Skip rendering if nothing changed

Author: pandamicro

Diff for: cocos2d/core/CCDirector.js

@@ -218,8 +218,6 @@ cc.Director = cc.Class.extend(/** @lends cc.Director# */{
             cc.eventManager.dispatchEvent(this._eventAfterUpdate);
         }
 
-        renderer.clear();
-
         /* to avoid flickr, nextScene MUST be here: after tick and before draw.
          XXX: Which bug is this one. It seems that it can't be reproduced with v0.9 */
         if (this._nextScene) {
@@ -230,15 +228,25 @@ cc.Director = cc.Class.extend(/** @lends cc.Director# */{
             this._beforeVisitScene();
 
         // draw the scene
+        var skipRendering = false;
         if (this._runningScene) {
             if (renderer.childrenOrderDirty === true) {
                 cc.renderer.clearRenderCommands();
                 cc.renderer.assignedZ = 0;
                 this._runningScene._renderCmd._curLevel = 0;                          //level start from 0;
                 this._runningScene.visit();
                 renderer.resetFlag();
-            } else if (renderer.transformDirty() === true)
+            } 
+            else if (renderer.transformDirty() === true) {
                 renderer.transform();
+            }
+            else {
+                skipRendering = true;
+            }
+        }
+
+        if (!skipRendering) {
+            renderer.clear();
         }
 
         // draw the notifications node
@@ -251,7 +259,9 @@ cc.Director = cc.Class.extend(/** @lends cc.Director# */{
         if (this._afterVisitScene)
             this._afterVisitScene();
 
-        renderer.rendering(cc._renderContext);
+        if (!skipRendering) {
+            renderer.rendering(cc._renderContext);
+        }
         this._totalFrames++;
 
         cc.eventManager.dispatchEvent(this._eventAfterDraw);