new, ui, insights: stereo field

src/ui/src/helpers/correlationMeter.ts

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+let prevCorr = 0;
+
+const ATTACK_SMOOTHING = 1; // .85
+const DECAY_SMOOTHING = 0.1; //.16//.4
+
+const rotate45deg = (x, y) => {
+    var tmp = cartesian2polar(x, y);
+    tmp.angle -= 0.78539816; // Rotate coordinate by 45 degrees
+    var tmp2 = polar2cartesian(tmp.radius, tmp.angle);
+    return { x: tmp2.x, y: tmp2.y };
+};
+
+const getCorr = (x, y) => {
+    var tmp = cartesian2polar(x, y);
+    tmp.angle -= 0.78539816; // Rotate coordinate by 45 degrees
+    var radius = -1; // rotate again this time 180 degrees, is it this which break _left ?
+    var angle = Math.atan2(x, y); // atan2 gives full circle
+    return radius * angle;
+};
+const cartesian2polar = (x, y) => {
+    // Convert cartesian to polar coordinate
+    var radius = Math.sqrt(x * x + y * y);
+    var angle = Math.atan2(y, x); // atan2 gives full circle
+    return { radius: radius, angle: angle };
+};
+
+const polar2cartesian = (radius, angle) => {
+    // Convert polar coordinate to cartesian coordinate
+    var x = radius * Math.sin(angle);
+    var y = radius * Math.cos(angle);
+    return { x: x, y: y };
+};
+
+const getData = (leftChannel: any, rightChannel: any) => {
+    const data = [];
+
+    data.push(new Float32Array(leftChannel.frequencyBinCount));
+    leftChannel.getFloatTimeDomainData(data[0]);
+
+    data.push(new Float32Array(rightChannel.frequencyBinCount));
+    rightChannel.getFloatTimeDomainData(data[1]);
+
+    return data;
+};
+
+export const correlation = (leftChannel: any, rightChannel: any) => {
+    const data = getData(leftChannel, rightChannel);
+
+    const doSmooth = (oldV, newV) => {
+        var ret = oldV;
+        if (oldV > newV) {
+            ret -= DECAY_SMOOTHING * (oldV - newV);
+        } else {
+            ret += ATTACK_SMOOTHING * (newV - oldV);
+        }
+        //if (oldV < 0) ret = 0;
+        //if (oldV > 1.0) ret = 1.0;
+        return ret;
+    };
+
+    // ---
+
+    var corr = 0;
+    var x;
+    // sum up corr
+    for (var i = 0; i < data[0].length; i++) {
+        x = data[1] ? data[1][i] : data[0][i]; // take care of single channel signals, for corr use same data
+        corr += getCorr(x, data[0][i]);
+    }
+    corr = corr / data[0].length;
+    // still something wrong where
+    if (corr > 1) corr = 1;
+    if (corr < -1) corr = -1;
+    //this.corr = (corr + this.corr*this.damp)/2.0;
+
+    prevCorr = doSmooth(prevCorr, corr);
+    return prevCorr;
+};
+
+export const stereoField = (leftChannel: any, rightChannel: any) => {
+    const data = getData(leftChannel, rightChannel);
+
+    var x = data[1] ? data[1][0] : 0; // take care of single channel signals
+    let rotated = rotate45deg(x, data[0][0]); // Right channel is mapped to x axis
+
+    const points = [] as { x: number; y: number }[];
+
+    points.push({ x: rotated.x, y: rotated.y });
+
+    for (var i = 1; i < data[0].length; i++) {
+        x = data[1] ? data[1][i] : 0; // take care of single channel signals
+        rotated = rotate45deg(x, data[0][i]);
+
+        points.push({ x: rotated.x, y: rotated.y });
+    }
+
+    return points;
+};