fix normal morph target

ios/include/filament/Engine.h

@@ -444,7 +444,7 @@ public:
 
     /**
      * Kicks the hardware thread (e.g. the OpenGL, Vulkan or Metal thread) and blocks until
-     * all commands to this point are executed. Note that this doesn't guarantee that the
+     * all commands to this point are executed. Note that does guarantee that the
      * hardware is actually finished.
      *
      * <p>This is typically used right after destroying the <code>SwapChain</code>,
@@ -454,8 +454,25 @@ public:
      */
     void flushAndWait();
 
+    /**
+     * Kicks the hardware thread (e.g. the OpenGL, Vulkan or Metal thread) but does not wait
+     * for commands to be either executed or the hardware finished.
+     *
+     * <p>This is typically used after creating a lot of objects to start draining the command
+     * queue which has a limited size.</p>
+      */
     void flush();
 
+    /**
+     * Drains the user callback message queue and immediately execute all pending callbacks.
+     *
+     * <p> Typically this should be called once per frame right after the application's vsync tick,
+     * and typically just before computing parameters (e.g. object positions) for the next frame.
+     * This is useful because otherwise callbacks will be executed by filament at a later time,
+     * which may increase latency in certain applications.</p>
+     */
+    void pumpMessageQueues();
+
     /**
      * Returns the default Material.
      *