smoothie.js

// MIT License:
//
// Copyright (c) 2010-2013, Joe Walnes
//               2013-2014, Drew Noakes
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

/**
 * Smoothie Charts - http://smoothiecharts.org/
 * (c) 2010-2013, Joe Walnes
 *     2013-2014, Drew Noakes
 *
 * v1.0: Main charting library, by Joe Walnes
 * v1.1: Auto scaling of axis, by Neil Dunn
 * v1.2: fps (frames per second) option, by Mathias Petterson
 * v1.3: Fix for divide by zero, by Paul Nikitochkin
 * v1.4: Set minimum, top-scale padding, remove timeseries, add optional timer to reset bounds, by Kelley Reynolds
 * v1.5: Set default frames per second to 50... smoother.
 *       .start(), .stop() methods for conserving CPU, by Dmitry Vyal
 *       options.interpolation = 'bezier' or 'line', by Dmitry Vyal
 *       options.maxValue to fix scale, by Dmitry Vyal
 * v1.6: minValue/maxValue will always get converted to floats, by Przemek Matylla
 * v1.7: options.grid.fillStyle may be a transparent color, by Dmitry A. Shashkin
 *       Smooth rescaling, by Kostas Michalopoulos
 * v1.8: Set max length to customize number of live points in the dataset with options.maxDataSetLength, by Krishna Narni
 * v1.9: Display timestamps along the bottom, by Nick and Stev-io
 *       (https://groups.google.com/forum/?fromgroups#!topic/smoothie-charts/-Ywse8FCpKI%5B1-25%5D)
 *       Refactored by Krishna Narni, to support timestamp formatting function
 * v1.10: Switch to requestAnimationFrame, removed the now obsoleted options.fps, by Gergely Imreh
 * v1.11: options.grid.sharpLines option added, by @drewnoakes
 *        Addressed warning seen in Firefox when seriesOption.fillStyle undefined, by @drewnoakes
 * v1.12: Support for horizontalLines added, by @drewnoakes
 *        Support for yRangeFunction callback added, by @drewnoakes
 * v1.13: Fixed typo (#32), by @alnikitich
 * v1.14: Timer cleared when last TimeSeries removed (#23), by @davidgaleano
 *        Fixed diagonal line on chart at start/end of data stream, by @drewnoakes
 * v1.15: Support for npm package (#18), by @dominictarr
 *        Fixed broken removeTimeSeries function (#24) by @davidgaleano
 *        Minor performance and tidying, by @drewnoakes
 * v1.16: Bug fix introduced in v1.14 relating to timer creation/clearance (#23), by @drewnoakes
 *        TimeSeries.append now deals with out-of-order timestamps, and can merge duplicates, by @zacwitte (#12)
 *        Documentation and some local variable renaming for clarity, by @drewnoakes
 * v1.17: Allow control over font size (#10), by @drewnoakes
 *        Timestamp text won't overlap, by @drewnoakes
 * v1.18: Allow control of max/min label precision, by @drewnoakes
 *        Added 'borderVisible' chart option, by @drewnoakes
 *        Allow drawing series with fill but no stroke (line), by @drewnoakes
 * v1.19: Avoid unnecessary repaints, and fixed flicker in old browsers having multiple charts in document (#40), by @asbai
 * v1.20: Add SmoothieChart.getTimeSeriesOptions and SmoothieChart.bringToFront functions, by @drewnoakes
 * v1.21: Add 'step' interpolation mode, by @drewnoakes
 * v1.22: Add support for different pixel ratios. Also add optional y limit formatters, by @copacetic
 * v1.23: Fix bug introduced in v1.22 (#44), by @drewnoakes
 * v1.24: Fix bug introduced in v1.23, re-adding parseFloat to y-axis formatter defaults, by @siggy_sf
 * v1.25: Fix bug seen when adding a data point to TimeSeries which is older than the current data, by @Nking92
 *        Draw time labels on top of series, by @comolosabia
 *        Add TimeSeries.clear function, by @drewnoakes
 * v1.26: Add support for resizing on high device pixel ratio screens, by @copacetic
 * v1.27: Fix bug introduced in v1.26 for non whole number devicePixelRatio values, by @zmbush
 */

;(function(exports) {

  var Util = {
    extend: function() {
      arguments[0] = arguments[0] || {};
      for (var i = 1; i < arguments.length; i++)
      {
        for (var key in arguments[i])
        {
          if (arguments[i].hasOwnProperty(key))
          {
            if (typeof(arguments[i][key]) === 'object') {
              if (arguments[i][key] instanceof Array) {
                arguments[0][key] = arguments[i][key];
              } else {
                arguments[0][key] = Util.extend(arguments[0][key], arguments[i][key]);
              }
            } else {
              arguments[0][key] = arguments[i][key];
            }
          }
        }
      }
      return arguments[0];
    }
  };

  /**
   * Initialises a new <code>TimeSeries</code> with optional data options.
   *
   * Options are of the form (defaults shown):
   *
   * <pre>
   * {
   *   resetBounds: true,        // enables/disables automatic scaling of the y-axis
   *   resetBoundsInterval: 3000 // the period between scaling calculations, in millis
   * }
   * </pre>
   *
   * Presentation options for TimeSeries are specified as an argument to <code>SmoothieChart.addTimeSeries</code>.
   *
   * @constructor
   */
  function TimeSeries(options) {
    this.options = Util.extend({}, TimeSeries.defaultOptions, options);
    this.clear();
  }

  TimeSeries.defaultOptions = {
    resetBoundsInterval: 3000,
    resetBounds: true
  };

  /**
   * Clears all data and state from this TimeSeries object.
   */
  TimeSeries.prototype.clear = function() {
    this.data = [];
    this.maxValue = Number.NaN; // The maximum value ever seen in this TimeSeries.
    this.minValue = Number.NaN; // The minimum value ever seen in this TimeSeries.
  };

  /**
   * Recalculate the min/max values for this <code>TimeSeries</code> object.
   *
   * This causes the graph to scale itself in the y-axis.
   */
  TimeSeries.prototype.resetBounds = function() {
    if (this.data.length) {
      // Walk through all data points, finding the min/max value
      this.maxValue = this.data[0][1];
      this.minValue = this.data[0][1];
      for (var i = 1; i < this.data.length; i++) {
        var value = this.data[i][1];
        if (value > this.maxValue) {
          this.maxValue = value;
        }
        if (value < this.minValue) {
          this.minValue = value;
        }
      }
    } else {
      // No data exists, so set min/max to NaN
      this.maxValue = Number.NaN;
      this.minValue = Number.NaN;
    }
  };

  /**
   * Adds a new data point to the <code>TimeSeries</code>, preserving chronological order.
   *
   * @param timestamp the position, in time, of this data point
   * @param value the value of this data point
   * @param sumRepeatedTimeStampValues if <code>timestamp</code> has an exact match in the series, this flag controls
   * whether it is replaced, or the values summed (defaults to false.)
   */
  TimeSeries.prototype.append = function(timestamp, value, sumRepeatedTimeStampValues) {
    // Rewind until we hit an older timestamp
    var i = this.data.length - 1;
    while (i >= 0 && this.data[i][0] > timestamp) {
      i--;
    }

    if (i === -1) {
      // This new item is the oldest data
      this.data.splice(0, 0, [timestamp, value]);
    } else if (this.data.length > 0 && this.data[i][0] === timestamp) {
      // Update existing values in the array
      if (sumRepeatedTimeStampValues) {
        // Sum this value into the existing 'bucket'
        this.data[i][1] += value;
        value = this.data[i][1];
      } else {
        // Replace the previous value
        this.data[i][1] = value;
      }
    } else if (i < this.data.length - 1) {
      // Splice into the correct position to keep timestamps in order
      this.data.splice(i + 1, 0, [timestamp, value]);
    } else {
      // Add to the end of the array
      this.data.push([timestamp, value]);
    }

    this.maxValue = isNaN(this.maxValue) ? value : Math.max(this.maxValue, value);
    this.minValue = isNaN(this.minValue) ? value : Math.min(this.minValue, value);
  };

  TimeSeries.prototype.dropOldData = function(oldestValidTime, maxDataSetLength) {
    // We must always keep one expired data point as we need this to draw the
    // line that comes into the chart from the left, but any points prior to that can be removed.
    var removeCount = 0;
    while (this.data.length - removeCount >= maxDataSetLength && this.data[removeCount + 1][0] < oldestValidTime) {
      removeCount++;
    }
    if (removeCount !== 0) {
      this.data.splice(0, removeCount);
    }
  };

  /**
   * Initialises a new <code>SmoothieChart</code>.
   *
   * Options are optional, and should be of the form below. Just specify the values you
   * need and the rest will be given sensible defaults as shown:
   *
   * <pre>
   * {
   *   minValue: undefined,                      // specify to clamp the lower y-axis to a given value
   *   maxValue: undefined,                      // specify to clamp the upper y-axis to a given value
   *   maxValueScale: 1,                         // allows proportional padding to be added above the chart. for 10% padding, specify 1.1.
   *   yRangeFunction: undefined,                // function({min: , max: }) { return {min: , max: }; }
   *   scaleSmoothing: 0.125,                    // controls the rate at which y-value zoom animation occurs
   *   millisPerPixel: 20,                       // sets the speed at which the chart pans by
   *   enableDpiScaling: true,                   // support rendering at different DPI depending on the device
   *   yMinFormatter: function(min, precision) { // callback function that formats the min y value label
   *     return parseFloat(min).toFixed(precision);
   *   },
   *   yMaxFormatter: function(max, precision) { // callback function that formats the max y value label
   *     return parseFloat(max).toFixed(precision);
   *   },
   *   maxDataSetLength: 2,
   *   interpolation: 'bezier'                   // one of 'bezier', 'linear', or 'step'
   *   timestampFormatter: null,                 // optional function to format time stamps for bottom of chart
   *                                             // you may use SmoothieChart.timeFormatter, or your own: function(date) { return ''; }
   *   horizontalLines: [],                      // [ { value: 0, color: '#ffffff', lineWidth: 1 } ]
   *   grid:
   *   {
   *     fillStyle: '#000000',                   // the background colour of the chart
   *     lineWidth: 1,                           // the pixel width of grid lines
   *     strokeStyle: '#777777',                 // colour of grid lines
   *     millisPerLine: 1000,                    // distance between vertical grid lines
   *     sharpLines: false,                      // controls whether grid lines are 1px sharp, or softened
   *     verticalSections: 2,                    // number of vertical sections marked out by horizontal grid lines
   *     borderVisible: true                     // whether the grid lines trace the border of the chart or not
   *   },
   *   labels
   *   {
   *     disabled: false,                        // enables/disables labels showing the min/max values
   *     fillStyle: '#ffffff',                   // colour for text of labels,
   *     fontSize: 15,
   *     fontFamily: 'sans-serif',
   *     precision: 2
   *   }
   * }
   * </pre>
   *
   * @constructor
   */
  function SmoothieChart(options) {
    this.options = Util.extend({}, SmoothieChart.defaultChartOptions, options);
    this.seriesSet = [];
    this.currentValueRange = 1;
    this.currentVisMinValue = 0;
    this.lastRenderTimeMillis = 0;
  }

  SmoothieChart.defaultChartOptions = {
    millisPerPixel: 20,
    enableDpiScaling: true,
    yMinFormatter: function(min, precision) {
      return parseFloat(min).toFixed(precision);
    },
    yMaxFormatter: function(max, precision) {
      return parseFloat(max).toFixed(precision);
    },
    maxValueScale: 1,
    interpolation: 'bezier',
    scaleSmoothing: 0.125,
    maxDataSetLength: 2,
    grid: {
      fillStyle: '#000000',
      strokeStyle: '#777777',
      lineWidth: 1,
      sharpLines: false,
      millisPerLine: 1000,
      verticalSections: 2,
      borderVisible: true
    },
    labels: {
      fillStyle: '#ffffff',
      disabled: false,
      fontSize: 10,
      fontFamily: 'monospace',
      precision: 2
    },
    horizontalLines: []
  };

  // Based on http://inspirit.github.com/jsfeat/js/compatibility.js
  SmoothieChart.AnimateCompatibility = (function() {
    var requestAnimationFrame = function(callback, element) {
          var requestAnimationFrame =
            window.requestAnimationFrame        ||
            window.webkitRequestAnimationFrame  ||
            window.mozRequestAnimationFrame     ||
            window.oRequestAnimationFrame       ||
            window.msRequestAnimationFrame      ||
            function(callback) {
              return window.setTimeout(function() {
                callback(new Date().getTime());
              }, 16);
            };
          return requestAnimationFrame.call(window, callback, element);
        },
        cancelAnimationFrame = function(id) {
          var cancelAnimationFrame =
            window.cancelAnimationFrame ||
            function(id) {
              clearTimeout(id);
            };
          return cancelAnimationFrame.call(window, id);
        };

    return {
      requestAnimationFrame: requestAnimationFrame,
      cancelAnimationFrame: cancelAnimationFrame
    };
  })();

  SmoothieChart.defaultSeriesPresentationOptions = {
    lineWidth: 1,
    strokeStyle: '#ffffff'
  };

  /**
   * Adds a <code>TimeSeries</code> to this chart, with optional presentation options.
   *
   * Presentation options should be of the form (defaults shown):
   *
   * <pre>
   * {
   *   lineWidth: 1,
   *   strokeStyle: '#ffffff',
   *   fillStyle: undefined
   * }
   * </pre>
   */
  SmoothieChart.prototype.addTimeSeries = function(timeSeries, options) {
    this.seriesSet.push({timeSeries: timeSeries, options: Util.extend({}, SmoothieChart.defaultSeriesPresentationOptions, options)});
    if (timeSeries.options.resetBounds && timeSeries.options.resetBoundsInterval > 0) {
      timeSeries.resetBoundsTimerId = setInterval(
        function() {
          timeSeries.resetBounds();
        },
        timeSeries.options.resetBoundsInterval
      );
    }
  };

  /**
   * Removes the specified <code>TimeSeries</code> from the chart.
   */
  SmoothieChart.prototype.removeTimeSeries = function(timeSeries) {
    // Find the correct timeseries to remove, and remove it
    var numSeries = this.seriesSet.length;
    for (var i = 0; i < numSeries; i++) {
      if (this.seriesSet[i].timeSeries === timeSeries) {
        this.seriesSet.splice(i, 1);
        break;
      }
    }
    // If a timer was operating for that timeseries, remove it
    if (timeSeries.resetBoundsTimerId) {
      // Stop resetting the bounds, if we were
      clearInterval(timeSeries.resetBoundsTimerId);
    }
  };

  /**
   * Gets render options for the specified <code>TimeSeries</code>.
   *
   * As you may use a single <code>TimeSeries</code> in multiple charts with different formatting in each usage,
   * these settings are stored in the chart.
   */
  SmoothieChart.prototype.getTimeSeriesOptions = function(timeSeries) {
    // Find the correct timeseries to remove, and remove it
    var numSeries = this.seriesSet.length;
    for (var i = 0; i < numSeries; i++) {
      if (this.seriesSet[i].timeSeries === timeSeries) {
        return this.seriesSet[i].options;
      }
    }
  };

  /**
   * Brings the specified <code>TimeSeries</code> to the top of the chart. It will be rendered last.
   */
  SmoothieChart.prototype.bringToFront = function(timeSeries) {
    // Find the correct timeseries to remove, and remove it
    var numSeries = this.seriesSet.length;
    for (var i = 0; i < numSeries; i++) {
      if (this.seriesSet[i].timeSeries === timeSeries) {
        var set = this.seriesSet.splice(i, 1);
        this.seriesSet.push(set[0]);
        break;
      }
    }
  };

  /**
   * Instructs the <code>SmoothieChart</code> to start rendering to the provided canvas, with specified delay.
   *
   * @param canvas the target canvas element
   * @param delayMillis an amount of time to wait before a data point is shown. This can prevent the end of the series
   * from appearing on screen, with new values flashing into view, at the expense of some latency.
   */
  SmoothieChart.prototype.streamTo = function(canvas, delayMillis) {
    this.canvas = canvas;
    this.delay = delayMillis;
    this.start();
  };

  /**
   * Make sure the canvas has the optimal resolution for the device's pixel ratio.
   */
  SmoothieChart.prototype.resize = function() {
    // TODO this function doesn't handle the value of enableDpiScaling changing during execution
    if (!this.options.enableDpiScaling || !window || window.devicePixelRatio === 1)
      return;

    var dpr = window.devicePixelRatio;
    var width = parseInt(this.canvas.getAttribute('width'));
    var height = parseInt(this.canvas.getAttribute('height'));

    if (!this.originalWidth || (Math.floor(this.originalWidth * dpr) !== width)) {
      this.originalWidth = width;
      this.canvas.setAttribute('width', (Math.floor(width * dpr)).toString());
      this.canvas.style.width = width + 'px';
      this.canvas.getContext('2d').scale(dpr, dpr);
    }

    if (!this.originalHeight || (Math.floor(this.originalHeight * dpr) !== height)) {
      this.originalHeight = height;
      this.canvas.setAttribute('height', (Math.floor(height * dpr)).toString());
      this.canvas.style.height = height + 'px';
      this.canvas.getContext('2d').scale(dpr, dpr);
    }
  };

  /**
   * Starts the animation of this chart.
   */
  SmoothieChart.prototype.start = function() {
    if (this.frame) {
      // We're already running, so just return
      return;
    }

    // Renders a frame, and queues the next frame for later rendering
    var animate = function() {
      this.frame = SmoothieChart.AnimateCompatibility.requestAnimationFrame(function() {
        this.render();
        animate();
      }.bind(this));
    }.bind(this);

    animate();
  };

  /**
   * Stops the animation of this chart.
   */
  SmoothieChart.prototype.stop = function() {
    if (this.frame) {
      SmoothieChart.AnimateCompatibility.cancelAnimationFrame(this.frame);
      delete this.frame;
    }
  };

  SmoothieChart.prototype.updateValueRange = function() {
    // Calculate the current scale of the chart, from all time series.
    var chartOptions = this.options,
        chartMaxValue = Number.NaN,
        chartMinValue = Number.NaN;

    for (var d = 0; d < this.seriesSet.length; d++) {
      // TODO(ndunn): We could calculate / track these values as they stream in.
      var timeSeries = this.seriesSet[d].timeSeries;
      if (!isNaN(timeSeries.maxValue)) {
        chartMaxValue = !isNaN(chartMaxValue) ? Math.max(chartMaxValue, timeSeries.maxValue) : timeSeries.maxValue;
      }

      if (!isNaN(timeSeries.minValue)) {
        chartMinValue = !isNaN(chartMinValue) ? Math.min(chartMinValue, timeSeries.minValue) : timeSeries.minValue;
      }
    }

    // Scale the chartMaxValue to add padding at the top if required
    if (chartOptions.maxValue != null) {
      chartMaxValue = chartOptions.maxValue;
    } else {
      chartMaxValue *= chartOptions.maxValueScale;
    }

    // Set the minimum if we've specified one
    if (chartOptions.minValue != null) {
      chartMinValue = chartOptions.minValue;
    }

    // If a custom range function is set, call it
    if (this.options.yRangeFunction) {
      var range = this.options.yRangeFunction({min: chartMinValue, max: chartMaxValue});
      chartMinValue = range.min;
      chartMaxValue = range.max;
    }

    if (!isNaN(chartMaxValue) && !isNaN(chartMinValue)) {
      var targetValueRange = chartMaxValue - chartMinValue;
      var valueRangeDiff = (targetValueRange - this.currentValueRange);
      var minValueDiff = (chartMinValue - this.currentVisMinValue);
      this.isAnimatingScale = Math.abs(valueRangeDiff) > 0.1 || Math.abs(minValueDiff) > 0.1;
      this.currentValueRange += chartOptions.scaleSmoothing * valueRangeDiff;
      this.currentVisMinValue += chartOptions.scaleSmoothing * minValueDiff;
    }

    this.valueRange = { min: chartMinValue, max: chartMaxValue };
  };

  SmoothieChart.prototype.render = function(canvas, time) {
    var nowMillis = new Date().getTime();

    if (!this.isAnimatingScale) {
      // We're not animating. We can use the last render time and the scroll speed to work out whether
      // we actually need to paint anything yet. If not, we can return immediately.

      // Render at least every 1/6th of a second. The canvas may be resized, which there is
      // no reliable way to detect.
      var maxIdleMillis = Math.min(1000/6, this.options.millisPerPixel);

      if (nowMillis - this.lastRenderTimeMillis < maxIdleMillis) {
        return;
      }
    }

    this.resize();

    this.lastRenderTimeMillis = nowMillis;

    canvas = canvas || this.canvas;
    time = time || nowMillis - (this.delay || 0);

    // Round time down to pixel granularity, so motion appears smoother.
    time -= time % this.options.millisPerPixel;

    var context = canvas.getContext('2d'),
        chartOptions = this.options,
        dimensions = { top: 0, left: 0, width: canvas.clientWidth, height: canvas.clientHeight },
        // Calculate the threshold time for the oldest data points.
        oldestValidTime = time - (dimensions.width * chartOptions.millisPerPixel),
        valueToYPixel = function(value) {
          var offset = value - this.currentVisMinValue;
          return this.currentValueRange === 0
            ? dimensions.height
            : dimensions.height - (Math.round((offset / this.currentValueRange) * dimensions.height));
        }.bind(this),
        timeToXPixel = function(t) {
          return Math.round(dimensions.width - ((time - t) / chartOptions.millisPerPixel));
        };

    this.updateValueRange();

    context.font = chartOptions.labels.fontSize + 'px ' + chartOptions.labels.fontFamily;

    // Save the state of the canvas context, any transformations applied in this method
    // will get removed from the stack at the end of this method when .restore() is called.
    context.save();

    // Move the origin.
    context.translate(dimensions.left, dimensions.top);

    // Create a clipped rectangle - anything we draw will be constrained to this rectangle.
    // This prevents the occasional pixels from curves near the edges overrunning and creating
    // screen cheese (that phrase should need no explanation).
    context.beginPath();
    context.rect(0, 0, dimensions.width, dimensions.height);
    context.clip();

    // Clear the working area.
    context.save();
    context.fillStyle = chartOptions.grid.fillStyle;
    context.clearRect(0, 0, dimensions.width, dimensions.height);
    context.fillRect(0, 0, dimensions.width, dimensions.height);
    context.restore();

    // Grid lines...
    context.save();
    context.lineWidth = chartOptions.grid.lineWidth;
    context.strokeStyle = chartOptions.grid.strokeStyle;
    // Vertical (time) dividers.
    if (chartOptions.grid.millisPerLine > 0) {
      context.beginPath();
      for (var t = time - (time % chartOptions.grid.millisPerLine);
           t >= oldestValidTime;
           t -= chartOptions.grid.millisPerLine) {
        var gx = timeToXPixel(t);
        if (chartOptions.grid.sharpLines) {
          gx -= 0.5;
        }
        context.moveTo(gx, 0);
        context.lineTo(gx, dimensions.height);
      }
      context.stroke();
      context.closePath();
    }

    // Horizontal (value) dividers.
    for (var v = 1; v < chartOptions.grid.verticalSections; v++) {
      var gy = Math.round(v * dimensions.height / chartOptions.grid.verticalSections);
      if (chartOptions.grid.sharpLines) {
        gy -= 0.5;
      }
      context.beginPath();
      context.moveTo(0, gy);
      context.lineTo(dimensions.width, gy);
      context.stroke();
      context.closePath();
    }
    // Bounding rectangle.
    if (chartOptions.grid.borderVisible) {
      context.beginPath();
      context.strokeRect(0, 0, dimensions.width, dimensions.height);
      context.closePath();
    }
    context.restore();

    // Draw any horizontal lines...
    if (chartOptions.horizontalLines && chartOptions.horizontalLines.length) {
      for (var hl = 0; hl < chartOptions.horizontalLines.length; hl++) {
        var line = chartOptions.horizontalLines[hl],
            hly = Math.round(valueToYPixel(line.value)) - 0.5;
        context.strokeStyle = line.color || '#ffffff';
        context.lineWidth = line.lineWidth || 1;
        context.beginPath();
        context.moveTo(0, hly);
        context.lineTo(dimensions.width, hly);
        context.stroke();
        context.closePath();
      }
    }

    // For each data set...
    for (var d = 0; d < this.seriesSet.length; d++) {
      context.save();
      var timeSeries = this.seriesSet[d].timeSeries,
          dataSet = timeSeries.data,
          seriesOptions = this.seriesSet[d].options;

      // Delete old data that's moved off the left of the chart.
      timeSeries.dropOldData(oldestValidTime, chartOptions.maxDataSetLength);

      // Set style for this dataSet.
      context.lineWidth = seriesOptions.lineWidth;
      context.strokeStyle = seriesOptions.strokeStyle;
      // Draw the line...
      context.beginPath();
      // Retain lastX, lastY for calculating the control points of bezier curves.
      var firstX = 0, lastX = 0, lastY = 0;
      for (var i = 0; i < dataSet.length && dataSet.length !== 1; i++) {
        var x = timeToXPixel(dataSet[i][0]),
            y = valueToYPixel(dataSet[i][1]);

        if (i === 0) {
          firstX = x;
          context.moveTo(x, y);
        } else {
          switch (chartOptions.interpolation) {
            case "linear":
            case "line": {
              context.lineTo(x,y);
              break;
            }
            case "bezier":
            default: {
              // Great explanation of Bezier curves: http://en.wikipedia.org/wiki/Bezier_curve#Quadratic_curves
              //
              // Assuming A was the last point in the line plotted and B is the new point,
              // we draw a curve with control points P and Q as below.
              //
              // A---P
              //     |
              //     |
              //     |
              //     Q---B
              //
              // Importantly, A and P are at the same y coordinate, as are B and Q. This is
              // so adjacent curves appear to flow as one.
              //
              context.bezierCurveTo( // startPoint (A) is implicit from last iteration of loop
                Math.round((lastX + x) / 2), lastY, // controlPoint1 (P)
                Math.round((lastX + x)) / 2, y, // controlPoint2 (Q)
                x, y); // endPoint (B)
              break;
            }
            case "step": {
              context.lineTo(x,lastY);
              context.lineTo(x,y);
              break;
            }
          }
        }

        lastX = x; lastY = y;
      }

      if (dataSet.length > 1) {
        if (seriesOptions.fillStyle) {
          // Close up the fill region.
          context.lineTo(dimensions.width + seriesOptions.lineWidth + 1, lastY);
          context.lineTo(dimensions.width + seriesOptions.lineWidth + 1, dimensions.height + seriesOptions.lineWidth + 1);
          context.lineTo(firstX, dimensions.height + seriesOptions.lineWidth);
          context.fillStyle = seriesOptions.fillStyle;
          context.fill();
        }

        if (seriesOptions.strokeStyle && seriesOptions.strokeStyle !== 'none') {
          context.stroke();
        }
        context.closePath();
      }
      context.restore();
    }

    // Draw the axis values on the chart.
    if (!chartOptions.labels.disabled && !isNaN(this.valueRange.min) && !isNaN(this.valueRange.max)) {
      var maxValueString = chartOptions.yMaxFormatter(this.valueRange.max, chartOptions.labels.precision),
          minValueString = chartOptions.yMinFormatter(this.valueRange.min, chartOptions.labels.precision);
      context.fillStyle = chartOptions.labels.fillStyle;
      context.fillText(maxValueString, dimensions.width - context.measureText(maxValueString).width - 2, chartOptions.labels.fontSize);
      context.fillText(minValueString, dimensions.width - context.measureText(minValueString).width - 2, dimensions.height - 2);
    }

    // Display timestamps along x-axis at the bottom of the chart.
    if (chartOptions.timestampFormatter && chartOptions.grid.millisPerLine > 0) {
      var textUntilX = dimensions.width - context.measureText(minValueString).width + 4;
      for (var t = time - (time % chartOptions.grid.millisPerLine);
           t >= oldestValidTime;
           t -= chartOptions.grid.millisPerLine) {
        var gx = timeToXPixel(t);
        // Only draw the timestamp if it won't overlap with the previously drawn one.
        if (gx < textUntilX) {
          // Formats the timestamp based on user specified formatting function
          // SmoothieChart.timeFormatter function above is one such formatting option
          var tx = new Date(t),
            ts = chartOptions.timestampFormatter(tx),
            tsWidth = context.measureText(ts).width;
          textUntilX = gx - tsWidth - 2;
          context.fillStyle = chartOptions.labels.fillStyle;
          context.fillText(ts, gx - tsWidth, dimensions.height - 2);
        }
      }
    }

    context.restore(); // See .save() above.
  };

  // Sample timestamp formatting function
  SmoothieChart.timeFormatter = function(date) {
    function pad2(number) { return (number < 10 ? '0' : '') + number }
    return pad2(date.getHours()) + ':' + pad2(date.getMinutes()) + ':' + pad2(date.getSeconds());
  };

  exports.TimeSeries = TimeSeries;
  exports.SmoothieChart = SmoothieChart;

})(typeof exports === 'undefined' ? this : exports);