cubism.v1.js

(function(exports){
var cubism = exports.cubism = {version: "1.3.0"};
var cubism_id = 0;
function cubism_identity(d) { return d; }
cubism.option = function(name, defaultValue) {
  var values = cubism.options(name);
  return values.length ? values[0] : defaultValue;
};

cubism.options = function(name, defaultValues) {
  var options = location.search.substring(1).split("&"),
      values = [],
      i = -1,
      n = options.length,
      o;
  while (++i < n) {
    if ((o = options[i].split("="))[0] == name) {
      values.push(decodeURIComponent(o[1]));
    }
  }
  return values.length || arguments.length < 2 ? values : defaultValues;
};
cubism.context = function() {
  var context = new cubism_context,
      step = 1e4, // ten seconds, in milliseconds
      size = 1440, // four hours at ten seconds, in pixels
      start0, stop0, // the start and stop for the previous change event
      start1, stop1, // the start and stop for the next prepare event
      serverDelay = 5e3,
      clientDelay = 5e3,
      event = d3.dispatch("prepare", "beforechange", "change", "focus"),
      scale = context.scale = d3.time.scale().range([0, size]),
      timeout,
      focus;

  function update() {
    var now = Date.now();
    stop0 = new Date(Math.floor((now - serverDelay - clientDelay) / step) * step);
    start0 = new Date(stop0 - size * step);
    stop1 = new Date(Math.floor((now - serverDelay) / step) * step);
    start1 = new Date(stop1 - size * step);
    scale.domain([start0, stop0]);
    return context;
  }

  context.start = function() {
    if (timeout) clearTimeout(timeout);
    var delay = +stop1 + serverDelay - Date.now();

    // If we're too late for the first prepare event, skip it.
    if (delay < clientDelay) delay += step;

    timeout = setTimeout(function prepare() {
      stop1 = new Date(Math.floor((Date.now() - serverDelay) / step) * step);
      start1 = new Date(stop1 - size * step);
      event.prepare.call(context, start1, stop1);

      setTimeout(function() {
        scale.domain([start0 = start1, stop0 = stop1]);
        event.beforechange.call(context, start1, stop1);
        event.change.call(context, start1, stop1);
        event.focus.call(context, focus);
      }, clientDelay);

      timeout = setTimeout(prepare, step);
    }, delay);
    return context;
  };

  context.stop = function() {
    timeout = clearTimeout(timeout);
    return context;
  };

  timeout = setTimeout(context.start, 10);

  // Set or get the step interval in milliseconds.
  // Defaults to ten seconds.
  context.step = function(_) {
    if (!arguments.length) return step;
    step = +_;
    return update();
  };

  // Set or get the context size (the count of metric values).
  // Defaults to 1440 (four hours at ten seconds).
  context.size = function(_) {
    if (!arguments.length) return size;
    scale.range([0, size = +_]);
    return update();
  };

  // The server delay is the amount of time we wait for the server to compute a
  // metric. This delay may result from clock skew or from delays collecting
  // metrics from various hosts. Defaults to 4 seconds.
  context.serverDelay = function(_) {
    if (!arguments.length) return serverDelay;
    serverDelay = +_;
    return update();
  };

  // The client delay is the amount of additional time we wait to fetch those
  // metrics from the server. The client and server delay combined represent the
  // age of the most recent displayed metric. Defaults to 1 second.
  context.clientDelay = function(_) {
    if (!arguments.length) return clientDelay;
    clientDelay = +_;
    return update();
  };

  // Sets the focus to the specified index, and dispatches a "focus" event.
  context.focus = function(i) {
    event.focus.call(context, focus = i);
    return context;
  };

  // Add, remove or get listeners for events.
  context.on = function(type, listener) {
    if (arguments.length < 2) return event.on(type);

    event.on(type, listener);

    // Notify the listener of the current start and stop time, as appropriate.
    // This way, metrics can make requests for data immediately,
    // and likewise the axis can display itself synchronously.
    if (listener != null) {
      if (/^prepare(\.|$)/.test(type)) listener.call(context, start1, stop1);
      if (/^beforechange(\.|$)/.test(type)) listener.call(context, start0, stop0);
      if (/^change(\.|$)/.test(type)) listener.call(context, start0, stop0);
      if (/^focus(\.|$)/.test(type)) listener.call(context, focus);
    }

    return context;
  };

  d3.select(window).on("keydown.context-" + ++cubism_id, function() {
    switch (!d3.event.metaKey && d3.event.keyCode) {
      case 37: // left
        if (focus == null) focus = size - 1;
        if (focus > 0) context.focus(--focus);
        break;
      case 39: // right
        if (focus == null) focus = size - 2;
        if (focus < size - 1) context.focus(++focus);
        break;
      default: return;
    }
    d3.event.preventDefault();
  });

  return update();
};

function cubism_context() {}

var cubism_contextPrototype = cubism.context.prototype = cubism_context.prototype;

cubism_contextPrototype.constant = function(value) {
  return new cubism_metricConstant(this, +value);
};
cubism_contextPrototype.cube = function(host) {
  if (!arguments.length) host = "";
  var source = {},
      context = this;

  source.metric = function(expression) {
    return context.metric(function(start, stop, step, callback) {
      d3.json(host + "/1.0/metric"
          + "?expression=" + encodeURIComponent(expression)
          + "&start=" + cubism_cubeFormatDate(start)
          + "&stop=" + cubism_cubeFormatDate(stop)
          + "&step=" + step, function(data) {
        if (!data) return callback(new Error("unable to load data"));
        callback(null, data.map(function(d) { return d.value; }));
      });
    }, expression += "");
  };

  // Returns the Cube host.
  source.toString = function() {
    return host;
  };

  return source;
};

var cubism_cubeFormatDate = d3.time.format.iso;
cubism_contextPrototype.graphite = function(host) {
  if (!arguments.length) host = "";
  var source = {},
      context = this;

  source.metric = function(expression) {
    var sum = "sum";

    var metric = context.metric(function(start, stop, step, callback) {
      var target = expression;

      // Apply the summarize, if necessary.
      if (step !== 1e4) target = "summarize(" + target + ",'"
          + (!(step % 36e5) ? step / 36e5 + "hour" : !(step % 6e4) ? step / 6e4 + "min" : step / 1e3 + "sec")
          + "','" + sum + "')";

      d3.text(host + "/render?format=raw"
          + "&target=" + encodeURIComponent("alias(" + target + ",'')")
          + "&from=" + cubism_graphiteFormatDate(start - 2 * step) // off-by-two?
          + "&until=" + cubism_graphiteFormatDate(stop - 1000), function(text) {
        if (!text) return callback(new Error("unable to load data"));
        callback(null, cubism_graphiteParse(text));
      });
    }, expression += "");

    metric.summarize = function(_) {
      sum = _;
      return metric;
    };

    return metric;
  };

  source.find = function(pattern, callback) {
    d3.json(host + "/metrics/find?format=completer"
        + "&query=" + encodeURIComponent(pattern), function(result) {
      if (!result) return callback(new Error("unable to find metrics"));
      callback(null, result.metrics.map(function(d) { return d.path; }));
    });
  };

  // Returns the graphite host.
  source.toString = function() {
    return host;
  };

  return source;
};

// Graphite understands seconds since UNIX epoch.
function cubism_graphiteFormatDate(time) {
  return Math.floor(time / 1000);
}

// Helper method for parsing graphite's raw format.
function cubism_graphiteParse(text) {
  var i = text.indexOf("|"),
      meta = text.substring(0, i),
      c = meta.lastIndexOf(","),
      b = meta.lastIndexOf(",", c - 1),
      a = meta.lastIndexOf(",", b - 1),
      start = meta.substring(a + 1, b) * 1000,
      step = meta.substring(c + 1) * 1000;
  return text
      .substring(i + 1)
      .split(",")
      .slice(1) // the first value is always None?
      .map(function(d) { return +d; });
}
cubism_contextPrototype.gangliaWeb = function(config) {
  var host = '',
      uriPathPrefix = '/ganglia2/';
 
  if (arguments.length) {
    if (config.host) {
      host = config.host;
    }

    if (config.uriPathPrefix) {
      uriPathPrefix = config.uriPathPrefix;

      /* Add leading and trailing slashes, as appropriate. */
      if( uriPathPrefix[0] != '/' ) {
        uriPathPrefix = '/' + uriPathPrefix;
      }

      if( uriPathPrefix[uriPathPrefix.length - 1] != '/' ) {
        uriPathPrefix += '/';
      }
    }
  }

  var source = {},
      context = this;

  source.metric = function(metricInfo) {

    /* Store the members from metricInfo into local variables. */
    var clusterName = metricInfo.clusterName, 
        metricName = metricInfo.metricName, 
        hostName = metricInfo.hostName,
        isReport = metricInfo.isReport || false,
        titleGenerator = metricInfo.titleGenerator ||
          /* Reasonable (not necessarily pretty) default for titleGenerator. */
          function(unusedMetricInfo) {
            /* unusedMetricInfo is, well, unused in this default case. */
            return ('clusterName:' + clusterName + 
                    ' metricName:' + metricName +
                    (hostName ? ' hostName:' + hostName : ''));
          },
        onChangeCallback = metricInfo.onChangeCallback;
    
    /* Default to plain, simple metrics. */
    var metricKeyName = isReport ? 'g' : 'm';

    var gangliaWebMetric = context.metric(function(start, stop, step, callback) {

      function constructGangliaWebRequestQueryParams() {
        return ('c=' + clusterName +
                '&' + metricKeyName + '=' + metricName + 
                (hostName ? '&h=' + hostName : '') + 
                '&cs=' + start/1000 + '&ce=' + stop/1000 + '&step=' + step/1000 + '&graphlot=1');
      }

      d3.json(host + uriPathPrefix + 'graph.php?' + constructGangliaWebRequestQueryParams(),
        function(result) {
          if( !result ) {
            return callback(new Error("Unable to fetch GangliaWeb data"));
          }

          callback(null, result[0].data);
        });

    }, titleGenerator(metricInfo));

    gangliaWebMetric.toString = function() {
      return titleGenerator(metricInfo);
    };

    /* Allow users to run their custom code each time a gangliaWebMetric changes.
     *
     * TODO Consider abstracting away the naked Cubism call, and instead exposing 
     * a callback that takes in the values array (maybe alongwith the original
     * start and stop 'naked' parameters), since it's handy to have the entire
     * dataset at your disposal (and users will likely implement onChangeCallback
     * primarily to get at this dataset).
     */
    if (onChangeCallback) {
      gangliaWebMetric.on('change', onChangeCallback);
    }

    return gangliaWebMetric;
  };

  // Returns the gangliaWeb host + uriPathPrefix.
  source.toString = function() {
    return host + uriPathPrefix;
  };

  return source;
};

function cubism_metric(context) {
  if (!(context instanceof cubism_context)) throw new Error("invalid context");
  this.context = context;
}

var cubism_metricPrototype = cubism_metric.prototype;

cubism.metric = cubism_metric;

cubism_metricPrototype.valueAt = function() {
  return NaN;
};

cubism_metricPrototype.alias = function(name) {
  this.toString = function() { return name; };
  return this;
};

cubism_metricPrototype.extent = function() {
  var i = 0,
      n = this.context.size(),
      value,
      min = Infinity,
      max = -Infinity;
  while (++i < n) {
    value = this.valueAt(i);
    if (value < min) min = value;
    if (value > max) max = value;
  }
  return [min, max];
};

cubism_metricPrototype.on = function(type, listener) {
  return arguments.length < 2 ? null : this;
};

cubism_metricPrototype.shift = function() {
  return this;
};

cubism_metricPrototype.on = function() {
  return arguments.length < 2 ? null : this;
};

cubism_contextPrototype.metric = function(request, name) {
  var context = this,
      metric = new cubism_metric(context),
      id = ".metric-" + ++cubism_id,
      start = -Infinity,
      stop,
      step = context.step(),
      size = context.size(),
      values = [],
      event = d3.dispatch("change"),
      listening = 0,
      fetching;

  // Prefetch new data into a temporary array.
  function prepare(start1, stop) {
    var steps = Math.min(size, Math.round((start1 - start) / step));
    if (!steps || fetching) return; // already fetched, or fetching!
    fetching = true;
    steps = Math.min(size, steps + cubism_metricOverlap);
    var start0 = new Date(stop - steps * step);
    request(start0, stop, step, function(error, data) {
      fetching = false;
      if (error) return console.warn(error);
      var i = isFinite(start) ? Math.round((start0 - start) / step) : 0;
      for (var j = 0, m = data.length; j < m; ++j) values[j + i] = data[j];
      event.change.call(metric, start, stop);
    });
  }

  // When the context changes, switch to the new data, ready-or-not!
  function beforechange(start1, stop1) {
    if (!isFinite(start)) start = start1;
    values.splice(0, Math.max(0, Math.min(size, Math.round((start1 - start) / step))));
    start = start1;
    stop = stop1;
  }

  //
  metric.valueAt = function(i) {
    return values[i];
  };

  //
  metric.shift = function(offset) {
    return context.metric(cubism_metricShift(request, +offset));
  };

  //
  metric.on = function(type, listener) {
    if (!arguments.length) return event.on(type);

    // If there are no listeners, then stop listening to the context,
    // and avoid unnecessary fetches.
    if (listener == null) {
      if (event.on(type) != null && --listening == 0) {
        context.on("prepare" + id, null).on("beforechange" + id, null);
      }
    } else {
      if (event.on(type) == null && ++listening == 1) {
        context.on("prepare" + id, prepare).on("beforechange" + id, beforechange);
      }
    }

    event.on(type, listener);

    // Notify the listener of the current start and stop time, as appropriate.
    // This way, charts can display synchronous metrics immediately.
    if (listener != null) {
      if (/^change(\.|$)/.test(type)) listener.call(context, start, stop);
    }

    return metric;
  };

  //
  if (arguments.length > 1) metric.toString = function() {
    return name;
  };

  return metric;
};

// Number of metric to refetch each period, in case of lag.
var cubism_metricOverlap = 6;

// Wraps the specified request implementation, and shifts time by the given offset.
function cubism_metricShift(request, offset) {
  return function(start, stop, step, callback) {
    request(new Date(+start + offset), new Date(+stop + offset), step, callback);
  };
}
function cubism_metricConstant(context, value) {
  cubism_metric.call(this, context);
  value = +value;
  var name = value + "";
  this.valueOf = function() { return value; };
  this.toString = function() { return name; };
}

var cubism_metricConstantPrototype = cubism_metricConstant.prototype = Object.create(cubism_metric.prototype);

cubism_metricConstantPrototype.valueAt = function() {
  return +this;
};

cubism_metricConstantPrototype.extent = function() {
  return [+this, +this];
};
function cubism_metricOperator(name, operate) {

  function cubism_metricOperator(left, right) {
    if (!(right instanceof cubism_metric)) right = new cubism_metricConstant(left.context, right);
    else if (left.context !== right.context) throw new Error("mismatch context");
    cubism_metric.call(this, left.context);
    this.left = left;
    this.right = right;
    this.toString = function() { return left + " " + name + " " + right; };
  }

  var cubism_metricOperatorPrototype = cubism_metricOperator.prototype = Object.create(cubism_metric.prototype);

  cubism_metricOperatorPrototype.valueAt = function(i) {
    return operate(this.left.valueAt(i), this.right.valueAt(i));
  };

  cubism_metricOperatorPrototype.shift = function(offset) {
    return new cubism_metricOperator(this.left.shift(offset), this.right.shift(offset));
  };

  cubism_metricOperatorPrototype.on = function(type, listener) {
    if (arguments.length < 2) return this.left.on(type);
    this.left.on(type, listener);
    this.right.on(type, listener);
    return this;
  };

  return function(right) {
    return new cubism_metricOperator(this, right);
  };
}

cubism_metricPrototype.add = cubism_metricOperator("+", function(left, right) {
  return left + right;
});

cubism_metricPrototype.subtract = cubism_metricOperator("-", function(left, right) {
  return left - right;
});

cubism_metricPrototype.multiply = cubism_metricOperator("*", function(left, right) {
  return left * right;
});

cubism_metricPrototype.divide = cubism_metricOperator("/", function(left, right) {
  return left / right;
});
cubism_contextPrototype.horizon = function() {
  var context = this,
      mode = "offset",
      buffer = document.createElement("canvas"),
      width = buffer.width = context.size(),
      height = buffer.height = 30,
      scale = d3.scale.linear().interpolate(d3.interpolateRound),
      metric = cubism_identity,
      extent = null,
      title = cubism_identity,
      format = d3.format(".2s"),
      colors = ["#08519c","#3182bd","#6baed6","#bdd7e7","#bae4b3","#74c476","#31a354","#006d2c"];

  function horizon(selection) {

    selection
        .on("mousemove.horizon", function() { context.focus(Math.round(d3.mouse(this)[0])); })
        .on("mouseout.horizon", function() { context.focus(null); });

    selection.append("canvas")
        .attr("width", width)
        .attr("height", height);

    selection.append("span")
        .attr("class", "title")
        .text(title);

    selection.append("span")
        .attr("class", "value");

    selection.each(function(d, i) {
      var that = this,
          id = ++cubism_id,
          metric_ = typeof metric === "function" ? metric.call(that, d, i) : metric,
          colors_ = typeof colors === "function" ? colors.call(that, d, i) : colors,
          extent_ = typeof extent === "function" ? extent.call(that, d, i) : extent,
          start = -Infinity,
          step = context.step(),
          canvas = d3.select(that).select("canvas"),
          span = d3.select(that).select(".value"),
          max_,
          m = colors_.length >> 1,
          ready;

      canvas.datum({id: id, metric: metric_});
      canvas = canvas.node().getContext("2d");

      function change(start1, stop) {
        canvas.save();

        // compute the new extent and ready flag
        var extent = metric_.extent();
        ready = extent.every(isFinite);
        if (extent_ != null) extent = extent_;

        // if this is an update (with no extent change), copy old values!
        var i0 = 0, max = Math.max(-extent[0], extent[1]);
        if (this === context) {
          if (max == max_) {
            i0 = width - cubism_metricOverlap;
            var dx = (start1 - start) / step;
            if (dx < width) {
              var canvas0 = buffer.getContext("2d");
              canvas0.clearRect(0, 0, width, height);
              canvas0.drawImage(canvas.canvas, dx, 0, width - dx, height, 0, 0, width - dx, height);
              canvas.clearRect(0, 0, width, height);
              canvas.drawImage(canvas0.canvas, 0, 0);
            }
          }
          start = start1;
        }

        // update the domain
        scale.domain([0, max_ = max]);

        // clear for the new data
        canvas.clearRect(i0, 0, width - i0, height);

        // record whether there are negative values to display
        var negative;

        // positive bands
        for (var j = 0; j < m; ++j) {
          canvas.fillStyle = colors_[m + j];

          // Adjust the range based on the current band index.
          var y0 = (j - m + 1) * height;
          scale.range([m * height + y0, y0]);
          y0 = scale(0);

          for (var i = i0, n = width, y1; i < n; ++i) {
            y1 = metric_.valueAt(i);
            if (y1 <= 0) { negative = true; continue; }
            if (y1 === undefined) continue;
            canvas.fillRect(i, y1 = scale(y1), 1, y0 - y1);
          }
        }

        if (negative) {
          // enable offset mode
          if (mode === "offset") {
            canvas.translate(0, height);
            canvas.scale(1, -1);
          }

          // negative bands
          for (var j = 0; j < m; ++j) {
            canvas.fillStyle = colors_[m - 1 - j];

            // Adjust the range based on the current band index.
            var y0 = (j - m + 1) * height;
            scale.range([m * height + y0, y0]);
            y0 = scale(0);

            for (var i = i0, n = width, y1; i < n; ++i) {
              y1 = metric_.valueAt(i);
              if (y1 >= 0) continue;
              canvas.fillRect(i, scale(-y1), 1, y0 - scale(-y1));
            }
          }
        }

        canvas.restore();
      }

      function focus(i) {
        if (i == null) i = width - 1;
        var value = metric_.valueAt(i);
        span.datum(value).text(isNaN(value) ? null : format);
      }

      // Update the chart when the context changes.
      context.on("change.horizon-" + id, change);
      context.on("focus.horizon-" + id, focus);

      // Display the first metric change immediately,
      // but defer subsequent updates to the canvas change.
      // Note that someone still needs to listen to the metric,
      // so that it continues to update automatically.
      metric_.on("change.horizon-" + id, function(start, stop) {
        change(start, stop), focus();
        if (ready) metric_.on("change.horizon-" + id, cubism_identity);
      });
    });
  }

  horizon.remove = function(selection) {

    selection
        .on("mousemove.horizon", null)
        .on("mouseout.horizon", null);

    selection.selectAll("canvas")
        .each(remove)
        .remove();

    selection.selectAll(".title,.value")
        .remove();

    function remove(d) {
      d.metric.on("change.horizon-" + d.id, null);
      context.on("change.horizon-" + d.id, null);
      context.on("focus.horizon-" + d.id, null);
    }
  };

  horizon.mode = function(_) {
    if (!arguments.length) return mode;
    mode = _ + "";
    return horizon;
  };

  horizon.height = function(_) {
    if (!arguments.length) return height;
    buffer.height = height = +_;
    return horizon;
  };

  horizon.metric = function(_) {
    if (!arguments.length) return metric;
    metric = _;
    return horizon;
  };

  horizon.scale = function(_) {
    if (!arguments.length) return scale;
    scale = _;
    return horizon;
  };

  horizon.extent = function(_) {
    if (!arguments.length) return extent;
    extent = _;
    return horizon;
  };

  horizon.title = function(_) {
    if (!arguments.length) return title;
    title = _;
    return horizon;
  };

  horizon.format = function(_) {
    if (!arguments.length) return format;
    format = _;
    return horizon;
  };

  horizon.colors = function(_) {
    if (!arguments.length) return colors;
    colors = _;
    return horizon;
  };

  return horizon;
};
cubism_contextPrototype.comparison = function() {
  var context = this,
      width = context.size(),
      height = 120,
      scale = d3.scale.linear().interpolate(d3.interpolateRound),
      primary = function(d) { return d[0]; },
      secondary = function(d) { return d[1]; },
      extent = null,
      title = cubism_identity,
      formatPrimary = cubism_comparisonPrimaryFormat,
      formatChange = cubism_comparisonChangeFormat,
      colors = ["#9ecae1", "#225b84", "#a1d99b", "#22723a"],
      strokeWidth = 1.5;

  function comparison(selection) {

    selection
        .on("mousemove.comparison", function() { context.focus(Math.round(d3.mouse(this)[0])); })
        .on("mouseout.comparison", function() { context.focus(null); });

    selection.append("canvas")
        .attr("width", width)
        .attr("height", height);

    selection.append("span")
        .attr("class", "title")
        .text(title);

    selection.append("span")
        .attr("class", "value primary");

    selection.append("span")
        .attr("class", "value change");

    selection.each(function(d, i) {
      var that = this,
          id = ++cubism_id,
          primary_ = typeof primary === "function" ? primary.call(that, d, i) : primary,
          secondary_ = typeof secondary === "function" ? secondary.call(that, d, i) : secondary,
          extent_ = typeof extent === "function" ? extent.call(that, d, i) : extent,
          div = d3.select(that),
          canvas = div.select("canvas"),
          spanPrimary = div.select(".value.primary"),
          spanChange = div.select(".value.change"),
          ready;

      canvas.datum({id: id, primary: primary_, secondary: secondary_});
      canvas = canvas.node().getContext("2d");

      function change(start, stop) {
        canvas.save();
        canvas.clearRect(0, 0, width, height);

        // update the scale
        var primaryExtent = primary_.extent(),
            secondaryExtent = secondary_.extent(),
            extent = extent_ == null ? primaryExtent : extent_;
        scale.domain(extent).range([height, 0]);
        ready = primaryExtent.concat(secondaryExtent).every(isFinite);

        // consistent overplotting
        var round = start / context.step() & 1
            ? cubism_comparisonRoundOdd
            : cubism_comparisonRoundEven;

        // positive changes
        canvas.fillStyle = colors[2];
        for (var i = 0, n = width; i < n; ++i) {
          var y0 = scale(primary_.valueAt(i)),
              y1 = scale(secondary_.valueAt(i));
          if (y0 < y1) canvas.fillRect(round(i), y0, 1, y1 - y0);
        }

        // negative changes
        canvas.fillStyle = colors[0];
        for (i = 0; i < n; ++i) {
          var y0 = scale(primary_.valueAt(i)),
              y1 = scale(secondary_.valueAt(i));
          if (y0 > y1) canvas.fillRect(round(i), y1, 1, y0 - y1);
        }

        // positive values
        canvas.fillStyle = colors[3];
        for (i = 0; i < n; ++i) {
          var y0 = scale(primary_.valueAt(i)),
              y1 = scale(secondary_.valueAt(i));
          if (y0 <= y1) canvas.fillRect(round(i), y0, 1, strokeWidth);
        }

        // negative values
        canvas.fillStyle = colors[1];
        for (i = 0; i < n; ++i) {
          var y0 = scale(primary_.valueAt(i)),
              y1 = scale(secondary_.valueAt(i));
          if (y0 > y1) canvas.fillRect(round(i), y0 - strokeWidth, 1, strokeWidth);
        }

        canvas.restore();
      }

      function focus(i) {
        if (i == null) i = width - 1;
        var valuePrimary = primary_.valueAt(i),
            valueSecondary = secondary_.valueAt(i),
            valueChange = (valuePrimary - valueSecondary) / valueSecondary;

        spanPrimary
            .datum(valuePrimary)
            .text(isNaN(valuePrimary) ? null : formatPrimary);

        spanChange
            .datum(valueChange)
            .text(isNaN(valueChange) ? null : formatChange)
            .attr("class", "value change " + (valueChange > 0 ? "positive" : valueChange < 0 ? "negative" : ""));
      }

      // Display the first primary change immediately,
      // but defer subsequent updates to the context change.
      // Note that someone still needs to listen to the metric,
      // so that it continues to update automatically.
      primary_.on("change.comparison-" + id, firstChange);
      secondary_.on("change.comparison-" + id, firstChange);
      function firstChange(start, stop) {
        change(start, stop), focus();
        if (ready) {
          primary_.on("change.comparison-" + id, cubism_identity);
          secondary_.on("change.comparison-" + id, cubism_identity);
        }
      }

      // Update the chart when the context changes.
      context.on("change.comparison-" + id, change);
      context.on("focus.comparison-" + id, focus);
    });
  }

  comparison.remove = function(selection) {

    selection
        .on("mousemove.comparison", null)
        .on("mouseout.comparison", null);

    selection.selectAll("canvas")
        .each(remove)
        .remove();

    selection.selectAll(".title,.value")
        .remove();

    function remove(d) {
      d.primary.on("change.comparison-" + d.id, null);
      d.secondary.on("change.comparison-" + d.id, null);
      context.on("change.comparison-" + d.id, null);
      context.on("focus.comparison-" + d.id, null);
    }
  };

  comparison.height = function(_) {
    if (!arguments.length) return height;
    height = +_;
    return comparison;
  };

  comparison.primary = function(_) {
    if (!arguments.length) return primary;
    primary = _;
    return comparison;
  };

  comparison.secondary = function(_) {
    if (!arguments.length) return secondary;
    secondary = _;
    return comparison;
  };

  comparison.scale = function(_) {
    if (!arguments.length) return scale;
    scale = _;
    return comparison;
  };

  comparison.extent = function(_) {
    if (!arguments.length) return extent;
    extent = _;
    return comparison;
  };

  comparison.title = function(_) {
    if (!arguments.length) return title;
    title = _;
    return comparison;
  };

  comparison.formatPrimary = function(_) {
    if (!arguments.length) return formatPrimary;
    formatPrimary = _;
    return comparison;
  };

  comparison.formatChange = function(_) {
    if (!arguments.length) return formatChange;
    formatChange = _;
    return comparison;
  };

  comparison.colors = function(_) {
    if (!arguments.length) return colors;
    colors = _;
    return comparison;
  };

  comparison.strokeWidth = function(_) {
    if (!arguments.length) return strokeWidth;
    strokeWidth = _;
    return comparison;
  };

  return comparison;
};

var cubism_comparisonPrimaryFormat = d3.format(".2s"),
    cubism_comparisonChangeFormat = d3.format("+.0%");

function cubism_comparisonRoundEven(i) {
  return i & 0xfffffe;
}

function cubism_comparisonRoundOdd(i) {
  return ((i + 1) & 0xfffffe) - 1;
}
cubism_contextPrototype.axis = function() {
  var context = this,
      scale = context.scale,
      axis_ = d3.svg.axis().scale(scale);

  var format = context.step() < 6e4 ? cubism_axisFormatSeconds
      : context.step() < 864e5 ? cubism_axisFormatMinutes
      : cubism_axisFormatDays;

  function axis(selection) {
    var id = ++cubism_id,
        tick;

    var g = selection.append("svg")
        .datum({id: id})
        .attr("width", context.size())
        .attr("height", Math.max(28, -axis.tickSize()))
      .append("g")
        .attr("transform", "translate(0," + (axis_.orient() === "top" ? 27 : 4) + ")")
        .call(axis_);

    context.on("change.axis-" + id, function() {
      g.call(axis_);
      if (!tick) tick = d3.select(g.node().appendChild(g.selectAll("text").node().cloneNode(true)))
          .style("display", "none")
          .text(null);
    });

    context.on("focus.axis-" + id, function(i) {
      if (tick) {
        if (i == null) {
          tick.style("display", "none");
          g.selectAll("text").style("fill-opacity", null);
        } else {
          tick.style("display", null).attr("x", i).text(format(scale.invert(i)));
          var dx = tick.node().getComputedTextLength() + 6;
          g.selectAll("text").style("fill-opacity", function(d) { return Math.abs(scale(d) - i) < dx ? 0 : 1; });
        }
      }
    });
  }

  axis.remove = function(selection) {

    selection.selectAll("svg")
        .each(remove)
        .remove();

    function remove(d) {
      context.on("change.axis-" + d.id, null);
      context.on("focus.axis-" + d.id, null);
    }
  };

  return d3.rebind(axis, axis_,
      "orient",
      "ticks",
      "tickSubdivide",
      "tickSize",
      "tickPadding",
      "tickFormat");
};

var cubism_axisFormatSeconds = d3.time.format("%I:%M:%S %p"),
    cubism_axisFormatMinutes = d3.time.format("%I:%M %p"),
    cubism_axisFormatDays = d3.time.format("%B %d");
cubism_contextPrototype.rule = function() {
  var context = this,
      metric = cubism_identity;

  function rule(selection) {
    var id = ++cubism_id;

    var line = selection.append("div")
        .datum({id: id})
        .attr("class", "line")
        .call(cubism_ruleStyle);

    selection.each(function(d, i) {
      var that = this,
          id = ++cubism_id,
          metric_ = typeof metric === "function" ? metric.call(that, d, i) : metric;

      if (!metric_) return;

      function change(start, stop) {
        var values = [];

        for (var i = 0, n = context.size(); i < n; ++i) {
          if (metric_.valueAt(i)) {
            values.push(i);
          }
        }

        var lines = selection.selectAll(".metric").data(values);
        lines.exit().remove();
        lines.enter().append("div").attr("class", "metric line").call(cubism_ruleStyle);
        lines.style("left", cubism_ruleLeft);
      }

      context.on("change.rule-" + id, change);
      metric_.on("change.rule-" + id, change);
    });

    context.on("focus.rule-" + id, function(i) {
      line.datum(i)
          .style("display", i == null ? "none" : null)
          .style("left", i == null ? null : cubism_ruleLeft);
    });
  }

  rule.remove = function(selection) {

    selection.selectAll(".line")
        .each(remove)
        .remove();

    function remove(d) {
      context.on("focus.rule-" + d.id, null);
    }
  };

  rule.metric = function(_) {
    if (!arguments.length) return metric;
    metric = _;
    return rule;
  };

  return rule;
};

function cubism_ruleStyle(line) {
  line
      .style("position", "absolute")
      .style("top", 0)
      .style("bottom", 0)
      .style("width", "1px")
      .style("pointer-events", "none");
}

function cubism_ruleLeft(i) {
  return i + "px";
}
})(this);