatches/Brushes and dialogs, Japanese composition and PDF text, Hebrew/Arabic type, interface languages (Spanish among them), the font menu, saved selections, MCP and EPS, the missing-font export warning (#319), open paths in the Shape Builder (#374), PDF/`.ai` import keeping strokes live and hidden and nested layers (#372), per-corner Live Corners (#381), SVG type opening at the size it draws at (#396), the Wayland clipboard with copied-file paste (#398), ruler guides that can be selected, moved and deleted (#414), two batches of Preferences options that were stored but unused (#394), skeleton reads with `document.find` for large documents over MCP (#416) and anchors dragged with Direct Selection snapping to points, segments and smart guides, clipped SVG layers opening as clipping layers (#420), PDF/`.ai` layers read on pages of tens of millions of operators (#419), Document Color Mode putting RGB greys on the black plate on request and converting pattern tiles (#421) and movable dialogs with Offset Path's Joins dropdown (#423) and numeric fields scrubbed by dragging their label (#400), stroke weight presets in the stroke unit (#426), the Appearance panel's Opacity popup (#430), type on a path brackets, flip and Type on a Path Options that keep the type in place (#429), Layers rows dragged with a ghost and dropped on the trash or New Layer (#435), tool flyouts opening on a right or corner press (#436), tool flyouts torn off into floating toolbars (#437), the Shape Builder's erase mode deleting edges too (#439), installed fonts registered outside the font folders and fonts installed while the app runs listed in the font menus (#443), alike circular corners on rectangles that aren't square (#442), tool cursors as OS cursors so the pointer no longer trails over the canvas (#444), artboards copied and pasted with their art (#446), guides dragged out of the rulers snapping to the art's side midpoints and the artboards, artboard guides (#451), the toolbar's double arrow and Window › Toolbars › Double Column switching between one and two columns in any window height (#455), the Smart Guides display options and Snapping Tolerance (#394), Font Size and Leading combo boxes with preset lists in the Character and Properties panels and the Control bar (#458), screenshots pasted from the clipboard on macOS, Windows and the web (#457), the Properties panel's Fill and Stroke matching the Control bar's, Illustrator's Window menu panel keys (Shift+F7 for Align…) and Alt-wheel zoom whatever the wheel preference (Discord feedback), the point/area type widget (Discord feedback), groups in legacy Illustrator .ai files (Discord feedback), a rotating desktop log file (#465), image controls in the Control bar and Properties panel: Image Trace with its presets, Mask, Crop Image, Embed/Unembed, and an Image Trace object's preset, Expand and Release (Discord feedback), the Pen working as the Anchor Point tool with Alt held over a selected path's handles and anchors, and anchor buttons that convert, connect and cut paths at the selected anchors (Discord feedback), Japanese hanging punctuation (burasagari, #463), Escape leaving Presentation Mode with no screen mode saved across restarts, documents dropped on the desktop app opening as tabs of their own and a note that an `.ai` file's art off its artboards isn't in the part read (#472), Add/Delete Anchor Point tool icons drawn from the Pen tool's (#479), EPS import running more of PostScript Level 3 (patterns, Type 3 fonts, mesh shadings, masked images, VM and resource probes), and a preview that stands in saying why (Discord feedback, #466, #469, #474), chords with modifiers recorded in Edit › Keyboard Shortcuts (#487), Type Object Selection by Path Only (#394), Anti-aliased Artwork (#394), Show Pixel Grid (#394), pen and touch taps pressed and lifted within one frame clicking where they tapped and the Linux/Wayland pen-tablet workaround (#491), bounding-box resizes landing on the other objects' anchors and centres with labels, and the Rotate, Scale, Shear and Reflect tools snapping their drags (#482), Shift-drag marquees that toggle the objects or anchors they reach and a Lasso whose Alt subtraction keeps the rest of the selection (#483), the mouse wheel stepping the focused numeric field, the dialogs' and preferences' drag values made such fields (#485), Show The Home Screen When No Documents Are Open (#394), Numbers Without Units Are Points (#394), Auto-Collapse Iconic Panels (#394), the Contextual Task Bar moved by its handle and its More Options menu pinning and resetting its position, a designed macOS DMG windoLine truncated
+_Last updated: 2026-10-09 (after placed documents (File › Place of a `.vectorcraft` file, linked), M4.14–M4.98, M8.1–M8.20, M14.4–M14.7, the MCP prompts, resource templates, completions and logging, the 2026-10-07 issue fixes, the Layers panel rework and the 2026-10-08 community contributions: Pen and shape-tool modifiers, path editing, Layers, Artboards, Swatches/Brushes and dialogs, Japanese composition and PDF text, Hebrew/Arabic type, interface languages (Spanish among them), the font menu, saved selections, MCP and EPS, the missing-font export warning (#319), open paths in the Shape Builder (#374), PDF/`.ai` import keeping strokes live and hidden and nested layers (#372), per-corner Live Corners (#381), SVG type opening at the size it draws at (#396), the Wayland clipboard with copied-file paste (#398), ruler guides that can be selected, moved and deleted (#414), two batches of Preferences options that were stored but unused (#394), skeleton reads with `document.find` for large documents over MCP (#416) and anchors dragged with Direct Selection snapping to points, segments and smart guides, clipped SVG layers opening as clipping layers (#420), PDF/`.ai` layers read on pages of tens of millions of operators (#419), Document Color Mode putting RGB greys on the black plate on request and converting pattern tiles (#421) and movable dialogs with Offset Path's Joins dropdown (#423) and numeric fields scrubbed by dragging their label (#400), stroke weight presets in the stroke unit (#426), the Appearance panel's Opacity popup (#430), type on a path brackets, flip and Type on a Path Options that keep the type in place (#429), Layers rows dragged with a ghost and dropped on the trash or New Layer (#435), tool flyouts opening on a right or corner press (#436), tool flyouts torn off into floating toolbars (#437), the Shape Builder's erase mode deleting edges too (#439), installed fonts registered outside the font folders and fonts installed while the app runs listed in the font menus (#443), alike circular corners on rectangles that aren't square (#442), tool cursors as OS cursors so the pointer no longer trails over the canvas (#444), artboards copied and pasted with their art (#446), guides dragged out of the rulers snapping to the art's side midpoints and the artboards, artboard guides (#451), the toolbar's double arrow and Window › Toolbars › Double Column switching between one and two columns in any window height (#455), the Smart Guides display options and Snapping Tolerance (#394), Font Size and Leading combo boxes with preset lists in the Character and Properties panels and the Control bar (#458), screenshots pasted from the clipboard on macOS, Windows and the web (#457), the Properties panel's Fill and Stroke matching the Control bar's, Illustrator's Window menu panel keys (Shift+F7 for Align…) and Alt-wheel zoom whatever the wheel preference (Discord feedback), the point/area type widget (Discord feedback), groups in legacy Illustrator .ai files (Discord feedback), a rotating desktop log file (#465), image controls in the Control bar and Properties panel: Image Trace with its presets, Mask, Crop Image, Embed/Unembed, and an Image Trace object's preset, Expand and Release (Discord feedback), the Pen working as the Anchor Point tool with Alt held over a selected path's handles and anchors, and anchor buttons that convert, connect and cut paths at the selected anchors (Discord feedback), Japanese hanging punctuation (burasagari, #463), Escape leaving Presentation Mode with no screen mode saved across restarts, documents dropped on the desktop app opening as tabs of their own and a note that an `.ai` file's art off its artboards isn't in the part read (#472), Add/Delete Anchor Point tool icons drawn from the Pen tool's (#479), EPS import running more of PostScript Level 3 (patterns, Type 3 fonts, mesh shadings, masked images, VM and resource probes), and a preview that stands in saying why (Discord feedback, #466, #469, #474), chords with modifiers recorded in Edit › Keyboard Shortcuts (#487), Type Object Selection by Path Only (#394), Anti-aliased Artwork (#394), Show Pixel Grid (#394), pen and touch taps pressed and lifted within one frame clicking where they tapped and the Linux/Wayland pen-tablet workaround (#491), bounding-box resizes landing on the other objects' anchors and centres with labels, and the Rotate, Scale, Shear and Reflect tools snapping their drags (#482), Shift-drag marquees that toggle the objects or anchors they reach and a Lasso whose Alt subtraction keeps the rest of the selection (#483), the mouse wheel stepping the focused numeric field, the dialogs' and preferences' drag values made such fields (#485), Show The Home Screen When No Documents Are Open (#394), Numbers Without Units Are Points (#394), Auto-Collapse Iconic Panels (#394), the Contextual Task Bar moved by its handle and its More Options menu pinning and resetting its position, a designed macOS DMG windoLine truncated
 
 ## Where we are
 

apps/vectorcraft/Cargo.toml

@@ -19,6 +19,7 @@ windows7 = ["eframe/glow"]
 [dependencies]
 vectorcraft-engine = { workspace = true }
 vectorcraft-ui-egui = { workspace = true }
+vectorcraft-text = { workspace = true }
 eframe = { workspace = true, features = ["default_fonts", "wayland", "x11"] }
 egui = { workspace = true }
 serde_json = { workspace = true }
@@ -36,6 +37,11 @@ winit = { version = "0.30", default-features = false }
 [target.'cfg(windows)'.dependencies]
 clipboard-win = { workspace = true }
 
+# DirectWrite's system font collection (src/system_fonts.rs): fonts that font services such as
+# Adobe Fonts load in place (#579). MIT OR Apache-2.0, already in the build through accesskit.
+[target.'cfg(all(windows, not(target_vendor = "win7")))'.dependencies]
+windows = { version = "0.62", features = ["Win32_Graphics_DirectWrite"] }
+
 [target.'cfg(target_os = "macos")'.dependencies]
 # The macOS menu bar (src/mac_menu.rs): Tauri's menu crate, AppKit menus behind a safe API (no GTK
 # with default features off). Pinned exactly: review the diff before bumping.

apps/vectorcraft/src/main.rs

@@ -27,6 +27,8 @@ mod mac_menu;
 #[cfg(target_os = "macos")]
 mod open_documents;
 mod printing;
+#[cfg(all(windows, not(target_vendor = "win7")))]
+mod system_fonts;
 mod window;
 
 use vectorcraft_engine::Session;
@@ -314,6 +316,9 @@ fn main() -> std::process::ExitCode {
     // First, so every start-up warning is recorded (`logging`).
     let logger = logging::install();
     vectorcraft_ui_egui::i18n::detect_system_lang_in_background();
+    // Before the first font scan (the app's start): the fonts font services load (#579).
+    #[cfg(all(windows, not(target_vendor = "win7")))]
+    system_fonts::install();
     let mut control_port: Option<u16> = std::env::var("VECTORCRAFT_CONTROL_PORT").ok().and_then(|p| p.parse().ok());
     let mut files = Vec::new();
     let mut in_window_menus = std::env::var_os("VECTORCRAFT_IN_WINDOW_MENUS").is_some_and(|v| !v.is_empty() && v != "0");

apps/vectorcraft/src/system_fonts.rs

@@ -0,0 +1,91 @@
+//! Windows: the font files in DirectWrite's system font collection, scanned with the font folders
+//! (`vectorcraft_text::set_platform_font_files`).
+//!
+//! Font services such as Adobe Fonts load their fonts with GDI at run time, from files in their
+//! own folders, without installing them: the font folders and the registry don't list them. Since
+//! Windows 10 (version 1607) DirectWrite's system font collection holds them too
+//! (<https://learn.microsoft.com/windows/win32/directwrite/what-s-new-in-directwrite-for-windows-8-consumer-preview>,
+//! "Support for Adobe Typekit and other font-service clients"), so VectorCraft lists them as other
+//! apps do, reading the files in place (#579).
+//!
+//! DirectWrite is COM, which has no safe API, hence the scoped `unsafe_code` allowance.
+#![allow(unsafe_code)]
+
+use std::collections::BTreeSet;
+
+use windows::Win32::Graphics::DirectWrite::{
+    DWRITE_FACTORY_TYPE_SHARED, DWriteCreateFactory, IDWriteFactory3, IDWriteFontSet, IDWriteLocalFontFileLoader,
+};
+use windows::core::Interface;
+
+/// The most fonts read from the collection (a system has a few thousand).
+const MAX_FONTS: u32 = 1 << 16;
+/// The longest file path taken, in UTF-16 units (Windows' own limit).
+const MAX_PATH: u32 = 32_767;
+
+/// Have the font scans read the font files DirectWrite lists.
+pub fn install() {
+    vectorcraft_text::set_platform_font_files(font_files);
+}
+
+/// The local files of the fonts in DirectWrite's system font collection as it is now (fonts
+/// loaded since the last call included). None before Windows 10, or when DirectWrite fails: the
+/// font folders and the registry still list the installed fonts.
+fn font_files() -> Vec<String> {
+    match collection_files() {
+        Ok(files) => files.into_iter().collect(),
+        Err(e) => {
+            log::debug!("DirectWrite's system fonts aren't listed: {e}");
+            Vec::new()
+        }
+    }
+}
+
+fn collection_files() -> windows::core::Result<BTreeSet<String>> {
+    // SAFETY: plain DirectWrite calls on interfaces it returned, each checked for failure; the
+    // collection is asked to check for fonts loaded since the factory last looked.
+    let set = unsafe {
+        let factory: IDWriteFactory3 = DWriteCreateFactory(DWRITE_FACTORY_TYPE_SHARED)?;
+        let mut collection = None;
+        factory.GetSystemFontCollection(false, &mut collection, true)?;
+        let Some(collection) = collection else { return Ok(BTreeSet::new()) };
+        collection.GetFontSet()?
+    };
+    // SAFETY: a count of the set's fonts.
+    let count = unsafe { set.GetFontCount() }.min(MAX_FONTS);
+    // Faces of one file (a collection's, a variable font's instances) name it once.
+    Ok((0..count).filter_map(|i| local_path(&set, i)).collect())
+}
+
+/// The path of the file holding font `i` of `set`, when it is a local file (not a downloadable
+/// font, nor one in memory).
+fn local_path(set: &IDWriteFontSet, i: u32) -> Option<String> {
+    // SAFETY: `i` is below the set's count; the key DirectWrite hands back stays valid while
+    // `file` (which owns it) lives, and is passed back with its own size; the path buffer is
+    // sized from DirectWrite's answer plus the terminating NUL.
+    unsafe {
+        let file = set.GetFontFaceReference(i).ok()?.GetFontFile().ok()?;
+        let loader: IDWriteLocalFontFileLoader = file.GetLoader().ok()?.cast().ok()?;
+        let (mut key, mut size) = (std::ptr::null_mut(), 0u32);
+        file.GetReferenceKey(&mut key, &mut size).ok()?;
+        let len = loader.GetFilePathLengthFromKey(key, size).ok()?;
+        if len == 0 || len > MAX_PATH {
+            return None;
+        }
+        let mut path = vec![0u16; len as usize + 1];
+        loader.GetFilePathFromKey(key, size, &mut path).ok()?;
+        Some(String::from_utf16_lossy(path.get(..len as usize)?))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    /// DirectWrite lists the installed fonts, by their files' full paths.
+    #[test]
+    fn directwrite_lists_the_installed_font_files() {
+        let files = super::font_files();
+        assert!(files.iter().all(|f| std::path::Path::new(f).is_absolute()), "{:?}", files.first());
+        let fonts = std::path::Path::new(&std::env::var("WINDIR").unwrap()).join("Fonts").to_string_lossy().to_lowercase();
+        assert!(files.iter().any(|f| f.to_lowercase().starts_with(&fonts)), "{} files, {:?}", files.len(), files.first());
+    }
+}

crates/text/src/fontdb.rs

@@ -782,8 +782,29 @@ pub(crate) fn sfnt_of(tables: &[(&[u8; 4], &[u8])]) -> Option<Vec<u8>> {
     Some(font)
 }
 
-/// The platform's font folders (the system's and the user's) and, on Windows, the font files
-/// registered with it outside them, scanned by [`FontDb::global`].
+/// Lists the font files the platform's font service knows, for [`set_platform_font_files`].
+pub type PlatformFontFiles = fn() -> Vec<String>;
+
+/// What lists the platform's font files, set by the app ([`set_platform_font_files`]).
+#[cfg(not(target_arch = "wasm32"))]
+static PLATFORM_FONT_FILES: std::sync::OnceLock<PlatformFontFiles> = std::sync::OnceLock::new();
+
+/// Have [`system_font_dirs`] add the font files `list` gives (full paths) outside the font
+/// folders, asked again by each scan and each check for installed fonts
+/// ([`FontDb::installed_fonts_changed`]). The desktop app lists DirectWrite's system font
+/// collection on Windows: fonts a font service such as Adobe Fonts loads in place, from files
+/// outside the font folders and unknown to the registry (#579). Only the first call counts.
+pub fn set_platform_font_files(list: PlatformFontFiles) {
+    #[cfg(not(target_arch = "wasm32"))]
+    // A second call keeps the first lister, as documented.
+    let _ = PLATFORM_FONT_FILES.set(list);
+    #[cfg(target_arch = "wasm32")]
+    let _ = list;
+}
+
+/// The platform's font folders (the system's and the user's) and the font files known to it
+/// outside them (on Windows those registered with it, and those [`set_platform_font_files`]
+/// lists), scanned by [`FontDb::global`].
 pub fn system_font_dirs() -> Vec<PathBuf> {
     let mut dirs: Vec<PathBuf> = Vec::new();
     if cfg!(target_arch = "wasm32") {
@@ -824,6 +845,11 @@ pub fn system_font_dirs() -> Vec<PathBuf> {
         // In a Flatpak sandbox, the host's fonts (system, local and the user's).
         dirs.extend(["/run/host/fonts", "/run/host/local-fonts", "/run/host/user-fonts"].map(Into::into));
     }
+    #[cfg(not(target_arch = "wasm32"))]
+    if let Some(list) = PLATFORM_FONT_FILES.get() {
+        let files = fonts_outside(list(), &dirs);
+        dirs.extend(files);
+    }
     dirs
 }
 
@@ -848,7 +874,7 @@ fn registered_font_files(font_dirs: &[PathBuf]) -> Vec<PathBuf> {
 /// The full paths among `registered` (font registrations' data) that aren't in `font_dirs`
 /// (ignoring case, as Windows paths do), sorted and deduplicated. File names alone are files in
 /// the Windows font folder, which is scanned anyway. The count is capped.
-#[cfg(any(windows, test))]
+#[cfg(not(target_arch = "wasm32"))]
 pub(crate) fn fonts_outside(registered: impl IntoIterator<Item = String>, font_dirs: &[PathBuf]) -> Vec<PathBuf> {
     const MAX_REGISTERED: usize = 1 << 16;
     let lower = |p: &Path| PathBuf::from(p.to_string_lossy().to_lowercase());
@@ -1154,6 +1180,7 @@ impl FontDb {
         let mut n = 0;
         let paths = self.font_paths.get();
         let mut modified_at = Vec::new();
+        // Each file with whether it was named by itself rather than found in a folder.
         let mut files = Vec::new();
         let mut stack = paths.clone();
         // Each folder once, however links lead back to it.
@@ -1166,7 +1193,7 @@ impl FontDb {
             modified_at.push((d.clone(), modified(&d)));
             // Not a folder: a font file named by itself (or nothing, yet).
             let Ok(rd) = std::fs::read_dir(&d) else {
-                files.push(d);
+                files.push((d, true));
                 continue;
             };
             for e in rd.flatten() {
@@ -1174,13 +1201,15 @@ impl FontDb {
                 if p.is_dir() {
                     stack.push(p);
                 } else {
-                    files.push(p);
+                    files.push((p, false));
                 }
             }
         }
-        for p in files {
+        for (p, named) in files {
+            // A file named by itself is a font whatever its name (font services keep fonts in
+            // files without an extension); one of a folder's only with a font's extension.
             let ext = p.extension().and_then(|e| e.to_str()).map(|e| e.to_ascii_lowercase());
-            if !matches!(ext.as_deref(), Some("ttf" | "otf" | "ttc" | "otc")) {
+            if !named && !matches!(ext.as_deref(), Some("ttf" | "otf" | "ttc" | "otc")) {
                 continue;
             }
             for FaceStyle { family, style, keys, weight, italic, traits, .. } in file_face_names(&p) {

crates/text/src/lib.rs

@@ -24,7 +24,9 @@ pub mod thread;
 
 pub use craft_fonts::{CRAFT_FONTS, CraftFont};
 pub use features::{LIGATURE_TRACKING_LIMITS, OtFeatures, explicit_ligatures, ligatures_suppressed_by};
-pub use fontdb::{FALLBACK_FAMILY, FontClass, FontDb, FontFace, FontMatch, FontTraits, style_weight, system_font_dirs};
+pub use fontdb::{
+    FALLBACK_FAMILY, FontClass, FontDb, FontFace, FontMatch, FontTraits, PlatformFontFiles, set_platform_font_files, style_weight, system_font_dirs,
+};
 use kurbo::{Affine, BezPath, Point, Rect, Vec2};
 pub use layout::{layout, layout_with};
 pub use vectorcraft_doc::TextObject;

crates/text/src/tests_sysfonts.rs

@@ -237,3 +237,29 @@ fn the_database_tells_when_fonts_were_installed_or_removed_since_its_scan() {
     assert_eq!(db.load_system_fonts(), 2);
     assert_eq!(db.styles(FAMILY), ["Bold"]);
 }
+
+/// A font a font service loads from a file without an extension, outside the font folders.
+fn service_font() -> PathBuf {
+    std::env::temp_dir().join(format!("vc-sysfonts-{}-service", std::process::id())).join(".29457")
+}
+
+/// The fonts a font service (Adobe Fonts on Windows, through DirectWrite) loads in place are
+/// cataloged: named by the platform's lister, read whatever their file is called (#579).
+#[test]
+fn fonts_the_platform_lists_outside_the_font_folders_are_cataloged() {
+    let file = service_font();
+    std::fs::create_dir_all(file.parent().unwrap()).unwrap();
+    std::fs::write(&file, renamed_to("SourceSans3-Regular.ttf", "Service Sans3")).unwrap();
+    // The lister's files outside the font folders are scanned with them, each once (a collection
+    // lists its file once per face).
+    fn lister() -> Vec<String> {
+        vec![service_font().to_string_lossy().into_owned(); 2]
+    }
+    set_platform_font_files(lister);
+    let dirs = system_font_dirs();
+    assert_eq!(dirs.iter().filter(|d| **d == file).count(), 1, "{dirs:?}");
+    // A file named by itself is read without a font's extension, one in a folder isn't.
+    let db = FontDb::with_font_dirs(vec![file.clone()]);
+    assert_eq!(db.styles("Service Sans3"), ["Regular"]);
+    assert!(!FontDb::with_font_dirs(vec![file.parent().unwrap().to_path_buf()]).has_family("Service Sans3"));
+}

crates/ui-egui/src/lib.rs

@@ -347,6 +347,9 @@ pub struct VectorcraftApp {
     /// The thread that checks the system clipboard for `system_paste` instead
     /// ([`Services::clipboard_probe`]).
     clipboard_probe: Option<clipboard_probe::Probe>,
+    /// The look for fonts installed or removed while the app was in the background, running
+    /// ([`Self::refresh_installed_fonts`]): whether they were.
+    font_check: Option<std::sync::mpsc::Receiver<bool>>,
     /// Keyboard pastes of something other than text (see [`shortcuts::PasteChord`]).
     pub(crate) paste_chord: shortcuts::PasteChord,
     /// Saves and exports running in the background (Preferences → File Handling).
@@ -423,6 +426,7 @@ impl VectorcraftApp {
             system_paste: false,
             system_paste_at: f64::NEG_INFINITY,
             clipboard_probe: None,
+            font_check: None,
             paste_chord: Default::default(),
             background: Default::default(),
             recovery: Default::default(),
@@ -785,6 +789,7 @@ impl VectorcraftApp {
             self.system_paste_at = now;
             self.system_paste = wanted && self.system_clipboard_pasteable();
         }
+        self.poll_font_check(ctx);
         background::poll(self);
         if !self.background.jobs.is_empty() {
             // Keep the status bar's progress moving and pick the result up when it arrives.
@@ -858,10 +863,38 @@ impl VectorcraftApp {
 
     /// Fonts installed or removed while the app was in the background are listed when it comes
     /// back (Refresh Font List by itself): a look at the font folders, a scan only when they changed.
+    /// The look runs on another thread (asking DirectWrite for the fonts font services loaded
+    /// meanwhile takes tens of milliseconds on Windows, #579), [`Self::poll_font_check`] scans.
     fn refresh_installed_fonts(&mut self) {
-        if vectorcraft_text::FontDb::global().installed_fonts_changed() {
-            // A failure shows in the status bar, as the menu item's does.
-            let _ = self.run("text.rescanFonts", json!({}));
+        if self.font_check.is_some() {
+            return;
+        }
+        let (tx, rx) = std::sync::mpsc::channel();
+        let look = move || {
+            // The UI gone meanwhile has nothing to refresh.
+            let _ = tx.send(vectorcraft_text::FontDb::global().installed_fonts_changed());
+        };
+        let spawned =
+            if cfg!(target_arch = "wasm32") { None } else { std::thread::Builder::new().name("font-check".into()).spawn(look.clone()).ok() };
+        if spawned.is_none() {
+            look();
+        }
+        self.font_check = Some(rx);
+    }
+
+    /// Rescan the fonts once [`Self::refresh_installed_fonts`]'s look says they changed.
+    fn poll_font_check(&mut self, ctx: &egui::Context) {
+        let Some(check) = &self.font_check else { return };
+        match check.try_recv() {
+            Ok(changed) => {
+                self.font_check = None;
+                if changed {
+                    // A failure shows in the status bar, as the menu item's does.
+                    let _ = self.run("text.rescanFonts", json!({}));
+                }
+            }
+            Err(std::sync::mpsc::TryRecvError::Empty) => ctx.request_repaint_after(std::time::Duration::from_millis(50)),
+            Err(std::sync::mpsc::TryRecvError::Disconnected) => self.font_check = None,
         }
     }
 

docs/mcp.md

@@ -2310,7 +2310,8 @@ tone (mono, or CMYK screens multiplied over each other), clipped to the art's ou
 
 Type can use the bundled fonts, fonts added to the session and the fonts installed on the system (none on the web):
 the system's and the user's font folders (Windows: `Fonts` and `%LOCALAPPDATA%\Microsoft\Windows\Fonts`, plus fonts
-registered outside them, such as fonts installed as shortcuts; macOS: `/System/Library/Fonts`, `/Library/Fonts`,
+registered outside them, such as fonts installed as shortcuts, and in the desktop app the fonts in DirectWrite's system
+font collection, such as those Adobe Fonts activates while Creative Cloud runs; macOS: `/System/Library/Fonts`, `/Library/Fonts`,
 `/Network/Library/Fonts`, `~/Library/Fonts` and downloaded system fonts; Linux and BSD: `/usr/share/fonts`,
 `/usr/local/share/fonts`, `~/.fonts` and the XDG data folders' `fonts`, `~/.local/share/fonts` among them, and in a
 Flatpak sandbox the host's fonts). The installed fonts are cataloged once per session (in the background when the app starts, else on the first lookup