Merge pull request #160 from fredj/tile-canvas

Tile.Image and canvas. r=ahocevar,tschaub

lib/OpenLayers/Layer/Bing.js

@@ -107,6 +107,9 @@ OpenLayers.Layer.Bing = OpenLayers.Class(OpenLayers.Layer.XYZ, {
         
         var newArgs = [name, null, options];
         OpenLayers.Layer.XYZ.prototype.initialize.apply(this, newArgs);
+        this.tileOptions = OpenLayers.Util.extend({
+            crossOriginKeyword: 'anonymous'
+        }, this.options.tileOptions);
         this.loadMetadata(); 
     },
 

lib/OpenLayers/Layer/OSM.js

@@ -73,6 +73,12 @@ OpenLayers.Layer.OSM = OpenLayers.Class(OpenLayers.Layer.XYZ, {
      *     layer option can be set in this object (e.g.
      *     <OpenLayers.Layer.Grid.buffer>).
      */
+    initialize: function(name, url, options) {
+        OpenLayers.Layer.XYZ.prototype.initialize.apply(this, arguments);
+        this.tileOptions = OpenLayers.Util.extend({
+            crossOriginKeyword: 'anonymous'
+        }, this.options && this.options.tileOptions);
+    },
 
     /**
      * Method: clone

lib/OpenLayers/Renderer/Canvas.js

@@ -110,8 +110,7 @@ OpenLayers.Renderer.Canvas = OpenLayers.Class(OpenLayers.Renderer, {
      * {Boolean} Whether or not the browser supports the renderer class
      */
     supported: function() {
-        var canvas = document.createElement("canvas");
-        return !!canvas.getContext;
+        return OpenLayers.CANVAS_SUPPORTED;
     },    
     
     /**

lib/OpenLayers/Tile/Image.js

@@ -81,6 +81,23 @@ OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {
      */
     maxGetUrlLength: null,
 
+    /**
+     * Property: canvasContext
+     * {CanvasRenderingContext2D} A canvas context associated with
+     * the tile image.
+     */
+    canvasContext: null,
+    
+    /**
+     * APIProperty: crossOriginKeyword
+     * The value of the crossorigin keyword to use when loading images. This is
+     * only relevant when using <getCanvasContext> for tiles from remote
+     * origins and should be set to either 'anonymous' or 'use-credentials'
+     * for servers that send Access-Control-Allow-Origin headers with their
+     * tiles.
+     */
+    crossOriginKeyword: null,
+
     /** TBD 3.0 - reorder the parameters to the init function to remove 
      *             URL. the getUrl() function on the layer gets called on 
      *             each draw(), so no need to specify it here.
@@ -216,6 +233,7 @@ OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {
             }
             OpenLayers.Element.removeClass(img, "olImageLoadError");
         }
+        this.canvasContext = null;
     },
     
     /**
@@ -297,6 +315,9 @@ OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {
             } else {
                 OpenLayers.Event.observe(img, "load", load);
                 OpenLayers.Event.observe(img, "error", load);
+                if (img.crossOrigin) {
+                    img.crossOrigin = null;
+                }
                 img.src = this.blankImageUrl;
             }
         }
@@ -314,6 +335,10 @@ OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {
         img.style.visibility = 'hidden';
         img.style.opacity = 0;
         if (url) {
+            // don't set crossOrigin if the url is a data URL
+            if (this.crossOriginKeyword && url.substr(0, 5 !== 'data:')) {
+                img.crossOrigin = this.crossOriginKeyword;
+            }
             img.src = url;
         }
     },
@@ -366,6 +391,7 @@ OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {
         img.style.opacity = this.layer.opacity;
 
         this.isLoading = false;
+        this.canvasContext = null;
         this.events.triggerEvent("loadend");
 
         // IE<7 needs a reflow when the tiles are loaded because of the
@@ -406,6 +432,38 @@ OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {
         }
     },
 
+    /**
+     * APIMethod: getCanvasContext
+     * Returns a canvas context associated with the tile image (with
+     * the image drawn on it).
+     * Returns undefined if the browser does not support canvas, if
+     * the tile has no image or if it's currently loading.
+     *
+     * The function returns a canvas context instance but the
+     * underlying canvas is still available in the 'canvas' property:
+     * (code)
+     * var context = tile.getCanvasContext();
+     * if (context) {
+     *     var data = context.canvas.toDataURL('image/jpeg');
+     * }
+     * (end)
+     *
+     * Returns:
+     * {Boolean}
+     */
+    getCanvasContext: function() {
+        if (OpenLayers.CANVAS_SUPPORTED && this.imgDiv && !this.isLoading) {
+            if (!this.canvasContext) {
+                var canvas = document.createElement("canvas");
+                canvas.width = this.size.w;
+                canvas.height = this.size.h;
+                this.canvasContext = canvas.getContext("2d");
+                this.canvasContext.drawImage(this.imgDiv, 0, 0);
+            }
+            return this.canvasContext;
+        }
+    },
+
     CLASS_NAME: "OpenLayers.Tile.Image"
 
 });

lib/OpenLayers/Util.js

@@ -1435,6 +1435,15 @@ OpenLayers.IS_GECKO = (function() {
     return ua.indexOf("webkit") == -1 && ua.indexOf("gecko") != -1;
 })();
 
+/**
+ * Constant: CANVAS_SUPPORTED
+ * {Boolean} True if canvas 2d is supported.
+ */
+OpenLayers.CANVAS_SUPPORTED = (function() {
+    var elem = document.createElement('canvas');
+    return !!(elem.getContext && elem.getContext('2d'));
+})();
+
 /**
  * Constant: BROWSER_NAME
  * {String}