class SoundBuffer { constructor(genFn, duration = 1) { this.duration = duration; // Create an audio buffer. this.audioBuffer = ctx.createBuffer(1, ctx.sampleRate * this.duration, ctx.sampleRate); this.buffer = this.audioBuffer.getChannelData(0); let max = 0; for (let i = 0; i < this.audioBuffer.length; i++) { const value = genFn(i / ctx.sampleRate); this.buffer[i] = value; if (Math.abs(value) > max) max = Math.abs(value); } for (let i = 0; i < this.audioBuffer.length; i++) { this.buffer[i] = this.buffer[i] / max; } } play(maxVol = 0.3) { this.stop(); this.source = ctx.createBufferSource(); this.source.buffer = this.audioBuffer; const gain = ctx.createGain(); gain.gain.value = maxVol; this.source.connect(gain); gain.connect(ctx.destination); this.source.start(); } stop() { if (this.source) this.source.stop(); } draw(height = 50, width = width, color = 'blue') { const drawingCtx = DOM.context2d(width, height); // Draw the middle line. drawingCtx.strokeStyle = 'gainsboro'; drawingCtx.beginPath(); drawingCtx.moveTo(0, height / 2); drawingCtx.lineTo(width, height / 2); drawingCtx.stroke(); // Draw the waveform. drawingCtx.strokeStyle = color; drawingCtx.beginPath(); for (let i = 0; i < width; i++) { const value = this.buffer[Math.floor(i / width * this.audioBuffer.length)]; const y = height - Math.floor((value / 2 + 0.5) * height * 0.9 + height * 0.05); if (i == 0) { drawingCtx.moveTo(i, y); } else { drawingCtx.lineTo(i, y); } } drawingCtx.stroke(); return drawingCtx.canvas; } gui() { const ui = html`

▶ ◼ ${this.duration} s

`; const cursor = ui.querySelector('.cursor'); let interval = null; const resetInterval = () => { if (interval != null) { clearInterval(interval); interval = null; } }; const soundPlayer = ui.querySelector('.sound-player'); ui.querySelector('.sound-pane').appendChild(this.draw(46, width - 20)); ui.querySelector('.play-button').onclick = () => { cursor.style.left = '0'; this.play(); cursor.style.display = 'block'; const playTime = Date.now(); resetInterval(); interval = setInterval(() => { if (!document.contains(soundPlayer)) { resetInterval(); this.stop(); } let progress = (Date.now() - playTime) / this.duration / 1000; if (progress < 0) progress = 0; if (progress > 1) { progress = 1; resetInterval(); this.stop(); cursor.style.display = 'none'; } cursor.style.left = `${Math.floor(progress * (width - 20))}px`; }, 20); }; ui.querySelector('.stop-button').onclick = () => { resetInterval(); this.stop(); cursor.style.display = 'none'; }; return ui; } }