test if canvas has become tainted

Author: niklasvh

src/plugins/jquery.plugin.html2canvas.js

@@ -14,23 +14,37 @@
         options.elements = this;
         options.flashcanvas = "../external/flashcanvas.min.js";
 
-	html2canvas.logging = options && options.logging;
+        html2canvas.logging = options && options.logging;
         options.complete = function(images){
-                var queue = html2canvas.Parse(this[0], images, options),
-                $canvas = $(html2canvas.Renderer(queue, options)),
-                finishTime = new Date();
+            var queue = html2canvas.Parse(this[0], images, options),
+            $canvas = $(html2canvas.Renderer(queue, options)),
+            finishTime = new Date();
 
-                if (options && options.profile && window.console && window.console.profileEnd) {
-                    console.profileEnd();
-                }
-                $canvas.css({ position: 'absolute', left: 0, top: 0 }).appendTo(document.body);
-                $canvas.siblings().toggle();
+            if (options && options.profile && window.console && window.console.profileEnd) {
+                console.profileEnd();
+            }
+            $canvas.css({
+                position: 'absolute', 
+                left: 0, 
+                top: 0
+            }).appendTo(document.body);
+            $canvas.siblings().toggle();
 
-                $(window).click(function(){
-                        $canvas.toggle().siblings().toggle();
-                    throwMessage("Canvas Render " + ($canvas.is(':visible') ? "visible" : "hidden"));
-                });
-                throwMessage('Screenshot created in '+ ((finishTime.getTime()-timer)) + " ms<br />",4000);
+            $(window).click(function(){
+                $canvas.toggle().siblings().toggle();
+                throwMessage("Canvas Render " + ($canvas.is(':visible') ? "visible" : "hidden"));
+            });
+            throwMessage('Screenshot created in '+ ((finishTime.getTime()-timer)) + " ms<br />",4000);
+            
+            // test if canvas is read-able
+            try {
+                $canvas[0].toDataURL();
+            } catch(e) {
+                if ($canvas[0].nodeName.toLowerCase() === "canvas") {
+                    // TODO, maybe add a bit less offensive way to present this, but still something that can easily be noticed
+                    alert("Canvas is tainted, unable to read data");
+                }
+            }
 
         };
         html2canvas.Preload(this[0],  options);