Expose function that can be replaced during tests for mocking out the HTML5 canvas...

diff --git a/dygraph-canvas.js b/dygraph-canvas.js
index 522629c..2874990 100644 (file)
--- a/dygraph-canvas.js
+++ b/dygraph-canvas.js
@@ -277,10 +277,13 @@ DygraphLayout.prototype.unstackPointAtIndex = function(idx) {
 /**
  * Sets some PlotKit.CanvasRenderer options
  * @param {Object} element The canvas to attach to
+ * @param {Object} elementContext The 2d context of the canvas (injected so it
+ * can be mocked for testing.)
  * @param {Layout} layout The DygraphLayout object for this graph.
  * @param {Object} options Options to pass on to CanvasRenderer
  */
-DygraphCanvasRenderer = function(dygraph, element, layout, options) {
+DygraphCanvasRenderer = function(dygraph, element, elementContext, layout,
+    options) {
   // TODO(danvk): remove options, just use dygraph.attr_.
   this.dygraph_ = dygraph;
 
@@ -306,6 +309,7 @@ DygraphCanvasRenderer = function(dygraph, element, layout, options) {
 
   this.layout = layout;
   this.element = element;
+  this.elementContext = elementContext;
   this.container = this.element.parentNode;
 
   this.height = this.element.height;
@@ -360,12 +364,12 @@ DygraphCanvasRenderer = function(dygraph, element, layout, options) {
 
   // Set up a clipping area for the canvas (and the interaction canvas).
   // This ensures that we don't overdraw.
-  var ctx = this.dygraph_.canvas_.getContext("2d");
+  var ctx = this.dygraph_.canvas_ctx_;
   ctx.beginPath();
   ctx.rect(this.area.x, this.area.y, this.area.w, this.area.h);
   ctx.clip();
 
-  ctx = this.dygraph_.hidden_.getContext("2d");
+  ctx = this.dygraph_.hidden_ctx_;
   ctx.beginPath();
   ctx.rect(this.area.x, this.area.y, this.area.w, this.area.h);
   ctx.clip();
@@ -383,7 +387,7 @@ DygraphCanvasRenderer.prototype.clear = function() {
         this.clearDelay.cancel();
         this.clearDelay = null;
       }
-      var context = this.element.getContext("2d");
+      var context = this.elementContext;
     }
     catch (e) {
       // TODO(danvk): this is broken, since MochiKit.Async is gone.
@@ -393,7 +397,7 @@ DygraphCanvasRenderer.prototype.clear = function() {
     }
   }
 
-  var context = this.element.getContext("2d");
+  var context = this.elementContext;
   context.clearRect(0, 0, this.width, this.height);
 
   for (var i = 0; i < this.xlabels.length; i++) {
@@ -445,7 +449,7 @@ DygraphCanvasRenderer.isSupported = function(canvasName) {
 DygraphCanvasRenderer.prototype.render = function() {
   // Draw the new X/Y grid. Lines appear crisper when pixels are rounded to
   // half-integers. This prevents them from drawing in two rows/cols.
-  var ctx = this.element.getContext("2d");
+  var ctx = this.elementContext;
   function halfUp(x){return Math.round(x)+0.5};
   function halfDown(y){return Math.round(y)-0.5};
 
@@ -505,7 +509,7 @@ DygraphCanvasRenderer.prototype._renderAxis = function() {
   function halfUp(x){return Math.round(x)+0.5};
   function halfDown(y){return Math.round(y)-0.5};
 
-  var context = this.element.getContext("2d");
+  var context = this.elementContext;
 
   var labelStyle = {
     "position": "absolute",
@@ -823,7 +827,7 @@ DygraphCanvasRenderer.prototype._renderAnnotations = function() {
     this.container.appendChild(div);
     this.annotations.push(div);
 
-    var ctx = this.element.getContext("2d");
+    var ctx = this.elementContext;
     ctx.strokeStyle = this.colors[p.name];
     ctx.beginPath();
     if (!a.attachAtBottom) {
@@ -844,7 +848,7 @@ DygraphCanvasRenderer.prototype._renderAnnotations = function() {
  */
 DygraphCanvasRenderer.prototype._renderLineChart = function() {
   // TODO(danvk): use this.attr_ for many of these.
-  var context = this.element.getContext("2d");
+  var context = this.elementContext;
   var colorCount = this.options.colorScheme.length;
   var colorScheme = this.options.colorScheme;
   var fillAlpha = this.options.fillAlpha;

diff --git a/dygraph.js b/dygraph.js
index ae1faba..4ab665e 100644 (file)
--- a/dygraph.js
+++ b/dygraph.js
@@ -161,6 +161,22 @@ Dygraph.VERTICAL = 2;
 // Used for initializing annotation CSS rules only once.
 Dygraph.addedAnnotationCSS = false;
 
+/**
+ * Return the 2d context for a dygraph canvas.
+ *
+ * This method is only exposed for the sake of replacing the function in
+ * automated tests, e.g.
+ *
+ * var oldFunc = Dygraph.getContext();
+ * Dygraph.getContext = function(canvas) {
+ *   var realContext = oldFunc(canvas);
+ *   return new Proxy(realContext);
+ * };
+ */
+Dygraph.getContext = function(canvas) {
+  return canvas.getContext("2d");
+};
+
 Dygraph.prototype.__old_init__ = function(div, file, labels, attrs) {
   // Labels is no longer a constructor parameter, since it's typically set
   // directly from the data source. It also conains a name for the x-axis,
@@ -657,8 +673,11 @@ Dygraph.prototype.createInterface_ = function() {
   this.canvas_.style.width = this.width_ + "px";    // for IE
   this.canvas_.style.height = this.height_ + "px";  // for IE
 
+  this.canvas_ctx_ = Dygraph.getContext(this.canvas_);
+
   // ... and for static parts of the chart.
   this.hidden_ = this.createPlotKitCanvas_(this.canvas_);
+  this.hidden_ctx_ = Dygraph.getContext(this.hidden_);
 
   // The interactive parts of the graph are drawn on top of the chart.
   this.graphDiv.appendChild(this.hidden_);
@@ -1218,9 +1237,7 @@ Dygraph.endZoom = function(event, g, context) {
     g.doZoomY_(Math.min(context.dragStartY, context.dragEndY),
                Math.max(context.dragStartY, context.dragEndY));
   } else {
-    g.canvas_.getContext("2d").clearRect(0, 0,
-                                       g.canvas_.width,
-                                       g.canvas_.height);
+    g.canvas_ctx_.clearRect(0, 0, g.canvas_.width, g.canvas_.height);
   }
   context.dragStartX = null;
   context.dragStartY = null;
@@ -1398,7 +1415,7 @@ Dygraph.prototype.createDragInterface_ = function() {
 Dygraph.prototype.drawZoomRect_ = function(direction, startX, endX, startY,
                                            endY, prevDirection, prevEndX,
                                            prevEndY) {
-  var ctx = this.canvas_.getContext("2d");
+  var ctx = this.canvas_ctx_;
 
   // Clean up from the previous rect if necessary
   if (prevDirection == Dygraph.HORIZONTAL) {
@@ -1681,7 +1698,7 @@ Dygraph.prototype.setLegendHTML_ = function(x, sel_points) {
  */
 Dygraph.prototype.updateSelection_ = function() {
   // Clear the previously drawn vertical, if there is one
-  var ctx = this.canvas_.getContext("2d");
+  var ctx = this.canvas_ctx_;
   if (this.previousVerticalX_ >= 0) {
     // Determine the maximum highlight circle size.
     var maxCircleSize = 0;
@@ -1780,8 +1797,7 @@ Dygraph.prototype.mouseOut_ = function(event) {
  */
 Dygraph.prototype.clearSelection = function() {
   // Get rid of the overlay data
-  var ctx = this.canvas_.getContext("2d");
-  ctx.clearRect(0, 0, this.width_, this.height_);
+  this.canvas_ctx_.clearRect(0, 0, this.width_, this.height_);
   this.setLegendHTML_();
   this.selPoints_ = [];
   this.lastx_ = -1;
@@ -2429,7 +2445,9 @@ Dygraph.prototype.predraw_ = function() {
   // Create a new plotter.
   if (this.plotter_) this.plotter_.clear();
   this.plotter_ = new DygraphCanvasRenderer(this,
-                                            this.hidden_, this.layout_,
+                                            this.hidden_,
+                                            this.hidden_ctx_,
+                                            this.layout_,
                                             this.renderOptions_);
 
   // The roller sits in the bottom left corner of the chart. We don't know where