From cecd467dd2e2cbdb90a92ce29b76f5ee271fcdef Mon Sep 17 00:00:00 2001
From: Thomas Weber <muffin@muffin.ink>
Date: Sat, 31 Oct 2026 15:31:42 -0500
Subject: [PATCH] Wait for custom fonts to load before continuing (#401)

---
 src/engine/tw-font-manager.js       | 16 +++++++---
 test/integration/tw_font_manager.js | 46 +++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 4 deletions(-)

diff --git a/src/engine/tw-font-manager.js b/src/engine/tw-font-manager.js
index f617a67f..54b98b0f 100644
--- a/src/engine/tw-font-manager.js
+++ b/src/engine/tw-font-manager.js
@@ -160,6 +160,7 @@ class FontManager extends EventEmitter {
      * @param {string} family
      * @param {string} fallback
      * @param {Asset} asset scratch-storage asset
+     * @returns {Promise<unknown>} Resolves when the font is ready.
      */
     addCustomFont (family, fallback, asset) {
         if (!this.isValidCustomFont(family)) {
@@ -171,8 +172,9 @@ class FontManager extends EventEmitter {
             fallback,
             asset
         });
-        this.updateRenderer();
+        const promise = this.updateRenderer();
         this.changed();
+        return promise;
     }
 
     /**
@@ -208,9 +210,12 @@ class FontManager extends EventEmitter {
         this.changed();
     }
 
+    /**
+     * @returns {Promise<unknown>} Resolves when fonts are ready.
+     */
     updateRenderer () {
         if (!this.runtime.renderer || !this.runtime.renderer.setCustomFonts) {
-            return;
+            return Promise.resolve();
         }
 
         const fontfaces = {};
@@ -222,7 +227,7 @@ class FontManager extends EventEmitter {
                 fontfaces[family] = fontface;
             }
         }
-        this.runtime.renderer.setCustomFonts(fontfaces);
+        return this.runtime.renderer.setCustomFonts(fontfaces);
     }
 
     /**
@@ -273,6 +278,7 @@ class FontManager extends EventEmitter {
             return;
         }
 
+        const fontPromises = [];
         for (const font of json) {
             if (!font || typeof font !== 'object') {
                 continue;
@@ -305,12 +311,14 @@ class FontManager extends EventEmitter {
                         this.runtime.storage.AssetType.Font,
                         md5ext
                     );
-                    this.addCustomFont(family, fallback, asset);
+                    fontPromises.push(this.addCustomFont(family, fallback, asset));
                 }
             } catch (e) {
                 log.error('could not add font', e);
             }
         }
+
+        await Promise.all(fontPromises);
     }
 }
 
diff --git a/test/integration/tw_font_manager.js b/test/integration/tw_font_manager.js
index 742799ce..834221e7 100644
--- a/test/integration/tw_font_manager.js
+++ b/test/integration/tw_font_manager.js
@@ -5,6 +5,7 @@ const assert = require('node:assert');
 const _makeTestStorage = require('../fixtures/make-test-storage');
 const Runtime = require('../../src/engine/runtime');
 const VirtualMachine = require('../../src/virtual-machine');
+const JSZip = require('@turbowarp/jszip');
 
 const emptyProjectFixture = path.join(__dirname, '..', 'fixtures', 'tw-empty-project.sb3');
 
@@ -731,3 +732,48 @@ test('overriding existing fonts', () => {
     assert.strictEqual(setCustomFontsCalls, 3);
     assert.deepEqual(fontManager.getFonts().map(i => i.name), ['TESTFONT']);
 });
+
+test('deserialize waits for renderer to load fonts', async () => {
+    const zip = new JSZip();
+    zip.file('8e0b5e4ad4e3b2b9a8b4e9bd0ec4de2c.ttf', new Uint8Array([1, 2, 3]));
+
+    let resolveSetCustomFontsCalled;
+    const setCustomFontsCalled = new Promise(resolve => {
+        resolveSetCustomFontsCalled = resolve;
+    });
+    let resolveFontsLoaded;
+    const mockRenderer = {
+        setLayerGroupOrdering: () => {},
+        setCustomFonts: () => {
+            resolveSetCustomFontsCalled();
+            return new Promise(resolve => {
+                resolveFontsLoaded = resolve;
+            });
+        }
+    };
+
+    const rt = new Runtime();
+    rt.attachRenderer(mockRenderer);
+    rt.attachStorage(makeTestStorage());
+
+    let deserialized = false;
+    const promise = rt.fontManager.deserialize([
+        {
+            system: false,
+            family: 'TestFont',
+            fallback: 'sans-serif',
+            md5ext: '8e0b5e4ad4e3b2b9a8b4e9bd0ec4de2c.ttf'
+        }
+    ], zip, false).then(() => {
+        deserialized = true;
+    });
+
+    await setCustomFontsCalled;
+    await new Promise(resolve => setTimeout(resolve));
+    assert.strictEqual(deserialized, false, 'still waiting for fonts');
+
+    resolveFontsLoaded();
+    await promise;
+    assert.strictEqual(deserialized, true);
+    assert.deepEqual(rt.fontManager.getFonts().map(i => i.name), ['TestFont']);
+});