diff --git a/blockly.json b/blockly.json
index acce31a..17d16e6 100644
--- a/blockly.json
+++ b/blockly.json
@@ -8,7 +8,7 @@
     "waspot_touch_actor",
     "waspot_get_canvas"
   ],
-  "category": "catPlus",
+  "category": "catEduExtension",
   "scripts": [
     "blockly/blocks.js",
     "blockly/javascript.js"
diff --git a/blockly/javascript.js b/blockly/javascript.js
index 546a8c3..ddbfae3 100644
--- a/blockly/javascript.js
+++ b/blockly/javascript.js
@@ -108,5 +108,6 @@ Blockly.JavaScript['waspot_get_camera'] = function (block) {
   var screenSize = block.getFieldValue('screenSize');
   var text_src = block.getFieldValue('src');
   var code = variable_camera + ' = createCamera("' + text_src + '",' + screenSize + ',' + checkbox_rotate + ',' + checkbox_flip + ');\n';
+  code += variable_camera+".onCanvas();";
   return code;
 };
\ No newline at end of file
diff --git a/camera.js b/camera.js
index 9e890bc..7b10294 100644
--- a/camera.js
+++ b/camera.js
@@ -203,7 +203,10 @@ var Camera = (function () {
     onCanvas(eleOrId, callback) {
       var self = this;
       //check if it's callback function
-      if (arguments.length == 1 &&
+      if (arguments.length == 0) {
+        callback = function () {};
+        eleOrId = this.getCanvas();
+      } else if (arguments.length == 1 &&
         typeof eleOrId == 'function') {
         callback = eleOrId;
         eleOrId = this.getCanvas();
diff --git a/waspot-blockly.js b/waspot-blockly.js
index dbd61d3..ccb1203 100644
--- a/waspot-blockly.js
+++ b/waspot-blockly.js
@@ -34,6 +34,8 @@
     if (rotate) {
       cam.setRotate(90);
     }
+    c1.style.position='absolute';
+    c1.style.top='0';
     return cam;
   }
 }(window, window.webduino));
\ No newline at end of file