New OpenLayers.Tile.Image.getCanvasContext function

lib/OpenLayers/Tile/Image.js

@@ -81,6 +81,13 @@ OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {
      */
     maxGetUrlLength: null,
 
+    /**
+     * Property: canvasContext
+     * {CanvasRenderingContext2D} A canvas context associated with
+     * the tile image.
+     */
+    canvasContext: 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 +223,7 @@ OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {
             }
             OpenLayers.Element.removeClass(img, "olImageLoadError");
         }
+        this.canvasContext = null;
     },
     
     /**
@@ -369,6 +377,7 @@ 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
@@ -409,6 +418,29 @@ 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.
+     *
+     * 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"
 
 });

tests/Tile/Image.html

@@ -399,6 +399,31 @@
             map.destroy();
         });
     }
+
+    function test_getCanvasContext(t) {
+        if (!OpenLayers.CANVAS_SUPPORTED) {
+            t.plan(0);
+        } else {
+            t.plan(1);
+
+            var map = new OpenLayers.Map('map');
+            var layer = new OpenLayers.Layer.WMS("OpenLayers WMS",
+                "http://labs.metacarta.com/wms/vmap0?", {layers: 'basic'});
+            map.addLayer(layer);
+            map.setCenter(new OpenLayers.LonLat(0, 0), 5);
+
+            t.delay_call(5, function() {
+                var tile = layer.grid[0][0];
+                if (tile.isLoading) {
+                    t.ok(false, "test_getCanvasContext timeout");
+                } else {
+                    t.ok(tile.getCanvasContext() instanceof CanvasRenderingContext2D,
+                         "getCanvasContext() returns CanvasRenderingContext2D instance");
+                }
+                map.destroy();
+            });
+        }
+    }
     
   </script>
 </head>