I'm working with an NES emulator that was written in JavaScript, updating it so it runs better. I'm not knowledgeable with the Web Audio API. Can someone point me in the right direction as to where the audio is being output in the following script?
I've spent a pretty long time going through it, but can't figure it out. My goal is to bring most of the math part of the emulation into a web worker. I have already brought most of the emulator over to the web worker and improved the performance greatly. This is the part I am stuck on though.
var masterVolumeValue = 0; //0.15;
const enableAudioEmulation = true;
function SetMasterVolume(value) {
masterVolumeValue = value;
Unmute();
}
function Mute() {
if (masterVolume) masterVolume.gain.setValueAtTime(0, audio.currentTime);
}
function Unmute() {
if (masterVolume) masterVolume.gain.setValueAtTime(masterVolumeValue, audio.currentTime);
}
var audio;
var masterVolume;
var pulse1 = {
oscillator: null,
haltLengthCounter: false,
constantFlag: false,
dutyCycle: 0,
volume: 0
};
var pulse2 = {
oscillator: null,
haltLengthCounter: false,
constantFlag: false,
dutyCycle: 0,
volume: 0
};
var triangle = {};
var noise = {};
var dmc = {};
var NewApu = (function() {
var running = false;
var pulseCycles = [
[0, 1, 0, 0, 0, 0, 0, 0],
[0, 1, 1, 0, 0, 0, 0, 0],
[0, 1, 1, 1, 1, 0, 0, 0],
[1, 0, 0, 1, 1, 1, 1, 1]
];
var triangleCycle = [15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15];
var bufferSize = 1024;
var mixer;
var wave, ctx;
function initAudio() {
if (audio || !enableAudioEmulation) return;
audio = new AudioContext();
masterVolume = audio.createGain();
masterVolume.gain.setValueAtTime(masterVolumeValue, audio.currentTime);
mixer = audio.createScriptProcessor(bufferSize, 0, 1);
masterVolume.connect(audio.destination);
mixer.connect(masterVolume);
clockStep = 1789773 / 2 / audio.sampleRate; // NES clock frequency / 2 = APU sample rate
clockStep *= 0.97;
mixer.onaudioprocess = resample;
initChannel(pulse1);
initChannel(pulse2);
initChannel(triangle);
noise.lengthCounter = 0;
dmc.load = 0;
dmc.loop = false;
dmc.frequency = 0;
dmc.timer = 0;
dmc.address = 0;
dmc.bytesRemaining = 0;
dmc.currentByte = 0;
dmc.shiftPointer = 0;
dmc.length = 0;
dmc.sample = 0;
if (debug) {
wave = new Float32Array(bufferSize);
ctx = document.createElement('canvas').getContext('2d');
ctx.canvas.width = 300;
ctx.canvas.height = 50;
ctx.canvas.style.width = "300px";
output.canvas.parentNode.appendChild(ctx.canvas);
}
}
var npulse1 = {
cycle: 2,
pointer: 0,
timer: 0,
sample: 0
};
var npulse2 = {
cycle: 2,
pointer: 0,
timer: 0,
sample: 0
};
var ntriangle = {
pointer: 0,
timer: 0,
sample: 0
};
var nnoise = {
shiftRegister: 1,
timer: 0,
sample: 0
}
var counting = 0;
function updateWaveform() {
var c = ctx;
c.clearRect(0, 0, 300, 50);
c.strokeStyle = "#ffffff";
c.beginPath()
c.moveTo(0, (-wave[0] * 10) + 50);
for (var i = 1; i < wave.length; i++) {
c.lineTo((i / wave.length) * 300, (-wave[i] * 10) + 50);
}
c.stroke();
}
// More accurate, but doesn't match output rate due to emulation, so will course clicks and/or lag
var buffer = new Float32Array(bufferSize * 10);
var bufferPointer = 100;
var readPointer = 0;
var bufferLength = 0;
var bufferStep;
function resample(e) {
if (!running) return;
if (bufferLength < 400) {
//console.log('buffer underrun');
return; // extreme underflow, in case of performance issues or the tab went into the background, we just want to skip this update
}
var output = e.outputBuffer.getChannelData(0);
var l = Math.min(bufferLength, output.length);
for (var i = 0; i < l; i++) {
//output[i] = Math.tanh(buffer[readPointer] / (15*3));
output[i] = buffer[readPointer];
readPointer++;
if (readPointer == buffer.length) readPointer = 0;
}
l = output.length;
for (var i = bufferLength; i < l; i++) {
asyncTick(clockStep);
//output[i] = Math.tanh(sample / (15*3)); // 15 = sequencer "full" volume
output[i] = sample;
}
bufferLength = Math.max(0, bufferLength - output.length);
if (debug) {
for (var i = 0; i < output.length; i++) wave[i] = output[i];
updateWaveform();
}
}
// Inaccurate, and might cause precise timing issues, but prevents buffer underflow
var sample = 0; // mixed sample from all 5 channels
var clockStep = 1789773 / 2 / 48000; // NES clock frequency / 2 = APU sample rate
function clockToOutput(e) {
if (!running) return;
var output = e.outputBuffer.getChannelData(0);
var l = output.length;
for (var i = 0; i < l; i++) {
asyncTick(clockStep);
output[i] = sample / (15); // 15 = sequencer "full" volume
}
if (debug) {
for (var i = 0; i < output.length; i++) wave[i] = output[i];
updateWaveform();
}
}
// APU clock updates:
function updatePulse(channel, ref) {
if (!ref.frequency) return;
channel.timer -= click;
while (channel.timer < 0) {
channel.timer += ref.frequency;
channel.pointer = (channel.pointer + 1) & 7;
}
var duty = ref.dutyCycle;
channel.sample = ref.lengthCounter && pulseCycles[duty][channel.pointer] ? (ref.constantFlag ? ref.volume : ref.decay) : 0;
//channel.sample >>= 1;
}
function updateTriangle(channel, ref) {
if (!ref.frequency) return;
channel.timer -= click + click;
while (channel.timer < 0) {
channel.timer += ref.frequency;
channel.pointer = (channel.pointer + 1) & 31;
}
channel.sample = ref.lengthCounter && ref.linearCounter ? triangleCycle[channel.pointer] : 0;
}
function updateNoise(channel, ref) {
if (!ref.frequency) return;
channel.timer -= click;
while (channel.timer < 0) {
channel.timer += ref.frequency;
var feedback = (channel.shiftRegister & 1) ^ ((channel.shiftRegister >> ref.mode) & 1);
channel.shiftRegister >>= 1;
if (feedback) channel.shiftRegister |= 0b100000000000000;
channel.high = channel.shiftRegister & 1;
}
channel.sample = (ref.lengthCounter && channel.high) ? (ref.constantFlag ? ref.volume : ref.decay) : 0;
}
function updateDmc(channel) {
if (!channel.frequency) return;
channel.timer -= click + click;
// TODO: average multiple samples if this loops multiple times
while (channel.timer < 0) {
channel.timer += channel.frequency;
if (channel.bytesRemaining) {
if (channel.shiftPointer == 0) {
// TODO: add 4 CPU cycles
var address = channel.address + channel.length - channel.bytesRemaining;
while (address > 0xFFFF) address -= 0x8000;
channel.currentByte = cpuMemory[address];
}
var delta = (channel.currentByte >> channel.shiftPointer) & 1;
if (delta) {
if (channel.load < 126) channel.load += 2;
} else {
if (channel.load > 1) channel.load -= 2;
}
channel.shiftPointer++;
if (channel.shiftPointer == 8) {
channel.shiftPointer = 0;
channel.bytesRemaining--;
if (channel.bytesRemaining == 0 && channel.loop) channel.bytesRemaining = channel.length;
}
}
channel.sample = channel.load;
//channel.sample >>= 2;
}
}
var click = 0; // The number of accumulated APU clock cycles (½CPU). Generate sample for output buffer ever 10 clicks
var step = 0; // Counts the frame counters steps (currently only LC/Sweep clocks count up)
function asyncTick(amount) {
click = amount;
apuFrames += click;
if (apuFrames >= lcClock0 && step == 0) {
apuClockLcSw(false);
step = 1;
}
if (apuFrames >= lcClock1 && step == 1) {
apuClockLcSw(true);
step = 2;
}
if (apuFrames >= lcClock2 && step == 2) {
apuClockLcSw(false);
step = 3;
}
if (apuFrames >= lcClock3 && step == 3) {
apuClockLcSw(true);
if (enableFrameIrq) pendingFrameCount = true;
apuFrames -= lcClock2 + 1;
step = 0;
}
updatePulse(npulse1, pulse1);
updatePulse(npulse2, pulse2);
updateTriangle(ntriangle, triangle);
updateNoise(nnoise, noise);
updateDmc(dmc);
var mixPulse = 95.88 / ((8128 / (npulse1.sample + npulse2.sample)) + 100);
var mixTnd = 159.79 / (1 / ((ntriangle.sample / 8227) + (nnoise.sample / 12241) + (dmc.sample / 22638)) + 100);
sample = mixPulse + mixTnd;
//sample = (npulse1.sample + npulse2.sample);
}
function tick(amount) {
running = true;
if (bufferLength >= bufferSize * 4) return; // Avoid buffer overflow
click += amount;
if (click > clockStep) {
asyncTick(click);
buffer[bufferPointer] = sample;
//buffer[bufferPointer] = ntriangle.sample;
bufferPointer++;
bufferLength++;
if (bufferPointer == buffer.length) bufferPointer = 0;
click -= clockStep;
}
}
function initChannel(channel) {
channel.volume = 0;
channel.lengthCounter = 0;
channel.sweepTimer = 0;
channel.linearReload = false;
}
var lengthCounterValues = [10, 254, 20, 2, 40, 4, 80, 6, 160, 8, 60, 10, 14, 12, 26, 14, 12, 16, 24, 18, 48, 20, 96, 22, 192, 24, 72, 26, 16, 28, 32, 30];
var noisePeriodValues = [4, 8, 16, 32, 64, 96, 128, 160, 202, 254, 380, 508, 762, 1016, 2034, 4068];
var dmcTimerValues = [428, 380, 340, 320, 286, 254, 226, 214, 190, 160, 142, 128, 106, 84, 72, 54];
var apuFrames = 0;
var lcClock0 = 3728;
var lcClock1 = 7456;
var lcClock2 = 11185;
var lcClock3 = 14914;
var enableFrameIrq = false;
var frameCounterMode = false;
function apuClockLcSw(updateSweeps) {
apuFrameLinearCounter();
if (!updateSweeps) return;
apuFrameSweepChannel(pulse1);
apuFrameSweepChannel(pulse2);
apuFrameSweepChannel(triangle);
apuFrameSweepChannel(noise);
}
function apuFrameSweepChannel(channel) {
if (channel.sweepEnabled) {
if (channel.sweepTimer <= 0) {
channel.sweepTimer += channel.sweepPeriod + 1;
var amount = ((channel.frequency >> channel.sweepShift));
if (channel.sweepNegate) amount = -amount - 1;
var target = (channel.frequency + amount) & 0xfff;
if (target < 0x800 && channel.frequency > 7) channel.frequency = target;
}
channel.sweepTimer -= 1;
}
if (!channel.haltLengthCounter) channel.lengthCounter = Math.max(0, channel.lengthCounter - 1);
}
function apuFrameLinearCounter() {
if (triangle.linearReload) {
triangle.linearCounter = triangle.linearReloadValue;
} else {
triangle.linearCounter = Math.max(0, triangle.linearCounter - 1);
}
if (!triangle.haltLengthCounter) triangle.linearReload = false;
clockDivider(pulse1);
clockDivider(pulse2);
clockDivider(noise);
}
function clockDivider(channel) {
if (channel.startFlag) {
channel.startFlag = false;
channel.decay = 15;
channel.divider = channel.volume;
} else {
if (channel.divider) {
channel.divider--;
return;
}
if (channel.decay) {
channel.divider = channel.volume;
channel.decay--;
return;
}
if (channel.haltLengthCounter) channel.decay = 15; // HLC flag is the same as the Decay loop flag
}
}
function dutyCycle(channel, value) {
channel.haltLengthCounter = ((value & 0x20) != 0);
channel.constantFlag = ((value & 0x10) != 0);
channel.dutyCycle = ((value & 0xC0) >> 6);
channel.volume = (value & 0x0F);
//if (!channel.started) channel.oscillator.start();
channel.started = true;
}
function triangleHalt(channel, value) {
channel.haltLengthCounter = ((value & 0x80) != 0);
channel.linearReloadValue = value & 0x7f;
}
function noisePeriod(value) {
var period = value & 0x0F;
noise.mode = (value & 0x80) ? 6 : 1;
noise.frequency = noisePeriodValues[period];
//noise.oscillator.playbackRate.setValueAtTime(1 / (1 << ((period)/6)), audio.currentTime);
}
function noiseLength(value) {
noise.lengthCounter = lengthCounterValues[(value & 0xf8) >> 3];
noise.startFlag = true;
}
function timer(channel, value) {
channel.frequency &= 0xf00;
channel.frequency |= value;
}
function length(channel, value) {
channel.frequency &= 0x0ff;
channel.frequency |= (value & 0x07) << 8;
channel.lengthCounter = lengthCounterValues[(value & 0xf8) >> 3];
channel.linearReload = true;
channel.startFlag = true;
}
function sweep(channel, value) {
channel.sweepEnabled = ((value & 0x80) != 0);
channel.sweepPeriod = (value & 0x70) >> 4;
channel.sweepTimer = channel.sweepPeriod + 1;
channel.sweepNegate = ((value & 0x08) != 0);
channel.sweepShift = (value & 0x07);
}
function frameCounter(value) {
//enableFrameIrq = (value & 0x40) == 0;
frameCounterMode = (value & 0x80) != 0;
lcClock3 = frameCounterMode ? 18640 : 14914;
if (frameCounterMode) resetStep();
}
function statusRead() {
//enableFrameIrq = true;
return (pulse1.lengthCounter == 0 ? 0 : 0x01) |
(pulse2.lengthCounter == 0 ? 0 : 0x02) |
(triangle.lengthCounter == 0 ? 0 : 0x04) |
(noise.lengthCounter == 0 ? 0 : 0x08) |
(dmc.bytesRemaining ? 0x10 : 0);
}
function statusWrite(value) {
if ((value & 0x01) == 0) pulse1.lengthCounter = 0;
if ((value & 0x02) == 0) pulse2.lengthCounter = 0;
if ((value & 0x04) == 0) triangle.lengthCounter = 0;
if ((value & 0x08) == 0) noise.lengthCounter = 0;
if (value & 0x10) {
if (dmc.bytesRemaining == 0) {
dmc.bytesRemaining = dmc.length;
dmc.shiftPointer = 0;
}
} else {
dmc.bytesRemaining = 0;
}
}
function dmcControl(value) {
dmc.irq = (value & 0x80) != 0;
dmc.loop = (value & 0x40) != 0;
dmc.frequency = dmcTimerValues[value & 0xf];
}
function dmcLoad(value) {
dmc.load = value & 0x7f;
}
function dmcAddress(value) {
dmc.address = 0xC000 | (value << 6);
}
function dmcLength(value) {
dmc.length = (value << 4) | 1;
}
function setApuRegisters() {
if (enableAudioEmulation) {
hwRegisters[0x4000] = new HwRegister(null, function(val) { dutyCycle(pulse1, val); });
hwRegisters[0x4004] = new HwRegister(null, function(val) { dutyCycle(pulse2, val); });
hwRegisters[0x400c] = new HwRegister(null, function(val) { dutyCycle(noise, val); });
hwRegisters[0x4001] = new HwRegister(null, function(val) { sweep(pulse1, val); });
hwRegisters[0x4005] = new HwRegister(null, function(val) { sweep(pulse2, val); });
hwRegisters[0x4002] = new HwRegister(null, function(val) { timer(pulse1, val); });
hwRegisters[0x4006] = new HwRegister(null, function(val) { timer(pulse2, val); });
hwRegisters[0x400A] = new HwRegister(null, function(val) { timer(triangle, val); });
hwRegisters[0x400E] = new HwRegister(null, noisePeriod);
hwRegisters[0x4003] = new HwRegister(null, function(val) { length(pulse1, val); });
hwRegisters[0x4007] = new HwRegister(null, function(val) { length(pulse2, val); });
hwRegisters[0x400B] = new HwRegister(null, function(val) { length(triangle, val); });
hwRegisters[0x400F] = new HwRegister(null, noiseLength);
hwRegisters[0x4008] = new HwRegister(null, function(val) { triangleHalt(triangle, val); });
hwRegisters[0x4010] = new HwRegister(null, dmcControl);
hwRegisters[0x4011] = new HwRegister(null, dmcLoad);
hwRegisters[0x4012] = new HwRegister(null, dmcAddress);
hwRegisters[0x4013] = new HwRegister(null, dmcLength);
}
hwRegisters[0x4015] = new HwRegister(statusRead, statusWrite);
hwRegisters[0x4017].write = frameCounter;
}
function resetStep() {
step = 0;
apuFrames = 0;
}
var apuInterface = {
tick: tick, // function() { running = true; },
init: initAudio,
setRegisters: setApuRegisters
};
return apuInterface;
});
apu = NewApu();