Simple SVG Path Demo

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1">

<title>Simple SVG Path</title>

svg {
      border: solid 1px #ccc;
      background-color: #fff;
    }

.axis path,
    .axis line {
        fill: none;
        stroke: #ccc;
        shape-rendering: crispEdges;
    }

.axis text {
        font-family: sans-serif;
        font-size: 11px;
    }

.route {
      fill: none;
      stroke: red;
      stroke-width: 2px;
    }

/* Points */
    circle.main {
      fill: #EDC951;
      stroke: #CC333F;
      stroke-width: 1px;
    }

circle.control {
      fill: white;
      stroke: #00A0B0;
    }

.control-line {
      stroke-width: 1px;
      stroke: #00A0B0;
      stroke-dasharray: 1,1;
    }

.curve {
      fill: none;
      stroke: #CC333F;
      stroke-width: 2px;
    }

pre {
      font-family: Courier;
    }
  </style>

var width  = 400,
        height = 400,
        margin = 30;

var lines = d3.range(-20, 20);

var svg = d3.select('svg'),
        xaxis = svg.select('g.xaxis'),
        yaxis = svg.select('g.yaxis');

// Translate the groups for the axis
    xaxis.attr('transform', function() {
      var dx = margin,
          dy = height - margin;
      return 'translate(' + [dx, dy] + ')';
    });

yaxis.attr('transform', function() {
      var dx = margin,
          dy = margin;
      return 'translate(' + [dx, dy] + ')';
    });

var xScale = d3.scale.linear()
      .domain(d3.extent(lines))
      .range([0, width - 2 * margin]);

var yScale = d3.scale.linear()
      .domain(d3.extent(lines))
      .range([0, height - 2 * margin]);

var xAxis = d3.svg.axis()
      .orient('bottom')
      .scale(xScale)
      .tickSize(-width + 2 * margin);

var yAxis = d3.svg.axis()
      .orient('left')
      .scale(yScale)
      .tickSize(-height + 2 * margin);

xaxis.call(xAxis);
    yaxis.call(yAxis);

// Compute the path string
    function computePath(points) {

function p(point) {
        return xScale(point.x) + ' ' + yScale(point.y);
      }

var p1 = p(points[0]),
          c1 = p(points[1]),
          p2 = p(points[2]),
          c2 = p(points[3]);

return 'M ' + p1 + 'C ' + [c1, c2, p2].join(',');
    }

function computePathText(points) {

function p(point) {
        return d3.round(point.x, 2) + ' ' + d3.round(point.y, 2);
      }

var p1 = p(points[0]),
          c1 = p(points[1]),
          p2 = p(points[2]),
          c2 = p(points[3]);

return 'M ' + p1 + ' C ' + [c1, c2, p2].join(', ');
    }

// Path Editor

var points = [
      {x:  5, y:   5, type: 'main'},
      {x: 10, y: -15, type: 'control'},
      {x: 10, y:  10, type: 'main'},
      {x: 15, y:  10, type: 'control'}
    ];

var lineData = [
      [points[0], points[1]],
      [points[2], points[3]]
    ];

var gPaths  = svg.select('g.paths'),
        circles = gPaths.selectAll('circle').data(points);
    var lines = gPaths.selectAll('line').data(lineData);

// Tension Lines
    lines.enter().append('line').classed('control-line', true);

lines
      .attr('x1', function(d) { return xScale(d[0].x); })
      .attr('y1', function(d) { return yScale(d[0].y); })
      .attr('x2', function(d) { return xScale(d[1].x); })
      .attr('y2', function(d) { return yScale(d[1].y); });

lines.exit().remove();

// Bezier Curve
    var curve = gPaths.selectAll('path.curve').data([points]);
    curve.enter().append('path').classed('curve', true);
    curve.attr('d', computePath);
    curve.exit().remove();

// Control and Curve Points
    circles.enter().append('circle').classed('point', true);

circles
      .attr('cx', function(d) { return xScale(d.x); })
      .attr('cy', function(d) { return yScale(d.y); })
      .attr('r', 6)
      .each(function(d) { d3.select(this).classed(d.type, true); });

circles.exit().remove();

// Path String
    var text = d3.selectAll('pre').data([points]);
    text.enter().append('text').classed('path', true);
    text
      .attr('x', margin + 5)
      .attr('y', margin - 5)
      .text(computePathText);
    text.exit().remove();

// Drag behaviour
    var drag = d3.behavior.drag()
      .on('drag', function(d, i) {

var cx = +d3.select(this).attr('cx'),
            cy = +d3.select(this).attr('cy');

cx += d3.event.dx;
        cy += d3.event.dy;

// Update the point coordinates
        d.x = xScale.invert(cx);
        d.y = yScale.invert(cy);

// Update the points, tension lines, Bezier curve and
        // SVG path string
        circles
          .attr('cx', function(d) { return xScale(d.x); })
          .attr('cy', function(d) { return yScale(d.y); });

lines
          .attr('x1', function(d) { return xScale(d[0].x); })
          .attr('y1', function(d) { return yScale(d[0].y); })
          .attr('x2', function(d) { return xScale(d[1].x); })
          .attr('y2', function(d) { return yScale(d[1].y); });

curve.attr('d', computePath);
        text.text(computePathText);
      });

// Attach the drag behaviour to the points
    circles.call(drag);
  </script>

</body>
</html>

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