Avoid using data urls in ImageTileSource.

src/imagetilesource.js

@@ -205,6 +205,20 @@
             }
             return url;
         },
+        /**
+         * Retrieves a tile context 2D
+         * @function
+         * @param {Number} level Level of the tile
+         * @param {Number} x x coordinate of the tile
+         * @param {Number} y y coordinate of the tile
+         */
+        getContext2D: function (level, x, y) {
+            var context = null;
+            if (level >= this.minLevel && level <= this.maxLevel) {
+                context = this.levels[level].context2D;
+            }
+            return context;
+        },
         /**
          * @private Build the differents levels of the pyramid if possible
          * (canvas API enabled and no canvas tainting issue)
@@ -239,33 +253,28 @@
                 return levels;
             }
             levels.splice(0, 0, {
-                url: bigCanvas.toDataURL(),
+                context2D: bigContext,
                 width: currentWidth,
                 height: currentHeight
             });
 
-            var smallCanvas = document.createElement("canvas");
-            var smallContext = smallCanvas.getContext("2d");
             while (currentWidth >= minWidth * 2 && currentHeight >= minHeight * 2) {
                 currentWidth = Math.floor(currentWidth / 2);
                 currentHeight = Math.floor(currentHeight / 2);
+                var smallCanvas = document.createElement("canvas");
+                var smallContext = smallCanvas.getContext("2d");
                 smallCanvas.width = currentWidth;
                 smallCanvas.height = currentHeight;
                 smallContext.drawImage(bigCanvas, 0, 0, currentWidth, currentHeight);
 
                 levels.splice(0, 0, {
-                    url: smallCanvas.toDataURL(),
+                    context2D: smallContext,
                     width: currentWidth,
                     height: currentHeight
                 });
 
-                var tempCanvas = bigCanvas;
                 bigCanvas = smallCanvas;
-                smallCanvas = tempCanvas;
-
-                var tempContext = bigContext;
                 bigContext = smallContext;
-                smallContext = tempContext;
             }
             return levels;
         }

src/tile.js

@@ -45,8 +45,10 @@
  * @param {Boolean} exists Is this tile a part of a sparse image? ( Also has
  *      this tile failed to load? )
  * @param {String} url The URL of this tile's image.
+ * @param {CanvasRenderingContext2D} context2D The context2D of this tile if it
+ * is provided directly by the tile source.
  */
-$.Tile = function(level, x, y, bounds, exists, url) {
+$.Tile = function(level, x, y, bounds, exists, url, context2D) {
     /**
      * The zoom level this tile belongs to.
      * @member {Number} level
@@ -83,6 +85,12 @@ $.Tile = function(level, x, y, bounds, exists, url) {
      * @memberof OpenSeadragon.Tile#
      */
     this.url     = url;
+    /**
+     * The context2D of this tile if it is provided directly by the tile source.
+     * @member {CanvasRenderingContext2D} context2D
+     * @memberOf OpenSeadragon.Tile#
+     */
+    this.context2D = context2D;
     /**
      * Is this tile loaded?
      * @member {Boolean} loaded
@@ -247,14 +255,14 @@ $.Tile.prototype = /** @lends OpenSeadragon.Tile.prototype */{
             size     = this.size,
             rendered;
 
-        if (!this.cacheImageRecord) {
+        if (!this.context2D && !this.cacheImageRecord) {
             $.console.warn(
                 '[Tile.drawCanvas] attempting to draw tile %s when it\'s not cached',
                 this.toString());
             return;
         }
 
-        rendered = this.cacheImageRecord.getRenderedContext();
+        rendered = this.context2D || this.cacheImageRecord.getRenderedContext();
 
         if ( !this.loaded || !rendered ){
             $.console.warn(
@@ -273,7 +281,8 @@ $.Tile.prototype = /** @lends OpenSeadragon.Tile.prototype */{
         //ie its done fading or fading is turned off, and if we are drawing
         //an image with an alpha channel, then the only way
         //to avoid seeing the tile underneath is to clear the rectangle
-        if( context.globalAlpha == 1 && this.url.match('.png') ){
+        if (context.globalAlpha === 1 &&
+                (this.context2D || this.url.match('.png'))) {
             //clearing only the inside of the rectangle occupied
             //by the png prevents edge flikering
             context.clearRect(

src/tiledimage.js

@@ -791,7 +791,7 @@ function updateViewport( tiledImage ) {
     drawTiles( tiledImage, tiledImage.lastDrawn );
 
     // Load the new 'best' tile
-    if ( best ) {
+    if (best && !best.context2D) {
         loadTile( tiledImage, best, currentTime );
     }
 
@@ -936,12 +936,16 @@ function updateTile( tiledImage, drawLevel, haveDrawn, x, y, level, levelOpacity
     );
 
     if (!tile.loaded) {
+        if (tile.context2D) {
+            setTileLoaded(tiledImage, tile);
+        } else {
             var imageRecord = tiledImage._tileCache.getImageRecord(tile.url);
             if (imageRecord) {
                 var image = imageRecord.getImage();
                 setTileLoaded(tiledImage, tile, image);
             }
         }
+    }
 
     if ( tile.loaded ) {
         var needsDraw = blendTile(
@@ -972,6 +976,7 @@ function getTile( x, y, level, tileSource, tilesMatrix, time, numTiles, worldWid
         bounds,
         exists,
         url,
+        context2D,
         tile;
 
     if ( !tilesMatrix[ level ] ) {
@@ -987,6 +992,8 @@ function getTile( x, y, level, tileSource, tilesMatrix, time, numTiles, worldWid
         bounds  = tileSource.getTileBounds( level, xMod, yMod );
         exists  = tileSource.tileExists( level, xMod, yMod );
         url     = tileSource.getTileUrl( level, xMod, yMod );
+        context2D = tileSource.getContext2D ?
+            tileSource.getContext2D(level, xMod, yMod) : undefined;
 
         bounds.x += ( x - xMod ) / numTiles.x;
         bounds.y += (worldHeight / worldWidth) * (( y - yMod ) / numTiles.y);
@@ -997,7 +1004,8 @@ function getTile( x, y, level, tileSource, tilesMatrix, time, numTiles, worldWid
             y,
             bounds,
             exists,
-            url
+            url,
+            context2D
         );
     }
 
@@ -1076,12 +1084,14 @@ function setTileLoaded(tiledImage, tile, image, cutoff) {
         if (increment === 0) {
             tile.loading = false;
             tile.loaded = true;
+            if (!tile.context2D) {
                 tiledImage._tileCache.cacheTile({
                     image: image,
                     tile: tile,
                     cutoff: cutoff,
                     tiledImage: tiledImage
                 });
+            }
             tiledImage._needsDraw = true;
         }
     }