1 files changed, 57 insertions, 4 deletions
diff --git a/static/main.js b/static/main.js
index 144254f..183b117 100644
--- a/static/main.js
+++ b/static/main.js
@@ -6,10 +6,10 @@ function getContext() {
   return _context;
 }
 
-function loadSample(url) {
-  return fetch(url)
-    .then((response) => response.arrayBuffer())
-    .then((buffer) => getContext().decodeAudioData(buffer));
+async function loadSample(url) {
+  const res = await fetch(url);
+  const buffer = res.arrayBuffer();
+  return getContext().decodeAudioData(buffer);
 }
 
 function playSoundSample(sample, sampleNote, noteToPlay) {
@@ -20,3 +20,56 @@ function playSoundSample(sample, sampleNote, noteToPlay) {
   source.connect(ctx.destination);
   source.start(0);
 }
+
+function sigmoid(x) {
+  return 1 / (1 + Math.exp(-x));
+}
+
+function drawNoteLines(canvas) {
+  const ctx = canvas.getContext("2d");
+
+  let clicks = [];
+
+  function render() {
+    const W = 256;
+    const H = 512;
+    ctx.clearRect(0, 0, W, H);
+
+    const L = 1.0;
+    ctx.lineWidth = L;
+    ctx.strokeStyle = "#ccc";
+
+    for (let note = 0; note <= 12; note++) {
+      ctx.beginPath();
+      const y = (note / 12) * (H - L) + L / 2;
+      ctx.moveTo(0, y);
+      ctx.lineTo(W, y);
+      ctx.stroke();
+    }
+
+    let now = Date.now();
+    const R = 10.0;
+    for (const [x, y, t] of clicks) {
+      ctx.beginPath();
+      ctx.arc(x - R, y - R, 10, 0, 2 * Math.PI);
+      const tt = (now - t) / 1000; // [0, 1]
+      const alpha = sigmoid(5 - 10 * tt);
+      ctx.fillStyle = `rgb(0, 99, 228, ${alpha})`;
+      ctx.fill();
+    }
+
+    clicks = clicks.filter((o) => now < o[2] + 1_000);
+    if (clicks.length > 0) {
+      requestAnimationFrame(render);
+    }
+  }
+  render();
+
+  canvas.addEventListener("mousedown", (e) => {
+    const { layerX, layerY } = e;
+    clicks.push([layerX, layerY, Date.now()]);
+    render();
+  });
+}
+
+window.drawNoteLines = drawNoteLines;