feat(noise.js):Add webaudio noise class

main.js

@@ -1,4 +1,5 @@
 import Oscillator from './src/nes/webaudio/oscillator.js'
+import Noise from './src/nes/webaudio/noise.js'
 let buf = null
 
 const convertKeyCode = (key) => {
@@ -39,13 +40,15 @@ const startArrayBuf = (arrayBuf) => {
   const canvas = document.querySelector('canvas')
   const ctx = canvas.getContext('2d')
   if (Module.NES) {
-    Module.NES.oscs.forEach(o => o.close());
+    Module.NES.oscs.forEach(o => o.close())
+    Module.NES.noise.close()
   }
   Module.NES = {
     ctx,
     canvas,
     image: ctx.createImageData(256, 240),
     oscs: [new Oscillator(), new Oscillator()],
+    noise: new Noise(),
   }
   canvas.width = 256
   canvas.height = 240
@@ -62,7 +65,7 @@ const startArrayBuf = (arrayBuf) => {
 }
 
 // called from html
-export const start = async (rom = './roms/apu/square_timer_div2.nes') => {
+export const start = async (rom = './roms/apu/sweep_cutoff.nes') => {
   const res = await fetch(rom);
   const arrayBuf = await res.arrayBuffer();
   startArrayBuf(arrayBuf);

src/externs/lib.js

@@ -21,5 +21,17 @@ mergeInto(LibraryManager.library, {
   },
   set_oscillator_duty: function (index, duty) {
     Module.NES.oscs[index].setDuty(duty)
+  },
+  set_noise_frequency: function(freq) {
+    Module.NES.noise.setFrequency(freq)
+  },
+  set_noise_volume: function (volume) {
+    Module.NES.noise.setVolume(volume)
+  },
+  start_noise: function () {
+    Module.NES.noise.start()
+  },
+  stop_noise: function () {
+    Module.NES.noise.stop()
   }
 });

src/nes/webaudio/noise.js

@@ -0,0 +1,55 @@
+export default class Noise {
+  constructor () {
+    try {
+      const AudioContext = window.AudioContext || window.webkitAudioContext
+      this.context = new AudioContext();
+    } catch (e) {
+      throw new Error('Web Audio isn\'t supported in this browser!');
+    }
+    this.createSource()
+    this.playing = false
+  }
+
+  createSource() {
+    const node = this.context.createBufferSource()
+    const buffer = this.context.createBuffer(1, this.context.sampleRate, this.context.sampleRate)
+    const data = buffer.getChannelData(0)
+    for (let i = 0; i < this.context.sampleRate; i++) {
+      data[i] = Math.random();
+    }
+    node.buffer = buffer
+    node.loop = true
+    this.gain = this.context.createGain()
+    this.gain.gain.value = 0.01
+    node.connect(this.gain)
+    this.bandpass = this.context.createBiquadFilter()
+    this.gain.connect(this.bandpass)
+    this.bandpass.connect(this.context.destination)
+    this.source = node
+    this.setVolume(0)
+  }
+
+  setVolume (v) {
+    v = Math.max(0, Math.min(1, v))
+    this.gain.gain.value = v
+  }
+
+  setFrequency (freq) {
+    this.bandpass.frequency.value = freq > 22050 ? 22050 : freq
+  }
+
+  start () {
+    if (!this.playing) {
+      this.playing = true
+      this.source.start(0)
+    }
+  }
+
+  stop() {
+    if (this.playing) {
+      this.playing = false
+      this.source.stop()
+      this.createSource()
+    }
+  }
+}