Run operations in a worker

src/ol/imagecanvas.js

@@ -1,5 +1,6 @@
 goog.provide('ol.ImageCanvas');
 
+goog.require('goog.asserts');
 goog.require('ol.ImageBase');
 goog.require('ol.ImageState');
 
@@ -13,12 +14,23 @@ goog.require('ol.ImageState');
  * @param {number} pixelRatio Pixel ratio.
  * @param {Array.<ol.Attribution>} attributions Attributions.
  * @param {HTMLCanvasElement} canvas Canvas.
+ * @param {ol.ImageCanvasLoader=} opt_loader Optional loader function to
+ *     support asynchronous canvas drawing.
  */
 ol.ImageCanvas = function(extent, resolution, pixelRatio, attributions,
-    canvas) {
+    canvas, opt_loader) {
 
-  goog.base(this, extent, resolution, pixelRatio, ol.ImageState.LOADED,
-      attributions);
+  /**
+   * Optional canvas loader function.
+   * @type {?ol.ImageCanvasLoader}
+   * @private
+   */
+  this.loader_ = goog.isDef(opt_loader) ? opt_loader : null;
+
+  var state = goog.isDef(opt_loader) ?
+      ol.ImageState.IDLE : ol.ImageState.LOADED;
+
+  goog.base(this, extent, resolution, pixelRatio, state, attributions);
 
   /**
    * @private
@@ -26,13 +38,68 @@ ol.ImageCanvas = function(extent, resolution, pixelRatio, attributions,
    */
   this.canvas_ = canvas;
 
+  /**
+   * @private
+   * @type {Error}
+   */
+  this.error_ = null;
+
 };
 goog.inherits(ol.ImageCanvas, ol.ImageBase);
 
 
+/**
+ * Get any error associated with asynchronous rendering.
+ * @return {Error} Any error that occurred during rendering.
+ */
+ol.ImageCanvas.prototype.getError = function() {
+  return this.error_;
+};
+
+
+/**
+ * Handle async drawing complete.
+ * @param {Error} err Any error during drawing.
+ * @private
+ */
+ol.ImageCanvas.prototype.handleLoad_ = function(err) {
+  if (err) {
+    this.error_ = err;
+    this.state = ol.ImageState.ERROR;
+  } else {
+    this.state = ol.ImageState.LOADED;
+  }
+  this.changed();
+};
+
+
+/**
+ * Trigger drawing on canvas.
+ */
+ol.ImageCanvas.prototype.load = function() {
+  if (this.state == ol.ImageState.IDLE) {
+    goog.asserts.assert(!goog.isNull(this.loader_));
+    this.state = ol.ImageState.LOADING;
+    this.changed();
+    this.loader_(goog.bind(this.handleLoad_, this));
+  }
+};
+
+
 /**
  * @inheritDoc
  */
 ol.ImageCanvas.prototype.getImage = function(opt_context) {
   return this.canvas_;
 };
+
+
+/**
+ * A function that is called to trigger asynchronous canvas drawing.  It is
+ * called with a "done" callback that should be called when drawing is done.
+ * If any error occurs during drawing, the "done" callback should be called with
+ * that error.
+ *
+ * @typedef {function(function(Error))}
+ */
+ol.ImageCanvasLoader;