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)
​
​
/////////////  RUNNER  ///////////////////////
​
Vector.prototype.add = function(v)
            {
                this.x += v.x;
                this.y += v.y;
            };
  
Vector.prototype.magnitude = function()
{
  return Math.sqrt(Math.pow(this.x, 2) + Math.pow(this.y, 2));
}
​
Vector.prototype.multiply = function(n)
{
  this.x *= n;
  this.y *= n;
}
​
Vector.prototype.normalize = function()
{  
  magnitude = this.magnitude();
  this.x/= magnitude; 
  this.y/= magnitude;
}
​
Vector.prototype.limit = function(max)
            {
                magnitude = this.magnitude();
​
            if(magnitude > max)
          {
            this.normalize();
            this.multiply(max);            
          }
            };
function Vector(x,y)
            {
                this.x = x;
                this.y = y;
            }
  
​
Runner.prototype.get_random_color = function()
                                {
                                    var colors = ["red", "green", "blue", "orange"]
                        random_color = Math.floor(Math.random()*colors.length);
                        return colors[random_color];
                                };
​
  
//Runner.prototype.r = 15;
  
Runner.prototype.checkEdges = function()
                                {
                                    /*if((this.location.x > w) || (this.location.x < 0))
                  {
                    this.velocity.x = this.velocity.x * -1
                  }
                if((this.location.y > h) || (this,location.y < 0))
                  {
                    this.velocity.x = this.velocity.y * -1
                  }*/
  
                                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;
                    }
                                }; 
  
Runner.prototype.update = function()
                                {
                                this.velocity.add(this.acceleration);
                                this.velocity.limit(this.topspeed);
                  this.location.add(this.velocity);
                                };  
​
            function Runner(r,color,path, coordinates)
            {
                this.r = r;
                this.color = color;
                this.path = path;
        this.location = new Vector(coordinates[0], coordinates[1]);
        // velocity: the rate of change of location
        this.velocity = new Vector(Math.random() * 5, 0);//Math.random() * 5;
        // acceleration: the rate of change of velocity
        this.acceleration = new Vector(-.001, .01);
        this.topspeed = 10;
            }
​
  ///////////////////////////////////////////////
​
​
​
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")
    .data([points2])
    .attr("d", d3.svg.line()
    .tension(0) // Catmull–Rom
    .interpolate("cardinal-closed"));
  
/* 
// OPTIONAL
svg.selectAll(".point")
    .data(points)
    .enter()
    .append("circle")
    .attr("r", 4)
    .attr("transform", function(d) { return "translate(" + d + ")"; });
// OPTIONAL
  
​
var circle = svg.append("circle")
    .attr("r", 13)
    .attr("transform", "translate(" + points[0] + ")");
*/
  
  
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>
​
    