Support Chrome Endure graphs in perf dashboard.

dashboard/ui/endure_js/plotter.js

+/*
+  Copyright (c) 2012 The Chromium Authors. All rights reserved.
+  Use of this source code is governed by a BSD-style license that can be
+  found in the LICENSE file.
+*/
+
+/**
+ * @fileoverview Collection of functions and classes used to plot data in a
+ *     <canvas>.  Create a Plotter() to generate a plot.
+ */
+
+/**
+ * Adds commas to a given number.
+ *
+ * Examples:
+ *  1234.56 => "1,234.56"
+ *  99999 => "99,999"
+ *
+ * @param {string|number} number The number to format.
+ * @return {string} String representation of |number| with commas for every
+ *     three digits to the left of a decimal point.
+ */
+function addCommas(number) {
+  number += '';  // Convert number to string if not already a string.
+  var numberParts = number.split('.');
+  var integralPart = numberParts[0];
+  var fractionalPart = numberParts.length > 1 ? '.' + numberParts[1] : '';
+  var reThreeDigits = /(\d+)(\d{3})/;
+  while (reThreeDigits.test(integralPart))
+    integralPart = integralPart.replace(reThreeDigits, '$1' + ',' + '$2');
+  return integralPart + fractionalPart;
+}
+
+/**
+ * Vertical marker to highlight data points that are being hovered over by the
+ * mouse.
+ *
+ * @param {string} color The color to make the marker, e.g., 'rgb(100,80,240)'.
+ * @return {Element} A div Element object representing the vertical marker.
+ */
+function VerticalMarker(color) {
+  var m = document.createElement('div');
+  m.style.backgroundColor = color;
+  m.style.opacity = '0.3';
+  m.style.position = 'absolute';
+  m.style.left = '-2px';
+  m.style.top = '-2px';
+  m.style.width = '0px';
+  m.style.height = '0px';
+  return m;
+}
+
+/**
+ * Class representing a horizontal marker at the indicated mouse location.
+ * @constructor
+ *
+ * @param {Element} canvasElement The canvas bounds.
+ * @param {Number} yValue The data value corresponding to the vertical click
+ *     location.
+ * @param {Number} yOtherValue If the plot is overlaying two coordinate systems,
+ *     this is the data value corresponding to the vertical click location in
+ *     the second coordinate system.  Can be null.
+ */
+function HorizontalMarker(canvasElement, yValue, yOtherValue) {
+  var m = document.createElement('div');
+  m.style.backgroundColor = HorizontalMarker.COLOR;
+  m.style.opacity = '0.3';
+  m.style.position = 'absolute';
+  m.style.width = canvasElement.offsetWidth + 'px';
+  m.style.height = HorizontalMarker.HEIGHT + 'px';
+
+  this.markerDiv = m;
+  this.value = yValue;
+  this.otherValue = yOtherValue;
+}
+
+HorizontalMarker.HEIGHT = 5;
+HorizontalMarker.COLOR = 'rgb(0,100,100)';
+
+/**
+ * Locates this element at a specified position.
+ *
+ * @param {Element} canvasElement The canvas element at which this element is
+ *     to be placed.
+ * @param {number} y Y position relative to the canvas element.
+ */
+HorizontalMarker.prototype.locateAt = function(canvasElement, y) {
+  var div = this.markerDiv;
+  div.style.left = domUtils.pageXY(canvasElement).x -
+                   domUtils.pageXY(div.offsetParent) + 'px';
+  div.style.top = (y + domUtils.pageXY(canvasElement).y
+                   - domUtils.pageXY(div.offsetParent).y
+                   - (HorizontalMarker.HEIGHT / 2)) + 'px';
+};
+
+/**
+ * Removes the horizontal marker from the graph.
+ */
+HorizontalMarker.prototype.remove = function() {
+  this.markerDiv.parentNode.removeChild(this.markerDiv);
+};
+
+/**
+ * An information indicator hovering around the mouse cursor on the graph.
+ * This class is used to show a legend near the mouse cursor.
+ *
+ * A set of legends under the graph is managed separately in
+ * {@code Plotter.createLegendsSummaryElement_}.
+ *
+ * @constructor
+ */
+function HoveringInfo() {
+  this.containerDiv_ = document.createElement('div');
+  this.containerDiv_.style.display = 'none';
+  this.containerDiv_.style.position = 'absolute';
+  this.containerDiv_.style.border = '1px solid #000';
+  this.containerDiv_.style.padding = '0.12em';
+  this.containerDiv_.style.backgroundColor = '#ddd';
+  this.colorIndicator_ = document.createElement('div');
+  this.colorIndicator_.style.display = 'inline-block';
+  this.colorIndicator_.style.width = '1em';
+  this.colorIndicator_.style.height = '1em';
+  this.colorIndicator_.style.verticalAlign = 'text-bottom';
+  this.colorIndicator_.style.margin = '0 0.24em 0 0';
+  this.colorIndicator_.style.border = '1px solid #000';
+  this.legendText_ = document.createElement('span');
+  this.itemValueText_ = document.createElement('span');
+
+  this.containerDiv_.appendChild(this.colorIndicator_);
+  this.containerDiv_.appendChild(this.legendText_);
+  var div = document.createElement('div');
+  div.appendChild(this.itemValueText_);
+  this.containerDiv_.appendChild(div);
+}
+
+/**
+ * Returns the container element;
+ *
+ * @return {Element} The container element.
+ */
+HoveringInfo.prototype.getElement = function() {
+  return this.containerDiv_;
+};
+
+/**
+ * Shows or hides the element.
+ *
+ * @param {boolean} show Shows the element if true, or hides it.
+ */
+HoveringInfo.prototype.show = function(show) {
+  this.containerDiv_.style.display = show ? 'block' : 'none';
+};
+
+/**
+ * Returns the position of the container element in the page coordinate.
+ *
+ * @return {Object} A point object which has {@code x} and {@code y} fields.
+ */
+HoveringInfo.prototype.pageXY = function() {
+  return domUtils.pageXY(this.containerDiv_);
+};
+
+/**
+ * Locates the element at the specified position.
+ *
+ * @param {number} x X position in the page coordinate.
+ * @param {number} y Y position in the page coordinate.
+ */
+HoveringInfo.prototype.locateAtPageXY = function(x, y) {
+  var parentXY = domUtils.pageXY(this.containerDiv_.offsetParent);
+  this.containerDiv_.style.left = x - parentXY.x + 'px';
+  this.containerDiv_.style.top = y - parentXY.y + 'px';
+};
+
+/**
+ * Returns the legend text.
+ *
+ * @return {?string} The legend text.
+ */
+HoveringInfo.prototype.getLegendText = function() {
+  return this.legendText_.textContent;
+};
+
+/**
+ * Changes the legend text.
+ *
+ * @param {string} text The new text to be set.
+ */
+HoveringInfo.prototype.setLegendText = function(text) {
+  this.legendText_.textContent = text;
+};
+
+/**
+ * Changes the item value.
+ *
+ * @param {number} value The new value to be shown.
+ */
+HoveringInfo.prototype.setItemValue = function(value) {
+  this.itemValueText_.textContent = 'Item value = ' + addCommas(value);
+};
+
+/**
+ * Changes the color of the color indicator.
+ *
+ * @param {string} color The new color to be set.
+ */
+HoveringInfo.prototype.setColorIndicator = function(color) {
+  this.colorIndicator_.style.backgroundColor = color;
+};
+
+/**
+ * Main class that does the actual plotting.
+ *
+ * Draws a chart using a canvas element. Takes an array of lines to draw.
+ * @constructor
+ *
+ * @param {Array} plotData list of arrays that represent individual lines. The
+ *     line itself is an Array of points.
+ * @param {Array} dataDescriptions list of data descriptions for each line in
+ *     |plotData|.
+ * @param {string} eventName The string name of an event to overlay on the
+ *     graph.  Should be 'null' if there are no events to overlay.
+ * @param {Object} eventInfo If |eventName| is specified, an array of event
+ *     points to overlay on the graph.  Each event point in the array is itself
+ *     a 2-element array, where the first element is the x-axis value at which
+ *     the event occurred during the test, and the second element is a
+ *     dictionary of kay/value pairs representing metadata associated with the
+ *     event.
+ * @param {string} unitsX The x-axis units of the data being plotted.
+ * @param {string} unitsY The y-axis units of the data being plotted.
+ * @param {string} unitsYOther If another graph (with different y-axis units) is
+ *     being overlayed over the first graph, this represents the units of the
+ *     other graph.  Otherwise, this should be 'null'.
+ * @param {?number} graphsOtherStartIndex Specifies the starting index of
+ *     the second set of lines.  {@code plotData} in the range of
+ *     [0, {@code graphsOtherStartIndex}) are treated as the first set of lines,
+ *     and ones in the range of
+ *     [{@code graphsOtherStartIndex}, {@code plotData.length}) are as
+ *     the second set.  0, {@code plotData.length} and {@code null} mean
+ *     no second set, i.e. all the data in {@code plotData} represent the single
+ *     set of lines.
+ * @param {Element} resultNode A DOM Element object representing the DOM node to
+ *     which the plot should be attached.
+ * @param {boolean} is_lookout Whether or not the graph should be drawn
+ *     in 'lookout' mode, which is a summarized view that is made for overview
+ *     pages when the graph is drawn in a more confined space.
+ * @param {boolean} stackedGraph Whether or not the first set of lines is
+ *     a stacked graph.
+ * @param {boolean} stackedGraphOther Whether or not the second set of lines is
+ *     a stacked graph.
+ *
+ * Example of the |plotData|:
+ *  [
+ *    [line 1 data],
+ *    [line 2 data]
+ *  ].
+ *  Line data looks like  [[point one], [point two]].
+ *  And individual points are [x value, y value]
+ */
+function Plotter(plotData, dataDescriptions, eventName, eventInfo, unitsX,
+                 unitsY, unitsYOther, graphsOtherStartIndex, resultNode,
+                 is_lookout, stackedGraph, stackedGraphOther) {
+  this.plotData_ = plotData;
+  this.dataDescriptions_ = dataDescriptions;
+  this.eventName_ = eventName;
+  this.eventInfo_ = eventInfo;
+  this.unitsX_ = unitsX;
+  this.unitsY_ = unitsY;
+  this.unitsYOther_ = unitsYOther;
+  this.graphsOtherStartIndex_ =
+      (0 < graphsOtherStartIndex && graphsOtherStartIndex < plotData.length) ?
+      graphsOtherStartIndex : null;
+  this.resultNode_ = resultNode;
+  this.is_lookout_ = is_lookout;
+  this.stackedGraph_ = stackedGraph;
+  this.stackedGraphOther_ = stackedGraphOther;
+
+  this.dataColors_ = [];
+
+  this.coordinates = null;
+  this.coordinatesOther = null;
+  if (this.unitsYOther_ && this.graphsOtherStartIndex_) {
+    // Need two different coordinate systems to overlay on the same graph.
+    this.coordinates = new Coordinates(
+        this.plotData_.slice(0, this.graphsOtherStartIndex_));
+    this.coordinatesOther = new Coordinates(
+        this.plotData_.slice(this.graphsOtherStartIndex_));
+  } else {
+    this.coordinates = new Coordinates(this.plotData_);
+  }
+
+  // A color palette that's unambigous for normal and color-deficient viewers.
+  // Values are (red, green, blue) on a scale of 255.
+  // Taken from http://jfly.iam.u-tokyo.ac.jp/html/manuals/pdf/color_blind.pdf.
+  this.colors = [[0, 114, 178],   // Blue.
+                 [230, 159, 0],   // Orange.
+                 [0, 158, 115],   // Green.
+                 [204, 121, 167], // Purplish pink.
+                 [86, 180, 233],  // Sky blue.
+                 [213, 94, 0],    // Dark orange.
+                 [0, 0, 0],       // Black.
+                 [240, 228, 66]   // Yellow.
+                ];
+
+  for (var i = 0, colorIndex = 0; i < this.dataDescriptions_.length; ++i)
+    this.dataColors_[i] = this.makeColor(colorIndex++);
+}
+
+/**
+ * Generates a string representing a color corresponding to the given index
+ * in a color array.  Handles wrapping around the color array if necessary.
+ *
+ * @param {number} i An index into the |this.colors| array.
+ * @return {string} A string representing a color in 'rgb(X,Y,Z)' format.
+ */
+Plotter.prototype.makeColor = function(i) {
+  var index = i % this.colors.length;
+  return 'rgb(' + this.colors[index][0] + ',' +
+                  this.colors[index][1] + ',' +
+                  this.colors[index][2] + ')';
+};
+
+/**
+ * Same as function makeColor above, but also takes a transparency value
+ * indicating how transparent to make the color appear.
+ *
+ * @param {number} i An index into the |this.colors| array.
+ * @param {number} transparencyPercent Percentage transparency to make the
+ *     color, e.g., 0.75.
+ * @return {string} A string representing a color in 'rgb(X,Y,Z,A)' format,
+ *     where A is the percentage transparency.
+ */
+Plotter.prototype.makeColorTransparent = function(i, transparencyPercent) {
+  var index = i % this.colors.length;
+  return 'rgba(' + this.colors[index][0] + ',' +
+                   this.colors[index][1] + ',' +
+                   this.colors[index][2] + ',' + transparencyPercent + ')';
+};
+
+/**
+ * Gets the data color value associated with a specified color index.
+ *
+ * @param {number} i An index into the |this.colors| array.
+ * @return {string} A string representing a color in 'rgb(X,Y,Z,A)' format,
+ *     where A is the percentage transparency.
+ */
+Plotter.prototype.getDataColor = function(i) {
+  if (this.dataColors_[i])
+    return this.dataColors_[i];
+  else
+    return this.makeColor(i);
+};
+
+/**
+ * Gets the fill color value associated with a specified color index.
+ *
+ * @param {number} i An index into the |this.colors| array.
+ * @return {string} A string representing a color in 'rgba(R,G,B,A)' format,
+ *     where A is the percentage transparency.
+ */
+Plotter.prototype.getFillColor = function(i) {
+  return this.makeColorTransparent(i, 0.4);
+};
+
+/**
+ * Does the actual plotting.
+ */
+Plotter.prototype.plot = function() {
+  var self = this;
+
+  this.canvasElement_ = this.canvas_();
+  this.rulerDiv_ = this.ruler_();
+
+  // Markers for the result point(s)/events that the mouse is currently
+  // hovering over.
+  this.cursorDiv_ = new VerticalMarker('rgb(100,80,240)');
+  this.cursorDivOther_ = new VerticalMarker('rgb(50,50,50)');
+  this.eventDiv_ = new VerticalMarker('rgb(255, 0, 0)');
+  this.hoveringInfo_ = new HoveringInfo();
+
+  this.resultNode_.appendChild(this.canvasElement_);
+  this.resultNode_.appendChild(this.coordinates_());
+  this.resultNode_.appendChild(this.rulerDiv_);
+  this.resultNode_.appendChild(this.cursorDiv_);
+  this.resultNode_.appendChild(this.cursorDivOther_);
+  this.resultNode_.appendChild(this.eventDiv_);
+  this.resultNode_.appendChild(this.hoveringInfo_.getElement());
+  this.attachEventListeners_();
+
+  // Now draw the canvas.
+  var ctx = this.canvasElement_.getContext('2d');
+
+  // Clear it with white: otherwise canvas will draw on top of existing data.
+  ctx.clearRect(0, 0, this.canvasElement_.width, this.canvasElement_.height);
+
+  // Draw all data lines in the reverse order so the last graph appears on
+  // the backmost and the first graph appears on the frontmost.
+  function draw(plotData, coordinates, colorOffset, stack) {
+    for (var i = plotData.length - 1; i >= 0; --i) {
+      if (stack) {
+        self.plotAreaUnderLine_(ctx, self.getFillColor(colorOffset + i),
+                                plotData[i], coordinates);
+      }
+      self.plotLine_(ctx, self.getDataColor(colorOffset + i),
+                     plotData[i], coordinates);
+    }
+  }
+  draw(this.plotData_.slice(0,
+                            this.graphsOtherStartIndex_ ?
+                            this.graphsOtherStartIndex_ :
+                            this.plotData_.length),
+       this.coordinates, 0, this.stackedGraph_);
+  if (this.graphsOtherStartIndex_) {
+    draw(this.plotData_.slice(this.graphsOtherStartIndex_),
+         this.unitsYOther_ ? this.coordinatesOther : this.coordinates,
+         this.graphsOtherStartIndex_, this.stackedGraphOther_);
+  }
+
+  // Draw events overlayed on graph if needed.
+  if (this.eventName_ && this.eventInfo_)
+    this.plotEvents_(ctx, 'rgb(255, 150, 150)', this.coordinates);
+
+  this.graduation_divs_ = this.graduations_(this.coordinates, 0, false);
+  if (this.unitsYOther_) {
+    this.graduation_divs_ = this.graduation_divs_.concat(
+        this.graduations_(this.coordinatesOther, 1, true));
+  }
+  for (var i = 0; i < this.graduation_divs_.length; ++i)
+    this.resultNode_.appendChild(this.graduation_divs_[i]);
+};
+
+/**
+ * Draws events overlayed on top of an existing graph.
+ *
+ * @param {Object} ctx A canvas element object for drawing.
+ * @param {string} strokeStyles A string representing the drawing style.
+ * @param {Object} coordinateSystem A Coordinates object representing the
+ *     coordinate system of the graph.
+ */
+Plotter.prototype.plotEvents_ = function(ctx, strokeStyles, coordinateSystem) {
+  ctx.strokeStyle = strokeStyles;
+  ctx.fillStyle = strokeStyles;
+  ctx.lineWidth = 1.0;
+
+  ctx.beginPath();
+  var data = this.eventInfo_;
+  for (var index = 0; index < data.length; ++index) {
+    var event_time = data[index][0];
+    var x = coordinateSystem.xPixel(event_time);
+    ctx.moveTo(x, 0);
+    ctx.lineTo(x, this.canvasElement_.offsetHeight);
+  }
+  ctx.closePath();
+  ctx.stroke();
+};
+
+/**
+ * Draws a line on the graph.
+ *
+ * @param {Object} ctx A canvas element object for drawing.
+ * @param {string} strokeStyles A string representing the drawing style.
+ * @param {Array} data A list of [x, y] values representing the line to plot.
+ * @param {Object} coordinateSystem A Coordinates object representing the
+ *     coordinate system of the graph.
+ */
+Plotter.prototype.plotLine_ = function(ctx, strokeStyles, data,
+                                       coordinateSystem) {
+  ctx.strokeStyle = strokeStyles;
+  ctx.fillStyle = strokeStyles;
+  ctx.lineWidth = 2.0;
+
+  ctx.beginPath();
+  var initial = true;
+  var allPoints = [];
+  for (var i = 0; i < data.length; ++i) {
+    var pointX = parseFloat(data[i][0]);
+    var pointY = parseFloat(data[i][1]);
+    var x = coordinateSystem.xPixel(pointX);
+    var y = coordinateSystem.yPixel(0);
+    if (isNaN(pointY)) {
+      // Re-set 'initial' if we're at a gap in the data.
+      initial = true;
+    } else {
+      y = coordinateSystem.yPixel(pointY);
+      if (initial)
+        initial = false;
+      else
+        ctx.lineTo(x, y);
+    }
+
+    ctx.moveTo(x, y);
+    if (!data[i].interpolated) {
+      allPoints.push([x, y]);
+    }
+  }
+  ctx.closePath();
+  ctx.stroke();
+
+  if (!this.is_lookout_) {
+    // Draw a small dot at each point.
+    for (var i = 0; i < allPoints.length; ++i) {
+      ctx.beginPath();
+      ctx.arc(allPoints[i][0], allPoints[i][1], 3, 0, Math.PI*2, true);
+      ctx.fill();
+    }
+  }
+};
+
+/**
+ * Fills an area under the given line on the graph.
+ *
+ * @param {Object} ctx A canvas element object for drawing.
+ * @param {string} fillStyle A string representing the drawing style.
+ * @param {Array} data A list of [x, y] values representing the line to plot.
+ * @param {Object} coordinateSystem A Coordinates object representing the
+ *     coordinate system of the graph.
+ */
+Plotter.prototype.plotAreaUnderLine_ = function(ctx, fillStyle, data,
+                                                coordinateSystem) {
+  if (!data[0]) {
+    return;  // nothing to draw
+  }
+
+  ctx.beginPath();
+  var x = coordinateSystem.xPixel(parseFloat(data[0][0]) || 0);
+  var y = coordinateSystem.yPixel(parseFloat(data[0][1]) || 0);
+  var y0 = coordinateSystem.yPixel(coordinateSystem.yMinValue());
+  ctx.moveTo(x, y0);
+  for (var point, i = 0; point = data[i]; ++i) {
+    var pointX = parseFloat(point[0]);
+    var pointY = parseFloat(point[1]);
+    if (isNaN(pointX)) { continue; }  // Skip an invalid point.
+    if (isNaN(pointY)) {
+      ctx.lineTo(x, y0);
+      var yWasNaN = true;
+    } else {
+      x = coordinateSystem.xPixel(pointX);
+      y = coordinateSystem.yPixel(pointY);
+      if (yWasNaN) {
+        ctx.lineTo(x, y0);
+        yWasNaN = false;
+      }
+      ctx.lineTo(x, y);
+    }
+  }
+  ctx.lineTo(x, y0);
+
+  ctx.lineWidth = 0;
+  // Clear the area with white color first.
+  var COLOR_WHITE = 'rgb(255,255,255)';
+  ctx.strokeStyle = COLOR_WHITE;
+  ctx.fillStyle = COLOR_WHITE;
+  ctx.fill();
+  // Then, fill the area with the specified color.
+  ctx.strokeStyle = fillStyle;
+  ctx.fillStyle = fillStyle;
+  ctx.fill();
+};
+
+/**
+ * Attaches event listeners to DOM nodes.
+ */
+Plotter.prototype.attachEventListeners_ = function() {
+  var self = this;
+  this.canvasElement_.parentNode.addEventListener(
+    'mousemove', function(evt) { self.onMouseMove_(evt); }, false);
+  this.canvasElement_.parentNode.addEventListener(
+    'mouseover', function(evt) { self.onMouseOver_(evt); }, false);
+  this.canvasElement_.parentNode.addEventListener(
+    'mouseout', function(evt) { self.onMouseOut_(evt); }, false);
+  this.cursorDiv_.addEventListener(
+    'click', function(evt) { self.onMouseClick_(evt); }, false);
+  this.cursorDivOther_.addEventListener(
+    'click', function(evt) { self.onMouseClick_(evt); }, false);
+  this.eventDiv_.addEventListener(
+    'click', function(evt) { self.onMouseClick_(evt); }, false);
+};
+
+/**
+ * Update the horizontal line that is following where the mouse is hovering.
+ *
+ * @param {Object} evt A mouse event object representing a mouse move event.
+ */
+Plotter.prototype.updateRuler_ = function(evt) {
+  var r = this.rulerDiv_;
+  r.style.left = this.canvasElement_.offsetLeft + 'px';
+  r.style.top = this.canvasElement_.offsetTop + 'px';
+  r.style.width = this.canvasElement_.offsetWidth + 'px';
+  var h = domUtils.pageXYOfEvent(evt).y -
+          domUtils.pageXY(this.canvasElement_).y;
+  if (h > this.canvasElement_.offsetHeight)
+    h = this.canvasElement_.offsetHeight;
+  r.style.height = h + 'px';
+};
+
+/**
+ * Update the highlighted data point at the x value that the mouse is hovering
+ * over.
+ *
+ * @param {Object} coordinateSystem A Coordinates object representing the
+ *     coordinate system of the graph.
+ * @param {number} currentIndex The index into the |this.plotData| array of the
+ *     data point being hovered over, for a given line.
+ * @param {Object} cursorDiv A DOM element div object representing the highlight
+ *     itself.
+ * @param {number} dataIndex The index into the |this.plotData| array of the
+ *     line being hovered over.
+ */
+Plotter.prototype.updateCursor_ = function(coordinateSystem, currentIndex,
+                                           cursorDiv, dataIndex) {
+  var c = cursorDiv;
+  c.style.top = this.canvasElement_.offsetTop + 'px';
+  c.style.height = this.canvasElement_.offsetHeight + 'px';
+
+  // Left point is half-way to the previous x value, unless it's the first
+  // point, in which case it's the x value of the current point.
+  var leftPoint = null;
+  if (currentIndex == 0) {
+    leftPoint = this.canvasElement_.offsetLeft +
+        coordinateSystem.xPixel(this.plotData_[dataIndex][0][0]);
+  }
+  else {
+    var left_x = this.canvasElement_.offsetLeft +
+        coordinateSystem.xPixel(this.plotData_[dataIndex][currentIndex - 1][0]);
+    var curr_x = this.canvasElement_.offsetLeft +
+        coordinateSystem.xPixel(this.plotData_[dataIndex][currentIndex][0]);
+    leftPoint = (left_x + curr_x) / 2;
+  }
+  c.style.left = leftPoint;
+
+  // Width is half-way to the next x value minus the left point, unless it's
+  // the last point, in which case it's the x value of the current point minus
+  // the left point.
+  if (currentIndex == this.plotData_[dataIndex].length - 1) {
+    var curr_x = this.canvasElement_.offsetLeft +
+        coordinateSystem.xPixel(this.plotData_[dataIndex][currentIndex][0]);
+    c.style.width = curr_x - leftPoint;
+  }
+  else {
+    var next_x = this.canvasElement_.offsetLeft +
+        coordinateSystem.xPixel(this.plotData_[dataIndex][currentIndex + 1][0]);
+    var curr_x = this.canvasElement_.offsetLeft +
+        coordinateSystem.xPixel(this.plotData_[dataIndex][currentIndex][0]);
+    c.style.width = ((next_x + curr_x) / 2) - leftPoint;
+  }
+};
+
+/**
+ * Update the highlighted event at the x value that the mouse is hovering over.
+ *
+ * @param {number} x The x-value (pixel) at which to draw the event highlight
+ *     div.
+ * @param {boolean} show Whether or not to show the highlight div.
+ */
+Plotter.prototype.updateEventDiv_ = function(x, show) {
+  var c = this.eventDiv_;
+  c.style.top = this.canvasElement_.offsetTop + 'px';
+  c.style.height = this.canvasElement_.offsetHeight + 'px';
+
+  if (show) {
+    c.style.left = this.canvasElement_.offsetLeft + (x - 2);
+    c.style.width = 8;
+  } else {
+    c.style.width = 0;
+  }
+};
+
+/**
+ * Updates the hovering information.
+ *
+ * @param {Event} evt An event object, which specifies the position of the mouse
+ *     cursor.
+ * @param {boolean} show Whether or not to show the hovering info.  Even if it's
+ *     true, if the cursor position is out of the appropriate area, nothing will
+ *     be shown.
+ */
+Plotter.prototype.updateHoveringInfo_ = function(evt, show) {
+  var evtPageXY = domUtils.pageXYOfEvent(evt);
+  var hoveringInfoPageXY = this.hoveringInfo_.pageXY();
+  var canvasPageXY = domUtils.pageXY(this.canvasElement_);
+
+  var coord = this.coordinates;
+  // p = the mouse cursor position in value coordinates.
+  var p = {'x': coord.xValue(evtPageXY.x - canvasPageXY.x),
+           'y': coord.yValue(evtPageXY.y - canvasPageXY.y)};
+  if (!show ||
+      !(this.stackedGraph_ || this.stackedGraphOther_) ||
+      p.x < coord.xMinValue() || coord.xMaxValue() < p.x ||
+      p.y < coord.yMinValue() || coord.yMaxValue() < p.y) {
+    this.hoveringInfo_.show(false);
+    return;
+  } else {
+    this.hoveringInfo_.show(true);
+  }
+
+  /**
+   * Finds the closest lines (upside and downside of the cursor position).
+   * Returns a set of upside/downside line indices and point index on success
+   * or null.
+   */
+  function findClosestLines(lines, opt_startIndex, opt_endIndex) {
+    var offsetIndex = opt_startIndex || 0;
+    lines =
+        opt_endIndex != null ? lines.slice(offsetIndex, opt_endIndex) :
+        opt_startIndex != null ? lines.slice(offsetIndex) :
+        lines;
+
+    var upsideClosestLineIndex = null;
+    var upsideClosestYDistance = coord.yValueRange();
+    var downsideClosestLineIndex = null;
+    var downsideClosestYDistance = coord.yValueRange();
+    var upsideClosestPointIndex = null;
+
+    for (var lineIndex = 0, line; line = lines[lineIndex]; ++lineIndex) {
+      for (var i = 1; line[i]; ++i) {
+        var p0 = line[i - 1], p1 = line[i];
+        if (p0[0] <= p.x && p.x < p1[0]) {
+          // Calculate y-value of the line at p.x, which is the cursor point.
+          var y = (p.x - p0[0]) / (p1[0] - p0[0]) * (p1[1] - p0[1]) + p0[1];
+          if (p.y < y && y - p.y < upsideClosestYDistance) {
+            upsideClosestLineIndex = lineIndex;
+            upsideClosestYDistance = y - p.y;
+
+            if (p.x - p0[0] < p1[0] - p.x) {
+              upsideClosestPointIndex = i - 1;
+            } else {
+              upsideClosestPointIndex = i;
+            }
+          } else if (y <= p.y && p.y - y < downsideClosestYDistance) {
+            downsideClosestLineIndex = lineIndex;
+            downsideClosestYDistance = p.y - y;
+          }
+          break;
+        }
+      }
+    }
+
+    return (upsideClosestLineIndex != null &&
+            upsideClosestPointIndex != null) ?
+        {'upsideLineIndex': offsetIndex + upsideClosestLineIndex,
+         'downsideLineIndex': downsideClosestYDistance == null ? null :
+                              offsetIndex + downsideClosestLineIndex,
+         'upsidePointIndex': offsetIndex + upsideClosestPointIndex} :
+        null;
+  }
+
+  // Find the closest lines above and below the mouse cursor.
+  var closest = null;
+  // Since the other set of graphs are drawn over the first set, try to find
+  // the closest lines from the other set of graphs first.
+  if (this.graphsOtherStartIndex_ && this.stackedGraphOther_) {
+    closest = findClosestLines(this.plotData_, this.graphsOtherStartIndex_);
+  }
+  if (!closest && this.stackedGraph_) {
+    closest = this.graphsOtherStartIndex_ ?
+        findClosestLines(this.plotData_, 0, this.graphsOtherStartIndex_) :
+        findClosestLines(this.plotData_);
+  }
+  if (!closest) {
+    this.hoveringInfo_.show(false);
+    return;
+  }
+
+  // Update the contents of the hovering info box.
+  // Color indicator, description and the value of the item.
+  this.hoveringInfo_.setColorIndicator(
+    this.getDataColor(closest.upsideLineIndex));
+  this.hoveringInfo_.setLegendText(
+    this.dataDescriptions_[closest.upsideLineIndex]);
+  var y1 = this.plotData_[closest.upsideLineIndex][closest.upsidePointIndex][1];
+  var y0 = closest.downsideLineIndex == null ?
+      0 :
+      this.plotData_[closest.downsideLineIndex][closest.upsidePointIndex][1];
+  this.hoveringInfo_.setItemValue(y1 - y0);
+
+  // Locate the hovering info box near the mouse cursor.
+  var DIV_X_OFFSET = 10, DIV_Y_OFFSET = -20;
+  if (evtPageXY.x + this.hoveringInfo_.getElement().offsetWidth <
+      canvasPageXY.x + this.canvasElement_.offsetWidth) {
+    this.hoveringInfo_.locateAtPageXY(evtPageXY.x + DIV_X_OFFSET,
+                                      evtPageXY.y + DIV_Y_OFFSET);
+  } else {  // If lacking space at the right side, locate it at the left side.
+    this.hoveringInfo_.locateAtPageXY(
+      evtPageXY.x - this.hoveringInfo_.getElement().offsetWidth - DIV_X_OFFSET,
+      evtPageXY.y + DIV_Y_OFFSET);
+  }
+};
+
+/**
+ * Handle a mouse move event.
+ *
+ * @param {Object} evt A mouse event object representing a mouse move event.
+ */
+Plotter.prototype.onMouseMove_ = function(evt) {
+  var self = this;
+
+  var canvas = evt.currentTarget.firstChild;
+  var evtPageXY = domUtils.pageXYOfEvent(evt);
+  var canvasPageXY = domUtils.pageXY(this.canvasElement_);
+  var positionX = evtPageXY.x - canvasPageXY.x;
+  var positionY = evtPageXY.y - canvasPageXY.y;
+
+  // Identify the index of the x value that is closest to the mouse x value.
+  var xValue = this.coordinates.xValue(positionX);
+  var lineIndex = !this.stackedGraph_ ? 0 :
+      this.graphsOtherStartIndex_ ? this.graphsOtherStartIndex_ - 1 :
+      this.plotData_.length - 1;
+  var line = this.plotData_[lineIndex];
+  var min_diff = Math.abs(line[0][0] - xValue);
+  indexValueX = 0;
+  for (var i = 1; i < line.length; ++i) {
+    var diff = Math.abs(line[i][0] - xValue);
+    if (diff < min_diff) {
+      min_diff = diff;
+      indexValueX = i;
+    }
+  }
+
+  // Identify the index of the x value closest to the mouse x value for the
+  // other graph being overlayed on top of the original graph, if one exists.
+  if (this.unitsYOther_) {
+    var xValue = this.coordinatesOther.xValue(positionX);
+    var lineIndexOther = !this.stackedGraphOther_ ?
+        this.graphsOtherStartIndex_ : this.plotData_.length - 1;
+    var lineOther = this.plotData_[lineIndexOther];
+    var min_diff = Math.abs(lineOther[0][0] - xValue);
+    var indexValueXOther = 0;
+    for (var i = 1; i < lineOther.length; ++i) {
+      var diff = Math.abs(lineOther[i][0] - xValue);
+      if (diff < min_diff) {
+        min_diff = diff;
+        indexValueXOther = i;
+      }
+    }
+  }
+
+  // Update coordinate information displayed directly underneath the graph.
+  function legendLabel(lineIndex, opt_labelText) {
+    return '<span style="color:' + self.getDataColor(lineIndex) + '">' +
+        (opt_labelText || self.dataDescriptions_[lineIndex]) +
+        '</span>:&nbsp;&nbsp;';
+  }
+  function valuesAtCursor(lineIndex, pointIndex, unitsY, yValue) {
+    return '<span style="color:' + self.getDataColor(lineIndex) + '">' +
+        self.plotData_[lineIndex][pointIndex][0] + ' ' + self.unitsX_ + ': ' +
+        addCommas(self.plotData_[lineIndex][pointIndex][1].toFixed(2)) + ' ' +
+        unitsY  + '</span> [hovering at ' + addCommas(yValue.toFixed(2)) +
+        ' ' + unitsY + ']';
+  }
+
+  this.infoBox_.rows[0].label.innerHTML = legendLabel(lineIndex);
+  this.infoBox_.rows[0].content.innerHTML = valuesAtCursor(
+    lineIndex, indexValueX, this.unitsY_, this.coordinates.yValue(positionY));
+  var row = this.infoBox_.rows[1];
+  if (this.unitsYOther_) {
+    row.label.innerHTML = legendLabel(lineIndexOther);
+    row.content.innerHTML = valuesAtCursor(
+      lineIndexOther, indexValueXOther, this.unitsYOther_,
+      this.coordinatesOther.yValue(positionY));
+  } else if (this.graphsOtherStartIndex_) {
+    row.label.innerHTML = legendLabel(
+      this.stackedGraphOther_ ?
+          this.plotData_.length - 1 : this.graphsOtherStartIndex_);
+    row.content.innerHTML = valuesAtCursor(
+      this.stackedGraphOther_ ?
+          this.plotData_.length - 1 : this.graphsOtherStartIndex_,
+      indexValueX, this.unitsY_, this.coordinates.yValue(positionY));
+  } else if (!this.stackedGraph_ && this.dataDescriptions_.length > 1) {
+    row.label.innerHTML = legendLabel(1);
+    row.content.innerHTML = valuesAtCursor(
+      1, indexValueX, this.unitsY_, this.coordinates.yValue(positionY));
+  } else if (row) {
+    row.label.innerHTML = '';
+    row.content.innerHTML = '';
+  }
+
+  // If there is a horizontal marker, also display deltas relative to it.
+  if (this.horizontal_marker_) {
+    var baseline = this.horizontal_marker_.value;
+    var delta = this.coordinates.yValue(positionY) - baseline;
+    var fraction = delta / baseline;  // Allow division by 0.
+
+    var deltaStr = (delta >= 0 ? '+' : '') + delta.toFixed(0) + ' ' +
+        this.unitsY_;
+    var percentStr = (fraction >= 0 ? '+' : '') + (fraction * 100).toFixed(3) +
+        '%';
+
+    this.baselineDeltasTd_.innerHTML = deltaStr + ': ' + percentStr;
+
+    if (this.unitsYOther_) {
+      var baseline = this.horizontal_marker_.otherValue;
+      var yValue2 = this.coordinatesOther.yValue(positionY);
+      var delta = yValue2 - baseline;
+      var fraction = delta / baseline;  // Allow division by 0.
+
+      var deltaStr = (delta >= 0 ? '+' : '') + delta.toFixed(0) + ' ' +
+          this.unitsYOther_;
+      var percentStr = (fraction >= 0 ? '+' : '') +
+          (fraction * 100).toFixed(3) + '%';
+      this.baselineDeltasTd_.innerHTML += '<br>' + deltaStr + ': ' + percentStr;
+    }
+  }
+
+  this.updateRuler_(evt);
+  this.updateCursor_(this.coordinates, indexValueX, this.cursorDiv_, 0);
+  if (this.unitsYOther_ && this.graphsOtherStartIndex_) {
+    this.updateCursor_(this.coordinatesOther, indexValueXOther,
+                       this.cursorDivOther_, this.graphsOtherStartIndex_);
+  }
+
+  // If there are events displayed, see if we're hovering close to an existing
+  // event on the graph, and if so, display the metadata associated with it.
+  if (this.eventName_ != null && this.eventInfo_ != null) {
+    this.infoBox_.rows[1].label.innerHTML = 'Event "' + this.eventName_ +
+        '":&nbsp;&nbsp;';
+    var data = this.eventInfo_;
+    var showed_event = false;
+    var x = 0;
+    for (var index = 0; index < data.length; ++index) {
+      var event_time = data[index][0];
+      x = this.coordinates.xPixel(event_time);
+      if (positionX >= x - 10 && positionX <= x + 10) {
+        var metadata = data[index][1];
+        var metadata_str = "";
+        for (var meta_key in metadata)
+          metadata_str += meta_key + ': ' + metadata[meta_key] + ', ';
+        metadata_str = metadata_str.substring(0, metadata_str.length - 2);
+        this.infoBox_.rows[1].content.innerHTML = event_time + ' ' +
+            this.unitsX_ + ': {' + metadata_str + '}';
+        showed_event = true;
+        this.updateEventDiv_(x, true);
+        break;
+      }
+    }
+    if (!showed_event) {
+      this.coordinatesTdOther_.innerHTML =
+          'move mouse close to vertical event marker';
+      this.updateEventDiv_(x, false);
+    }
+  }
+
+  this.updateHoveringInfo_(evt, true);
+};
+
+/**
+ * Handle a mouse over event.
+ *
+ * @param {Object} evt A mouse event object representing a mouse move event.
+ */
+Plotter.prototype.onMouseOver_ = function(evt) {
+  this.updateHoveringInfo_(evt, true);
+};
+
+/**
+ * Handle a mouse out event.
+ *
+ * @param {Object} evt A mouse event object representing a mouse move event.
+ */
+Plotter.prototype.onMouseOut_ = function(evt) {
+  this.updateHoveringInfo_(evt, false);
+};
+
+/**
+ * Handle a mouse click event.
+ *
+ * @param {Object} evt A mouse event object representing a mouse click event.
+ */
+Plotter.prototype.onMouseClick_ = function(evt) {
+  // Shift-click controls the horizontal reference line.
+  if (evt.shiftKey) {
+    if (this.horizontal_marker_)
+      this.horizontal_marker_.remove();
+
+    var canvasY = domUtils.pageXYOfEvent(evt).y -
+                  domUtils.pageXY(this.canvasElement_).y;
+    this.horizontal_marker_ = new HorizontalMarker(
+        this.canvasElement_,
+        this.coordinates.yValue(canvasY),
+        (this.coordinatesOther ? this.coordinatesOther.yValue(canvasY) : null));
+    // Insert before cursor node, otherwise it catches clicks.
+    this.cursorDiv_.parentNode.insertBefore(
+        this.horizontal_marker_.markerDiv, this.cursorDiv_);
+    this.horizontal_marker_.locateAt(this.canvasElement_, canvasY);
+  }
+};
+
+/**
+ * Generates and returns a list of div objects representing horizontal lines in
+ * the graph that indicate y-axis values at a computed interval.
+ *
+ * @param {Object} coordinateSystem a Coordinates object representing the
+ *     coordinate system for which the graduations should be created.
+ * @param {number} colorIndex An index into the |this.colors| array representing
+ *     the color to make the graduations in the event that two graphs with
+ *     different coordinate systems are being overlayed on the same plot.
+ * @param {boolean} isRightSide Whether or not the graduations should have
+ *     right-aligned text (used when the graduations are for a second graph
+ *     that is being overlayed on top of another graph).
+ * @return {Array} An array of DOM Element objects representing the divs.
+ */
+Plotter.prototype.graduations_ = function(coordinateSystem, colorIndex,
+                                          isRightSide) {
+  // Don't allow a graduation in the bottom 5% of the chart or the number label
+  // would overflow the chart bounds.
+  var yMin = coordinateSystem.yLowerLimitValue() +
+      .05 * coordinateSystem.yValueRange();
+  var yRange = coordinateSystem.yUpperLimitValue() - yMin;
+
+  // Use the largest scale that fits 3 or more graduations.
+  // We allow scales of [...,500, 250, 100, 50, 25, 10,...].
+  var scale = 5000000000;
+  while (scale) {
+    if (Math.floor(yRange / scale) > 2) break;  // 5s.
+    scale /= 2;
+    if (Math.floor(yRange / scale) > 2) break;  // 2.5s.
+    scale /= 2.5;
+    if (Math.floor(yRange / scale) > 2) break;  // 1s.
+    scale /= 2;
+  }
+
+  var graduationPosition = yMin + (scale - yMin % scale);
+  var graduationDivs = [];
+  while (graduationPosition < coordinateSystem.yUpperLimitValue() ||
+         yRange == 0) {
+    var graduation = document.createElement('div');
+    var canvasPosition;
+    if (yRange == 0) {
+      // Center the graduation vertically.
+      canvasPosition = this.canvasElement_.offsetHeight / 2;
+    } else {
+      canvasPosition = coordinateSystem.yPixel(graduationPosition);
+    }
+    if (this.unitsYOther_) {
+      graduation.style.borderTop = '1px dashed ' +
+          this.makeColorTransparent(colorIndex, 0.4)
+    } else {
+      graduation.style.borderTop = '1px dashed rgba(0,0,0,.08)';
+    }
+    graduation.style.position = 'absolute';
+    graduation.style.left = this.canvasElement_.offsetLeft + 'px';
+    graduation.style.top = canvasPosition + this.canvasElement_.offsetTop +
+        'px';
+    graduation.style.width = this.canvasElement_.offsetWidth -
+        this.canvasElement_.offsetLeft + 'px';
+    graduation.style.paddingLeft = '4px';
+    if (this.unitsYOther_)
+      graduation.style.color = this.makeColorTransparent(colorIndex, 0.9)
+    else
+      graduation.style.color = 'rgba(0,0,0,.4)';
+    graduation.style.fontSize = '9px';
+    graduation.style.paddingTop = '0';
+    graduation.style.zIndex = '-1';
+    if (isRightSide)
+      graduation.style.textAlign = 'right';
+    if (yRange == 0)
+      graduation.innerHTML = addCommas(yMin);
+    else
+      graduation.innerHTML = addCommas(graduationPosition);
+    graduationDivs.push(graduation);
+    if (yRange == 0)
+      break;
+    graduationPosition += scale;
+  }
+  return graduationDivs;
+};
+
+/**
+ * Generates and returns a div object representing the horizontal line that
+ * follows the mouse pointer around the plot.
+ *
+ * @return {Object} A DOM Element object representing the div.
+ */
+Plotter.prototype.ruler_ = function() {
+  var ruler = document.createElement('div');
+  ruler.setAttribute('class', 'plot-ruler');
+  ruler.style.borderBottom = '1px dotted black';
+  ruler.style.position = 'absolute';
+  ruler.style.left = '-2px';
+  ruler.style.top = '-2px';
+  ruler.style.width = '0px';
+  ruler.style.height = '0px';
+  return ruler;
+};
+
+/**
+ * Generates and returns a canvas object representing the plot itself.
+ *
+ * @return {Object} A DOM Element object representing the canvas.
+ */
+Plotter.prototype.canvas_ = function() {
+  var canvas = document.createElement('canvas');
+  canvas.setAttribute('id', '_canvas');
+  canvas.setAttribute('class', 'plot');
+  canvas.setAttribute('width', this.coordinates.widthMax);
+  canvas.setAttribute('height', this.coordinates.heightMax);
+  canvas.plotter = this;
+  return canvas;
+};
+
+/**
+ * Generates and returns a div object representing the coordinate information
+ * displayed directly underneath a graph.
+ *
+ * @return {Object} A DOM Element object representing the div.
+ */
+Plotter.prototype.coordinates_ = function() {
+  var coordinatesDiv = document.createElement('div');
+  var table_html = '<table border=0 width="100%"';
+  if (this.is_lookout_) {
+    table_html += ' style="font-size:0.8em"';
+  }
+  table_html += '><tbody><tr>';
+  table_html += '<td><span class="legend_item"></span>' +
+      '<span class="plot-coordinates"><i>move mouse over graph</i></span></td>';
+  table_html += '<td align="right">x-axis is ' + this.unitsX_ + '</td>';
+  table_html += '</tr><tr>';
+  table_html += '<td><span class="legend_item"></span>' +
+      '<span class="plot-coordinates"></span></td>';
+
+  if (!this.is_lookout_) {
+    table_html += '<td align="right" style="color: ' + HorizontalMarker.COLOR +
+        '"><i>Shift-click to place baseline.</i></td>';
+  }
+  table_html += '</tr></tbody></table>';
+  coordinatesDiv.innerHTML = table_html;
+
+  var trs = coordinatesDiv.querySelectorAll('tr');
+  this.infoBox_ = {rows: []};
+  this.infoBox_.rows.push({
+    label: trs[0].querySelector('span.legend_item'),
+    content: trs[0].querySelector('span.plot-coordinates')});
+  if (this.dataDescriptions_.length > 1 || this.eventName_) {
+    this.infoBox_.rows.push({
+      label: trs[1].querySelector('span.legend_item'),
+      content: trs[1].querySelector('span.plot-coordinates')});
+  }
+
+  this.baselineDeltasTd_ = trs[1].childNodes[1];
+
+  // Add a summary of legends in case of stacked graphs.
+  if (this.stackedGraph_ || this.stackedGraphOther_) {
+    var legendPane = document.createElement('div');
+    legendPane.style.fontSize = '80%';
+    coordinatesDiv.appendChild(legendPane);
+
+    if (this.graphsOtherStartIndex_) {
+      legendPane.appendChild(
+        this.createLegendsSummaryElement_(
+          this.dataDescriptions_.slice(0, this.graphsOtherStartIndex_),
+          0));
+      legendPane.appendChild(
+        this.createLegendsSummaryElement_(
+          this.dataDescriptions_.slice(this.graphsOtherStartIndex_),
+          this.graphsOtherStartIndex_));
+    } else {
+      legendPane.appendChild(
+        this.createLegendsSummaryElement_(this.dataDescriptions_, 0));
+    }
+  }
+
+  return coordinatesDiv;
+};
+
+/**
+ * Creates and returns a DOM element which shows a summary of legends.
+ *
+ * @param {!Array.<string>} legendTexts An array of legend texts.
+ * @param {number} colorIndexOffset Offset index for color.  i-th legend text
+ *     has an indicator in {@code (colorIndexOffset + i)}-th color
+ * @return {!Element} An element which shows a summary of legends.
+ */
+Plotter.prototype.createLegendsSummaryElement_ = function(legendTexts,
+                                                          colorIndexOffset) {
+  var containerElem = document.createElement('div');
+
+  for (var i = 0, text; text = legendTexts[i]; ++i) {
+    var colorIndicatorElem = document.createElement('div');
+    colorIndicatorElem.style.display = 'inline-block';
+    colorIndicatorElem.style.width = '1em';
+    colorIndicatorElem.style.height = '1em';
+    colorIndicatorElem.style.verticalAlign = 'text-bottom';
+    colorIndicatorElem.style.margin = '0 0.24em 0 0';
+    colorIndicatorElem.style.border = '1px solid #000';
+    colorIndicatorElem.style.backgroundColor =
+        this.getDataColor(colorIndexOffset + i);
+    var legendTextElem = document.createElement('span');
+    legendTextElem.textContent = text;
+    var legendElem = document.createElement('span');
+    legendElem.style.whiteSpace = 'nowrap';
+    legendElem.appendChild(colorIndicatorElem);
+    legendElem.appendChild(legendTextElem);
+    legendElem.style.margin = '0 0.8em 0 0';
+    containerElem.appendChild(legendElem);
+    // Add a space to break lines if necessary.
+    containerElem.appendChild(document.createTextNode(' '));
+  }
+
+  return containerElem;
+};