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// For the record, these distance formulas were taken from the OpenAL
// spec
// not the code. The Web Audio spec follows the OpenAL formulas.
function linearDistance(panner, x, y, z) {
let distance = Math.sqrt(x * x + y * y + z * z);
let dref = Math.min(panner.refDistance, panner.maxDistance);
let dmax = Math.max(panner.refDistance, panner.maxDistance);
distance = Math.max(Math.min(distance, dmax), dref);
let rolloff = Math.max(Math.min(panner.rolloffFactor, 1), 0);
if (dref === dmax)
return 1 - rolloff;
let gain = (1 - rolloff * (distance - dref) / (dmax - dref));
return gain;
}
function inverseDistance(panner, x, y, z) {
let distance = Math.sqrt(x * x + y * y + z * z);
distance = Math.max(distance, panner.refDistance);
let rolloff = panner.rolloffFactor;
let gain = panner.refDistance /
(panner.refDistance +
rolloff * (Math.max(distance, panner.refDistance) - panner.refDistance));
return gain;
}
function exponentialDistance(panner, x, y, z) {
let distance = Math.sqrt(x * x + y * y + z * z);
distance = Math.max(distance, panner.refDistance);
let rolloff = panner.rolloffFactor;
let gain = Math.pow(distance / panner.refDistance, -rolloff);
return gain;
}
// Simple implementations of 3D vectors implemented as a 3-element array.
// x - y
function vec3Sub(x, y) {
let z = new Float32Array(3);
z[0] = x[0] - y[0];
z[1] = x[1] - y[1];
z[2] = x[2] - y[2];
return z;
}
// x/|x|
function vec3Normalize(x) {
let mag = Math.hypot(...x);
return x.map(function(c) {
return c / mag;
});
}
// x == 0?
function vec3IsZero(x) {
return x[0] === 0 && x[1] === 0 && x[2] === 0;
}
// Vector cross product
function vec3Cross(u, v) {
let cross = new Float32Array(3);
cross[0] = u[1] * v[2] - u[2] * v[1];
cross[1] = u[2] * v[0] - u[0] * v[2];
cross[2] = u[0] * v[1] - u[1] * v[0];
return cross;
}
// Dot product
function vec3Dot(x, y) {
return x[0] * y[0] + x[1] * y[1] + x[2] * y[2];
}
// a*x, for scalar a
function vec3Scale(a, x) {
return x.map(function(c) {
return a * c;
});
}
function calculateAzimuth(source, listener, listenerForward, listenerUp) {
let sourceListener = vec3Sub(source, listener);
if (vec3IsZero(sourceListener))
return 0;
sourceListener = vec3Normalize(sourceListener);
let listenerRight = vec3Normalize(vec3Cross(listenerForward, listenerUp));
let listenerForwardNorm = vec3Normalize(listenerForward);
let up = vec3Cross(listenerRight, listenerForwardNorm);
let upProjection = vec3Dot(sourceListener, up);
let projectedSource =
vec3Normalize(vec3Sub(sourceListener, vec3Scale(upProjection, up)));
let azimuth =
180 / Math.PI * Math.acos(vec3Dot(projectedSource, listenerRight));
// Source in front or behind the listener
let frontBack = vec3Dot(projectedSource, listenerForwardNorm);
if (frontBack < 0)
azimuth = 360 - azimuth;
// Make azimuth relative to "front" and not "right" listener vector.
if (azimuth >= 0 && azimuth <= 270)
azimuth = 90 - azimuth;
else
azimuth = 450 - azimuth;
// We don't need elevation, so we're skipping that computation.
return azimuth;
}
// Map our position angle to the azimuth angle (in degrees).
//
// An angle of 0 corresponds to an azimuth of 90 deg; pi, to -90 deg.
function angleToAzimuth(angle) {
return 90 - angle * 180 / Math.PI;
}
// The gain caused by the EQUALPOWER panning model
function equalPowerGain(azimuth, numberOfChannels) {
let halfPi = Math.PI / 2;
if (azimuth < -90)
azimuth = -180 - azimuth;
else
azimuth = 180 - azimuth;
if (numberOfChannels == 1) {
let panPosition = (azimuth + 90) / 180;
let gainL = Math.cos(halfPi * panPosition);
let gainR = Math.sin(halfPi * panPosition);
return {left: gainL, right: gainR};
} else {
if (azimuth <= 0) {
let panPosition = (azimuth + 90) / 90;
let gainL = Math.cos(halfPi * panPosition);
let gainR = Math.sin(halfPi * panPosition);
return {left: gainL, right: gainR};
} else {
let panPosition = azimuth / 90;
let gainL = Math.cos(halfPi * panPosition);
let gainR = Math.sin(halfPi * panPosition);
return {left: gainL, right: gainR};
}
}
}
function applyPanner(azimuth, srcL, srcR, numberOfChannels) {
let length = srcL.length;
let outL = new Float32Array(length);
let outR = new Float32Array(length);
if (numberOfChannels == 1) {
for (let k = 0; k < length; ++k) {
let gains = equalPowerGain(azimuth[k], numberOfChannels);
outL[k] = srcL[k] * gains.left;
outR[k] = srcR[k] * gains.right;
}
} else {
for (let k = 0; k < length; ++k) {
let gains = equalPowerGain(azimuth[k], numberOfChannels);
if (azimuth[k] <= 0) {
outL[k] = srcL[k] + srcR[k] * gains.left;
outR[k] = srcR[k] * gains.right;
} else {
outL[k] = srcL[k] * gains.left;
outR[k] = srcR[k] + srcL[k] * gains.right;
}
}
}
return {left: outL, right: outR};
}