From 8d4f1e20a590380e8ead1a2327d2ef647b9f299d Mon Sep 17 00:00:00 2001
From: CrispyBaguette <alexandre.bruyant@gmail.com>
Date: Tue, 23 Nov 2021 21:49:50 +0100
Subject: [PATCH 1/2] Web worker and HTML tweaks

---
 dist/index.html |  29 ++++++++----
 dist/main.js    | 122 +++++++++++++++++++++++++++++++++++-------------
 dist/worker.js  |  61 ++++++++++++++++++++++++
 3 files changed, 171 insertions(+), 41 deletions(-)
 create mode 100644 dist/worker.js
diff --git a/dist/index.html b/dist/index.html
index 6503e09..d2b3675 100644
--- a/dist/index.html
+++ b/dist/index.html
@@ -1,8 +1,8 @@
 <html>
   <head>
     <meta charset="utf-8" />
-    <script src="./wasm_exec.js"></script>
-    <script async src="./main.js"></script>
+    <script type="module" src="./wasm_exec.js"></script>
+    <script type="module" src="./main.js"></script>
     <style>
       @media (prefers-color-scheme: dark) {
         body {
@@ -57,8 +57,19 @@
         algorithm.
       </p>
       <p>
-        Performance isn't great, as Go+Wasm only runs on a single thread. The
-        Wasm call also blocks the rendering (that would be fixable, though).
+        Running in the browser with Wasm causes a bit of a performance penalty.
+        Multithreading is not available (not that it matters much since
+        Floyd-Steinberg is single-threaded), and sending data back and forth
+        between JS and Wasm can take a little while.
+      </p>
+      <p>
+        I've re-used code from
+        <a
+          href="https://www.sitepen.com/blog/using-webassembly-with-web-workers"
+          >this article</a
+        >
+        to make the Wasm code run in a web worker, with some adaptations for Go
+        oddities.
       </p>
       <p>
         If you're into that sort of thing, source code is available on
@@ -68,11 +79,13 @@
       </p>
       <form>
         <input type="file" id="source-image" accept="image/png, image/jpeg" />
-        <button id="go-btn" type="button">Go</button>
+        <button id="go-btn" type="button" disabled>Go</button>
       </form>
-      <div class="container">
-        <img id="output" />
-      </div>
+      <a id="output-wrapper" download="output.png">
+        <div class="container">
+          <img id="output" />
+        </div>
+      </a>
     </article>
   </body>
 </html>
diff --git a/dist/main.js b/dist/main.js
index e366403..138ee15 100644
--- a/dist/main.js
+++ b/dist/main.js
@@ -1,38 +1,94 @@
-(async () => {
-  // Load  element references
-  const fileInput = document.getElementById("source-image");
-  const btn = document.getElementById("go-btn");
+const fileInput = document.getElementById("source-image");
+const btn = document.getElementById("go-btn");
+const output = document.getElementById("output");
+const outputWrapper = document.getElementById("output-wrapper");
 
-  // Setup Wasm stuff
-  const go = new Go();
-  vm = await WebAssembly.instantiateStreaming(
-    fetch("./main.wasm"),
-    go.importObject
-  );
-  go.run(vm.instance);
+function wasmWorker(modulePath) {
+  // Create an object to later interact with
+  const proxy = {};
 
-  // Setup event listener
-  btn.addEventListener("click", async () => {
-    // Clear image
-    outputElement = document.getElementById("output");
-    outputElement.src = "";
+  // Keep track of the messages being sent
+  // so we can resolve them correctly
+  let id = 0;
+  let idPromises = {};
 
-    // Check if a file was selected
-    if (fileInput.files.length === 0) {
-      alert("No file selected");
-      return;
-    }
-    reader = new FileReader();
-    reader.readAsArrayBuffer(fileInput.files[0]);
-    reader.Read;
-    reader.onloadend = async (evt) => {
-      if (evt.target.readyState === FileReader.DONE) {
-        const array = new Uint8Array(evt.target.result);
-        // Wasm magic happens here
-        ditheredImageData = await DitherNord(array);
-        document.getElementById("output").src =
-          "data:image/png;base64," + ditheredImageData;
+  return new Promise((resolve, reject) => {
+    const worker = new Worker("worker.js");
+    worker.postMessage({ eventType: "INITIALISE", eventData: modulePath });
+    worker.addEventListener("message", function (event) {
+      const { eventType, eventData, eventId } = event.data;
+
+      if (eventType === "INITIALISED") {
+        const methods = event.data.eventData;
+        methods.forEach((method) => {
+          proxy[method] = function () {
+            return new Promise((resolve, reject) => {
+              worker.postMessage({
+                eventType: "CALL",
+                eventData: {
+                  method: method,
+                  arguments: Array.from(arguments), // arguments is not an array
+                },
+                eventId: id,
+              });
+
+              idPromises[id] = { resolve, reject };
+              id++;
+            });
+          };
+        });
+        resolve(proxy);
+        return;
+      } else if (eventType === "RESULT") {
+        if (eventId !== undefined && idPromises[eventId]) {
+          idPromises[eventId].resolve(eventData);
+          delete idPromises[eventId];
+        }
+      } else if (eventType === "ERROR") {
+        if (eventId !== undefined && idPromises[eventId]) {
+          idPromises[eventId].reject(event.data.eventData);
+          delete idPromises[eventId];
+        }
       }
-    };
+    });
+
+    worker.addEventListener("error", function (error) {
+      reject(error);
+    });
   });
-})();
+}
+
+let workerResolve;
+const wasmReady = new Promise((resolve) => {
+  workerResolve = resolve;
+});
+
+let workerProxy;
+wasmWorker("./main.wasm").then((w) => {
+  workerProxy = w;
+  workerResolve();
+  btn.removeAttribute("disabled");
+});
+
+btn.addEventListener("click", async () => {
+  // Clear image
+  output.src = "";
+
+  // Check if a file was selected
+  if (fileInput.files.length === 0) {
+    alert("No file selected");
+    return;
+  }
+  const reader = new FileReader();
+  reader.readAsArrayBuffer(fileInput.files[0]);
+  reader.onloadend = async (evt) => {
+    if (evt.target.readyState === FileReader.DONE) {
+      const imageData = new Uint8Array(evt.target.result);
+      const ditheredImage = await workerProxy.DitherNord(imageData);
+
+      const outputValue = `data:image/png;base64,${ditheredImage}`;
+      output.src = outputValue;
+      outputWrapper.href = outputValue;
+    }
+  };
+});
diff --git a/dist/worker.js b/dist/worker.js
new file mode 100644
index 0000000..256baa3
--- /dev/null
+++ b/dist/worker.js
@@ -0,0 +1,61 @@
+importScripts("./wasm_exec.js");
+
+if (!WebAssembly.instantiateStreaming) {
+  WebAssembly.instantiateStreaming = async (resp, importObject) => {
+    const source = await (await resp).arrayBuffer();
+    return await WebAssembly.instantiate(source, importObject);
+  };
+}
+
+// Create promise to handle Worker calls whilst
+// module is still initialising
+let wasmResolve;
+const wasmReady = new Promise((resolve) => {
+  wasmResolve = resolve;
+});
+
+const go = new self.Go();
+
+addEventListener(
+  "message",
+  async (e) => {
+    const { eventType, eventData, eventId } = e.data;
+
+    if (eventType === "INITIALISE") {
+      const instantiatedSource = await WebAssembly.instantiateStreaming(
+        fetch(eventData),
+        go.importObject
+      );
+      go.run(instantiatedSource.instance);
+
+      // Go does nor exposes the exports in the instantiated module :(((
+      const methods = ["DitherNord"];
+      wasmResolve(methods);
+      postMessage({
+        eventType: "INITIALISED",
+        eventData: methods,
+      });
+    } else if (eventType === "CALL") {
+      await wasmReady;
+      try {
+        const method = self[eventData.method];
+        const result = await method.apply(null, eventData.arguments);
+        self.postMessage({
+          eventType: "RESULT",
+          eventData: result,
+          eventId: eventId,
+        });
+      } catch (e) {
+        console.error(e);
+        self.postMessage({
+          eventType: "ERROR",
+          eventData:
+            "An error occured executing WASM instance function: " +
+            error.toString(),
+          eventId: eventId,
+        });
+      }
+    }
+  },
+  false
+);

From f67080127bd0151db0edf35b5ba8f09947916e58 Mon Sep 17 00:00:00 2001
From: CrispyBaguette <alexandre.bruyant@gmail.com>
Date: Tue, 23 Nov 2021 22:06:02 +0100
Subject: [PATCH 2/2] Update CID

---
 README.md | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index c1ac59c..63539f4 100644
--- a/README.md
+++ b/README.md
@@ -1,19 +1,24 @@
 # wasm-palette-converter
+
 Go+Wasm image palette converter
 
 Build with:
+
 ```bash
 GOOS=js GOARCH=wasm go build -o dist/main.wasm .
 ```
 
 Access with:
+
 ```
 cd dist
 npx http-server
 ```
 
 A version is also available on IPFS:
+
 ```
-/ipfs/QmQ4ptP2z6SonqyZfF5AiqgPa8RzHpPVyZWvZ8aVNxcoC9
+/ipfs/QmU6MmYFEvEYcNLdJZKJ7LfTuAPhPnpLwiUt4YcmANQESP
 ```
-You can access it directly [here](https://ipfs.io/ipfs/QmQ4ptP2z6SonqyZfF5AiqgPa8RzHpPVyZWvZ8aVNxcoC9/).
+
+You can access it directly [here](https://ipfs.io/ipfs/QmU6MmYFEvEYcNLdJZKJ7LfTuAPhPnpLwiUt4YcmANQESP/).
