vega.js

vg = (function(d3){ // take d3 instance as sole import
var vg = {};

// semantic versioning
vg.version = '1.3.0';

// type checking functions
var toString = Object.prototype.toString;

vg.isObject = function(obj) {
  return obj === Object(obj);
};

vg.isFunction = function(obj) {
  return toString.call(obj) == '[object Function]';
};

vg.isString = function(obj) {
  return toString.call(obj) == '[object String]';
};
  
vg.isArray = Array.isArray || function(obj) {
  return toString.call(obj) == '[object Array]';
};

vg.isNumber = function(obj) {
  return toString.call(obj) == '[object Number]';
};

vg.isBoolean = function(obj) {
  return toString.call(obj) == '[object Boolean]';
};

vg.number = function(s) { return +s; };

vg.boolean = function(s) { return !!s; };

// utility functions

vg.identity = function(x) { return x; };

vg.extend = function(obj) {
  for (var x, name, i=1, len=arguments.length; i<len; ++i) {
    x = arguments[i];
    for (name in x) { obj[name] = x[name]; }
  }
  return obj;
};

vg.duplicate = function(obj) {
  return JSON.parse(JSON.stringify(obj));
};

vg.field = function(f) {
  return f.split("\\.")
    .map(function(d) { return d.split("."); })
    .reduce(function(a, b) {
      if (a.length) { a[a.length-1] += "." + b.shift(); }
      a.push.apply(a, b);
      return a;
    }, []);
};

vg.accessor = function(f) {
  var s;
  return (vg.isFunction(f) || f==null)
    ? f : vg.isString(f) && (s=vg.field(f)).length > 1
    ? function(x) { return s.reduce(function(x,f) { return x[f]; }, x); }
    : function(x) { return x[f]; };
};

vg.comparator = function(sort) {
  var sign = [];
  if (sort === undefined) sort = [];
  sort = vg.array(sort).map(function(f) {
    var s = 1;
    if      (f[0] === "-") { s = -1; f = f.slice(1); }
    else if (f[0] === "+") { s = +1; f = f.slice(1); }
    sign.push(s);
    return vg.accessor(f);
  });
  return function(a,b) {
    var i, n, f, x, y;
    for (i=0, n=sort.length; i<n; ++i) {
      f = sort[i]; x = f(a); y = f(b);
      if (x < y) return -1 * sign[i];
      if (x > y) return sign[i];
    }
    return 0;
  };
};

vg.numcmp = function(a, b) { return a - b; };

vg.array = function(x) {
  return x != null ? (vg.isArray(x) ? x : [x]) : [];
};

vg.values = function(x) {
  return (vg.isObject(x) && !vg.isArray(x) && x.values) ? x.values : x;
};

vg.str = function(str) {
  return vg.isArray(str)
    ? "[" + str.map(vg.str) + "]"
    : vg.isString(str) ? ("'"+str+"'") : str;
};

vg.keys = function(x) {
  var keys = [];
  for (var key in x) keys.push(key);
  return keys;
};

vg.unique = function(data, f) {
  f = f || vg.identity;
  var results = [], v;
  for (var i=0; i<data.length; ++i) {
    v = f(data[i]);
    if (results.indexOf(v) < 0) results.push(v);
  }
  return results;
};

// Logging

function vg_write(msg) {
  vg.config.isNode
    ? process.stderr.write(msg + "\n")
    : console.log(msg);
}

vg.log = function(msg) {
  vg_write("[Vega Log] " + msg);
};

vg.error = function(msg) {
  msg = "[Vega Err] " + msg;
  vg_write(msg);
  if (typeof alert !== "undefined") alert(msg);
};vg.config = {};

// are we running in node.js?
// via timetler.com/2012/10/13/environment-detection-in-javascript/
vg.config.isNode = typeof exports !== 'undefined' && this.exports !== exports;

// base url for loading external data files
// used only for server-side operation
vg.config.baseURL = "";

// version and namepsaces for exported svg
vg.config.svgNamespace =
  'version="1.1" xmlns="http://www.w3.org/2000/svg" ' +
  'xmlns:xlink="http://www.w3.org/1999/xlink"';

// default axis properties
vg.config.axis = {
  ticks: 10,
  padding: 3,
  axisColor: "#000",
  gridColor: "#ccc",
  tickColor: "#000",
  tickLabelColor: "#000",
  axisWidth: 1,
  tickWidth: 1,
  tickSize: 6,
  tickLabelFontSize: 11,
  tickLabelFont: "sans-serif"
};

// default scale ranges
vg.config.range = {
  category10: [
    "#1f77b4",
    "#ff7f0e",
    "#2ca02c",
    "#d62728",
    "#9467bd",
    "#8c564b",
    "#e377c2",
    "#7f7f7f",
    "#bcbd22",
    "#17becf"
  ],
  category20: [
    "#1f77b4",
    "#aec7e8",
    "#ff7f0e",
    "#ffbb78",
    "#2ca02c",
    "#98df8a",
    "#d62728",
    "#ff9896",
    "#9467bd",
    "#c5b0d5",
    "#8c564b",
    "#c49c94",
    "#e377c2",
    "#f7b6d2",
    "#7f7f7f",
    "#c7c7c7",
    "#bcbd22",
    "#dbdb8d",
    "#17becf",
    "#9edae5"
  ],
  shapes: [
    "circle",
    "cross",
    "diamond",
    "square",
    "triangle-down",
    "triangle-up"
  ]
};vg.Bounds = (function() {
  var bounds = function(b) {
    this.clear();
    if (b) this.union(b);
  };
  
  var prototype = bounds.prototype;
  
  prototype.clear = function() {
    this.x1 = +Number.MAX_VALUE;
    this.y1 = +Number.MAX_VALUE;
    this.x2 = -Number.MAX_VALUE;
    this.y2 = -Number.MAX_VALUE;
    return this;
  };
  
  prototype.set = function(x1, y1, x2, y2) {
    this.x1 = x1;
    this.y1 = y1;
    this.x2 = x2;
    this.y2 = y2;
    return this;
  };

  prototype.add = function(x, y) {
    if (x < this.x1) this.x1 = x;
    if (y < this.y1) this.y1 = y;
    if (x > this.x2) this.x2 = x;
    if (y > this.y2) this.y2 = y;
    return this;
  };

  prototype.expand = function(d) {
    this.x1 -= d;
    this.y1 -= d;
    this.x2 += d;
    this.y2 += d;
    return this;
  };
  
  prototype.round = function() {
    this.x1 = Math.floor(this.x1);
    this.y1 = Math.floor(this.y1);
    this.x2 = Math.ceil(this.x2);
    this.y2 = Math.ceil(this.y2);
    return this;
  };

  prototype.translate = function(dx, dy) {
    this.x1 += dx;
    this.x2 += dx;
    this.y1 += dy;
    this.y2 += dy;
    return this;
  };
  
  prototype.rotate = function(angle, x, y) {
    var cos = Math.cos(angle),
        sin = Math.sin(angle),
        cx = x - x*cos + y*sin,
        cy = y - x*sin - y*cos,
        x1 = this.x1, x2 = this.x2,
        y1 = this.y1, y2 = this.y2;

    return this.clear()
      .add(cos*x1 - sin*y1 + cx,  sin*x1 + cos*y1 + cy)
      .add(cos*x1 - sin*y2 + cx,  sin*x1 + cos*y2 + cy)
      .add(cos*x2 - sin*y1 + cx,  sin*x2 + cos*y1 + cy)
      .add(cos*x2 - sin*y2 + cx,  sin*x2 + cos*y2 + cy);
  }

  prototype.union = function(b) {
    if (b.x1 < this.x1) this.x1 = b.x1;
    if (b.y1 < this.y1) this.y1 = b.y1;
    if (b.x2 > this.x2) this.x2 = b.x2;
    if (b.y2 > this.y2) this.y2 = b.y2;
    return this;
  };

  prototype.encloses = function(b) {
    return b && (
      this.x1 <= b.x1 &&
      this.x2 >= b.x2 &&
      this.y1 <= b.y1 &&
      this.y2 >= b.y2
    );
  };

  prototype.intersects = function(b) {
    return b && !(
      this.x2 < b.x1 ||
      this.x1 > b.x2 ||
      this.y2 < b.y1 ||
      this.y1 > b.y2
    );
  };

  prototype.contains = function(x, y) {
    return !(
      x < this.x1 ||
      x > this.x2 ||
      y < this.y1 ||
      y > this.y2
    );
  };

  prototype.width = function() {
    return this.x2 - this.x1;
  };

  prototype.height = function() {
    return this.y2 - this.y1;
  };

  return bounds;
})();vg.canvas = {};vg.canvas.path = (function() {

  // Path parsing and rendering code taken from fabric.js -- Thanks!
  var cmdLength = { m:2, l:2, h:1, v:1, c:6, s:4, q:4, t:2, a:7 },
      re = [/([MLHVCSQTAZmlhvcsqtaz])/g, /###/, /(\d)-/g, /\s|,|###/];

  function parse(path) {
    var result = [],
        currentPath,
        chunks,
        parsed;

    // First, break path into command sequence
    path = path.slice().replace(re[0], '###$1').split(re[1]).slice(1);

    // Next, parse each command in turn
    for (var i=0, j, chunksParsed, len=path.length; i<len; i++) {
      currentPath = path[i];
      chunks = currentPath.slice(1).trim().replace(re[2],'$1###-').split(re[3]);
      chunksParsed = [currentPath.charAt(0)];

      for (var j = 0, jlen = chunks.length; j < jlen; j++) {
        parsed = parseFloat(chunks[j]);
        if (!isNaN(parsed)) {
          chunksParsed.push(parsed);
        }
      }

      var command = chunksParsed[0].toLowerCase(),
          commandLength = cmdLength[command];

      if (chunksParsed.length - 1 > commandLength) {
        for (var k = 1, klen = chunksParsed.length; k < klen; k += commandLength) {
          result.push([ chunksParsed[0] ].concat(chunksParsed.slice(k, k + commandLength)));
        }
      }
      else {
        result.push(chunksParsed);
      }
    }

    return result;
  }

  function drawArc(g, x, y, coords, bounds, l, t) {
    var rx = coords[0];
    var ry = coords[1];
    var rot = coords[2];
    var large = coords[3];
    var sweep = coords[4];
    var ex = coords[5];
    var ey = coords[6];
    var segs = arcToSegments(ex, ey, rx, ry, large, sweep, rot, x, y);
    for (var i=0; i<segs.length; i++) {
      var bez = segmentToBezier.apply(null, segs[i]);
      g.bezierCurveTo.apply(g, bez);
      bounds.add(bez[0]-l, bez[1]-t);
      bounds.add(bez[2]-l, bez[3]-t);
      bounds.add(bez[4]-l, bez[5]-t);
    }
  }

  var arcToSegmentsCache = { },
      segmentToBezierCache = { },
      join = Array.prototype.join,
      argsStr;

  // Copied from Inkscape svgtopdf, thanks!
  function arcToSegments(x, y, rx, ry, large, sweep, rotateX, ox, oy) {
    argsStr = join.call(arguments);
    if (arcToSegmentsCache[argsStr]) {
      return arcToSegmentsCache[argsStr];
    }

    var th = rotateX * (Math.PI/180);
    var sin_th = Math.sin(th);
    var cos_th = Math.cos(th);
    rx = Math.abs(rx);
    ry = Math.abs(ry);
    var px = cos_th * (ox - x) * 0.5 + sin_th * (oy - y) * 0.5;
    var py = cos_th * (oy - y) * 0.5 - sin_th * (ox - x) * 0.5;
    var pl = (px*px) / (rx*rx) + (py*py) / (ry*ry);
    if (pl > 1) {
      pl = Math.sqrt(pl);
      rx *= pl;
      ry *= pl;
    }

    var a00 = cos_th / rx;
    var a01 = sin_th / rx;
    var a10 = (-sin_th) / ry;
    var a11 = (cos_th) / ry;
    var x0 = a00 * ox + a01 * oy;
    var y0 = a10 * ox + a11 * oy;
    var x1 = a00 * x + a01 * y;
    var y1 = a10 * x + a11 * y;

    var d = (x1-x0) * (x1-x0) + (y1-y0) * (y1-y0);
    var sfactor_sq = 1 / d - 0.25;
    if (sfactor_sq < 0) sfactor_sq = 0;
    var sfactor = Math.sqrt(sfactor_sq);
    if (sweep == large) sfactor = -sfactor;
    var xc = 0.5 * (x0 + x1) - sfactor * (y1-y0);
    var yc = 0.5 * (y0 + y1) + sfactor * (x1-x0);

    var th0 = Math.atan2(y0-yc, x0-xc);
    var th1 = Math.atan2(y1-yc, x1-xc);

    var th_arc = th1-th0;
    if (th_arc < 0 && sweep == 1){
      th_arc += 2*Math.PI;
    } else if (th_arc > 0 && sweep == 0) {
      th_arc -= 2 * Math.PI;
    }

    var segments = Math.ceil(Math.abs(th_arc / (Math.PI * 0.5 + 0.001)));
    var result = [];
    for (var i=0; i<segments; i++) {
      var th2 = th0 + i * th_arc / segments;
      var th3 = th0 + (i+1) * th_arc / segments;
      result[i] = [xc, yc, th2, th3, rx, ry, sin_th, cos_th];
    }

    return (arcToSegmentsCache[argsStr] = result);
  }

  function segmentToBezier(cx, cy, th0, th1, rx, ry, sin_th, cos_th) {
    argsStr = join.call(arguments);
    if (segmentToBezierCache[argsStr]) {
      return segmentToBezierCache[argsStr];
    }

    var a00 = cos_th * rx;
    var a01 = -sin_th * ry;
    var a10 = sin_th * rx;
    var a11 = cos_th * ry;

    var cos_th0 = Math.cos(th0);
    var sin_th0 = Math.sin(th0);
    var cos_th1 = Math.cos(th1);
    var sin_th1 = Math.sin(th1);

    var th_half = 0.5 * (th1 - th0);
    var sin_th_h2 = Math.sin(th_half * 0.5);
    var t = (8/3) * sin_th_h2 * sin_th_h2 / Math.sin(th_half);
    var x1 = cx + cos_th0 - t * sin_th0;
    var y1 = cy + sin_th0 + t * cos_th0;
    var x3 = cx + cos_th1;
    var y3 = cy + sin_th1;
    var x2 = x3 + t * sin_th1;
    var y2 = y3 - t * cos_th1;

    return (segmentToBezierCache[argsStr] = [
      a00 * x1 + a01 * y1,  a10 * x1 + a11 * y1,
      a00 * x2 + a01 * y2,  a10 * x2 + a11 * y2,
      a00 * x3 + a01 * y3,  a10 * x3 + a11 * y3
    ]);
  }

  function render(g, path, l, t) {
    var current, // current instruction
        previous = null,
        x = 0, // current x
        y = 0, // current y
        controlX = 0, // current control point x
        controlY = 0, // current control point y
        tempX,
        tempY,
        tempControlX,
        tempControlY,
        bounds = new vg.Bounds();
    if (l == undefined) l = 0;
    if (t == undefined) t = 0;

    g.beginPath();
  
    for (var i=0, len=path.length; i<len; ++i) {
      current = path[i];

      switch (current[0]) { // first letter

        case 'l': // lineto, relative
          x += current[1];
          y += current[2];
          g.lineTo(x + l, y + t);
          bounds.add(x, y);
          break;

        case 'L': // lineto, absolute
          x = current[1];
          y = current[2];
          g.lineTo(x + l, y + t);
          bounds.add(x, y);
          break;

        case 'h': // horizontal lineto, relative
          x += current[1];
          g.lineTo(x + l, y + t);
          bounds.add(x, y);
          break;

        case 'H': // horizontal lineto, absolute
          x = current[1];
          g.lineTo(x + l, y + t);
          bounds.add(x, y);
          break;

        case 'v': // vertical lineto, relative
          y += current[1];
          g.lineTo(x + l, y + t);
          bounds.add(x, y);
          break;

        case 'V': // verical lineto, absolute
          y = current[1];
          g.lineTo(x + l, y + t);
          bounds.add(x, y);
          break;

        case 'm': // moveTo, relative
          x += current[1];
          y += current[2];
          g.moveTo(x + l, y + t);
          bounds.add(x, y);
          break;

        case 'M': // moveTo, absolute
          x = current[1];
          y = current[2];
          g.moveTo(x + l, y + t);
          bounds.add(x, y);
          break;

        case 'c': // bezierCurveTo, relative
          tempX = x + current[5];
          tempY = y + current[6];
          controlX = x + current[3];
          controlY = y + current[4];
          g.bezierCurveTo(
            x + current[1] + l, // x1
            y + current[2] + t, // y1
            controlX + l, // x2
            controlY + t, // y2
            tempX + l,
            tempY + t
          );
          bounds.add(x + current[1], y + current[2]);
          bounds.add(controlX, controlY);
          bounds.add(tempX, tempY);
          x = tempX;
          y = tempY;
          break;

        case 'C': // bezierCurveTo, absolute
          x = current[5];
          y = current[6];
          controlX = current[3];
          controlY = current[4];
          g.bezierCurveTo(
            current[1] + l,
            current[2] + t,
            controlX + l,
            controlY + t,
            x + l,
            y + t
          );
          bounds.add(current[1], current[2]);
          bounds.add(controlX, controlY);
          bounds.add(x, y);
          break;

        case 's': // shorthand cubic bezierCurveTo, relative
          // transform to absolute x,y
          tempX = x + current[3];
          tempY = y + current[4];
          // calculate reflection of previous control points
          controlX = 2 * x - controlX;
          controlY = 2 * y - controlY;
          g.bezierCurveTo(
            controlX + l,
            controlY + t,
            x + current[1] + l,
            y + current[2] + t,
            tempX + l,
            tempY + t
          );
          bounds.add(controlX, controlY);
          bounds.add(x + current[1], y + current[2]);
          bounds.add(tempX, tempY);

          // set control point to 2nd one of this command
          // "... the first control point is assumed to be the reflection of the second control point on the previous command relative to the current point."
          controlX = x + current[1];
          controlY = y + current[2];

          x = tempX;
          y = tempY;
          break;

        case 'S': // shorthand cubic bezierCurveTo, absolute
          tempX = current[3];
          tempY = current[4];
          // calculate reflection of previous control points
          controlX = 2*x - controlX;
          controlY = 2*y - controlY;
          g.bezierCurveTo(
            controlX + l,
            controlY + t,
            current[1] + l,
            current[2] + t,
            tempX + l,
            tempY + t
          );
          x = tempX;
          y = tempY;
          bounds.add(current[1], current[2]);
          bounds.add(controlX, controlY);
          bounds.add(tempX, tempY);
          // set control point to 2nd one of this command
          // "... the first control point is assumed to be the reflection of the second control point on the previous command relative to the current point."
          controlX = current[1];
          controlY = current[2];

          break;

        case 'q': // quadraticCurveTo, relative
          // transform to absolute x,y
          tempX = x + current[3];
          tempY = y + current[4];

          controlX = x + current[1];
          controlY = y + current[2];

          g.quadraticCurveTo(
            controlX + l,
            controlY + t,
            tempX + l,
            tempY + t
          );
          x = tempX;
          y = tempY;
          bounds.add(controlX, controlY);
          bounds.add(tempX, tempY);
          break;

        case 'Q': // quadraticCurveTo, absolute
          tempX = current[3];
          tempY = current[4];

          g.quadraticCurveTo(
            current[1] + l,
            current[2] + t,
            tempX + l,
            tempY + t
          );
          x = tempX;
          y = tempY;
          controlX = current[1];
          controlY = current[2];
          bounds.add(controlX, controlY);
          bounds.add(tempX, tempY);
          break;

        case 't': // shorthand quadraticCurveTo, relative

          // transform to absolute x,y
          tempX = x + current[1];
          tempY = y + current[2];

          if (previous[0].match(/[QqTt]/) === null) {
            // If there is no previous command or if the previous command was not a Q, q, T or t,
            // assume the control point is coincident with the current point
            controlX = x;
            controlY = y;
          }
          else if (previous[0] === 't') {
            // calculate reflection of previous control points for t
            controlX = 2 * x - tempControlX;
            controlY = 2 * y - tempControlY;
          }
          else if (previous[0] === 'q') {
            // calculate reflection of previous control points for q
            controlX = 2 * x - controlX;
            controlY = 2 * y - controlY;
          }

          tempControlX = controlX;
          tempControlY = controlY;

          g.quadraticCurveTo(
            controlX + l,
            controlY + t,
            tempX + l,
            tempY + t
          );
          x = tempX;
          y = tempY;
          controlX = x + current[1];
          controlY = y + current[2];
          bounds.add(controlX, controlY);
          bounds.add(tempX, tempY);
          break;

        case 'T':
          tempX = current[1];
          tempY = current[2];

          // calculate reflection of previous control points
          controlX = 2 * x - controlX;
          controlY = 2 * y - controlY;
          g.quadraticCurveTo(
            controlX + l,
            controlY + t,
            tempX + l,
            tempY + t
          );
          x = tempX;
          y = tempY;
          bounds.add(controlX, controlY);
          bounds.add(tempX, tempY);
          break;

        case 'a':
          drawArc(g, x + l, y + t, [
            current[1],
            current[2],
            current[3],
            current[4],
            current[5],
            current[6] + x + l,
            current[7] + y + t
          ], bounds, l, t);
          x += current[6];
          y += current[7];
          break;

        case 'A':
          drawArc(g, x + l, y + t, [
            current[1],
            current[2],
            current[3],
            current[4],
            current[5],
            current[6] + l,
            current[7] + t
          ], bounds, l, t);
          x = current[6];
          y = current[7];
          break;

        case 'z':
        case 'Z':
          g.closePath();
          break;
      }
      previous = current;
    }
    return bounds.translate(l, t);
  };
  
  return {
    parse: parse,
    render: render
  };
  
})();vg.canvas.marks = (function() {
  
  var parsePath = vg.canvas.path.parse,
      renderPath = vg.canvas.path.render,
      sqrt3 = Math.sqrt(3),
      tan30 = Math.tan(30 * Math.PI / 180),
      tmpBounds = new vg.Bounds();

  // path generators

  function arcPath(g, o) {
    var x = o.x || 0,
        y = o.y || 0,
        ir = o.innerRadius || 0,
        or = o.outerRadius || 0,
        sa = (o.startAngle || 0) - Math.PI/2,
        ea = (o.endAngle || 0) - Math.PI/2;
    g.beginPath();
    if (ir === 0) g.moveTo(x, y);
    else g.arc(x, y, ir, sa, ea, 0);
    g.arc(x, y, or, ea, sa, 1);
    g.closePath();
    return new vg.Bounds()
      .set(x-or, y-or, x+or, y+or);
  }

  function pathPath(g, o) {
    return renderPath(g, parsePath(o.path), o.x, o.y);
  }
  
  function symbolPath(g, o) {
    g.beginPath();
    var size = o.size != undefined ? o.size : 100,
        x = o.x, y = o.y, r, t, rx, ry,
        bounds = new vg.Bounds();

    if (o.shape == undefined || o.shape === "circle") {
      r = Math.sqrt(size/Math.PI);
      g.arc(x, y, r, 0, 2*Math.PI, 0);
      g.closePath();
      return bounds.set(x-r, y-r, x+r, y+r);
    }

    switch (o.shape) {
      case "cross":
        r = Math.sqrt(size / 5) / 2;
        t = 3*r;
        g.moveTo(x-t, y-r);
        g.lineTo(x-r, y-r);
        g.lineTo(x-r, y-t);
        g.lineTo(x+r, y-t);
        g.lineTo(x+r, y-r);
        g.lineTo(x+t, y-r);
        g.lineTo(x+t, y+r);
        g.lineTo(x+r, y+r);
        g.lineTo(x+r, y+t);
        g.lineTo(x-r, y+t);
        g.lineTo(x-r, y+r);
        g.lineTo(x-t, y+r);
        bounds.set(x-t, y-t, x+y, y+t);
        break;

      case "diamond":
        ry = Math.sqrt(size / (2 * tan30));
        rx = ry * tan30;
        g.moveTo(x, y-ry);
        g.lineTo(x+rx, y);
        g.lineTo(x, y+ry);
        g.lineTo(x-rx, y);
        bounds.set(x-rx, y-ry, x+rx, y+ry);
        break;

      case "square":
        t = Math.sqrt(size);
        r = t / 2;
        g.rect(x-r, y-r, t, t);
        bounds.set(x-r, y-r, x+r, y+r);
        break;

      case "triangle-down":
        rx = Math.sqrt(size / sqrt3);
        ry = rx * sqrt3 / 2;
        g.moveTo(x, y+ry);
        g.lineTo(x+rx, y-ry);
        g.lineTo(x-rx, y-ry);
        bounds.set(x-rx, y-ry, x+rx, y+ry);
        break;

      case "triangle-up":
        rx = Math.sqrt(size / sqrt3);
        ry = rx * sqrt3 / 2;
        g.moveTo(x, y-ry);
        g.lineTo(x+rx, y+ry);
        g.lineTo(x-rx, y+ry);
        bounds.set(x-rx, y-ry, x+rx, y+ry);
    }
    g.closePath();
    return bounds;
  }
  
  function areaPath(g, items) {
    var area = d3.svg.area()
     .x(function(d) { return d.x; })
     .y1(function(d) { return d.y; })
     .y0(function(d) { return d.y + d.height; });
    var o = items[0];
    if (o.interpolate) area.interpolate(o.interpolate);
    if (o.tension != undefined) area.tension(o.tension);
    return renderPath(g, parsePath(area(items)));
  }

  function linePath(g, items) {
    var line = d3.svg.line()
     .x(function(d) { return d.x; })
     .y(function(d) { return d.y; });
    var o = items[0];
    if (o.interpolate) line.interpolate(o.interpolate);
    if (o.tension != undefined) line.tension(o.tension);
    return renderPath(g, parsePath(line(items)));
  }
  
  // drawing functions
  
  function drawPathOne(path, g, o, items) {
    var fill = o.fill, stroke = o.stroke, opac, lc, lw;
    o.bounds = path(g, items);
    
    opac = o.opacity == null ? 1 : o.opacity;
    if (opac == 0 || !fill && !stroke) return;

    if (fill) {
      g.globalAlpha = opac * (o.fillOpacity==null ? 1 : o.fillOpacity);
      g.fillStyle = fill;
      g.fill();
    }

    if (stroke) {
      lw = (lw = o.strokeWidth) != undefined ? lw : 1;
      if (lw > 0) {
        g.globalAlpha = opac * (o.strokeOpacity==null ? 1 : o.strokeOpacity);
        g.strokeStyle = stroke;
        g.lineWidth = lw;
        g.lineCap = (lc = o.strokeCap) != undefined ? lc : "butt";
        g.stroke();
        o.bounds.expand(lw);
      }
    }
  }

  function drawPathAll(path, g, scene, bounds) {
    var i, len, item;
    for (i=0, len=scene.items.length; i<len; ++i) {
      item = scene.items[i];
      if (bounds && !bounds.intersects(item.bounds))
        continue; // bounds check
      drawPathOne(path, g, item, item);
    }
  }
  
  function drawRect(g, scene, bounds) {
    if (!scene.items.length) return;
    var items = scene.items,
        o, fill, stroke, opac, lc, lw, x, y;

    for (var i=0, len=items.length; i<len; ++i) {
      o = items[i];
      if (bounds && !bounds.intersects(o.bounds))
        continue; // bounds check

      x = o.x || 0;
      y = o.y || 0;
      o.bounds = (o.bounds || new vg.Bounds())
        .set(x, y, x+o.width, y+o.height);

      opac = o.opacity == null ? 1 : o.opacity;
      if (opac == 0) return;

      if (fill = o.fill) {
        g.globalAlpha = opac * (o.fillOpacity==null ? 1 : o.fillOpacity);
        g.fillStyle = fill;
        g.fillRect(x, y, o.width, o.height);
      }

      if (stroke = o.stroke) {
        lw = (lw = o.strokeWidth) != undefined ? lw : 1;
        if (lw > 0) {
          g.globalAlpha = opac * (o.strokeOpacity==null ? 1 : o.strokeOpacity);
          g.strokeStyle = stroke;
          g.lineWidth = lw;
          g.lineCap = (lc = o.strokeCap) != undefined ? lc : "butt";
          g.strokeRect(x, y, o.width, o.height);
          o.bounds.expand(lw);
        }
      }
    }
  }

  function drawRule(g, scene, bounds) {
    if (!scene.items.length) return;
    var items = scene.items,
        o, stroke, opac, lc, lw, x1, y1, x2, y2;

    for (var i=0, len=items.length; i<len; ++i) {
      o = items[i];
      if (bounds && !bounds.intersects(o.bounds))
        continue; // bounds check

      x1 = o.x || 0;
      y1 = o.y || 0;
      x2 = o.x2 !== undefined ? o.x2 : x1;
      y2 = o.y2 !== undefined ? o.y2 : y1;
      o.bounds = (o.bounds || new vg.Bounds())
        .set(x1, y1, x2, y2);

      opac = o.opacity == null ? 1 : o.opacity;
      if (opac == 0) return;

      if (stroke = o.stroke) {
        lw = (lw = o.strokeWidth) != undefined ? lw : 1;
        if (lw > 0) {
          g.globalAlpha = opac * (o.strokeOpacity==null ? 1 : o.strokeOpacity);
          g.strokeStyle = stroke;
          g.lineWidth = lw;
          g.lineCap = (lc = o.strokeCap) != undefined ? lc : "butt";
          g.beginPath();
          g.moveTo(x1, y1);
          g.lineTo(x2, y2);
          g.stroke();
          o.bounds.expand(lw);
        }
      }
    }
  }
  
  function drawImage(g, scene, bounds) {
    if (!scene.items.length) return;
    var renderer = this,
        items = scene.items, o;

    for (var i=0, len=items.length; i<len; ++i) {
      o = items[i];
      if (bounds && !bounds.intersects(o.bounds))
        continue; // bounds check

      if (!(o.image && o.image.url === o.url)) {
        o.image = renderer.loadImage(o.url);
        o.image.url = o.url;
      }

      var x, y, w, h, opac;
      w = o.width || (o.image && o.image.width) || 0;
      h = o.height || (o.image && o.image.height) || 0;
      x = o.x - (o.align === "center"
        ? w/2 : (o.align === "right" ? w : 0));
      y = o.y - (o.baseline === "middle"
        ? h/2 : (o.baseline === "bottom" ? h : 0));
      o.bounds = (o.bounds || new vg.Bounds()).set(x, y, x+w, y+h);

      if (o.image.loaded) {
        g.globalAlpha = (opac = o.opacity) != undefined ? opac : 1;
        g.drawImage(o.image, x, y, w, h);
      }
    }
  }
  
  function fontString(o) {
    return (o.fontStyle ? o.fontStyle + " " : "")
      + (o.fontVariant ? o.fontVariant + " " : "")
      + (o.fontWeight ? o.fontWeight + " " : "")
      + (o.fontSize != undefined ? o.fontSize + "px " : "11px ")
      + (o.font || "sans-serif");
  }
  
  function drawText(g, scene, bounds) {
    if (!scene.items.length) return;
    var items = scene.items,
        o, fill, stroke, opac, lw, text, ta, tb;

    for (var i=0, len=items.length; i<len; ++i) {
      o = items[i];
      if (bounds && !bounds.intersects(o.bounds))
        continue; // bounds check

      g.font = fontString(o);
      g.textAlign = o.align || "left";
      g.textBaseline = o.baseline || "alphabetic";
      o.bounds = textBounds(g, o, (o.bounds || new vg.Bounds())).expand(1);

      opac = o.opacity == null ? 1 : o.opacity;
      if (opac == 0) return;

      if (o.angle) {
        g.save();
        g.translate(o.x, o.y);
        g.rotate(o.angle * Math.PI/180);
        x = o.dx || 0;
        y = o.dy || 0;
      } else {
        x = o.x + (o.dx || 0);
        y = o.y + (o.dy || 0);
      }

      if (fill = o.fill) {
        g.globalAlpha = opac * (o.fillOpacity==null ? 1 : o.fillOpacity);
        g.fillStyle = fill;
        g.fillText(o.text, x, y);
      }
      
      if (stroke = o.stroke) {
        lw = (lw = o.strokeWidth) != undefined ? lw : 1;
        if (lw > 0) {
          g.globalAlpha = opac * (o.strokeOpacity==null ? 1 : o.strokeOpacity);
          g.strokeStyle = stroke;
          g.lineWidth = lw;
          g.strokeText(o.text, x, y);
        }
      }
      
      if (o.angle) {
        g.restore();
      }
    }
  }
  
  function textBounds(g, o, bounds, noRotate) {
    var x = o.x + (o.dx || 0),
        y = o.y + (o.dy || 0),
        w = g.measureText(o.text).width,
        h = o.fontSize,
        a = o.align,
        b = o.baseline,
        angle, cos, sin, cx, cy;
    
    // horizontal
    if (a === "center") {
      x = x - (w / 2);
    } else if (a === "right") {
      x = x - w;
    } else {
      // left by default, do nothing
    }
    
    /// TODO find a robust solution for heights!
    /// These offsets work for some but not all fonts.
    
    // vertical
    if (b === "top") {
      y = y + (h/5);
    } else if (b === "bottom") {
      y = y - h;
    } else if (b === "middle") {
      y = y - (h/2) + (h/10);
    } else {
      // alphabetic by default
      y = y - 4*h/5;
    }
    
    bounds.set(x, y, x+w, y+h);
    if (!noRotate && o.angle) {
      bounds.rotate(o.angle*Math.PI/180, o.x, o.y);
    }
    return bounds;
  }
  
  function drawAll(pathFunc) {
    return function(g, scene, bounds) {
      drawPathAll(pathFunc, g, scene, bounds);
    }
  }
  
  function drawOne(pathFunc) {
    return function(g, scene, bounds) {
      if (!scene.items.length) return;
      if (bounds && !bounds.intersects(scene.items[0].bounds))
        return; // bounds check
      drawPathOne(pathFunc, g, scene.items[0], scene.items);
    }
  }
  
  function drawGroup(g, scene, bounds) {
    if (!scene.items.length) return;
    var items = scene.items, group, axes,
        renderer = this, gx, gy, i, n, j, m;
    
    drawRect(g, scene, bounds);
    
    for (i=0, n=items.length; i<n; ++i) {
      group = items[i];
      axes = group.axisItems || [];
      gx = group.x || 0;
      gy = group.y || 0;
      
      // render group contents
      g.save();
      g.translate(gx, gy);
      if (bounds) bounds.translate(-gx, -gy);
      for (j=0, m=axes.length; j<m; ++j) {
        if (axes[j].def.layer === "back") {
          renderer.draw(g, axes[j], bounds);
        }
      }
      for (j=0, m=group.items.length; j<m; ++j) {
        renderer.draw(g, group.items[j], bounds);
      }
      for (j=0, m=axes.length; j<m; ++j) {
        if (axes[j].def.layer !== "back") {
          renderer.draw(g, axes[j], bounds);
        }
      }
      if (bounds) bounds.translate(gx, gy);
      g.restore(); 
    }
  }
  
  // hit testing
  
  function pickGroup(g, scene, x, y, gx, gy) {
    if (scene.items.length === 0 ||
        scene.bounds && !scene.bounds.contains(gx, gy)) {
      return false;
    }
    var items = scene.items, subscene, group, hit, dx, dy,
        handler = this;

    for (var i=0, len=items.length; i<len; ++i) {
      group = items[i];
      dx = group.x || 0;
      dy = group.y || 0;
      
      g.save();
      g.translate(dx, dy);
      for (var j=0, llen=group.items.length; j<llen; ++j) {
        subscene = group.items[j];
        if (subscene.interactive === false) continue;
        hit = handler.pick(subscene, x, y, gx-dx, gy-dy);
        if (hit) {
          g.restore();
          return hit;
        }
      }
      g.restore();
    }
    
    return scene.interactive
      ? pickAll(hitTests.rect, g, scene, x, y, gx, gy)
      : false;
  }
  
  function pickAll(test, g, scene, x, y, gx, gy) {
    if (!scene.items.length) return false;
    var o, b, i;

    if (g._ratio !== 1) {
      x *= g._ratio;
      y *= g._ratio;
    }

    for (i=scene.items.length; --i >= 0;) {
      o = scene.items[i]; b = o.bounds;
      // first hit test against bounding box
      if ((b && !b.contains(gx, gy)) || !b) continue;
      // if in bounding box, perform more careful test
      if (test(g, o, x, y, gx, gy)) return o;
    }
    return false;
  }
  
  function pickArea(g, scene, x, y, gx, gy) {
    if (!scene.items.length) return false;
    var items = scene.items,
        o, b, i, di, dd, od, dx, dy;

    b = items[0].bounds;
    if (b && !b.contains(gx, gy)) return false;
    if (g._ratio !== 1) {
      x *= g._ratio;
      y *= g._ratio;
    }
    if (!hitTests.area(g, items, x, y)) return false;
    return items[0];
  }
  
  function pickLine(g, scene, x, y, gx, gy) {
    // TODO...
    return false;
  }
  
  function pickRule(g, scene, x, y, gx, gy) {
    // TODO...
    return false;
  }
  
  function pick(test) {
    return function (g, scene, x, y, gx, gy) {
      return pickAll(test, g, scene, x, y, gx, gy);
    };
  }

  var hitTests = {
    text:   hitTestText,
    rect:   function(g,o,x,y) { return true; }, // bounds test is sufficient
    image:  function(g,o,x,y) { return true; }, // bounds test is sufficient
    arc:    function(g,o,x,y) { arcPath(g,o);  return g.isPointInPath(x,y); },
    area:   function(g,s,x,y) { areaPath(g,s); return g.isPointInPath(x,y); },
    path:   function(g,o,x,y) { pathPath(g,o); return g.isPointInPath(x,y); },
    symbol: function(g,o,x,y) {symbolPath(g,o); return g.isPointInPath(x,y);},
  };
  
  function hitTestText(g, o, x, y, gx, gy) {
    if (!o.fontSize) return false;
    if (!o.angle) return true; // bounds sufficient if no rotation

    g.font = fontString(o);
    
    var b = textBounds(g, o, tmpBounds, true),
        a = -o.angle * Math.PI / 180,
        cos = Math.cos(a),
        sin = Math.sin(a),
        x = o.x,
        y = o.y,
        px = cos*gx - sin*gy + (x - x*cos + y*sin),
        py = sin*gx + cos*gy + (y - x*sin - y*cos);
        
    return b.contains(px, py);
  }
  
  return {
    draw: {
      group:   drawGroup,
      area:    drawOne(areaPath),
      line:    drawOne(linePath),
      arc:     drawAll(arcPath),
      path:    drawAll(pathPath),
      symbol:  drawAll(symbolPath),
      rect:    drawRect,
      rule:    drawRule,
      text:    drawText,
      image:   drawImage,
      drawOne: drawOne, // expose for extensibility
      drawAll: drawAll  // expose for extensibility
    },
    pick: {
      group:   pickGroup,
      area:    pickArea,
      line:    pickLine,
      arc:     pick(hitTests.arc),
      path:    pick(hitTests.path),
      symbol:  pick(hitTests.symbol),
      rect:    pick(hitTests.rect),
      rule:    pickRule,
      text:    pick(hitTests.text),
      image:   pick(hitTests.image),
      pickAll: pickAll  // expose for extensibility
    }
  };
  
})();vg.canvas.Renderer = (function() {  
  var renderer = function() {
    this._ctx = null;
    this._el = null;
    this._imgload = 0;
  };
  
  var prototype = renderer.prototype;
  
  prototype.initialize = function(el, width, height, pad) {
    this._el = el;
    this._width = width;
    this._height = height;
    this._padding = pad;
    
    if (!el) return this; // early exit if no DOM element

    // select canvas element
    var canvas = d3.select(el)
      .selectAll("canvas.marks")
      .data([1]);
    
    // create new canvas element if needed
    canvas.enter()
      .append("canvas")
      .attr("class", "marks");
    
    // initialize canvas attributes
    canvas
      .attr("width", width + pad.left + pad.right)
      .attr("height", height + pad.top + pad.bottom);
    
    // get the canvas graphics context
    var s;
    this._ctx = canvas.node().getContext("2d");
    this._ctx._ratio = (s = scaleCanvas(canvas.node(), this._ctx) || 1);
    this._ctx.setTransform(s, 0, 0, s, s*pad.left, s*pad.top);
    
    return this;
  };
  
  function scaleCanvas(canvas, ctx) {
    // get canvas pixel data
    var devicePixelRatio = window.devicePixelRatio || 1,
        backingStoreRatio = (
          ctx.webkitBackingStorePixelRatio ||
          ctx.mozBackingStorePixelRatio ||
          ctx.msBackingStorePixelRatio ||
          ctx.oBackingStorePixelRatio ||
          ctx.backingStorePixelRatio) || 1,
        ratio = devicePixelRatio / backingStoreRatio;

    if (devicePixelRatio !== backingStoreRatio) {
      var w = canvas.width, h = canvas.height;
      // set actual and visible canvas size
      canvas.setAttribute("width", w * ratio);
      canvas.setAttribute("height", h * ratio);
      canvas.style.width = w + 'px';
      canvas.style.height = h + 'px';
    }
    return ratio;
  }
  
  prototype.context = function(ctx) {
    if (ctx) { this._ctx = ctx; return this; }
    else return this._ctx;
  };
  
  prototype.element = function() {
    return this._el;
  };
  
  prototype.pendingImages = function() {
    return this._imgload;
  };

  function translatedBounds(item) {
    var b = new vg.Bounds(item.bounds);
    while ((item = item.mark.group) != null) {
      b.translate(item.x || 0, item.y || 0);
    }
    return b;
  }
    
  function getBounds(items) {
    return !items ? null :
      vg.array(items).reduce(function(b, item) {
        return b.union(translatedBounds(item));
      }, new vg.Bounds());  
  }
  
  function setBounds(g, bounds) {
    var bbox = null;
    if (bounds) {
      bbox = (new vg.Bounds(bounds)).round();
      g.beginPath();
      g.rect(bbox.x1, bbox.y1, bbox.width(), bbox.height());
      g.clip();
    }
    return bbox;
  }
  
  prototype.render = function(scene, items) {
    var g = this._ctx,
        pad = this._padding,
        w = this._width + pad.left + pad.right,
        h = this._height + pad.top + pad.bottom,
        bb = null, bb2;

    // setup
    this._scene = scene;
    g.save();
    bb = setBounds(g, getBounds(items));
    g.clearRect(-pad.left, -pad.top, w, h);

    // render
    this.draw(g, scene, bb);

    // render again to handle possible bounds change
    if (items) {
      g.restore();
      g.save();
      bb2 = setBounds(g, getBounds(items));
      if (!bb.encloses(bb2)) {
        g.clearRect(-pad.left, -pad.top, w, h);
        this.draw(g, scene, bb2);
      }
    }
    
    // takedown
    g.restore();
    this._scene = null;
  };
  
  prototype.draw = function(ctx, scene, bounds) {
    var marktype = scene.marktype,
        renderer = vg.canvas.marks.draw[marktype];
    renderer.call(this, ctx, scene, bounds);
  };
  
  prototype.renderAsync = function(scene) {
    // TODO make safe for multiple scene rendering?
    var renderer = this;
    if (renderer._async_id) {
      clearTimeout(renderer._async_id);
    }
    renderer._async_id = setTimeout(function() {
      renderer.render(scene);
      delete renderer._async_id;
    }, 50);
  };
  
  prototype.loadImage = function(uri) {
    var renderer = this,
        scene = renderer._scene,
        image = null;

    renderer._imgload += 1;
    if (vg.config.isNode) {
      image = new (require("canvas").Image)();
      vg.data.load(uri, function(err, data) {
        if (err) { vg.error(err); return; }
        image.src = data;
        image.loaded = true;
        renderer._imgload -= 1;
      });
    } else {
      image = new Image();
      image.onload = function() {
        vg.log("LOAD IMAGE: "+uri);
        image.loaded = true;
        renderer._imgload -= 1;
        renderer.renderAsync(scene);
      };
      image.src = uri;
    }

    return image;
  };
  
  return renderer;
})();vg.canvas.Handler = (function() {
  var handler = function(el, model) {
    this._active = null;
    this._handlers = {};
    if (el) this.initialize(el);
    if (model) this.model(model);
  };
  
  var prototype = handler.prototype;

  prototype.initialize = function(el, pad, obj) {
    this._el = d3.select(el).node();
    this._canvas = d3.select(el).select("canvas.marks").node();
    this._padding = pad;
    this._obj = obj || null;
    
    // add event listeners
    var canvas = this._canvas, that = this;
    events.forEach(function(type) {
      canvas.addEventListener(type, function(evt) {
        prototype[type].call(that, evt);
      });
    });
    
    return this;
  };
  
  prototype.model = function(model) {
    if (!arguments.length) return this._model;
    this._model = model;
    return this;
  };

  prototype.handlers = function() {
    var h = this._handlers;
    return vg.keys(h).reduce(function(a, k) {
      return h[k].reduce(function(a, x) { return (a.push(x), a); }, a);
    }, []);
  };

  // setup events
  var events = [
    "mousedown",
    "mouseup",
    "click",
    "dblclick",
    "wheel",
    "keydown",
    "keypress",
    "keyup",
    "mousewheel"
  ];
  events.forEach(function(type) {
    prototype[type] = function(evt) {
      this.fire(type, evt);
    };
  });
  events.push("mousemove");
  events.push("mouseout");

  function eventName(name) {
    var i = name.indexOf(".");
    return i < 0 ? name : name.slice(0,i);
  }

  prototype.mousemove = function(evt) {
    var pad = this._padding,
        b = evt.target.getBoundingClientRect(),
        x = evt.clientX - b.left,
        y = evt.clientY - b.top,
        a = this._active,
        p = this.pick(this._model.scene(), x, y, x-pad.left, y-pad.top);

    if (p === a) {
      this.fire("mousemove", evt);
      return;
    } else if (a) {
      this.fire("mouseout", evt);
    }
    this._active = p;
    if (p) {
      this.fire("mouseover", evt);
    }
  };
  
  prototype.mouseout = function(evt) {
    if (this._active) {
      this.fire("mouseout", evt);
    }
    this._active = null;
  };

  // to keep firefox happy
  prototype.DOMMouseScroll = function(evt) {
    this.fire("mousewheel", evt);
  };

  // fire an event
  prototype.fire = function(type, evt) {
    var a = this._active,
        h = this._handlers[type];
    if (a && h) {
      for (var i=0, len=h.length; i<len; ++i) {
        h[i].handler.call(this._obj, evt, a);
      }
    }
  };

  // add an event handler
  prototype.on = function(type, handler) {
    var name = eventName(type),
        h = this._handlers;
    h = h[name] || (h[name] = []);
    h.push({
      type: type,
      handler: handler
    });
    return this;
  };

  // remove an event handler
  prototype.off = function(type, handler) {
    var name = eventName(type),
        h = this._handlers[name];
    if (!h) return;
    for (var i=h.length; --i>=0;) {
      if (h[i].type !== type) continue;
      if (!handler || h[i].handler === handler) h.splice(i, 1);
    }
    return this;
  };
  
  // retrieve the current canvas context
  prototype.context = function() {
    return this._canvas.getContext("2d");
  };
  
  // find the scenegraph item at the current mouse position
  // returns an array of scenegraph items, from leaf node up to the root
  // x, y -- the absolute x, y mouse coordinates on the canvas element
  // gx, gy -- the relative coordinates within the current group
  prototype.pick = function(scene, x, y, gx, gy) {
    var g = this.context(),
        marktype = scene.marktype,
        picker = vg.canvas.marks.pick[marktype];
    return picker.call(this, g, scene, x, y, gx, gy);
  };

  return handler;
})();vg.svg = {};vg.svg.marks = (function() {

  function x(o)     { return o.x || 0; }
  function y(o)     { return o.y || 0; }
  function yh(o)    { return o.y + o.height || 0; }
  function key(o)   { return o.key; }
  function size(o)  { return o.size==null ? 100 : o.size; }
  function shape(o) { return o.shape || "circle"; }
      
  var arc_path    = d3.svg.arc(),
      area_path   = d3.svg.area().x(x).y1(y).y0(yh),
      line_path   = d3.svg.line().x(x).y(y),
      symbol_path = d3.svg.symbol().type(shape).size(size);
  
  var textAlign = {
    "left":   "start",
    "center": "middle",
    "right":  "end"
  };
  
  var styles = {
    "fill":          "fill",
    "fillOpacity":   "fill-opacity",
    "stroke":        "stroke",
    "strokeWidth":   "stroke-width",
    "strokeOpacity": "stroke-opacity",
    "opacity":       "opacity"
  };
  
  var styleProps = vg.keys(styles);
  
  function style(d) {
    var o = d.mark ? d : d[0],
        i, n, prop, name, value;
    for (i=0, n=styleProps.length; i<n; ++i) {
      prop = styleProps[i];
      name = styles[prop];
      value = o[prop];
      if (value == null) {
        if (name === "fill") this.style.setProperty(name, "none", null);
        else this.style.removeProperty(name);
      }
      else this.style.setProperty(name, value, null);
    }
  }
  
  function arc(o) {
    var x = o.x || 0,
        y = o.y || 0;
    this.setAttribute("transform", "translate("+x+","+y+")");
    this.setAttribute("d", arc_path(o));
  }
  
  function area(items) {
    var o = items[0];
    area_path
      .interpolate(o.interpolate || "linear")
      .tension(o.tension == undefined ? 0.7 : o.tension);
    this.setAttribute("d", area_path(items));
  }
  
  function line(items) {
    var o = items[0];
    line_path
      .interpolate(o.interpolate || "linear")
      .tension(o.tension == undefined ? 0.7 : o.tension);
    this.setAttribute("d", line_path(items));
  }
  
  function path(o) {
    var x = o.x || 0,
        y = o.y || 0;
    this.setAttribute("transform", "translate("+x+","+y+")");
    this.setAttribute("d", o.path);
  }

  function rect(o) {
    this.setAttribute("x", o.x || 0);
    this.setAttribute("y", o.y || 0);
    this.setAttribute("width", o.width || 0);
    this.setAttribute("height", o.height || 0);
  }

  function rule(o) {
    var x1 = o.x || 0,
        y1 = o.y || 0;
    this.setAttribute("x1", x1);
    this.setAttribute("y1", y1);
    this.setAttribute("x2", o.x2 !== undefined ? o.x2 : x1);
    this.setAttribute("y2", o.y2 !== undefined ? o.y2 : y1);
  }
  
  function symbol(o) {
    var x = o.x || 0,
        y = o.y || 0;
    this.setAttribute("transform", "translate("+x+","+y+")");
    this.setAttribute("d", symbol_path(o));
  }
  
  function image(o) {
    var w = o.width || (o.image && o.image.width) || 0,
        h = o.height || (o.image && o.image.height) || 0,
        x = o.x - (o.align === "center"
          ? w/2 : (o.align === "right" ? w : 0)),
        y = o.y - (o.baseline === "middle"
          ? h/2 : (o.baseline === "bottom" ? h : 0));
    
    this.setAttributeNS("http://www.w3.org/1999/xlink", "href", o.url);
    this.setAttribute("x", x);
    this.setAttribute("y", y);
    this.setAttribute("width", w);
    this.setAttribute("height", h);
  }
    
  function fontString(o) {
    return (o.fontStyle ? o.fontStyle + " " : "")
      + (o.fontVariant ? o.fontVariant + " " : "")
      + (o.fontWeight ? o.fontWeight + " " : "")
      + (o.fontSize != undefined ? o.fontSize + "px " : "11px ")
      + (o.font || "sans-serif");
  }
  
  function text(o) {
    var x = o.x || 0,
        y = o.y || 0,
        dx = o.dx || 0,
        dy = o.dy || 0,
        a = o.angle || 0,
        align = textAlign[o.align || "left"],
        base = o.baseline==="top" ? ".9em"
             : o.baseline==="middle" ? ".35em" : 0;
  
    this.setAttribute("x", x + dx);
    this.setAttribute("y", y + dy);
    this.setAttribute("dy", dy);
    this.setAttribute("text-anchor", align);
    
    if (a) this.setAttribute("transform", "rotate("+a+" "+x+","+y+")");
    else this.removeAttribute("transform");
    
    if (base) this.setAttribute("dy", base);
    else this.removeAttribute("dy");
    
    this.textContent = o.text;
    this.style.setProperty("font", fontString(o), null);
  }
  
  function group(o) {
    var x = o.x || 0,
        y = o.y || 0;
    this.setAttribute("transform", "translate("+x+","+y+")");
  }

  function group_bg(o) {
    var w = o.width || 0,
        h = o.height || 0;
    this.setAttribute("width", w);
    this.setAttribute("height", h);
  }

  function draw(tag, attr, nest) {
    return function(g, scene, index) {
      drawMark(g, scene, index, "mark_", tag, attr, nest);
    };
  }
  
  var mark_id = 0;
  
  function drawMark(g, scene, index, prefix, tag, attr, nest) {
    var data = nest ? [scene.items] : scene.items,
        evts = scene.interactive===false ? "none" : null,
        grps = g.node().childNodes,
        notG = (tag !== "g"),
        p = grps[index+1] // +1 to skip group background rect
          ? d3.select(grps[index+1])
          : g.append("g").attr("id","g"+(++mark_id));

    var id = "#" + p.attr("id"),
        s = id + " > " + tag,
        m = p.selectAll(s).data(data),
        e = m.enter().append(tag);

    if (notG) {
      p.style("pointer-events", evts);
      e.each(function(d) { (d.mark ? d : d[0])._svg = this; });
    } else {
      e.append("rect").attr("class","background").style("pointer-events",evts);
    }
    
    m.exit().remove();
    m.each(attr);
    if (notG) m.each(style);
    else p.selectAll(s+" > rect.background").each(group_bg).each(style);
    
    return p;
  }

  function drawGroup(g, scene, index, prefix) {
    var p = drawMark(g, scene, index, prefix || "group_", "g", group),
        c = p.node().childNodes, n = c.length, i, j, m;
    
    for (i=0; i<n; ++i) {
      var items = c[i].__data__.items,
          axes = c[i].__data__.axisItems || [],
          sel = d3.select(c[i])
          idx = 0;

      for (j=0, m=axes.length; j<m; ++j) {
        if (axes[j].def.layer === "back") {
          drawGroup.call(this, sel, axes[j], idx++, "axis_");
        }
      }
      for (j=0, m=items.length; j<m; ++j) {
        this.draw(sel, items[j], idx++);
      }
      for (j=0, m=axes.length; j<m; ++j) {
        if (axes[j].def.layer !== "back") {
          drawGroup.call(this, sel, axes[j], idx++, "axis_");
        }
      }
    }
  }

  return {
    update: {
      group:   rect,
      area:    area,
      line:    line,
      arc:     arc,
      path:    path,
      symbol:  symbol,
      rect:    rect,
      rule:    rule,
      text:    text,
      image:   image
    },
    nested: {
      "area": true,
      "line": true
    },
    style: style,
    draw: {
      group:   drawGroup,
      area:    draw("path", area, true),
      line:    draw("path", line, true),
      arc:     draw("path", arc),
      path:    draw("path", path),
      symbol:  draw("path", symbol),
      rect:    draw("rect", rect),
      rule:    draw("line", rule),
      text:    draw("text", text),
      image:   draw("image", image),
      draw:    draw // expose for extensibility
    }
  };
  
})();vg.svg.Renderer = (function() {  
  var renderer = function() {
    this._ctx = null;
    this._el = null;
  };
  
  var prototype = renderer.prototype;
  
  prototype.initialize = function(el, width, height, pad) {
    this._el = el;
    this._width = width;
    this._height = height;
    this._padding = pad;

    // remove any existing svg element
    d3.select(el).select("svg.marks").remove();

    // create svg element and initialize attributes
    var svg = d3.select(el)
      .append("svg")
      .attr("class", "marks")
      .attr("width", width + pad.left + pad.right)
      .attr("height", height + pad.top + pad.bottom);
    
    // set the svg root group
    this._ctx = svg.append("g")
      .attr("transform", "translate("+pad.left+","+pad.top+")");
    
    return this;
  };
  
  prototype.context = function() {
    return this._ctx;
  };
  
  prototype.element = function() {
    return this._el;
  };
  
  prototype.render = function(scene, items) {
    if (items) this.renderItems(vg.array(items));
    else this.draw(this._ctx, scene, 0);
  };
  
  prototype.renderItems = function(items) {
    var item, node, type, nest, i, n,
        marks = vg.svg.marks;

    for (i=0, n=items.length; i<n; ++i) {
      item = items[i];
      node = item._svg;
      type = item.mark.marktype;

      item = marks.nested[type] ? item.mark.items : item;
      marks.update[type].call(node, item);
      marks.style.call(node, item);
    }
  }
  
  prototype.draw = function(ctx, scene, index) {
    var marktype = scene.marktype,
        renderer = vg.svg.marks.draw[marktype];
    renderer.call(this, ctx, scene, index);
  };
  
  return renderer;
})();vg.svg.Handler = (function() {
  var handler = function(el, model) {
    this._active = null;
    this._handlers = {};
    if (el) this.initialize(el);
    if (model) this.model(model);
  };
  
  function svgHandler(handler) {
    var that = this;
    return function(evt) {
      var target = evt.target,
          item = target.__data__;
      if (item) {
        item = item.mark ? item : item[0];
        handler.call(that._obj, evt, item);
      }
    };
  }
  
  function eventName(name) {
    var i = name.indexOf(".");
    return i < 0 ? name : name.slice(0,i);
  }
  
  var prototype = handler.prototype;

  prototype.initialize = function(el, pad, obj) {
    this._el = d3.select(el).node();
    this._svg = d3.select(el).select("svg.marks").node();
    this._padding = pad;
    this._obj = obj || null;
    return this;
  };
  
  prototype.model = function(model) {
    if (!arguments.length) return this._model;
    this._model = model;
    return this;
  };
  
  prototype.handlers = function() {
    var h = this._handlers;
    return vg.keys(h).reduce(function(a, k) {
      return h[k].reduce(function(a, x) { return (a.push(x), a); }, a);
    }, []);
  };

  // add an event handler
  prototype.on = function(type, handler) {
    var name = eventName(type),
        h = this._handlers,
        dom = d3.select(this._svg).node();
        
    var x = {
      type: type,
      handler: handler,
      svg: svgHandler.call(this, handler)
    };
    h = h[name] || (h[name] = []);
    h.push(x);

    dom.addEventListener(name, x.svg);
    return this;
  };

  // remove an event handler
  prototype.off = function(type, handler) {
    var name = eventName(type),
        h = this._handlers[name],
        dom = d3.select(this._svg).node();
    if (!h) return;
    for (var i=h.length; --i>=0;) {
      if (h[i].type !== type) continue;
      if (!handler || h[i].handler === handler) {
        dom.removeEventListener(name, h[i].svg);
        h.splice(i, 1);
      }
    }
    return this;
  };

  return handler;
})();vg.data = {};

vg.data.ingest = function(datum, index) {
  return {
    data: datum,
    index: index
  };
};

vg.data.mapper = function(func) {
  return function(data) {
    data.forEach(func);
    return data;
  }
};

vg.data.size = function(size, group) {
  size = vg.isArray(size) ? size : [0, size];
  size = size.map(function(d) {
    return (typeof d === 'string') ? group[d] : d;
  });
  return size;
};vg.data.load = function(uri, callback) {
  if (vg.config.isNode) {
    // in node.js, consult base url and select file or http
    var url = vg_load_hasProtocol(uri) ? uri : vg.config.baseURL + uri,
        get = vg_load_isFile(url) ? vg_load_file : vg_load_http;
    get(url, callback);
  } else {
    // in browser, use xhr
    vg_load_xhr(uri, callback);
  }  
};

var vg_load_protocolRE = /^[A-Za-z]+\:\/\//;
var vg_load_fileProtocol = "file://";

function vg_load_hasProtocol(url) {
  return vg_load_protocolRE.test(url);
}

function vg_load_isFile(url) {
  return url.indexOf(vg_load_fileProtocol) === 0;
}

function vg_load_xhr(url, callback) {
  vg.log("LOAD: " + url);
  d3.xhr(url, function(err, resp) {
    if (resp) resp = resp.responseText;
    callback(err, resp);
  });
}

function vg_load_file(file, callback) {
  vg.log("LOAD FILE: " + file);
  var idx = file.indexOf(vg_load_fileProtocol);
  if (idx >= 0) file = file.slice(vg_load_fileProtocol.length);
  require("fs").readFile(file, callback);
}

function vg_load_http(url, callback) {
  vg.log("LOAD HTTP: " + url);
	var req = require("http").request(url, function(res) {
    var pos=0, data = new Buffer(parseInt(res.headers['content-length'],10));
		res.on("error", function(err) { callback(err, null); });
		res.on("data", function(x) { x.copy(data, pos); pos += x.length; });
		res.on("end", function() { callback(null, data); });
	});
	req.on("error", function(err) { callback(err); });
	req.end();
}vg.data.read = (function() {
  var formats = {},
      parsers = {
        "number": vg.number,
        "boolean": vg.boolean,
        "date": Date.parse
      };

  function read(data, format) {
    var type = (format && format.type) || "json";
    data = formats[type](data, format);
    if (format && format.parse) parseValues(data, format.parse);
    return data;
  }

  formats.json = function(data, format) {
    var d = JSON.parse(data);
    if (format && format.property) {
      d = vg.accessor(format.property)(d);
    }
    return d;
  };

  formats.csv = function(data, format) {
    var d = d3.csv.parse(data);
    return d;
  };

  formats.tsv = function(data, format) {
    var d = d3.tsv.parse(data);
    return d;
  };
  
  function parseValues(data, types) {
    var cols = vg.keys(types),
        p = cols.map(function(col) { return parsers[types[col]]; }),
        d, i, j, len, clen;        

    for (i=0, len=data.length; i<len; ++i) {
      d = data[i];
      for (j=0, clen=cols.length; j<clen; ++j) {
        d[cols[j]] = p[j](d[cols[j]]);
      }
    }
  }

  read.formats = formats;
  read.parse = parseValues;
  return read;
})();vg.data.array = function() {
  var fields = [];
   
  function array(data) {
    return data.map(function(d) {      
      var list = [];
      for (var i=0, len=fields.length; i<len; ++i) {
        list.push(fields[i](d));
      }
      return list;
    });
  }
  
  array.fields = function(fieldList) {
    fields = vg.array(fieldList).map(vg.accessor);
    return array;
  };
  
  return array;
};vg.data.copy = function() {
  var from = vg.accessor("data"),
      fields = [],
      as = null;
  
  var copy = vg.data.mapper(function(d) {
    var src = from(d), i, len,
        source = fields,
        target = as || fields;
    for (i=0, len=fields.length; i<len; ++i) {
      d[target[i]] = src[fields[i]];
    }
    return d;
  });

  copy.from = function(field) {
    from = vg.accessor(field);
    return copy;
  };
  
  copy.fields = function(fieldList) {
    fields = vg.array(fieldList);
    return copy;
  };
  
  copy.as = function(fieldList) {
    as = vg.array(fieldList);
    return copy;
  };

  return copy;
};vg.data.facet = function() {

  var keys = [],
      sort = null;

  function facet(data) {    
    var result = {
          key: "",
          keys: [],
          values: []
        },
        map = {}, 
        vals = result.values,
        obj, klist, kstr, len, i, j, k, kv, cmp;

    if (keys.length === 0) {
      // if no keys, skip collation step
      vals.push(obj = {
        key: "", keys: [], index: 0,
        values: sort ? data : data.slice()
      });
      if (sort) obj.values.sort(sort);
      return result;
    }

    for (i=0, len=data.length; i<len; ++i) {
      for (k=0, klist=[], kstr=""; k<keys.length; ++k) {
        kv = keys[k](data[i]);
        klist.push(kv);
        kstr += (k>0 ? "|" : "") + String(kv);
      }
      obj = map[kstr];
      if (obj === undefined) {
        vals.push(obj = map[kstr] = {
          key: kstr,
          keys: klist,
          index: vals.length,
          values: []
        });
      }
      obj.values.push(data[i]);
    }

    if (sort) {
      for (i=0, len=vals.length; i<len; ++i) {
        vals[i].values.sort(sort);
      }
    }

    return result;
  }
  
  facet.keys = function(k) {
    keys = vg.array(k).map(vg.accessor);
    return facet;
  };
  
  facet.sort = function(s) {
    sort = vg.comparator(s);
    return facet;
  };

  return facet;
};vg.data.filter = function() {

  var test = null;

  function filter(data) {
    return test ? data.filter(test) : data;
  }
  
  filter.test = function(func) {
    test = vg.isFunction(func) ? func : vg.parse.expr(func);
    return filter;
  };

  return filter;
};vg.data.fold = function() {
  var fields = [],
      accessors = [],
      output = {
        key: "key",
        value: "value"
      };

  function fold(data) {
    var values = [],
        item, i, j, n, m = fields.length;

    for (i=0, n=data.length; i<n; ++i) {
      item = data[i];
      for (j=0; j<m; ++j) {
        var o = {
          index: values.length,
          data: item.data
        };
        o[output.key] = fields[j];
        o[output.value] = accessors[j](item);
        values.push(o);
      }
    }

    return values;
  }  

  fold.fields = function(f) {
    fields = vg.array(f);
    accessors = fields.map(vg.accessor);
    return fold;
  };

  fold.output = function(map) {
    vg.keys(output).forEach(function(k) {
      if (map[k] !== undefined) {
        output[k] = map[k];
      }
    });
    return fold;
  };

  return fold;
};vg.data.force = function() {
  var layout = d3.layout.force(),
      links = null,
      linkDistance = 20,
      linkStrength = 1,
      charge = -30,
      iterations = 500,
      size = ["width", "height"],
      params = [
        "friction",
        "theta",
        "gravity",
        "alpha"
      ];

  function force(data, db, group) {    
    layout
      .size(vg.data.size(size, group))
      .nodes(data);
      
    if (links && db[links]) {
      layout.links(db[links]);
    }

    layout.start();      
    for (var i=0; i<iterations; ++i) {
      layout.tick();
    }
    layout.stop();
    
    return data;
  }

  force.links = function(dataSetName) {
    links = dataSetName;
    return force;
  };
  
  force.size = function(sz) {
    size = sz;
    return force;
  };
       
  force.linkDistance = function(field) {
    linkDistance = typeof field === 'number'
      ? field
      : vg.accessor(field);
    layout.linkDistance(linkDistance);
    return force;
  };

  force.linkStrength = function(field) {
    linkStrength = typeof field === 'number'
      ? field
      : vg.accessor(field);
    layout.linkStrength(linkStrength);
    return force;
  };
  
  force.charge = function(field) {
    charge = typeof field === 'number'
      ? field
      : vg.accessor(field);
    layout.charge(charge);
    return force;
  };
  
  force.iterations = function(iter) {
    iterations = iter;
    return force;
  };

  params.forEach(function(name) {
    force[name] = function(x) {
      layout[name](x);
      return force;
    }
  });

  return force;
};vg.data.formula = (function() {
  
  return function() {
    var field = null,
        expr = vg.identity;
  
    var formula = vg.data.mapper(function(d) {
      if (field) d[field] = expr.call(null, d);
      return d;
    });

    formula.field = function(name) {
      field = name;
      return formula;
    };
  
    formula.expr = function(func) {
      expr = vg.isFunction(func) ? func : vg.parse.expr(func);
      return formula;
    };

    return formula;
  };
})();vg.data.geo = (function() {
  var params = [
    "center",
    "scale",
    "translate",
    "rotate",
    "precision",
    "clipAngle"
  ];

  function geo() {
    var opt = {},
        projection = "mercator",
        func = d3.geo[projection](),
        lat = vg.identity,
        lon = vg.identity,
        output = {
          "x": "x",
          "y": "y"
        };
    
    var map = vg.data.mapper(function(d) {
      var ll = [lon(d), lat(d)],
          xy = func(ll);
      d[output.x] = xy[0];
      d[output.y] = xy[1];
      return d;
    });

    map.func = function() {
      return func;
    };
        
    map.projection = function(p) {
      if (projection !== p) {
        projection = p;
        func = d3.geo[projection]();
        for (var name in opt) {
          func[name](opt[name]);
        }
      }
      return map;
    };

    params.forEach(function(name) {
      map[name] = function(x) {
        opt[name] = x;
        func[name](x);
        return map;
      }
    });
    
    map.lon = function(field) {
      lon = vg.accessor(field);
      return map;
    };

    map.lat = function(field) {
      lat = vg.accessor(field);
      return map;
    };
    
    map.output = function(map) {
      vg.keys(output).forEach(function(k) {
        if (map[k] !== undefined) {
          output[k] = map[k];
        }
      });
      return map;
    };
    
    
    return map;
  };
  
  geo.params = params;
  return geo;
})();vg.data.geopath = function() {
  var geopath = d3.geo.path(),
      projection = "mercator",
      geojson = vg.identity,
      opt = {},
      output = {"path": "path"};

  var map = vg.data.mapper(function(d) {
    d[output.path] = geopath(geojson(d));
    return d;
  });
  
  map.projection = function(proj) {
    if (projection !== proj) {
      projection = proj;
      var p = d3.geo[projection]();
      for (var name in opt) {
        p[name](opt[name]);
      }
      geopath.projection(p);
    }
    return map;
  };
  
  vg.data.geo.params.forEach(function(name) {
    map[name] = function(x) {
      opt[name] = x;
      (geopath.projection())[name](x);
      return map;
    }
  });
   
  map.value = function(field) {
    geojson = vg.accessor(field);
    return map;
  };

  map.output = function(map) {
    vg.keys(output).forEach(function(k) {
      if (map[k] !== undefined) {
        output[k] = map[k];
      }
    });
    return map;
  };

  return map;
};vg.data.link = function() {
  var shape = "line",
      source = vg.accessor("source"),
      target = vg.accessor("target"),
      tension = 0.2,
      output = {"path": "path"};
  
  function line(d) {
    var s = source(d),
        t = target(d);
    return "M" + s.x + "," + s.y 
         + "L" + t.x + "," + t.y;
  }

  function curve(d) {
    var s = source(d),
        t = target(d),
        dx = t.x - s.x,
        dy = t.y - s.y,
        ix = tension * (dx + dy),
        iy = tension * (dy - dx);
    return "M" + s.x + "," + s.y
         + "C" + (s.x+ix) + "," + (s.y+iy)
         + " " + (t.x+iy) + "," + (t.y-ix)
         + " " + t.x + "," + t.y;
  }
  
  function diagonalX(d) {
    var s = source(d),
        t = target(d),
        m = (s.x + t.x) / 2;
    return "M" + s.x + "," + s.y
         + "C" + m   + "," + s.y
         + " " + m   + "," + t.y
         + " " + t.x + "," + t.y;
  }

  function diagonalY(d) {
    var s = source(d),
        t = target(d),
        m = (s.y + t.y) / 2;
    return "M" + s.x + "," + s.y
         + "C" + s.x + "," + m
         + " " + t.x + "," + m
         + " " + t.x + "," + t.y;
  }

  var shapes = {
    line:      line,
    curve:     curve,
    diagonal:  diagonalX,
    diagonalX: diagonalX,
    diagonalY: diagonalY
  };
  
  function link(data) {
    var path = shapes[shape];
        
    data.forEach(function(d) {
      d[output.path] = path(d);
    });
    
    return data;
  }

  link.shape = function(val) {
    shape = val;
    return link;
  };

  link.tension = function(val) {
    tension = val;
    return link;
  };
  
  link.source = function(field) {
    source = vg.accessor(field);
    return link;
  };
  
  link.target = function(field) {
    target = vg.accessor(field);
    return link;
  };
  
  link.output = function(map) {
    vg.keys(output).forEach(function(k) {
      if (map[k] !== undefined) {
        output[k] = map[k];
      }
    });
    return link;
  };
  
  return link;
};vg.data.pie = function() {
  var one = function() { return 1; },
      value = one,
      start = 0,
      end = 2 * Math.PI,
      sort = false,
      output = {
        "startAngle": "startAngle",
        "endAngle": "endAngle"
      };

  function pie(data) {
    var values = data.map(function(d, i) { return +value(d); }),
        a = start,
        k = (end - start) / d3.sum(values),
        index = d3.range(data.length);
    
    if (sort) {
      index.sort(function(a, b) {
        return values[a] - values[b];
      });
    }
    
    index.forEach(function(i) {
      var d;
      data[i].value = (d = values[i]);
      data[i][output.startAngle] = a;
      data[i][output.endAngle] = (a += d * k);
    });
    
    return data;
  }

  pie.sort = function(b) {
    sort = b;
    return pie;
  };
       
  pie.value = function(field) {
    value = field ? vg.accessor(field) : one;
    return pie;
  };
  
  pie.startAngle = function(startAngle) {
    start = Math.PI * startAngle / 180;
    return pie;
  };
  
  pie.endAngle = function(endAngle) {
    end = Math.PI * endAngle / 180;
    return pie;
  };

  pie.output = function(map) {
    vg.keys(output).forEach(function(k) {
      if (map[k] !== undefined) {
        output[k] = map[k];
      }
    });
    return pie;
  };

  return pie;
};vg.data.sort = function() {
  var by = null;

  function sort(data) {
    data = (vg.isArray(data) ? data : data.values || []);
    data.sort(by);
    for (var i=0, n=data.length; i<n; ++i) data[i].index = i; // re-index
    return data;
  }
  
  sort.by = function(s) {
    by = vg.comparator(s);
    return sort;
  };

  return sort;
};vg.data.stack = function() {
  var layout = d3.layout.stack()
                 .values(function(d) { return d.values; }),
      point = null,
      height = null,
      params = ["offset", "order"],
      output = {
        "y0": "y2",
        "y1": "y"
      };

  function stack(data) {
    var out_y0 = output["y0"],
        out_y1 = output["y1"];
    
    return layout
      .x(point)
      .y(height)
      .out(function(d, y0, y) {
        d[out_y0] = y0;
        d[out_y1] = y + y0;
      })
      (data.values);
  }
       
  stack.point = function(field) {
    point = vg.accessor(field);
    return stack;
  };
  
  stack.height = function(field) {
    height = vg.accessor(field);
    return stack;
  };

  params.forEach(function(name) {
    stack[name] = function(x) {
      layout[name](x);
      return stack;
    }
  });

  stack.output = function(map) {
    d3.keys(output).forEach(function(k) {
      if (map[k] !== undefined) {
        output[k] = map[k];
      }
    });
    return stack;
  };

  return stack;
};vg.data.stats = function() {
  var value = vg.accessor("data"),
      median = false,
      output = {
        "count":    "count",
        "min":      "min",
        "max":      "max",
        "sum":      "sum",
        "mean":     "mean",
        "variance": "variance",
        "stdev":    "stdev",
        "median":   "median"
      };
  
  function reduce(data) {
    var min = +Infinity,
        max = -Infinity,
        sum = 0,
        mean = 0,
        M2 = 0,
        i, len, v, delta;

    var list = (vg.isArray(data) ? data : data.values || []).map(value);
    
    // compute aggregates
    for (i=0, len=list.length; i<len; ++i) {
      v = list[i];
      if (v < min) min = v;
      if (v > max) max = v;
      sum += v;
      delta = v - mean;
      mean = mean + delta / (i+1);
      M2 = M2 + delta * (v - mean);
    }
    M2 = M2 / (len - 1);
    
    var o = vg.isArray(data) ? {} : data;
    if (median) {
      list.sort(vg.numcmp);
      i = list.length >> 1;
      o[output.median] = list.length % 2
        ? list[i]
        : (list[i-1] + list[i])/2;
    }
    o[output.count] = len;
    o[output.min] = min;
    o[output.max] = max;
    o[output.sum] = sum;
    o[output.mean] = mean;
    o[output.variance] = M2;
    o[output.stdev] = Math.sqrt(M2);
    return o;
  }
  
  function stats(data) {
    return (vg.isArray(data) ? [data] : data.values || [])
      .map(reduce); // no pun intended
  }
  
  stats.median = function(bool) {
    median = bool || false;
    return stats;
  };
  
  stats.value = function(field) {
    value = vg.accessor(field);
    return stats;
  };
  
  stats.output = function(map) {
    vg.keys(output).forEach(function(k) {
      if (map[k] !== undefined) {
        output[k] = map[k];
      }
    });
    return stats;
  };
  
  return stats;
};vg.data.treemap = function() {
  var layout = d3.layout.treemap()
                 .children(function(d) { return d.values; }),
      value = vg.accessor("data"),
      size = ["width", "height"],
      params = ["round", "sticky", "ratio", "padding"],
      output = {
        "x": "x",
        "y": "y",
        "dx": "width",
        "dy": "height"
      };

  function treemap(data, db, group) {
    data = layout
      .size(vg.data.size(size, group))
      .value(value)
      .nodes(data);
    
    var keys = vg.keys(output),
        len = keys.length;
    data.forEach(function(d) {
      var key, val;
      for (var i=0; i<len; ++i) {
        key = keys[i];
        if (key !== output[key]) {
          val = d[key];
          delete d[key];
          d[output[key]] = val;
        }
      }
    });
    
    return data;
  }

  treemap.size = function(sz) {
    size = sz;
    return treemap;
  };

  treemap.value = function(field) {
    value = vg.accessor(field);
    return treemap;
  };

  params.forEach(function(name) {
    treemap[name] = function(x) {
      layout[name](x);
      return treemap;
    }
  });

  treemap.output = function(map) {
    vg.keys(output).forEach(function(k) {
      if (map[k] !== undefined) {
        output[k] = map[k];
      }
    });
    return treemap;
  };

  return treemap;
};vg.data.unique = function() {

  var field = null,
      as = "field";

  function unique(data) {
    return vg.unique(data, field)
      .map(function(x) {
        var o = {};
        o[as] = x;
        return o;
      });
  }
  
  unique.field = function(f) {
    field = vg.accessor(f);
    return unique;
  };
  
  unique.as = function(x) {
    as = x;
    return unique;
  };

  return unique;
};vg.data.wordcloud = function() {
  var layout = d3.layout.cloud().size([900, 500]),
      text = vg.accessor("data"),
      size = ["width", "height"],
      fontSize = function() { return 14; },
      rotate = function() { return 0; },
      params = ["font", "fontStyle", "fontWeight", "padding"];
  
  var output = {
    "x": "x",
    "y": "y",
    "size": "fontSize",
    "font": "font",
    "rotate": "angle"
  };
  
  function cloud(data, db, group) {
    function finish(tags, bounds) {
      var size = layout.size(),
          dx = size[0] / 2,
          dy = size[1] / 2,
          keys = vg.keys(output),
          key, d, i, n, k, m = keys.length;

      // sort data to match wordcloud order
      data.sort(function(a,b) {
        return fontSize(b) - fontSize(a);
      });

      for (i=0, n=tags.length; i<n; ++i) {
        d = data[i];
        for (k=0; k<m; ++k) {
          key = keys[k];
          d[output[key]] = tags[i][key];
          if (key === "x") d[output.x] += dx;
          if (key === "y") d[output.y] += dy;
        }
      }
    }
    
    layout
      .size(vg.data.size(size, group))
      .text(text)
      .fontSize(fontSize)
      .rotate(rotate)
      .words(data)
      .on("end", finish)
      .start();
    return data;
  }

  cloud.text = function(field) {
    text = vg.accessor(field);
    return cloud;
  };
  
  cloud.size = function(sz) {
    size = sz;
    return cloud;
  };
         
  cloud.fontSize = function(field) {
    fontSize = vg.accessor(field);
    return cloud;
  };
  
  cloud.rotate = function(x) {
    var v;
    if (vg.isObject(x) && !Array.isArray(x)) {
      if (x.random !== undefined) {
        v = (v = x.random) ? vg.array(v) : [0];
        rotate = function() {
          return v[~~(Math.random()*v.length-0.00001)];
        };
      } else if (x.alternate !== undefined) {
        v = (v = x.alternate) ? vg.array(v) : [0];
        rotate = function(d, i) {
          return v[i % v.length];
        };
      }
    } else {
      rotate = vg.accessor(field);
    }
    return cloud;
  };

  params.forEach(function(name) {
    cloud[name] = function(x) {
      layout[name](x);
      return cloud;
    }
  });

  cloud.output = function(map) {
    vg.keys(output).forEach(function(k) {
      if (map[k] !== undefined) {
        output[k] = map[k];
      }
    });
    return cloud;
  };
  
  return cloud;
};vg.data.zip = function() {
  var z = null,
      as = "zip",
      key = vg.accessor("data"),
      defaultVal = undefined,
      withKey = null;

  function zip(data, db) {
    var zdata = db[z], zlen = zdata.length, d, i, len, map;
    
    if (withKey) {
      map = {};
      zdata.forEach(function(s) { map[withKey(s)] = s; });
    }
    
    for (i=0, len=data.length; i<len; ++i) {
      d = data[i];
      d[as] = map ? (map[key(d)] || defaultVal) : zdata[i % zlen];
    }
    
    return data;
  }

  zip["with"] = function(d) {
    z = d;
    return zip;
  };
  
  zip["default"] = function(d) {
    defaultVal = d;
    return zip;
  };

  zip.as = function(name) {
    as = name;
    return zip;
  };

  zip.key = function(k) {
    key = vg.accessor(k);
    return zip;
  };

  zip.withKey = function(k) {
    withKey = vg.accessor(k);
    return zip;
  };

  return zip;
};vg.parse = {};vg.parse.axes = (function() {
  var ORIENT = {
    "x":      "bottom",
    "y":      "left",
    "top":    "top",
    "bottom": "bottom",
    "left":   "left",
    "right":  "right"
  };

  function axes(spec, axes, scales) {
    (spec || []).forEach(function(def, index) {
      axes[index] = axes[index] || vg.scene.axis();
      axis(def, index, axes[index], scales);
    });
  };

  function axis(def, index, axis, scales) {
    // axis scale
    if (def.scale !== undefined) {
      axis.scale(scales[def.scale]);
    }

    // axis orientation
    var orient = def.orient || ORIENT[def.type];
    axis.orient(orient);

    // axis values
    if (def.values !== undefined) {
      axis.tickValues(def.values);
    }

    // axis label formatting
    if (def.format !== undefined) {
      axis.tickFormat(d3.format(def.format));
    }

    // axis tick subdivision
    if (def.subdivide !== undefined) {
      axis.tickSubdivide(def.subdivide);
    }

    // axis tick padding
    if (def.tickPadding !== undefined) {
      axis.tickPadding(def.tickPadding);
    }

    // axis tick size(s)
    var size = [];
    if (def.tickSize !== undefined) {
      for (var i=0; i<3; ++i) size.push(def.tickSize);
    } else {
      var ts = vg.config.axis.tickSize;
      size = [ts, ts, ts];
    }
    if (def.tickSizeMajor !== undefined) size[0] = def.tickSizeMajor;
    if (def.tickSizeMinor !== undefined) size[1] = def.tickSizeMinor;
    if (def.tickSizeEnd   !== undefined) size[2] = def.tickSizeEnd;
    if (size.length) {
      axis.tickSize.apply(axis, size);
    }

    // tick arguments
    if (def.ticks !== undefined) {
      var ticks = vg.isArray(def.ticks) ? def.ticks : [def.ticks];
      axis.ticks.apply(axis, ticks);
    }

    // axis offset
    if (def.offset) axis.offset(def.offset);

    // axis layer
    if (def.layer) axis.layer(def.layer);

    // axis grid lines
    if (def.grid) axis.grid(def.grid);
    
    // style properties
    if (def.properties) {
      var p = def.properties;
      if (p.ticks) {
        axis.majorTickProperties(p.majorTicks
          ? vg.extend({}, p.ticks, p.majorTicks) : p.ticks);
        axis.minorTickProperties(p.minorTicks
          ? vg.extend({}, p.ticks, p.minorTicks) : p.ticks);
      } else {
        if (p.majorTicks) axis.majorTickProperties(p.majorTicks);
        if (p.minorTicks) axis.minorTickProperties(p.minorTicks);
      }
      if (p.labels) axis.tickLabelProperties(p.labels);
      if (p.grid) axis.gridLineProperties(p.grid);
      if (p.axis) axis.domainProperties(p.axis);
    }
  }
  
  return axes;
})();vg.parse.data = function(spec, callback) {
  var model = {
    defs: spec,
    load: {},
    flow: {},
    source: {}
  };

  var count = 0;
  
  function load(d) {
    return function(error, data) {
      if (error) {
        vg.error("LOADING FAILED: " + d.url);
      } else {
        model.load[d.name] = vg.data.read(data.toString(), d.format);
      }
      if (--count === 0) callback();
    }
  }
  
  (spec || []).forEach(function(d) {
    if (d.url) {
      count += 1;
      vg.data.load(d.url, load(d)); 
    }
     
    if (d.values) {
      if (d.format && d.format.parse) {
        // run specified value parsers
        vg.data.read.parse(d.values, d.format.parse);
      }
      model.load[d.name] = d.values;
    }
    
    if (d.source) {
      var list = model.source[d.source] || (model.source[d.source] = []);
      list.push(d.name);
    }
    
    if (d.transform) {
      model.flow[d.name] = vg.parse.dataflow(d);
    }
  });
  
  if (count === 0) setTimeout(callback, 1);
  return model;
};vg.parse.dataflow = function(def) {
  var tx = (def.transform || []).map(vg.parse.transform);
  return !tx.length ? vg.identity :
    function(data, db, group) {
      return tx.reduce(function(d,t) { return t(d, db, group); }, data);
    };
};vg.parse.expr = (function() {
  
  var CONSTANT = {
  	"E":       "Math.E",
  	"LN2":     "Math.LN2",
  	"LN10":    "Math.LN10",
  	"LOG2E":   "Math.LOG2E",
  	"LOG10E":  "Math.LOG10E",
  	"PI":      "Math.PI",
  	"SQRT1_2": "Math.SQRT1_2",
  	"SQRT2":   "Math.SQRT2"
  };

  var FUNCTION = {
  	"abs":    "Math.abs",
  	"acos":   "Math.acos",
  	"asin":   "Math.asin",
  	"atan":   "Math.atan",
  	"atan2":  "Math.atan2",
  	"ceil":   "Math.ceil",
  	"cos":    "Math.cos",
  	"exp":    "Math.exp",
  	"floor":  "Math.floor",
  	"log":    "Math.log",
  	"max":    "Math.max",
  	"min":    "Math.min",
  	"pow":    "Math.pow",
  	"random": "Math.random",
  	"round":  "Math.round",
  	"sin":    "Math.sin",
  	"sqrt":   "Math.sqrt",
  	"tan":    "Math.tan"
  };
  
  var lexer = /([\"\']|[\=\<\>\~\&\|\?\:\+\-\/\*\%\!\^\,\;\[\]\{\}\(\) ]+)/;
      
  return function(x) {
    var tokens = x.split(lexer),
        t, v, i, n, sq, dq;

    for (sq=0, dq=0, i=0, n=tokens.length; i<n; ++i) {
      var t = tokens[i];
      if (t==="'") { if (!dq) sq = !sq; continue; }
      if (t==='"') { if (!sq) dq = !dq; continue; }
      if (dq || sq) continue;
      if (CONSTANT[t]) {
        tokens[i] = CONSTANT[t];
      }
      if (FUNCTION[t] && (v=tokens[i+1]) && v[0]==="(") {
        tokens[i] = FUNCTION[t];
      }
    }
    
    // TODO security check
    return Function("d", "return ("+tokens.join("")+");");
  };
  
})();vg.parse.mark = function(mark) {
  var props = mark.properties,
      group = mark.marks;
  
  // parse mark property definitions
  vg.keys(props).forEach(function(k) {
    props[k] = vg.parse.properties(props[k]);
  });
  // parse delay function
  if (mark.delay) mark.delay = vg.parse.properties({delay: mark.delay});
      
  // parse mark data definition
  if (mark.from) {
    var name = mark.from.data,
        tx = vg.parse.dataflow(mark.from);
    mark.from = function(db, group, parentData) {
      var data = vg.scene.data(name ? db[name] : null, parentData);
      return tx(data, db, group);
    };
  }
  
  // recurse if group type
  if (group) {
    mark.marks = group.map(vg.parse.mark);
  }
      
  return mark;
};vg.parse.marks = function(spec, width, height) {
  return {
    type: "group",
    width: width,
    height: height,
    axes: spec.axes || [],
    scales: spec.scales || [],
    marks: (spec.marks || []).map(vg.parse.mark)
  };
};vg.parse.padding = function(pad) {
  if (vg.isObject(pad)) return pad;
  var p = vg.isNumber(pad) ? pad : 20;
  return {top:p, left:p, right:p, bottom:p};
};
vg.parse.properties = (function() {
  function compile(spec) {
    var code = "",
        names = vg.keys(spec),
        i, len, name, ref, vars = {};
        
    code += "var o = trans ? {} : item;\n"
    
    for (i=0, len=names.length; i<len; ++i) {
      ref = spec[name = names[i]];
      code += (i > 0) ? "\n  " : "  ";
      code += "o."+name+" = "+valueRef(ref)+";";
      vars[name] = true;
    }
    
    if (vars.x2) {
      code += "\n  if (o.x > o.x2) { "
            + "var t = o.x; o.x = o.x2; o.x2 = t; };"
      code += "\n  o.width = (o.x2 - o.x);"
    }
    
    if (vars.y2) {
      code += "\n  if (o.y > o.y2) { "
            + "var t = o.y; o.y = o.y2; o.y2 = t; };"
      code += "\n  o.height = (o.y2 - o.y);"
    }
    
    code += "if (trans) trans.interpolate(item, o);";

    return Function("item", "group", "trans", code);
  }

  // TODO security check for strings emitted into code
  function valueRef(ref) {
    if (ref == null) return null;

    var val = ref.value !== undefined
              ? vg.str(ref.value)
              : "item.datum.data";

    // get value from enclosing group
    if (ref.group !== undefined) {
      val = "group." + ref.group;
    }

    // get data field value
    if (ref.field !== undefined) {
      val = "item.datum["
          + vg.field(ref.field).map(vg.str).join("][")
          + "]";
    }
    
    // run through scale function
    if (ref.scale !== undefined) {
      var scale = "group.scales['"+ref.scale+"']";
      if (ref.band) {
        val = scale + ".rangeBand()";
      } else {
        val = scale + "(" + val + ")";
      }
    }
    
    // multiply, offset, return value
    return "(" + (ref.mult ? (ref.mult+" * ") : "") + val + ")"
      + (ref.offset ? " + "+ref.offset : "");
  }
  
  return compile;
})();vg.parse.scales = (function() {
  var LINEAR = "linear",
      ORDINAL = "ordinal",
      LOG = "log",
      POWER = "pow",
      TIME = "time",
      GROUP_PROPERTY = {width: 1, height: 1};

  var SCALES = {
    "time": d3.time.scale,
    "utc":  d3.time.scale.utc
  };

  function scales(spec, scales, db, group) {
    return (spec || []).reduce(function(o, def) {
      var name = def.name, prev = name + ":prev";
      o[name] = scale(def, o[name], db, group);
      o[prev] = o[prev] || o[name];
      return o;
    }, scales || {});
  }

  function scale(def, scale, db, group) {
    var s = instance(def, scale),
        m = s.type===ORDINAL ? ordinal : quantitative,
        rng = range(def, group),
        data = vg.values(group.datum);

    m(def, s, rng, db, data);
    return s;
  }
  
  function instance(def, scale) {
    var type = def.type || LINEAR;
    if (!scale || type !== scale.type) {
      var ctor = SCALES[type] || d3.scale[type];
      if (!ctor) vg.error("Unrecognized scale type: " + type);
      (scale = ctor()).type = type;
      scale.scaleName = def.name;
    }
    return scale;
  }
  
  function ordinal(def, scale, rng, db, data) {
    var domain, dat, get, str;
    
    // domain
    domain = def.domain;
    if (vg.isArray(domain)) {
      scale.domain(domain);
    } else if (vg.isObject(domain)) {
      dat = db[domain.data] || data;
      get = vg.accessor(domain.field);      
      scale.domain(vg.unique(dat, get));
    }

    // range
    str = typeof rng[0] === 'string';
    if (str || rng.length > 2) {
      scale.range(rng); // color or shape values
    } else if (def.points) {
      scale.rangePoints(rng, def.padding||0);
    } else if (def.round || def.round===undefined) {
      scale.rangeRoundBands(rng, def.padding||0);
    } else {
      scale.rangeBands(rng, def.padding||0);
    }
  }
  
  function quantitative(def, scale, rng, db, data) {
    var domain, dat, interval;

    // domain
    domain = [null, null];
    if (def.domain !== undefined) {
      if (vg.isArray(def.domain)) {
        domain = def.domain.slice();
      } else if (vg.isObject(def.domain)) {
        dat = db[def.domain.data] || data;
        vg.array(def.domain.field).forEach(function(f,i) {
          f = vg.accessor(f);
          domain[0] = d3.min([domain[0], d3.min(dat, f)]);
          domain[1] = d3.max([domain[1], d3.max(dat, f)]);
        });
      } else {
        domain = def.domain;
      }
    }
    if (def.domainMin !== undefined) {
      if (vg.isObject(def.domainMin)) {
        domain[0] = null;
        dat = db[def.domainMin.data] || data;
        vg.array(def.domainMin.field).forEach(function(f,i) {
          f = vg.accessor(f);
          domain[0] = d3.min([domain[0], d3.min(dat, f)]);
        });
      } else {
        domain[0] = def.domainMin;
      }
    }
    if (def.domainMax !== undefined) {
      if (vg.isObject(def.domainMax)) {
        domain[1] = null;
        dat = db[def.domainMax.data] || data;
        vg.array(def.domainMax.field).forEach(function(f,i) {
          f = vg.accessor(f);
          domain[1] = d3.max([domain[1], d3.max(dat, f)]);
        });
      } else {
        domain[1] = def.domainMax;
      }
    }
    if (def.type !== LOG && def.type !== TIME && (def.zero || def.zero===undefined)) {
      domain[0] = Math.min(0, domain[0]);
      domain[1] = Math.max(0, domain[1]);
    }
    scale.domain(domain);

    // range
    // vertical scales should flip by default, so use XOR here
    if (def.range=='height') rng = rng.reverse();
    scale[def.round ? "rangeRound" : "range"](rng);

    if (def.exponent && def.type===POWER) scale.exponent(def.exponent);
    if (def.clamp) scale.clamp(true);
    if (def.nice) {
      if (def.type === TIME) {
        interval = d3.time[def.nice];
        if (!interval) vg.error("Unrecognized interval: " + interval);
        scale.nice(interval);
      } else {
        scale.nice();
      }
    }
  }
  
  function range(def, group) {
    var rng = [null, null];

    if (def.range !== undefined) {
      if (typeof def.range === 'string') {
        if (GROUP_PROPERTY[def.range]) {
          rng = [0, group[def.range]];
        } else if (vg.config.range[def.range]) {
          rng = vg.config.range[def.range];
        } else {
          vg.error("Unrecogized range: "+def.range);
          return rng;
        }
      } else if (vg.isArray(def.range)) {
        rng = def.range;
      } else {
        rng = [0, def.range];
      }
    }
    if (def.rangeMin !== undefined) {
      rng[0] = def.rangeMin;
    }
    if (def.rangeMax !== undefined) {
      rng[1] = def.rangeMax;
    }
    
    if (def.reverse !== undefined) {
      var rev = def.reverse;
      if (vg.isObject(rev)) {
        rev = vg.accessor(rev.field)(group.datum);
      }
      if (rev) rng = rng.reverse();
    }
    
    return rng;
  }
  
  return scales;
})();vg.parse.spec = function(spec, callback, viewFactory) {
  
  viewFactory = viewFactory || vg.ViewFactory;
  
  function parse(spec) {
    // protect against subsequent spec modification
    spec = vg.duplicate(spec);
    
    var width = spec.width || 500,
        height = spec.height || 500,
        viewport = spec.viewport || null;
    
    var defs = {
      width: width,
      height: height,
      viewport: viewport,
      padding: vg.parse.padding(spec.padding),
      marks: vg.parse.marks(spec, width, height),
      data: vg.parse.data(spec.data, function() { callback(viewConstructor); })
    };
    
    var viewConstructor = viewFactory(defs);
  }
  
  vg.isObject(spec) ? parse(spec) :
    d3.json(spec, function(error, json) {
      error ? vg.error(error) : parse(json);
    });
};vg.parse.transform = function(def) {
  var tx = vg.data[def.type]();
      
  vg.keys(def).forEach(function(k) {
    if (k === 'type') return;
    (tx[k])(def[k]);
  });
  
  return tx;
};vg.scene = {};

vg.scene.GROUP  = "group",
vg.scene.ENTER  = 0,
vg.scene.UPDATE = 1,
vg.scene.EXIT   = 2;

vg.scene.DEFAULT_DATA = {"sentinel":1}

vg.scene.data = function(data, parentData) {
  var DEFAULT = vg.scene.DEFAULT_DATA;

  // if data is undefined, inherit or use default
  data = vg.values(data || parentData || [DEFAULT]);

  // if inheriting default data, ensure its in an array
  if (data === DEFAULT) data = [DEFAULT];
  
  return data;
};vg.scene.Item = (function() {
  function item(mark) {
    this.mark = mark;
  }
  
  var prototype = item.prototype;

  prototype.hasPropertySet = function(name) {
    var props = this.mark.def.properties;
    return props && props[name] != null;
  };

  prototype.cousin = function(offset, index) {
    if (offset === 0) return this;
    offset = offset || -1;
    var mark = this.mark,
        group = mark.group,
        iidx = index==null ? mark.items.indexOf(this) : index,
        midx = group.items.indexOf(mark) + offset;
    return group.items[midx].items[iidx];
  };
  
  prototype.sibling = function(offset) {
    if (offset === 0) return this;
    offset = offset || -1;
    var mark = this.mark,
        iidx = mark.items.indexOf(this) + offset;
    return mark.items[iidx];
  };
  
  prototype.remove = function() {
    var item = this,
        list = item.mark.items,
        i = list.indexOf(item);
    if (i >= 0) (i===list.length-1) ? list.pop() : list.splice(i, 1);
    return item;
  };
  
  return item;
})();

vg.scene.item = function(mark) {
  return new vg.scene.Item(mark);
};vg.scene.build = (function() {
  var GROUP  = vg.scene.GROUP,
      ENTER  = vg.scene.ENTER,
      UPDATE = vg.scene.UPDATE,
      EXIT   = vg.scene.EXIT,
      DEFAULT= {"sentinel":1};
  
  function build(def, db, node, parentData) {
    var data = vg.scene.data(
      def.from ? def.from(db, node, parentData) : null,
      parentData);
    
    // build node and items
    node = buildNode(def, node);
    node.items = buildItems(def, data, node);
    buildTrans(def, node);
    
    // recurse if group
    if (def.type === GROUP) {
      buildGroup(def, db, node);
    }
    
    return node;
  };
  
  function buildNode(def, node) {
    node = node || {};
    node.def = def;
    node.marktype = def.type;
    node.interactive = !(def.interactive === false);
    return node;
  }
  
  function buildItems(def, data, node) {
    var keyf = keyFunction(def.key),
        prev = node.items || [],
        next = [],
        map = {},
        i, key, len, item, datum, enter;

    for (i=0, len=prev.length; i<len; ++i) {
      item = prev[i];
      item.status = EXIT;
      if (keyf) map[item.key] = item;
    }
    
    for (i=0, len=data.length; i<len; ++i) {
      datum = data[i];
      key = i;
      item = keyf ? map[key = keyf(datum)] : prev[i];
      enter = item ? false : (item = vg.scene.item(node), true);
      item.status = enter ? ENTER : UPDATE;
      item.datum = datum;
      item.key = key;
      next.push(item);
    }
    
    for (i=0, len=prev.length; i<len; ++i) {
      item = prev[i];
      if (item.status === EXIT) {
        item.key = keyf ? item.key : next.length;
        next.push(item);
      }
    }
    
    return next;
  }
  
  function buildGroup(def, db, node) {
    var groups = node.items,
        marks = def.marks,
        i, len, m, mlen, name, group;

    for (i=0, len=groups.length; i<len; ++i) {
      group = groups[i];
      
      // update scales
      if (group.scales) for (name in group.scales) {
        if (name.indexOf(":prev") < 0) {
          group.scales[name+":prev"] = group.scales[name].copy();
        }
      }

      // build items
      group.items = group.items || [];
      for (m=0, mlen=marks.length; m<mlen; ++m) {
        group.items[m] = build(marks[m], db, group.items[m], group.datum);
        group.items[m].group = group;
      }
    }
  }

  function buildTrans(def, node) {
    if (def.duration) node.duration = def.duration;
    if (def.ease) node.ease = d3.ease(def.ease)
    if (def.delay) {
      var items = node.items, group = node.group, n = items.length, i;
      for (i=0; i<n; ++i) def.delay.call(this, items[i], group);
    }
  }
  
  function keyFunction(key) {
    return key ? vg.accessor(key) : null;
  }
  
  return build;
})();vg.scene.encode = (function() {
  var GROUP  = vg.scene.GROUP,
      ENTER  = vg.scene.ENTER,
      UPDATE = vg.scene.UPDATE,
      EXIT   = vg.scene.EXIT;

  function main(scene, def, trans, request, items) {
    (request && items)
      ? update.call(this, scene, def, trans, request, items)
      : encode.call(this, scene, scene, def, trans, request);
    return scene;
  }
  
  function update(scene, def, trans, request, items) {
    items = vg.array(items);
    var i, len, item, group, props, prop;
    for (i=0, len=items.length; i<len; ++i) {
      item = items[i];
      group = item.mark.group || null;
      props = item.mark.def.properties;
      prop = props && props[request];
      if (prop) prop.call(this, item, group, trans);
    }
  }
  
  function encode(group, scene, def, trans, request) {
    encodeItems.call(this, group, scene.items, def, trans, request);
    if (scene.marktype === GROUP) {
      encodeGroup.call(this, scene, def, group, trans, request);
    }
  }
  
  function encodeGroup(scene, def, parent, trans, request) {
    var i, len, m, mlen, group, scales, axes, axisItems, axisDef;

    for (i=0, len=scene.items.length; i<len; ++i) {
      group = scene.items[i];

      // cascade scales recursively
      scales = group.scales || (group.scales = vg.extend({}, parent.scales));    
      
      // update group-level scales
      if (def.scales) {
        vg.parse.scales(def.scales, scales, this._data, group);
      }
      
      // update group-level axes
      if (def.axes) {
        axes = group.axes || (group.axes = []);
        axisItems = group.axisItems || (group.axisItems = []);
        vg.parse.axes(def.axes, axes, group.scales);
        axes.forEach(function(a, i) {
          axisDef = a.def();
          axisItems[i] = vg.scene.build(axisDef, this._data, axisItems[i]);
          encode.call(this, group, group.axisItems[i], axisDef, trans);
        });
      }
      
      // encode children marks
      for (m=0, mlen=group.items.length; m<mlen; ++m) {
        encode.call(this, group, group.items[m], def.marks[m], trans, request);
      }
    }
  }
  
  function encodeItems(group, items, def, trans, request) {
    if (def.properties == null) return;
    
    var props  = def.properties,
        enter  = props.enter,
        update = props.update,
        exit   = props.exit,
        i, len, item, prop;
    
    if (request && (prop = props[request])) {
      for (i=0, len=items.length; i<len; ++i) {
        prop.call(this, items[i], group, trans);
      }
      return; // exit early if given request
    }
    
    for (i=0; i<items.length; ++i) {
      item = items[i];
      
      // enter set
      if (item.status === ENTER) {
        if (enter) enter.call(this, item, group);
        item.status = UPDATE;
      }

      // update set      
      if (item.status !== EXIT && update) {
        update.call(this, item, group, trans);
      }
      
      // exit set
      if (item.status === EXIT) {
        if (exit && trans) exit.call(this, item, group, trans);
        if (!trans) items[i--].remove();
      }
    }
  }
  
  return main;
})();vg.scene.Transition = (function() {
  function trans(duration, ease) {
    this.duration = duration || 500;
    this.ease = ease && d3.ease(ease) || d3.ease("cubic-in-out");
    this.updates = {next: null};
  }
  
  var prototype = trans.prototype;
  
  prototype.interpolate = function(item, values) {
    var key, curr, next, interp, list = null;

    for (key in values) {
      curr = item[key];
      next = values[key];
      if (curr !== next) {
        interp = d3.interpolate(curr, next);
        interp.property = key;
        (list || (list=[])).push(interp);
      }
    }

    if (interp) {
      list.item = item;
      list.ease = item.mark.ease || this.ease;
      list.next = this.updates.next;
      this.updates.next = list;
    }
    return this;
  };
  
  prototype.start = function(callback) {
    var t = this, prev = t.updates, curr = prev.next;
    for (; curr!=null; prev=curr, curr=prev.next) {
      if (curr.item.status === vg.scene.EXIT) curr.remove = true;
    }
    t.callback = callback;
    d3.timer(function(elapsed) { return step.call(t, elapsed); });
  };

  function step(elapsed) {
    var list = this.updates, prev = list, curr = prev.next,
        duration = this.duration,
        item, delay, f, e, i, n, stop = true;

    for (; curr!=null; prev=curr, curr=prev.next) {
      item = curr.item;
      delay = item.delay || 0;

      f = (elapsed - delay) / duration;
      if (f < 0) { stop = false; continue; }
      if (f > 1) f = 1;
      e = curr.ease(f);

      for (i=0, n=curr.length; i<n; ++i) {
        item[curr[i].property] = curr[i](e);
      }

      if (f === 1) {
        if (curr.remove) item.remove();
        prev.next = curr.next;
        curr = prev;
      } else {
        stop = false;
      }
    }

    this.callback();
    return stop;
  };
  
  return trans;
  
})();

vg.scene.transition = function(dur, ease) {
  return new vg.scene.Transition(dur, ease);
};vg.scene.axis = function() {
  var scale,
      orient = vg_axisDefaultOrient,
      offset = 0,
      axisDef = null,
      layer = "front",
      grid = false,
      tickMajorSize = vg.config.axis.tickSize,
      tickMinorSize = vg.config.axis.tickSize,
      tickEndSize = vg.config.axis.tickSize,
      tickPadding = vg.config.axis.padding,
      tickValues = null,
      tickFormat = null,
      tickSubdivide = 0,
      tickArguments = [vg.config.axis.ticks],
      gridLineStyle = {},
      tickLabelStyle = {},
      majorTickStyle = {},
      minorTickStyle = {},
      domainStyle = {};

  var axis = {};

  axis.def = function() {
    // TODO: only generate def as-needed; use dirty bit?
    var def = axisDef = axis_def(scale);
    
    // generate data
    var major = tickValues == null
      ? (scale.ticks ? scale.ticks.apply(scale, tickArguments) : scale.domain())
      : tickValues;
    var minor = vg_axisSubdivide(scale, major, tickSubdivide).map(vg.data.ingest);
    major = major.map(vg.data.ingest);
    var fmt = tickFormat==null ? (scale.tickFormat ? scale.tickFormat.apply(scale, tickArguments) : String) : tickFormat;
    major.forEach(function(d) { d.label = fmt(d.data); });
    
    // update axis def
    def.marks[0].from = function() { return grid ? major : []; };
    def.marks[1].from = function() { return major; };
    def.marks[2].from = function() { return minor; };
    def.marks[3].from = def.marks[1].from;
    def.marks[4].from = function() { return [1]; };
    def.offset = offset;
    def.orient = orient;
    def.layer = layer;
    return def;
  };

  function axis_def(scale) {
    // setup scale mapping
    var newScale, oldScale, range;
    if (scale.type === "ordinal") {
      newScale = {scale: scale.scaleName, offset: 0.5 + scale.rangeBand()/2};
      oldScale = newScale;
    } else {
      newScale = {scale: scale.scaleName, offset: 0.5};
      oldScale = {scale: scale.scaleName+":prev", offset: 0.5};
    }
    range = vg_axisScaleRange(scale);

    // setup axis marks
    var gridLines = vg_axisTicks();
    var majorTicks = vg_axisTicks();
    var minorTicks = vg_axisTicks();
    var tickLabels = vg_axisTickLabels();
    var domain = vg_axisDomain();
    gridLines.properties.enter.stroke = {value: vg.config.axis.gridColor};

    // extend axis marks based on axis orientation
    vg_axisTicksExtend(orient, gridLines, oldScale, newScale, Infinity);
    vg_axisTicksExtend(orient, majorTicks, oldScale, newScale, tickMajorSize);
    vg_axisTicksExtend(orient, minorTicks, oldScale, newScale, tickMinorSize);
    vg_axisLabelExtend(orient, tickLabels, oldScale, newScale, tickMajorSize, tickPadding);
    vg_axisDomainExtend(orient, domain, range, tickEndSize);
    
    // add / override custom style properties
    vg.extend(gridLines.properties.update, gridLineStyle);
    vg.extend(majorTicks.properties.update, majorTickStyle);
    vg.extend(minorTicks.properties.update, minorTickStyle);
    vg.extend(tickLabels.properties.update, tickLabelStyle);
    vg.extend(domain.properties.update, domainStyle);

    var marks = [gridLines, majorTicks, minorTicks, tickLabels, domain];
    return {
      type: "group",
      interactive: false,
      properties: { update: vg_axisUpdate },
      marks: marks.map(vg.parse.mark)
    };
  }

  axis.scale = function(x) {
    if (!arguments.length) return scale;
    scale = x;
    return axis;
  };

  axis.orient = function(x) {
    if (!arguments.length) return orient;
    orient = x in vg_axisOrients ? x + "" : vg_axisDefaultOrient;
    return axis;
  };

  axis.ticks = function() {
    if (!arguments.length) return tickArguments;
    tickArguments = arguments;
    return axis;
  };

  axis.tickValues = function(x) {
    if (!arguments.length) return tickValues;
    tickValues = x;
    return axis;
  };

  axis.tickFormat = function(x) {
    if (!arguments.length) return tickFormat;
    tickFormat = x;
    return axis;
  };
  
  axis.tickSize = function(x, y) {
    if (!arguments.length) return tickMajorSize;
    var n = arguments.length - 1;
    tickMajorSize = +x;
    tickMinorSize = n > 1 ? +y : tickMajorSize;
    tickEndSize = n > 0 ? +arguments[n] : tickMajorSize;
    return axis;
  };

  axis.tickPadding = function(x) {
    if (!arguments.length) return tickPadding;
    tickPadding = +x;
    return axis;
  };

  axis.tickSubdivide = function(x) {
    if (!arguments.length) return tickSubdivide;
    tickSubdivide = +x;
    return axis;
  };
  
  axis.offset = function(x) {
    if (!arguments.length) return tickValues;
    offset = x;
    return axis;
  };

  axis.layer = function(x) {
    if (!arguments.length) return layer;
    layer = x;
    return axis;
  };

  axis.grid = function(x) {
    if (!arguments.length) return grid;
    grid = x;
    return axis;
  };

  axis.gridLineProperties = function(x) {
    if (!arguments.length) return gridLineStyle;
    gridLineStyle = x;
    return axis;
  };

  axis.majorTickProperties = function(x) {
    if (!arguments.length) return majorTickStyle;
    majorTickStyle = x;
    return axis;
  };

  axis.minorTickProperties = function(x) {
    if (!arguments.length) return minorTickStyle;
    minorTickStyle = x;
    return axis;
  };

  axis.tickLabelProperties = function(x) {
    if (!arguments.length) return tickLabelStyle;
    tickLabelStyle = x;
    return axis;
  };

  axis.domainProperties = function(x) {
    if (!arguments.length) return domainStyle;
    domainStyle = x;
    return axis;
  };

  return axis;
};

var vg_axisDefaultOrient = "bottom",
    vg_axisOrients = {top: 1, right: 1, bottom: 1, left: 1};

function vg_axisSubdivide(scale, ticks, m) {
  subticks = [];
  if (m && ticks.length > 1) {
    var extent = vg_axisScaleExtent(scale.domain()),
        subticks,
        i = -1,
        n = ticks.length,
        d = (ticks[1] - ticks[0]) / ++m,
        j,
        v;
    while (++i < n) {
      for (j = m; --j > 0;) {
        if ((v = +ticks[i] - j * d) >= extent[0]) {
          subticks.push(v);
        }
      }
    }
    for (--i, j = 0; ++j < m && (v = +ticks[i] + j * d) < extent[1];) {
      subticks.push(v);
    }
  }
  return subticks;
}

function vg_axisScaleExtent(domain) {
  var start = domain[0], stop = domain[domain.length - 1];
  return start < stop ? [start, stop] : [stop, start];
}

function vg_axisScaleRange(scale) {
  return scale.rangeExtent
    ? scale.rangeExtent()
    : vg_axisScaleExtent(scale.range());
}

var vg_axisAlign = {
  bottom: "center",
  top: "center",
  left: "right",
  right: "left"
};

var vg_axisBaseline = {
  bottom: "top",
  top: "bottom",
  left: "middle",
  right: "middle"
};

function vg_axisLabelExtend(orient, labels, oldScale, newScale, size, pad) {
  size = Math.max(size, 0) + pad;
  if (orient === "left" || orient === "top") {
    size *= -1;
  }  
  if (orient === "top" || orient === "bottom") {
    vg.extend(labels.properties.enter, {
      x: oldScale,
      y: {value: size},
    });
    vg.extend(labels.properties.update, {
      x: newScale,
      y: {value: size},
      align: {value: "center"},
      baseline: {value: vg_axisBaseline[orient]}
    });
  } else {
    vg.extend(labels.properties.enter, {
      x: {value: size},
      y: oldScale,
    });
    vg.extend(labels.properties.update, {
      x: {value: size},
      y: newScale,
      align: {value: vg_axisAlign[orient]},
      baseline: {value: "middle"}
    });
  }
}

function vg_axisTicksExtend(orient, ticks, oldScale, newScale, size) {
  var sign = (orient === "left" || orient === "top") ? -1 : 1;
  if (size === Infinity) {
    size = (orient === "top" || orient === "bottom")
      ? {group: "height", mult: -sign}
      : {group: "width", mult: -sign};
  } else {
    size = {value: sign * size};
  }
  if (orient === "top" || orient === "bottom") {
    vg.extend(ticks.properties.enter, {
      x:  oldScale,
      y:  {value: 0},
      y2: size
    });
    vg.extend(ticks.properties.update, {
      x:  newScale,
      y:  {value: 0},
      y2: size
    });
    vg.extend(ticks.properties.exit, {
      x:  newScale,
    });        
  } else {
    vg.extend(ticks.properties.enter, {
      x:  {value: 0},
      x2: size,
      y:  oldScale
    });
    vg.extend(ticks.properties.update, {
      x:  {value: 0},
      x2: size,
      y:  newScale
    });
    vg.extend(ticks.properties.exit, {
      y:  newScale,
    });
  }
}

function vg_axisDomainExtend(orient, domain, range, size) {
  var path;
  if (orient === "top" || orient === "left") {
    size = -1 * size;
  }
  if (orient === "bottom" || orient === "top") {
    path = "M" + range[0] + "," + size + "V0H" + range[1] + "V" + size;
  } else {
    path = "M" + size + "," + range[0] + "H0V" + range[1] + "H" + size;
  }
  domain.properties.update.path = {value: path};
}

function vg_axisUpdate(item, group, trans) {
  var o = trans ? {} : item,
      offset = item.mark.def.offset,
      orient = item.mark.def.orient,
      width  = group.width,
      height = group.height; // TODO fallback to global w,h?

  item.width = width;
  item.height = height;

  switch(orient) {
    case "left":   { o.x = -offset; o.y = 0; break; }
    case "right":  { o.x = width + offset; o.y = 0; break; }
    case "bottom": { o.x = 0; o.y = height + offset; break; }
    case "top":    { o.x = 0; o.y = -offset; break; }
    default:       { o.x = 0; o.y = 0; }
  }
  if (trans) trans.interpolate(item, o);
}

function vg_axisTicks() {
  return {
    type: "rule",
    interactive: false,
    key: "data",
    properties: {
      enter: {
        stroke: {value: vg.config.axis.tickColor},
        strokeWidth: {value: vg.config.axis.tickWidth},
        opacity: {value: 1e-6}
      },
      exit: { opacity: {value: 1e-6} },
      update: { opacity: {value: 1} }
    }
  };
}

function vg_axisTickLabels() {
  return {
    type: "text",
    interactive: false,
    key: "data",
    properties: {
      enter: {
        fill: {value: vg.config.axis.tickLabelColor},
        font: {value: vg.config.axis.tickLabelFont},
        fontSize: {value: vg.config.axis.tickLabelFontSize},
        opacity: {value: 1e-6},
        text: {field: "label"}
      },
      exit: { opacity: {value: 1e-6} },
      update: { opacity: {value: 1} }
    }
  };
}

function vg_axisDomain() {
  return {
    type: "path",
    interactive: false,
    properties: {
      enter: {
        x: {value: 0.5},
        y: {value: 0.5},
        stroke: {value: vg.config.axis.axisColor},
        strokeWidth: {value: vg.config.axis.axisWidth}
      },
      update: {}
    }
  };
}vg.Model = (function() {
  function model() {
    this._defs = null;
    this._data = {};
    this._scene = null;
  }
  
  var prototype = model.prototype;
  
  prototype.defs = function(defs) {
    if (!arguments.length) return this._defs;
    this._defs = defs;
    return this;
  };
  
  prototype.data = function(data) {
    if (!arguments.length) return this._data;

    var tx = this._defs.data.flow || {},
        keys = this._defs.data.defs.map(vg.accessor("name")),
        i, j, len, k, src;
        
    for (i=0, len=keys.length; i<len; ++i) {
      if (!data[k=keys[i]]) continue;
      
      this._data[k] = tx[k]
        ? tx[k](data[k], this._data, this._defs.marks)
        : data[k];
      
      src = this._defs.data.source[k] || [];
      for (j=0; j<src.length; ++j) {
        this._data[src[j]] = tx[src[j]]
          ? tx[src[j]](this._data[k], this._data, this._defs.marks)
          : this._data[k]
      }
    }

    return this;
  };
  
  prototype.width = function(width) {
    if (this._defs) this._defs.width = width;
    if (this._defs && this._defs.marks) this._defs.marks.width = width;
    if (this._scene) this._scene.items[0].width = width;
    return this;
  };
  
  prototype.height = function(height) {
    if (this._defs) this._defs.height = height;
    if (this._defs && this._defs.marks) this._defs.marks.height = height;
    if (this._scene) this._scene.items[0].height = height;
    return this;
  };
  
  prototype.scene = function(node) {
    if (!arguments.length) return this._scene;
    this._scene = node;
    return this;
  };
  
  prototype.build = function() {
    var m = this, data = m._data, marks = m._defs.marks;
    m._scene = vg.scene.build.call(m, marks, data, m._scene);
    m._scene.items[0].width = marks.width;
    m._scene.items[0].height = marks.height;
    m._scene.interactive = false;
    return this;
  };
  
  prototype.encode = function(trans, request, item) {
    var m = this, scene = m._scene, defs = m._defs;
    vg.scene.encode.call(m, scene, defs.marks, trans, request, item);
    return this;
  };
  
  return model;
})();vg.View = (function() {
  var view = function(el, width, height) {
    this._el = null;
    this._build = false;
    this._model = new vg.Model();
    this._width = width || 500;
    this._height = height || 500;
    this._padding = {top:0, left:0, bottom:0, right:0};
    this._viewport = null;
    this._renderer = null;
    this._handler = null;
    this._io = vg.canvas;
    if (el) this.initialize(el);
  };
  
  var prototype = view.prototype;
  
  prototype.width = function(width) {
    if (!arguments.length) return this._width;
    if (this._width !== width) {
      this._width = width;
      if (this._el) this.initialize(this._el.parentNode);
      this._model.width(width);
    }
    return this;
  };

  prototype.height = function(height) {
    if (!arguments.length) return this._height;
    if (this._height !== height) {
      this._height = height;
      if (this._el) this.initialize(this._el.parentNode);
      this._model.height(this._height);
    }
    return this;
  };

  prototype.padding = function(pad) {
    if (!arguments.length) return this._padding;
    if (this._padding !== pad) {
      this._padding = pad;
      if (this._el) this.initialize(this._el.parentNode);
    }
    return this;
  };

  prototype.viewport = function(size) {
    if (!arguments.length) return this._viewport;
    if (this._viewport !== size) {
      this._viewport = size;
      if (this._el) this.initialize(this._el.parentNode);
    }
    return this;
  };
  
  prototype.renderer = function(type) {
    if (!arguments.length) return this._io;
    if (type === "canvas") type = vg.canvas;
    if (type === "svg") type = vg.svg;
    if (this._io !== type) {
      this._io = type;
      this._renderer = null;
      if (this._el) this.initialize(this._el.parentNode);
      if (this._build) this.render();
    }
    return this;
  };

  prototype.defs = function(defs) {
    if (!arguments.length) return this._model.defs();
    this._model.defs(defs);
    return this;
  };

  prototype.data = function(data) {
    if (!arguments.length) return this._model.data();
    var ingest = vg.keys(data).reduce(function(d, k) {
      return (d[k] = data[k].map(vg.data.ingest), d);
    }, {});
    this._model.data(ingest);
    this._build = false;
    return this;
  };

  prototype.model = function(model) {
    if (!arguments.length) return this._model;
    if (this._model !== model) {
      this._model = model;
      if (this._handler) this._handler.model(model);
    }
    return this;
  };

  prototype.initialize = function(el) {
    var v = this, prevHandler,
        w = v._width, h = v._height, pad = v._padding;
    
    // clear pre-existing container
    d3.select(el).select("div.vega").remove();
    
    // add div container
    this._el = el = d3.select(el)
      .append("div")
      .attr("class", "vega")
      .style("position", "relative")
      .node();
    if (v._viewport) {
      d3.select(el)
        .style("width",  (v._viewport[0] || w)+"px")
        .style("height", (v._viewport[1] || h)+"px")
        .style("overflow", "auto");
    }
    
    // renderer
    v._renderer = (v._renderer || new this._io.Renderer())
      .initialize(el, w, h, pad);
    
    // input handler
    prevHandler = v._handler;
    v._handler = new this._io.Handler()
      .initialize(el, pad, v)
      .model(v._model);

    if (prevHandler) {
      prevHandler.handlers().forEach(function(h) {
        v._handler.on(h.type, h.handler);
      });
    }
    
    return this;
  };
  
  prototype.render = function(items) {
    this._renderer.render(this._model.scene(), items);
    return this;
  };
  
  prototype.on = function() {
    this._handler.on.apply(this._handler, arguments);
    return this;
  };
  
  prototype.off = function() {
    this._handler.off.apply(this._handler, arguments);
    return this;
  };
  
  prototype.update = function(opt) {
    opt = opt || {};
    var view = this,
        trans = opt.duration
          ? vg.scene.transition(opt.duration, opt.ease)
          : null;

    view._build = view._build || (view._model.build(), true);
    view._model.encode(trans, opt.props, opt.items);
    
    if (trans) {
      trans.start(function(items) {
        view._renderer.render(view._model.scene(), items);
      });
    }
    else view.render(opt.items);
    return view;
  };
      
  return view;
})();

// view constructor factory
// takes definitions from parsed specification as input
// returns a view constructor
vg.ViewFactory = function(defs) {
  return function(opt) {
    opt = opt || {};
    var v = new vg.View()
      .width(defs.width)
      .height(defs.height)
      .padding(defs.padding)
      .viewport(defs.viewport)
      .renderer(opt.renderer || "canvas")
      .defs(defs);

    if (defs.data.load) v.data(defs.data.load);
    if (opt.data) v.data(opt.data);
    if (opt.el) v.initialize(opt.el);

    if (opt.hover !== false) {
      v.on("mouseover", function(evt, item) {
        if (item.hasPropertySet("hover")) {
          this.update({props:"hover", items:item});
        }
      })
      .on("mouseout", function(evt, item) {
        if (item.hasPropertySet("hover")) {
          this.update({props:"update", items:item});
        }
      });
    }
  
    return v;
  };
};
vg.Spec = (function() {
  var spec = function(s) {
    this.spec = {
      width: 500,
      height: 500,
      padding: 0,
      data: [],
      scales: [],
      axes: [],
      marks: []
    };
    if (s) vg.extend(this.spec, s);
  };
  
  var prototype = spec.prototype;

  prototype.width = function(w) {
    this.spec.width = w;
    return this;
  };
  
  prototype.height = function(h) {
    this.spec.height = h;
    return this;
  };
  
  prototype.padding = function(p) {
    this.spec.padding = p;
    return this;
  };
  
  prototype.viewport = function(v) {
    this.spec.viewport = v;
    return this;
  };

  prototype.data = function(name, params) {
    if (!params) params = vg.isString(name) ? {name: name} : name;
    else params.name = name;
    this.spec.data.push(params);
    return this;
  };
  
  prototype.scale = function(name, params) {
    if (!params) params = vg.isString(name) ? {name: name} : name;
    else params.name = name;
    this.spec.scales.push(params);
    return this;
  };
  
  prototype.axis = function(params) {
    this.spec.axes.push(params);
    return this;
  };
  
  prototype.mark = function(type, mark) {
    if (!mark) mark = {type: type};
    else mark.type = type;
    mark.properties = {};
    this.spec.marks.push(mark);
    
    var that = this;
    return {
      from: function(name, obj) {
              mark.from = obj
                ? (obj.data = name, obj)
                : vg.isString(name) ? {data: name} : name;
              return this;
            },
      prop: function(name, obj) {
              mark.properties[name] = vg.keys(obj).reduce(function(o,k) {
                var v = obj[k];
                return (o[k] = vg.isObject(v) ? v : {value: v}, o);
              }, {});
              return this;
            },
      done: function() { return that; }
    };
  };

  prototype.parse = function(callback) {
    vg.parse.spec(this.spec, callback);
  };

  prototype.json = function() {
    return this.spec;
  };

  return spec;
})();

vg.spec = function(s) {
  return new vg.Spec(s);
};
vg.headless = {};vg.headless.View = (function() {
  
  var view = function(width, height, pad, type) {
    this._canvas = null;
    this._type = type;
    this._el = "body";
    this._build = false;
    this._model = new vg.Model();
    this._width = width || 500;
    this._height = height || 500;
    this._padding = pad || {top:0, left:0, bottom:0, right:0};
    this._renderer = new vg[type].Renderer();
    this.initialize();
  };
  
  var prototype = view.prototype;

  prototype.el = function(el) {
    if (!arguments.length) return this._el;
    if (this._el !== el) {
      this._el = el;
      this.initialize();
    }
    return this;
  };

  prototype.width = function(width) {
    if (!arguments.length) return this._width;
    if (this._width !== width) {
      this._width = width;
      this.initialize();
      this._model.width(width);
    }
    return this;
  };

  prototype.height = function(height) {
    if (!arguments.length) return this._height;
    if (this._height !== height) {
      this._height = height;
      this.initialize();
      this._model.height(this._height);
    }
    return this;
  };

  prototype.padding = function(pad) {
    if (!arguments.length) return this._padding;
    if (this._padding !== pad) {
      this._padding = pad;
      this.initialize();
    }
    return this;
  };

  prototype.defs = function(defs) {
    if (!arguments.length) return this._model.defs();
    this._model.defs(defs);
    return this;
  };

  prototype.data = function(data) {
    if (!arguments.length) return this._model.data();
    var ingest = vg.keys(data).reduce(function(d, k) {
      return (d[k] = data[k].map(vg.data.ingest), d);
    }, {});
    this._model.data(ingest);
    this._build = false;
    return this;
  };

  prototype.renderer = function() {
    return this._renderer;
  };

  prototype.canvas = function() {
    return this._canvas;
  };
  
  prototype.canvasAsync = function(callback) {
    var r = this._renderer;
    
    function wait() {
      if (r.pendingImages() === 0) {
        this.render(); // re-render with all images
        callback(this._canvas);
      } else {
        setTimeout(wait, 10);
      }
    }

    // if images loading, poll until ready
    (r.pendingImages() > 0) ? wait() : callback(this._canvas);
  };
  
  prototype.svg = function() {
    if (this._type !== "svg") return null;

    var p = this._padding,
        w = this._width  + (p ? p.left + p.right : 0),
        h = this._height + (p ? p.top + p.bottom : 0);

      // build svg text
    var svg = d3.select(this._el)
      .select("svg").node().innerHTML
      .replace(/ href=/g, " xlink:href="); // ns hack. sigh.

    return '<svg '
      + 'width="' + w + '" '
      + 'height="' + h + '" '
      + vg.config.svgNamespace + '>' + svg + '</svg>'
  };

  prototype.initialize = function() {    
    var w = this._width,
        h = this._height,
        pad = this._padding;
    
    if (this._type === "svg") {
      this.initSVG(w, h, pad);
    } else {
      this.initCanvas(w, h, pad);
    }
    
    return this;
  };
  
  prototype.initCanvas = function(w, h, pad) {
    var Canvas = require("canvas"),
        tw = w + pad.left + pad.right,
        th = h + pad.top + pad.bottom,
        canvas = this._canvas = new Canvas(tw, th),
        ctx = canvas.getContext("2d");
    
    // setup canvas context
    ctx.setTransform(1, 0, 0, 1, pad.left, pad.top);

    // configure renderer
    this._renderer.initialize(null, w, h, pad);
    this._renderer.context(ctx);
  };
  
  prototype.initSVG = function(w, h, pad) {
    var tw = w + pad.left + pad.right,
        th = h + pad.top + pad.bottom;

    // configure renderer
    this._renderer.initialize(this._el, w, h, pad);
  }
  
  prototype.render = function(items) {
    this._renderer.render(this._model.scene(), items);
    return this;
  };
  
  prototype.update = function(opt) {
    opt = opt || {};
    var view = this;
    view._build = view._build || (view._model.build(), true);
    view._model.encode(null, opt.props, opt.items);
    view.render(opt.items);
    return view;
  };
    
  return view;
})();

// headless view constructor factory
// takes definitions from parsed specification as input
// returns a view constructor
vg.headless.View.Factory = function(defs) {
  return function(opt) {
    opt = opt || {};
    var w = defs.width,
        h = defs.height,
        p = defs.padding,
        r = opt.renderer || "canvas",
        v = new vg.headless.View(w, h, p, r).defs(defs);
    if (defs.data.load) v.data(defs.data.load);
    if (opt.data) v.data(opt.data);
    return v;
  };
};vg.headless.render = function(opt, callback) {
  function draw(chart) {
    try {
      // create and render view
      var view = chart({
        data: opt.data,
        renderer: opt.renderer
      }).update();

      if (opt.renderer === "svg") {
        // extract rendered svg
        callback(null, {svg: view.svg()});
      } else {
        // extract rendered canvas, waiting for any images to load
        view.canvasAsync(function(canvas) {
          callback(null, {canvas: canvas});
        });
      }
    } catch (err) {
      callback(err, null);
    }
  }

  vg.parse.spec(opt.spec, draw, vg.headless.View.Factory);
};return vg;
})(d3); // assumes availability of D3 in global namespace