D3 Examples - Voronoï playground : undulating radial wave

Voronoï playground : undulating radial wave
No path is visible, only cells !
This block is a continuation of a previous one. The idea comes when I look at Voronoï tesselation where (sometimes) pathes emerge, due to the smooth chaining of cells's borders. This is put to its extreme in these blocks.
Acknowledgments to:
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<head>
<meta charset="utf-8">
<title>Voronoï playground : undulating radial wave</title>
<meta content="Voronoï playground : undulating radial wave" name="description">
<style>
  
  #under-construction {
    display: none;
    position: absolute;
    top: 200px;
    left: 300px;
    font-size: 40px;
  }
  
  svg {
    margin: 1px;
    border-radius: 1000px;
    box-shadow: 2px 2px 6px grey;
    cursor: crosshair;
  }
  
  #drawing-area {
    filter: url("#saturate-around-path");
  }
    
  #wave-path {
    fill: none;
    stroke: white;
    stroke-width: 20px;
  }
  
  .cell {
    fill: none;
    stroke: cyan;
  }
</style>
</head>
<body>
  <div id="under-construction">
    UNDER CONSTRUCTION
  </div>
  
  <svg>
    <defs>
      <filter id="saturate-around-path">
        <feGaussianBlur result="blured" in="SourceAlpha" stdDeviation="10" />
        <feComposite result="composed" in="SourceGraphic" in2="blured" operator="in"/>
      </filter>
    </defs>
    <g id="drawing-area">
      <path id="wave-path"/>
      <g id="voronoi-container"/>
    </g>
  </svg>
  
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <script src="simplex-noise.min.js"></script>
  <script>
    var _2PI = 2*Math.PI;
    
    //begin: layout conf.
    var svgbw = 1, //svg border width
        svgm = 10, //svg margin
            totalWidth = 500,
        totalHeight = 500,
        width = totalWidth-(svgm+svgbw)*2,
        height = totalHeight-(svgm+svgbw)*2,
        midWidth = width/2,
        midHeight = height/2;
    //end: layout conf.
    
    //begin: Simplex conf.
    var simplex = new SimplexNoise(),
            angleBasedLength = 1, //lower values make more heratic waves' shapes
            timeBasedLength = 5000, //lower values make radiations' shapes evolving faster
        noiseStrength = midHeight/16;
    //end: Simplex conf.
    
    //begin: wave conf.
    var sampling=3,
        vertexCount = 360/sampling,     // segments per wave
        minWaveRadius = midHeight/2 - noiseStrength,
        maxWaveRadius = 5*midHeight/6 - noiseStrength
        waveRadius = (minWaveRadius + maxWaveRadius)/2,
        waveRadiusObjective = waveRadius    //allows to update the base wave's radius
        wave = [];
    //end: wave conf.
    
    //begin: voronoi conf.
    var maxSpread = 10;
    //end: voronoi conf.
    
    var strokeOpacityScale = d3.scaleLinear()
        .domain([0, 2*maxSpread])
        .range([1, 0]);
    var voronoiLayout = d3.voronoi()
          .x(function(d) { return d.x; })
          .y(function(d) { return d.y; })
          .extent([[-midWidth, -midHeight], [midWidth, midHeight]]);
    
    var svg, drawingArea, wavePath, voronoiContainer;
    
    initLayout();
    initWave();
    
    d3.interval(function(elapsed) {
      updateWave(elapsed);
      redrawRadialWave();
      redrawVoronoi();
    });
    
    
    function moved() {
      var coords = d3.mouse(this);
      var mouseRadius = Math.sqrt(Math.pow(coords[0]-midWidth,2)+Math.pow(coords[1]-midHeight,2));
      if (mouseRadius<minWaveRadius) {
        waveRadiusObjective = minWaveRadius;
      } else if (mouseRadius>maxWaveRadius) {
        waveRadiusObjective = maxWaveRadius;
      } else {
        waveRadiusObjective = mouseRadius;
      }
    }
    
    function exited() {
      waveRadiusObjective = (minWaveRadius+maxWaveRadius)/2;
    }
    
    function initLayout() {
      svg = d3.select("svg")
        .attr("width", width)
        .attr("height", height)
        .on("touchmove mousemove", moved)
        .on("mouseout", exited);
      
      drawingArea = d3.select("#drawing-area")
        .attr("transform", "translate("+[midWidth, midHeight]+")");
      
      wavePath = d3.select("#wave-path")
      
      voronoiContainer = d3.select("#voronoi-container")
    }
    
    function initWave() {
      var angle, oppositeAngle, noise, voronoiSpread;
      
      for (var v=0; v<vertexCount; v++) {
        angle = _2PI*v/vertexCount;
        voronoiSpread = maxSpread*Math.abs(d3.randomNormal()())
        wave[v] = {
          angle: angle,                                             // [0, vertexCount] -> [0, 2PI[; discontinuous around 0 rad; will produce noise values discontinued around 0 rad;
          oppositeAngle : (angle+Math.PI)%_2PI, // [0, vertexCount] -> [PI, ..., 2PI, 0, ..., PI[; discontinuous around PI; will produce noise values discontinued around PI;
          continuityCoef: (Math.cos(angle+Math.PI)+1)/2,    // allows to produce a continous noise from 'angle'-based noise and 'oppositeAngle'-based noise; allows to eliminate discontinuities around 0 rad and PI;
          cos: Math.cos(angle),
          sin: Math.sin(angle),
          angleNoise: 0,                                            // 'angle'-based noise; updated at each frame
          oppositeAngleNoise: 10,                           // 'opppositeAngle'-based noise; updated at each frame
          noisedRadius: 0,                                      // vertex's radius; updated at each frame
          position: [0, 0],                                     // vertex position; updated at each frame
          voronoi: {
            strokeColor: d3.hsl(v*sampling, 1, 0.45),
            spread: voronoiSpread,
            strokeOpacity: strokeOpacityScale(voronoiSpread),
            //spread: maxSpread,
            firstSeedPosition: [0, 0],              // updated at each frame
            secondSeedPosition: [0, 0]              // updated at each frame
          }
        };
      }
    }
    
    function updateWave(elapsed) {
      var timeBasedChange = elapsed/timeBasedLength;
      var vertex;
      
      //begin: damping wave's base radius towards target radius
      waveRadius = 0.95*waveRadius + 0.05*waveRadiusObjective;
      //end: damping wave's base radius towards target radius
      
      
      //begin: update the wave's data and Voronoi seeds
      updateVertex(wave[0], timeBasedChange);
      for (var v=1; v<vertexCount; v++) {
        updateVertex(wave[v], timeBasedChange);
        updateVertexSeeds(wave[v], wave[v-1]);
      }
      updateVertexSeeds(wave[0], wave[vertexCount-1]);
      //end: update the wave's data and Voronoi seeds
    }
    
    function updateVertex(vertex, timeBasedChange) {
      //begin: update vertex' radius using Simplex noise
      vertex.angleNoise = noiseStrength*simplex.noise2D(vertex.angle/angleBasedLength, timeBasedChange);
        vertex.oppositeAngleNoise = noiseStrength*simplex.noise2D(vertex.oppositeAngle/angleBasedLength, timeBasedChange+10);
        vertex.noisedRadius = (waveRadius+vertex.continuityCoef*vertex.angleNoise+(1-vertex.continuityCoef)*vertex.oppositeAngleNoise);
        vertex.position = [
          vertex.noisedRadius*vertex.cos,
          vertex.noisedRadius*vertex.sin
        ];
      //begin: update vertex' radius using Simplex noise
    }
    
    function updateVertexSeeds(vertex, prevVertex) {
      //begin: update vertex' seeds based on the trend of the segment [vertex, prevVertex]
      var midX, midY, dx, dy, length, unitDx, unitDy;
      
      midX = (vertex.position[0]+prevVertex.position[0])/2;
      midY = (vertex.position[1]+prevVertex.position[1])/2;
      dx = vertex.position[0]-prevVertex.position[0];
      dy = vertex.position[1]-prevVertex.position[1];
      length = Math.sqrt(Math.pow(dx, 2)+Math.pow(dy,2));
      unitDx = dx/length;
      unitDy = dy/length;
      //begin: first seed @ PI/2 from segment's trend
      vertex.voronoi.firstSeedPosition= [
        midX+vertex.voronoi.spread*unitDy,
        midY-vertex.voronoi.spread*unitDx
      ];
      //end: first seed @ PI/2 from segment's trend
      //begin: second seed @ -PI/2 from segment's trend
      vertex.voronoi.secondSeedPosition= [
        midX-vertex.voronoi.spread*unitDy,
        midY+vertex.voronoi.spread*unitDx
      ];
      //end: second seed @ -PI/2 from segment's trend
      //end: update vertex' seeds based on the trend of the segment [vertex, prevVertex]
    }
    
    function redrawRadialWave() {
      //update wave's path
      var newPath, noisedRadius;
      
      newPath = "M"+wave[0].position[0]+","+wave[0].position[1];
      for (var v=1; v<vertexCount; v++) {
        newPath += "L"+wave[v].position[0]+","+wave[v].position[1];
      }
      newPath += "Z";
      wavePath.attr("d", newPath);
    }
    
    
    function redrawVoronoi() {
      var seeds = [];
      var vertex;
      
      //begin: compute Voronoi seeds, close to the wave's path
      for (var v=0; v<vertexCount; v++) {
        vertex = wave[v];
        seeds.push({
            x: vertex.voronoi.firstSeedPosition[0],
          y: vertex.voronoi.firstSeedPosition[1],
          vertex: wave[v]
        });
        seeds.push({
            x: vertex.voronoi.secondSeedPosition[0],
          y: vertex.voronoi.secondSeedPosition[1],
          vertex: wave[v]
        });
      }
      //end: compute Voronoi seeds, close to the wave's path
      
      //begin: draw Voronoi cell
      cells = voronoiLayout.polygons(seeds);
      var drawnCells = voronoiContainer.selectAll(".cell")
        .data(cells);
      drawnCells.enter()
        .append("path")
          .classed("cell", true)
            .style("stroke-opacity", function(d) { return d.data.vertex.voronoi.strokeOpacity; })
        .merge(drawnCells)
            .style("stroke", function(d) { return d.data.vertex.voronoi.strokeColor; })
            .attr("d", function(d, i) { return d3.line()(d)+'z'; });
      //end: draw Voronoi cells
    }
  </script>
</body>
    