implement multithreaded rendering with context switch, gl state save/restore, add progress bar ui node, implement stencil texture for brush, implement multithreaded canvas load/save/export pano. Missing multithread in windows.

engine/app.h

@@ -22,6 +22,14 @@
 #import "GameViewController.h"
 #endif
 
+#if defined(__OBJC__) && defined(__OSX__)
+#import "main.h"
+#endif
+
+#ifdef __ANDROID__
+#include "main.h"
+#endif
+
 class App
 {
 public:
@@ -68,8 +76,14 @@ public:
 #if defined(__IOS__) && defined(__OBJC__)
     GameViewController* ios_view;
 #endif
+
+#if defined(__OSX__) && defined(__OBJC__)
+    View* osx_view;
+#endif
+
 #ifdef __ANDROID__
     struct android_app* and_app;
+    struct engine* and_engine;
 #endif
     void showKeyboard();
     void hideKeyboard();
@@ -83,6 +97,9 @@ public:
     void clear();
     void update_memory_usage(size_t bytes);
     void update(float dt);
+    void async_start();
+    void async_update();
+    void async_end();
     void resize(float w, float h);
     bool mouse_down(int button, float x, float y, float pressure, kEventSource source);
     bool mouse_move(float x, float y, float pressure, kEventSource source);