dygraph-canvas.js

   1 /**
   2  * @license
   3  * Copyright 2006 Dan Vanderkam (danvdk@gmail.com)
   4  * MIT-licensed (http://opensource.org/licenses/MIT)
   5  */
   6
   7 /**
   8  * @fileoverview Based on PlotKit.CanvasRenderer, but modified to meet the
   9  * needs of dygraphs.
  10  *
  11  * In particular, support for:
  12  * - grid overlays
  13  * - error bars
  14  * - dygraphs attribute system
  15  */
  16
  17 /**
  18  * The DygraphCanvasRenderer class does the actual rendering of the chart onto
  19  * a canvas. It's based on PlotKit.CanvasRenderer.
  20  * @param {Object} element The canvas to attach to
  21  * @param {Object} elementContext The 2d context of the canvas (injected so it
  22  * can be mocked for testing.)
  23  * @param {Layout} layout The DygraphLayout object for this graph.
  24  * @constructor
  25  */
  26
  27 "use strict";
  28
  29 var DygraphCanvasRenderer = function(dygraph, element, elementContext, layout) {
  30   this.dygraph_ = dygraph;
  31
  32   this.layout = layout;
  33   this.element = element;
  34   this.elementContext = elementContext;
  35   this.container = this.element.parentNode;
  36
  37   this.height = this.element.height;
  38   this.width = this.element.width;
  39
  40   // --- check whether everything is ok before we return
  41   if (!this.isIE && !(DygraphCanvasRenderer.isSupported(this.element)))
  42       throw "Canvas is not supported.";
  43
  44   // internal state
  45   this.xlabels = new Array();
  46   this.ylabels = new Array();
  47   this.annotations = new Array();
  48   this.chartLabels = {};
  49
  50   this.area = layout.getPlotArea();
  51   this.container.style.position = "relative";
  52   this.container.style.width = this.width + "px";
  53
  54   // Set up a clipping area for the canvas (and the interaction canvas).
  55   // This ensures that we don't overdraw.
  56   if (this.dygraph_.isUsingExcanvas_) {
  57     this._createIEClipArea();
  58   } else {
  59     var ctx = this.dygraph_.canvas_ctx_;
  60     ctx.beginPath();
  61     ctx.rect(this.area.x, this.area.y, this.area.w, this.area.h);
  62     ctx.clip();
  63
  64     ctx = this.dygraph_.hidden_ctx_;
  65     ctx.beginPath();
  66     ctx.rect(this.area.x, this.area.y, this.area.w, this.area.h);
  67     ctx.clip();
  68   }
  69 };
  70
  71 DygraphCanvasRenderer.prototype.attr_ = function(x) {
  72   return this.dygraph_.attr_(x);
  73 };
  74
  75 DygraphCanvasRenderer.prototype.clear = function() {
  76   if (this.isIE) {
  77     // VML takes a while to start up, so we just poll every this.IEDelay
  78     try {
  79       if (this.clearDelay) {
  80         this.clearDelay.cancel();
  81         this.clearDelay = null;
  82       }
  83       var context = this.elementContext;
  84     }
  85     catch (e) {
  86       // TODO(danvk): this is broken, since MochiKit.Async is gone.
  87       this.clearDelay = MochiKit.Async.wait(this.IEDelay);
  88       this.clearDelay.addCallback(bind(this.clear, this));
  89       return;
  90     }
  91   }
  92
  93   var context = this.elementContext;
  94   context.clearRect(0, 0, this.width, this.height);
  95
  96   for (var i = 0; i < this.xlabels.length; i++) {
  97     var el = this.xlabels[i];
  98     if (el.parentNode) el.parentNode.removeChild(el);
  99   }
 100   for (var i = 0; i < this.ylabels.length; i++) {
 101     var el = this.ylabels[i];
 102     if (el.parentNode) el.parentNode.removeChild(el);
 103   }
 104   for (var i = 0; i < this.annotations.length; i++) {
 105     var el = this.annotations[i];
 106     if (el.parentNode) el.parentNode.removeChild(el);
 107   }
 108   for (var k in this.chartLabels) {
 109     if (!this.chartLabels.hasOwnProperty(k)) continue;
 110     var el = this.chartLabels[k];
 111     if (el.parentNode) el.parentNode.removeChild(el);
 112   }
 113   this.xlabels = new Array();
 114   this.ylabels = new Array();
 115   this.annotations = new Array();
 116   this.chartLabels = {};
 117 };
 118
 119
 120 DygraphCanvasRenderer.isSupported = function(canvasName) {
 121   var canvas = null;
 122   try {
 123     if (typeof(canvasName) == 'undefined' || canvasName == null)
 124       canvas = document.createElement("canvas");
 125     else
 126       canvas = canvasName;
 127     var context = canvas.getContext("2d");
 128   }
 129   catch (e) {
 130     var ie = navigator.appVersion.match(/MSIE (\d\.\d)/);
 131     var opera = (navigator.userAgent.toLowerCase().indexOf("opera") != -1);
 132     if ((!ie) || (ie[1] < 6) || (opera))
 133       return false;
 134     return true;
 135   }
 136   return true;
 137 };
 138
 139 /**
 140  * @param { [String] } colors Array of color strings. Should have one entry for
 141  * each series to be rendered.
 142  */
 143 DygraphCanvasRenderer.prototype.setColors = function(colors) {
 144   this.colorScheme_ = colors;
 145 };
 146
 147 /**
 148  * Draw an X/Y grid on top of the existing plot
 149  */
 150 DygraphCanvasRenderer.prototype.render = function() {
 151   // Draw the new X/Y grid. Lines appear crisper when pixels are rounded to
 152   // half-integers. This prevents them from drawing in two rows/cols.
 153   var ctx = this.elementContext;
 154   function halfUp(x){return Math.round(x)+0.5};
 155   function halfDown(y){return Math.round(y)-0.5};
 156
 157   if (this.attr_('underlayCallback')) {
 158     // NOTE: we pass the dygraph object to this callback twice to avoid breaking
 159     // users who expect a deprecated form of this callback.
 160     this.attr_('underlayCallback')(ctx, this.area, this.dygraph_, this.dygraph_);
 161   }
 162
 163   if (this.attr_('drawYGrid')) {
 164     var ticks = this.layout.yticks;
 165     // TODO(konigsberg): I don't think these calls to save() have a corresponding restore().
 166     ctx.save();
 167     ctx.strokeStyle = this.attr_('gridLineColor');
 168     ctx.lineWidth = this.attr_('gridLineWidth');
 169     for (var i = 0; i < ticks.length; i++) {
 170       // TODO(danvk): allow secondary axes to draw a grid, too.
 171       if (ticks[i][0] != 0) continue;
 172       var x = halfUp(this.area.x);
 173       var y = halfDown(this.area.y + ticks[i][1] * this.area.h);
 174       ctx.beginPath();
 175       ctx.moveTo(x, y);
 176       ctx.lineTo(x + this.area.w, y);
 177       ctx.closePath();
 178       ctx.stroke();
 179     }
 180   }
 181
 182   if (this.attr_('drawXGrid')) {
 183     var ticks = this.layout.xticks;
 184     ctx.save();
 185     ctx.strokeStyle = this.attr_('gridLineColor');
 186     ctx.lineWidth = this.attr_('gridLineWidth');
 187     for (var i=0; i<ticks.length; i++) {
 188       var x = halfUp(this.area.x + ticks[i][0] * this.area.w);
 189       var y = halfDown(this.area.y + this.area.h);
 190       ctx.beginPath();
 191       ctx.moveTo(x, y);
 192       ctx.lineTo(x, this.area.y);
 193       ctx.closePath();
 194       ctx.stroke();
 195     }
 196   }
 197
 198   // Do the ordinary rendering, as before
 199   this._renderLineChart();
 200   this._renderAxis();
 201   this._renderChartLabels();
 202   this._renderAnnotations();
 203 };
 204
 205 DygraphCanvasRenderer.prototype._createIEClipArea = function() {
 206   var className = 'dygraph-clip-div';
 207   var graphDiv = this.dygraph_.graphDiv;
 208
 209   // Remove old clip divs.
 210   for (var i = graphDiv.childNodes.length-1; i >= 0; i--) {
 211     if (graphDiv.childNodes[i].className == className) {
 212       graphDiv.removeChild(graphDiv.childNodes[i]);
 213     }
 214   }
 215
 216   // Determine background color to give clip divs.
 217   var backgroundColor = document.bgColor;
 218   var element = this.dygraph_.graphDiv;
 219   while (element != document) {
 220     var bgcolor = element.currentStyle.backgroundColor;
 221     if (bgcolor && bgcolor != 'transparent') {
 222       backgroundColor = bgcolor;
 223       break;
 224     }
 225     element = element.parentNode;
 226   }
 227
 228   function createClipDiv(area) {
 229     if (area.w == 0 || area.h == 0) {
 230       return;
 231     }
 232     var elem = document.createElement('div');
 233     elem.className = className;
 234     elem.style.backgroundColor = backgroundColor;
 235     elem.style.position = 'absolute';
 236     elem.style.left = area.x + 'px';
 237     elem.style.top = area.y + 'px';
 238     elem.style.width = area.w + 'px';
 239     elem.style.height = area.h + 'px';
 240     graphDiv.appendChild(elem);
 241   }
 242
 243   var plotArea = this.area;
 244   // Left side
 245   createClipDiv({x:0, y:0, w:plotArea.x, h:this.height});
 246   // Top
 247   createClipDiv({x:plotArea.x, y:0, w:this.width-plotArea.x, h:plotArea.y});
 248   // Right side
 249   createClipDiv({x:plotArea.x+plotArea.w, y:0, w:this.width-plotArea.x-plotArea.w, h:this.height});
 250   // Bottom
 251   createClipDiv({x:plotArea.x, y:plotArea.y+plotArea.h, w:this.width-plotArea.x, h:this.height-plotArea.h-plotArea.y});
 252 }
 253
 254 DygraphCanvasRenderer.prototype._renderAxis = function() {
 255   if (!this.attr_('drawXAxis') && !this.attr_('drawYAxis')) return;
 256
 257   // Round pixels to half-integer boundaries for crisper drawing.
 258   function halfUp(x){return Math.round(x)+0.5};
 259   function halfDown(y){return Math.round(y)-0.5};
 260
 261   var context = this.elementContext;
 262
 263   var labelStyle = {
 264     position: "absolute",
 265     fontSize: this.attr_('axisLabelFontSize') + "px",
 266     zIndex: 10,
 267     color: this.attr_('axisLabelColor'),
 268     width: this.attr_('axisLabelWidth') + "px",
 269     // height: this.attr_('axisLabelFontSize') + 2 + "px",
 270     lineHeight: "normal", // Something other than "normal" line-height screws up label positioning.
 271     overflow: "hidden"
 272   };
 273   var makeDiv = function(txt, axis, prec_axis) {
 274     var div = document.createElement("div");
 275     for (var name in labelStyle) {
 276       if (labelStyle.hasOwnProperty(name)) {
 277         div.style[name] = labelStyle[name];
 278       }
 279     }
 280     var inner_div = document.createElement("div");
 281     inner_div.className = 'dygraph-axis-label' +
 282                           ' dygraph-axis-label-' + axis +
 283                           (prec_axis ? ' dygraph-axis-label-' + prec_axis : '');
 284     inner_div.appendChild(document.createTextNode(txt));
 285     div.appendChild(inner_div);
 286     return div;
 287   };
 288
 289   // axis lines
 290   context.save();
 291   context.strokeStyle = this.attr_('axisLineColor');
 292   context.lineWidth = this.attr_('axisLineWidth');
 293
 294   if (this.attr_('drawYAxis')) {
 295     if (this.layout.yticks && this.layout.yticks.length > 0) {
 296       var num_axes = this.dygraph_.numAxes();
 297       for (var i = 0; i < this.layout.yticks.length; i++) {
 298         var tick = this.layout.yticks[i];
 299         if (typeof(tick) == "function") return;
 300         var x = this.area.x;
 301         var sgn = 1;
 302         var prec_axis = 'y1';
 303         if (tick[0] == 1) {  // right-side y-axis
 304           x = this.area.x + this.area.w;
 305           sgn = -1;
 306           prec_axis = 'y2';
 307         }
 308         var y = this.area.y + tick[1] * this.area.h;
 309
 310         /* Tick marks are currently clipped, so don't bother drawing them.
 311         context.beginPath();
 312         context.moveTo(halfUp(x), halfDown(y));
 313         context.lineTo(halfUp(x - sgn * this.attr_('axisTickSize')), halfDown(y));
 314         context.closePath();
 315         context.stroke();
 316         */
 317
 318         var label = makeDiv(tick[2], 'y', num_axes == 2 ? prec_axis : null);
 319         var top = (y - this.attr_('axisLabelFontSize') / 2);
 320         if (top < 0) top = 0;
 321
 322         if (top + this.attr_('axisLabelFontSize') + 3 > this.height) {
 323           label.style.bottom = "0px";
 324         } else {
 325           label.style.top = top + "px";
 326         }
 327         if (tick[0] == 0) {
 328           label.style.left = (this.area.x - this.attr_('yAxisLabelWidth') - this.attr_('axisTickSize')) + "px";
 329           label.style.textAlign = "right";
 330         } else if (tick[0] == 1) {
 331           label.style.left = (this.area.x + this.area.w +
 332                               this.attr_('axisTickSize')) + "px";
 333           label.style.textAlign = "left";
 334         }
 335         label.style.width = this.attr_('yAxisLabelWidth') + "px";
 336         this.container.appendChild(label);
 337         this.ylabels.push(label);
 338       }
 339
 340       // The lowest tick on the y-axis often overlaps with the leftmost
 341       // tick on the x-axis. Shift the bottom tick up a little bit to
 342       // compensate if necessary.
 343       var bottomTick = this.ylabels[0];
 344       var fontSize = this.attr_('axisLabelFontSize');
 345       var bottom = parseInt(bottomTick.style.top) + fontSize;
 346       if (bottom > this.height - fontSize) {
 347         bottomTick.style.top = (parseInt(bottomTick.style.top) -
 348             fontSize / 2) + "px";
 349       }
 350     }
 351
 352     // draw a vertical line on the left to separate the chart from the labels.
 353     context.beginPath();
 354     context.moveTo(halfUp(this.area.x), halfDown(this.area.y));
 355     context.lineTo(halfUp(this.area.x), halfDown(this.area.y + this.area.h));
 356     context.closePath();
 357     context.stroke();
 358
 359     // if there's a secondary y-axis, draw a vertical line for that, too.
 360     if (this.dygraph_.numAxes() == 2) {
 361       context.beginPath();
 362       context.moveTo(halfDown(this.area.x + this.area.w), halfDown(this.area.y));
 363       context.lineTo(halfDown(this.area.x + this.area.w), halfDown(this.area.y + this.area.h));
 364       context.closePath();
 365       context.stroke();
 366     }
 367   }
 368
 369   if (this.attr_('drawXAxis')) {
 370     if (this.layout.xticks) {
 371       for (var i = 0; i < this.layout.xticks.length; i++) {
 372         var tick = this.layout.xticks[i];
 373         if (typeof(dataset) == "function") return;
 374
 375         var x = this.area.x + tick[0] * this.area.w;
 376         var y = this.area.y + this.area.h;
 377
 378         /* Tick marks are currently clipped, so don't bother drawing them.
 379         context.beginPath();
 380         context.moveTo(halfUp(x), halfDown(y));
 381         context.lineTo(halfUp(x), halfDown(y + this.attr_('axisTickSize')));
 382         context.closePath();
 383         context.stroke();
 384         */
 385
 386         var label = makeDiv(tick[1], 'x');
 387         label.style.textAlign = "center";
 388         label.style.top = (y + this.attr_('axisTickSize')) + 'px';
 389
 390         var left = (x - this.attr_('axisLabelWidth')/2);
 391         if (left + this.attr_('axisLabelWidth') > this.width) {
 392           left = this.width - this.attr_('xAxisLabelWidth');
 393           label.style.textAlign = "right";
 394         }
 395         if (left < 0) {
 396           left = 0;
 397           label.style.textAlign = "left";
 398         }
 399
 400         label.style.left = left + "px";
 401         label.style.width = this.attr_('xAxisLabelWidth') + "px";
 402         this.container.appendChild(label);
 403         this.xlabels.push(label);
 404       }
 405     }
 406
 407     context.beginPath();
 408     context.moveTo(halfUp(this.area.x), halfDown(this.area.y + this.area.h));
 409     context.lineTo(halfUp(this.area.x + this.area.w), halfDown(this.area.y + this.area.h));
 410     context.closePath();
 411     context.stroke();
 412   }
 413
 414   context.restore();
 415 };
 416
 417
 418 DygraphCanvasRenderer.prototype._renderChartLabels = function() {
 419   // Generate divs for the chart title, xlabel and ylabel.
 420   // Space for these divs has already been taken away from the charting area in
 421   // the DygraphCanvasRenderer constructor.
 422   if (this.attr_('title')) {
 423     var div = document.createElement("div");
 424     div.style.position = 'absolute';
 425     div.style.top = '0px';
 426     div.style.left = this.area.x + 'px';
 427     div.style.width = this.area.w + 'px';
 428     div.style.height = this.attr_('titleHeight') + 'px';
 429     div.style.textAlign = 'center';
 430     div.style.fontSize = (this.attr_('titleHeight') - 8) + 'px';
 431     div.style.fontWeight = 'bold';
 432     var class_div = document.createElement("div");
 433     class_div.className = 'dygraph-label dygraph-title';
 434     class_div.innerHTML = this.attr_('title');
 435     div.appendChild(class_div);
 436     this.container.appendChild(div);
 437     this.chartLabels.title = div;
 438   }
 439
 440   if (this.attr_('xlabel')) {
 441     var div = document.createElement("div");
 442     div.style.position = 'absolute';
 443     div.style.bottom = 0;  // TODO(danvk): this is lazy. Calculate style.top.
 444     div.style.left = this.area.x + 'px';
 445     div.style.width = this.area.w + 'px';
 446     div.style.height = this.attr_('xLabelHeight') + 'px';
 447     div.style.textAlign = 'center';
 448     div.style.fontSize = (this.attr_('xLabelHeight') - 2) + 'px';
 449
 450     var class_div = document.createElement("div");
 451     class_div.className = 'dygraph-label dygraph-xlabel';
 452     class_div.innerHTML = this.attr_('xlabel');
 453     div.appendChild(class_div);
 454     this.container.appendChild(div);
 455     this.chartLabels.xlabel = div;
 456   }
 457
 458   if (this.attr_('ylabel')) {
 459     var box = {
 460       left: 0,
 461       top: this.area.y,
 462       width: this.attr_('yLabelWidth'),
 463       height: this.area.h
 464     };
 465     // TODO(danvk): is this outer div actually necessary?
 466     var div = document.createElement("div");
 467     div.style.position = 'absolute';
 468     div.style.left = box.left;
 469     div.style.top = box.top + 'px';
 470     div.style.width = box.width + 'px';
 471     div.style.height = box.height + 'px';
 472     div.style.fontSize = (this.attr_('yLabelWidth') - 2) + 'px';
 473
 474     var inner_div = document.createElement("div");
 475     inner_div.style.position = 'absolute';
 476     inner_div.style.width = box.height + 'px';
 477     inner_div.style.height = box.width + 'px';
 478     inner_div.style.top = (box.height / 2 - box.width / 2) + 'px';
 479     inner_div.style.left = (box.width / 2 - box.height / 2) + 'px';
 480     inner_div.style.textAlign = 'center';
 481
 482     // CSS rotation is an HTML5 feature which is not standardized. Hence every
 483     // browser has its own name for the CSS style.
 484     inner_div.style.transform = 'rotate(-90deg)';        // HTML5
 485     inner_div.style.WebkitTransform = 'rotate(-90deg)';  // Safari/Chrome
 486     inner_div.style.MozTransform = 'rotate(-90deg)';     // Firefox
 487     inner_div.style.OTransform = 'rotate(-90deg)';       // Opera
 488     inner_div.style.msTransform = 'rotate(-90deg)';      // IE9
 489
 490     if (typeof(document.documentMode) !== 'undefined' &&
 491         document.documentMode < 9) {
 492       // We're dealing w/ an old version of IE, so we have to rotate the text
 493       // using a BasicImage transform. This uses a different origin of rotation
 494       // than HTML5 rotation (top left of div vs. its center).
 495       inner_div.style.filter =
 496        'progid:DXImageTransform.Microsoft.BasicImage(rotation=3)';
 497       inner_div.style.left = '0px';
 498       inner_div.style.top = '0px';
 499     }
 500
 501     var class_div = document.createElement("div");
 502     class_div.className = 'dygraph-label dygraph-ylabel';
 503     class_div.innerHTML = this.attr_('ylabel');
 504
 505     inner_div.appendChild(class_div);
 506     div.appendChild(inner_div);
 507     this.container.appendChild(div);
 508     this.chartLabels.ylabel = div;
 509   }
 510 };
 511
 512
 513 DygraphCanvasRenderer.prototype._renderAnnotations = function() {
 514   var annotationStyle = {
 515     "position": "absolute",
 516     "fontSize": this.attr_('axisLabelFontSize') + "px",
 517     "zIndex": 10,
 518     "overflow": "hidden"
 519   };
 520
 521   var bindEvt = function(eventName, classEventName, p, self) {
 522     return function(e) {
 523       var a = p.annotation;
 524       if (a.hasOwnProperty(eventName)) {
 525         a[eventName](a, p, self.dygraph_, e);
 526       } else if (self.dygraph_.attr_(classEventName)) {
 527         self.dygraph_.attr_(classEventName)(a, p, self.dygraph_,e );
 528       }
 529     };
 530   }
 531
 532   // Get a list of point with annotations.
 533   var points = this.layout.annotated_points;
 534   for (var i = 0; i < points.length; i++) {
 535     var p = points[i];
 536     if (p.canvasx < this.area.x || p.canvasx > this.area.x + this.area.w) {
 537       continue;
 538     }
 539
 540     var a = p.annotation;
 541     var tick_height = 6;
 542     if (a.hasOwnProperty("tickHeight")) {
 543       tick_height = a.tickHeight;
 544     }
 545
 546     var div = document.createElement("div");
 547     for (var name in annotationStyle) {
 548       if (annotationStyle.hasOwnProperty(name)) {
 549         div.style[name] = annotationStyle[name];
 550       }
 551     }
 552     if (!a.hasOwnProperty('icon')) {
 553       div.className = "dygraphDefaultAnnotation";
 554     }
 555     if (a.hasOwnProperty('cssClass')) {
 556       div.className += " " + a.cssClass;
 557     }
 558
 559     var width = a.hasOwnProperty('width') ? a.width : 16;
 560     var height = a.hasOwnProperty('height') ? a.height : 16;
 561     if (a.hasOwnProperty('icon')) {
 562       var img = document.createElement("img");
 563       img.src = a.icon;
 564       img.width = width;
 565       img.height = height;
 566       div.appendChild(img);
 567     } else if (p.annotation.hasOwnProperty('shortText')) {
 568       div.appendChild(document.createTextNode(p.annotation.shortText));
 569     }
 570     div.style.left = (p.canvasx - width / 2) + "px";
 571     if (a.attachAtBottom) {
 572       div.style.top = (this.area.h - height - tick_height) + "px";
 573     } else {
 574       div.style.top = (p.canvasy - height - tick_height) + "px";
 575     }
 576     div.style.width = width + "px";
 577     div.style.height = height + "px";
 578     div.title = p.annotation.text;
 579     div.style.color = this.colors[p.name];
 580     div.style.borderColor = this.colors[p.name];
 581     a.div = div;
 582
 583     Dygraph.addEvent(div, 'click',
 584         bindEvt('clickHandler', 'annotationClickHandler', p, this));
 585     Dygraph.addEvent(div, 'mouseover',
 586         bindEvt('mouseOverHandler', 'annotationMouseOverHandler', p, this));
 587     Dygraph.addEvent(div, 'mouseout',
 588         bindEvt('mouseOutHandler', 'annotationMouseOutHandler', p, this));
 589     Dygraph.addEvent(div, 'dblclick',
 590         bindEvt('dblClickHandler', 'annotationDblClickHandler', p, this));
 591
 592     this.container.appendChild(div);
 593     this.annotations.push(div);
 594
 595     var ctx = this.elementContext;
 596     ctx.strokeStyle = this.colors[p.name];
 597     ctx.beginPath();
 598     if (!a.attachAtBottom) {
 599       ctx.moveTo(p.canvasx, p.canvasy);
 600       ctx.lineTo(p.canvasx, p.canvasy - 2 - tick_height);
 601     } else {
 602       ctx.moveTo(p.canvasx, this.area.h);
 603       ctx.lineTo(p.canvasx, this.area.h - 2 - tick_height);
 604     }
 605     ctx.closePath();
 606     ctx.stroke();
 607   }
 608 };
 609
 610
 611 /**
 612  * Overrides the CanvasRenderer method to draw error bars
 613  */
 614 DygraphCanvasRenderer.prototype._renderLineChart = function() {
 615   var isNullOrNaN = function(x) {
 616     return (x === null || isNaN(x));
 617   };
 618
 619   // TODO(danvk): use this.attr_ for many of these.
 620   var context = this.elementContext;
 621   var fillAlpha = this.attr_('fillAlpha');
 622   var errorBars = this.attr_("errorBars") || this.attr_("customBars");
 623   var fillGraph = this.attr_("fillGraph");
 624   var stackedGraph = this.attr_("stackedGraph");
 625   var stepPlot = this.attr_("stepPlot");
 626   var points = this.layout.points;
 627   var pointsLength = points.length;
 628
 629   var setNames = [];
 630   for (var name in this.layout.datasets) {
 631     if (this.layout.datasets.hasOwnProperty(name)) {
 632       setNames.push(name);
 633     }
 634   }
 635   var setCount = setNames.length;
 636
 637   // TODO(danvk): Move this mapping into Dygraph and get it out of here.
 638   this.colors = {}
 639   for (var i = 0; i < setCount; i++) {
 640     this.colors[setNames[i]] = this.colorScheme_[i % this.colorScheme_.length];
 641   }
 642
 643   // Update Points
 644   // TODO(danvk): here
 645   for (var i = pointsLength; i--;) {
 646     var point = points[i];
 647     point.canvasx = this.area.w * point.x + this.area.x;
 648     point.canvasy = this.area.h * point.y + this.area.y;
 649   }
 650
 651   // create paths
 652   var ctx = context;
 653   if (errorBars) {
 654     if (fillGraph) {
 655       this.dygraph_.warn("Can't use fillGraph option with error bars");
 656     }
 657
 658     for (var i = 0; i < setCount; i++) {
 659       var setName = setNames[i];
 660       var axis = this.dygraph_.axisPropertiesForSeries(setName);
 661       var color = this.colors[setName];
 662
 663       // setup graphics context
 664       ctx.save();
 665       var prevX = NaN;
 666       var prevY = NaN;
 667       var prevYs = [-1, -1];
 668       var yscale = axis.yscale;
 669       // should be same color as the lines but only 15% opaque.
 670       var rgb = new RGBColor(color);
 671       var err_color = 'rgba(' + rgb.r + ',' + rgb.g + ',' + rgb.b + ',' +
 672                             fillAlpha + ')';
 673       ctx.fillStyle = err_color;
 674       ctx.beginPath();
 675       for (var j = 0; j < pointsLength; j++) {
 676         var point = points[j];
 677         if (point.name == setName) {
 678           if (!Dygraph.isOK(point.y)) {
 679             prevX = NaN;
 680             continue;
 681           }
 682
 683           // TODO(danvk): here
 684           if (stepPlot) {
 685             var newYs = [ point.y_bottom, point.y_top ];
 686             prevY = point.y;
 687           } else {
 688             var newYs = [ point.y_bottom, point.y_top ];
 689           }
 690           newYs[0] = this.area.h * newYs[0] + this.area.y;
 691           newYs[1] = this.area.h * newYs[1] + this.area.y;
 692           if (!isNaN(prevX)) {
 693             if (stepPlot) {
 694               ctx.moveTo(prevX, newYs[0]);
 695             } else {
 696               ctx.moveTo(prevX, prevYs[0]);
 697             }
 698             ctx.lineTo(point.canvasx, newYs[0]);
 699             ctx.lineTo(point.canvasx, newYs[1]);
 700             if (stepPlot) {
 701               ctx.lineTo(prevX, newYs[1]);
 702             } else {
 703               ctx.lineTo(prevX, prevYs[1]);
 704             }
 705             ctx.closePath();
 706           }
 707           prevYs = newYs;
 708           prevX = point.canvasx;
 709         }
 710       }
 711       ctx.fill();
 712     }
 713   } else if (fillGraph) {
 714     var baseline = []  // for stacked graphs: baseline for filling
 715
 716     // process sets in reverse order (needed for stacked graphs)
 717     for (var i = setCount - 1; i >= 0; i--) {
 718       var setName = setNames[i];
 719       var color = this.colors[setName];
 720       var axis = this.dygraph_.axisPropertiesForSeries(setName);
 721       var axisY = 1.0 + axis.minyval * axis.yscale;
 722       if (axisY < 0.0) axisY = 0.0;
 723       else if (axisY > 1.0) axisY = 1.0;
 724       axisY = this.area.h * axisY + this.area.y;
 725
 726       // setup graphics context
 727       ctx.save();
 728       var prevX = NaN;
 729       var prevYs = [-1, -1];
 730       var yscale = axis.yscale;
 731       // should be same color as the lines but only 15% opaque.
 732       var rgb = new RGBColor(color);
 733       var err_color = 'rgba(' + rgb.r + ',' + rgb.g + ',' + rgb.b + ',' +
 734                             fillAlpha + ')';
 735       ctx.fillStyle = err_color;
 736       ctx.beginPath();
 737       for (var j = 0; j < pointsLength; j++) {
 738         var point = points[j];
 739         if (point.name == setName) {
 740           if (!Dygraph.isOK(point.y)) {
 741             prevX = NaN;
 742             continue;
 743           }
 744           var newYs;
 745           if (stackedGraph) {
 746             lastY = baseline[point.canvasx];
 747             if (lastY === undefined) lastY = axisY;
 748             baseline[point.canvasx] = point.canvasy;
 749             newYs = [ point.canvasy, lastY ];
 750           } else {
 751             newYs = [ point.canvasy, axisY ];
 752           }
 753           if (!isNaN(prevX)) {
 754             ctx.moveTo(prevX, prevYs[0]);
 755             if (stepPlot) {
 756               ctx.lineTo(point.canvasx, prevYs[0]);
 757             } else {
 758               ctx.lineTo(point.canvasx, newYs[0]);
 759             }
 760             ctx.lineTo(point.canvasx, newYs[1]);
 761             ctx.lineTo(prevX, prevYs[1]);
 762             ctx.closePath();
 763           }
 764           prevYs = newYs;
 765           prevX = point.canvasx;
 766         }
 767       }
 768       ctx.fill();
 769     }
 770   }
 771
 772   // Drawing the lines.
 773   var firstIndexInSet = 0;
 774   var afterLastIndexInSet = 0;
 775   var setLength = 0;
 776   for (var i = 0; i < setCount; i += 1) {
 777     setLength = this.layout.setPointsLengths[i];
 778     afterLastIndexInSet += setLength;
 779     var setName = setNames[i];
 780     var color = this.colors[setName];
 781     var strokeWidth = this.dygraph_.attr_("strokeWidth", setName);
 782
 783     // setup graphics context
 784     context.save();
 785     var pointSize = this.dygraph_.attr_("pointSize", setName);
 786     var prevX = null, prevY = null;
 787     var drawPoints = this.dygraph_.attr_("drawPoints", setName);
 788     for (var j = firstIndexInSet; j < afterLastIndexInSet; j++) {
 789       var point = points[j];
 790       if (isNullOrNaN(point.canvasy)) {
 791         if (stepPlot && prevX != null) {
 792           // Draw a horizontal line to the start of the missing data
 793           ctx.beginPath();
 794           ctx.strokeStyle = color;
 795           ctx.lineWidth = this.attr_('strokeWidth');
 796           ctx.moveTo(prevX, prevY);
 797           ctx.lineTo(point.canvasx, prevY);
 798           ctx.stroke();
 799         }
 800         // this will make us move to the next point, not draw a line to it.
 801         prevX = prevY = null;
 802       } else {
 803         // A point is "isolated" if it is non-null but both the previous
 804         // and next points are null.
 805         var isIsolated = (!prevX && (j == points.length - 1 ||
 806                                      isNullOrNaN(points[j+1].canvasy)));
 807         if (prevX === null) {
 808           prevX = point.canvasx;
 809           prevY = point.canvasy;
 810         } else {
 811           // Skip over points that will be drawn in the same pixel.
 812           if (Math.round(prevX) == Math.round(point.canvasx) &&
 813               Math.round(prevY) == Math.round(point.canvasy)) {
 814             continue;
 815           }
 816           // TODO(antrob): skip over points that lie on a line that is already
 817           // going to be drawn. There is no need to have more than 2
 818           // consecutive points that are collinear.
 819           if (strokeWidth) {
 820             ctx.beginPath();
 821             ctx.strokeStyle = color;
 822             ctx.lineWidth = strokeWidth;
 823             ctx.moveTo(prevX, prevY);
 824             if (stepPlot) {
 825               ctx.lineTo(point.canvasx, prevY);
 826             }
 827             prevX = point.canvasx;
 828             prevY = point.canvasy;
 829             ctx.lineTo(prevX, prevY);
 830             ctx.stroke();
 831           }
 832         }
 833
 834         if (drawPoints || isIsolated) {
 835           ctx.beginPath();
 836           ctx.fillStyle = color;
 837           ctx.arc(point.canvasx, point.canvasy, pointSize,
 838                   0, 2 * Math.PI, false);
 839           ctx.fill();
 840         }
 841       }
 842     }
 843     firstIndexInSet = afterLastIndexInSet;
 844   }
 845
 846   context.restore();
 847 };