From 6ec259a0e71174651bae95d4628138bf6fd68742 Mon Sep 17 00:00:00 2001
From: kj_sh604
Date: Sun, 15 Mar 2026 16:19:35 -0400
Subject: refactor: packages/

---
 packages/excalidraw/subset/subset-shared.chunk.ts | 81 +++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 packages/excalidraw/subset/subset-shared.chunk.ts

(limited to 'packages/excalidraw/subset/subset-shared.chunk.ts')

diff --git a/packages/excalidraw/subset/subset-shared.chunk.ts b/packages/excalidraw/subset/subset-shared.chunk.ts
new file mode 100644
index 0000000..b64a382
--- /dev/null
+++ b/packages/excalidraw/subset/subset-shared.chunk.ts
@@ -0,0 +1,81 @@
+/**
+ * DON'T depend on anything from the outside like `promiseTry`, as this module is part of a separate lazy-loaded chunk.
+ *
+ * Including anything from the main chunk would include the whole chunk by default.
+ * Even it it would be tree-shaken during build, it won't be tree-shaken in dev.
+ *
+ * In the future consider separating common utils into a separate shared chunk.
+ */
+
+import loadWoff2 from "./woff2/woff2-loader";
+import loadHbSubset from "./harfbuzz/harfbuzz-loader";
+
+/**
+ * Shared commands between the main thread and worker threads.
+ */
+export const Commands = {
+  Subset: "SUBSET",
+} as const;
+
+/**
+ * Used by browser (main thread), node and jsdom, to subset the font based on the passed codepoints.
+ *
+ * @returns woff2 font as a base64 encoded string
+ */
+export const subsetToBase64 = async (
+  arrayBuffer: ArrayBuffer,
+  codePoints: Array<number>,
+): Promise<string> => {
+  try {
+    const buffer = await subsetToBinary(arrayBuffer, codePoints);
+    return toBase64(buffer);
+  } catch (e) {
+    console.error("Skipped glyph subsetting", e);
+    // Fallback to encoding whole font in case of errors
+    return toBase64(arrayBuffer);
+  }
+};
+
+/**
+ * Used by browser (worker thread) and as part of `subsetToBase64`, to subset the font based on the passed codepoints.
+ *
+ * @eturns woff2 font as an ArrayBuffer, to avoid copying large strings between worker threads and the main thread.
+ */
+export const subsetToBinary = async (
+  arrayBuffer: ArrayBuffer,
+  codePoints: Array<number>,
+): Promise<ArrayBuffer> => {
+  // lazy loaded wasm modules to avoid multiple initializations in case of concurrent triggers
+  // IMPORTANT: could be expensive, as each new worker instance lazy loads these to their own memory ~ keep the # of workes small!
+  const { compress, decompress } = await loadWoff2();
+  const { subset } = await loadHbSubset();
+
+  const decompressedBinary = decompress(arrayBuffer).buffer;
+  const snftSubset = subset(decompressedBinary, new Set(codePoints));
+  const compressedBinary = compress(snftSubset.buffer);
+
+  return compressedBinary.buffer;
+};
+
+/**
+ * Util for isomoprhic browser (main thread), node and jsdom usage.
+ *
+ * Isn't used inside the worker to avoid copying large binary strings (as dataurl) between worker threads and the main thread.
+ */
+export const toBase64 = async (arrayBuffer: ArrayBuffer) => {
+  let base64: string;
+
+  if (typeof Buffer !== "undefined") {
+    // node, jsdom
+    base64 = Buffer.from(arrayBuffer).toString("base64");
+  } else {
+    // browser (main thread)
+    // it's perfectly fine to treat each byte independently,
+    // as we care only about turning individual bytes into codepoints,
+    // not about multi-byte unicode characters
+    const byteString = String.fromCharCode(...new Uint8Array(arrayBuffer));
+    base64 = btoa(byteString);
+  }
+
+  return `data:font/woff2;base64,${base64}`;
+};
-- 
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