D3 Examples - Point-Along-Path Interpolation

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<!DOCTYPE html>
<meta charset="utf-8">
<body>
  
<style>
​
path {
  fill: none;
  stroke: #000;
  stroke-width: 3px;
}
​
circle {
  /*fill: steelblue; */
  stroke: #fff;
  stroke-width: 3px;
}
  
​
​
</style>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>
​
var points = [
  [200, 200],
  [500, 200],
  [500, 400],
  [200, 400],
  
];
  var points2 = [
  [100, 200],
  [400, 200],
  [400, 400],
  [100, 400],
  
];
​
var w = 960;
var h = 500;
  
var svg = d3.select("body").append("svg")
    .attr("width", w)
    .attr("height", h);
​
  
  
// Text to show "stopwatch"
svg.append("text").text("hey").attr("x", 700).attr("y", 50)
​
​
  
​
​
///////////////  VECTOR  ///////////////////////
​
class Vector
  {
    constructor(x,y)
     {
       this.x = x;
       this.y = y;     
     }
    
    
    static add(v1, v2)
    {
      return new Vector(v1.x + v2.x, v1.y + v2.y) 
    }
    
    
    static subtract(v1, v2)
    {
      return new Vector(v1.x - v2.x, v1.y - v2.y) 
    }
​
    
    copy()
    {
      return new Vector(this.x, this.y);
    }
    
      
    limit(max)
     {
        var magnitude = this.magnitude();
​
        if(magnitude > max)
          {
            this.normalize();
            this.multiply(max);            
          }
            }
    
     normalize()
      {  
        var magnitude = this.magnitude();
        this.x/= magnitude; 
        this.y/= magnitude;
      }
      
     multiply(n)
      {
        this.x *= n;
        this.y *= n;
      }
    
    divide(n)
     {
        this.x /= n;
        this.y /= n;
     }
     add(v)
            {
                this.x += v.x;
                this.y += v.y;
            }
  
         magnitude()
      {
        return Math.sqrt(Math.pow(this.x, 2) + Math.pow(this.y, 2));
      }
    
     dot(v)
    {
      return (this.x * v.x) + (this.y * v.y);
    }
    
    static angleBetween(v1, v2)
    {
      dot_product = v1.dot(v2);
      theta = Math.acos(dot_product/(v1.magnitude() + v2.magmitude()));
      return theta;
    }
      
 }
  
​
///////////////  RUNNER  ///////////////////////
  
class Runner
 {
     constructor(r, color, path, coordinates)
     {
       this.r = r;
       this.color = color;
       this.path = path;
       this.location = new Vector(coordinates[0], coordinates[1]);
       this.velocity = new Vector(0, 0);//Math.random() * 5;
       this.acceleration = new Vector(-.001, .01);
       this.maxspeed = 10;
       this.maxforce = 10;
       this.mass = 10;
     }
     
     get_random_color()
      {
        var colors = ["red", "green", "blue", "orange"]
        var random_color = Math.floor(Math.random()*colors.length);
        return colors[random_color];
      }
     
     checkEdges()
     {
        if(this.location.x > w)
          {
            this.location.x = 0;
          }
        else if(this.location.x < 0)
          {
            this.location.x = w;
          }
​
        if(this.location.y > h)
          {
            this.location.y = 0;
          }
        else if(this.location.y < 0)
          {
            this.location.y = h;
          }
            }
   
      applyForce(force)
      {
                //force.divide(mass);
        this.acceleration.add(force);
      }
​
​
      update()
      {
        this.velocity.add(this.acceleration);
        this.velocity.limit(this.topspeed);
        this.location.add(this.velocity);
        // this.acceleration.multiply(0);
      }
   
        
        followPath(target)
      {
        var desired = Vector.subtract(target, location);
        desired.normalize();
        desired.multiply(maxspeed);
        var steer = Vector.subtract(desired, location);
        steer.limit(maxforce);
        this.applyForce(steer);
      }
         
 }
​
​
  
 ///////////////////////////////////////////////
  
var dataset = [];
  
var path = svg.append("path")
    .data([points])
    .attr("d", d3.svg.line()
    .tension(0) // Catmull–Rom
    .interpolate("cardinal-closed"));
​
var path2 = svg.append("path")
    .attr("d", "M70 60 C 70 180, 370 180, 370 60")
        .attr({fill:"transparent", stroke:"black", "stroke-width":4});
​
  
  
d3.select("svg").on("click", function()
{
      // get the mouse position coordinates
      var coordinates = [0, 0];
      coordinates = d3.mouse(this);
​
​
      dataset.push(new Runner(15, "blue", 1, coordinates));
​
​
      var circles = svg.selectAll("circle") //Select all circles
                        .data(dataset);
​
      circles.enter()
              .append("circle")
              .attr({cx:0, cy:0, fill: function(d){return d.get_random_color()}})
              .attr("r", function(d){return d.r})
              //.transition()
              //.duration(2000)
              //.attr("transform", translator()); //"translate(" + points[0] + ")")
              //.each("end", transition);
​
​
      transition();
​
      function transition() 
      {
        circles.transition()
            .duration(10000)
            //.attrTween("transform", translateAlong(path.node(),path2.node()))
            .attrTween("transform", mover())
            .each("end", transition);
    }
            /*
      // Returns an attrTween for translating along the specified path element.
          function translateAlong(path1, path2) 
                {
            var length_1 = path1.getTotalLength();
            var length_2 = path2.getTotalLength();
            
            return function(d, i, a) 
            {
              return function(t) 
              {
                var p1 = path1.getPointAtLength(t * length_1);
                var p2 = path2.getPointAtLength(t * length_2);
                svg.select("text").text(Math.floor(t * 100))
                if (t < .3)
                {
                  p = p2
                }
                else
                {
                  p = p1
                  
                }
                return "translate(" + p.x + "," + p.y + ")";
              };
                    };
                    }
  
                */
  
  
      function mover() 
      {
          return function(d, i, a) 
          {
            return function(t) 
            {
              svg.select("text").text(Math.floor(t * 100))
​
              d.checkEdges(); // make sure objects remain on screen; bounce back
              d.update();           // update the object's position
​
                      // return the updated translated position
              return "translate(" + d.location.x + "," + d.location.y + ")";
            };
          };
      }
  
});
​
​
​
</script>
​
    