began soundfont implementation

packages/soundfonts/fontloader.mjs

@@ -0,0 +1,108 @@
+let loadCache = {};
+async function loadFont(name) {
+  if (loadCache[name]) {
+    return loadCache[name];
+  }
+  const load = async () => {
+    // TODO: make soundfont source configurable
+    const url = `https://surikov.github.io/webaudiofontdata/sound/${name}.js`;
+    console.log('load font', name, url);
+    const preset = await fetch(url).then((res) => res.text());
+    let [_, data] = preset.split('={');
+    return eval('{' + data);
+  };
+  loadCache[name] = load();
+  return loadCache[name];
+}
+
+let bufferCache = {};
+export async function getFontBufferSource(name, pitch, ac) {
+  const key = `${name}:::${pitch}`;
+  if (bufferCache[key]) {
+    return (await bufferCache[key])();
+  }
+  // console.log('load buffer', key);
+  const load = async () => {
+    const preset = await loadFont(name);
+    if (!preset) {
+      throw new Error(`Could not load soundfont ${name}`);
+    }
+    const zone = findZone(preset, pitch);
+    if (!zone) {
+      throw new Error('no soundfont zone found for preset ', name, 'pitch', pitch);
+    }
+    const buffer = await getBuffer(zone, ac);
+    if (!buffer) {
+      throw new Error(`no soundfont buffer found for preset ${name}, pitch: ${pitch}`);
+    }
+    return () => {
+      const src = ac.createBufferSource();
+      src.buffer = buffer;
+      const baseDetune = zone.originalPitch - 100.0 * zone.coarseTune - zone.fineTune;
+      const playbackRate = 1.0 * Math.pow(2, (100.0 * pitch - baseDetune) / 1200.0);
+      // src detune?
+      src.playbackRate.value = playbackRate;
+      const loop = zone.loopStart > 1 && zone.loopStart < zone.loopEnd;
+      if (!loop) {
+        /* const waveDuration = duration + this.afterTime;
+          if (waveDuration > zone.buffer.duration / playbackRate) {
+            waveDuration = zone.buffer.duration / playbackRate;
+            // TODO: do sth with waveduration
+          } */
+      } else {
+        src.loop = true;
+        /*         src.loopStart = zone.loopStart / zone.sampleRate + (zone.delay ? zone.delay : 0);
+        src.loopEnd = zone.loopEnd / zone.sampleRate + (zone.delay ? zone.delay : 0); */
+      }
+
+      return src;
+    };
+  };
+  bufferCache[key] = load(); // dont await here to cache promise immediately!
+  return (await bufferCache[key])();
+}
+
+function findZone(preset, pitch) {
+  return preset.find((zone) => {
+    return zone.keyRangeLow <= pitch && zone.keyRangeHigh + 1 >= pitch;
+  });
+}
+
+// promisified version of https://github.com/felixroos/webaudiofont/blob/c6f97249b60dcfafc20fca5bb381294a6b2f8f51/npm/dist/WebAudioFontPlayer.js#L740
+async function getBuffer(zone, audioContext) {
+  if (zone.sample) {
+    console.warn('zone.sample untested!');
+    const decoded = atob(zone.sample);
+    zone.buffer = audioContext.createBuffer(1, decoded.length / 2, zone.sampleRate);
+    const float32Array = zone.buffer.getChannelData(0);
+    let b1, b2, n;
+    for (var i = 0; i < decoded.length / 2; i++) {
+      b1 = decoded.charCodeAt(i * 2);
+      b2 = decoded.charCodeAt(i * 2 + 1);
+      if (b1 < 0) {
+        b1 = 256 + b1;
+      }
+      if (b2 < 0) {
+        b2 = 256 + b2;
+      }
+      n = b2 * 256 + b1;
+      if (n >= 65536 / 2) {
+        n = n - 65536;
+      }
+      float32Array[i] = n / 65536.0;
+    }
+  } else {
+    if (zone.file) {
+      const datalen = zone.file.length;
+      const arraybuffer = new ArrayBuffer(datalen);
+      const view = new Uint8Array(arraybuffer);
+      const decoded = atob(zone.file);
+      let b;
+      for (let i = 0; i < decoded.length; i++) {
+        b = decoded.charCodeAt(i);
+        view[i] = b;
+      }
+      return new Promise((resolve) => audioContext.decodeAudioData(arraybuffer, resolve));
+    }
+  }
+}