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.cpp

@@ -8,6 +8,12 @@
 #include <Foundation/Foundation.h>
 #endif
 
+#ifdef __ANDROID__
+void android_async_lock(struct engine* engine);
+void android_async_swap(struct engine* engine);
+void android_async_unlock(struct engine* engine);
+#endif
+
 using namespace ui;
 
 App App::I; // singleton
@@ -113,6 +119,49 @@ void App::init()
     glGetFloatv(GL_ALIASED_LINE_WIDTH_RANGE, width_range);
     LOG("GL line range: %f - %f", width_range[0], width_range[1]);
     LOG("Screen Size: %f %f", width, height);
+    
+    GLint fb0;
+    glGetIntegerv(GL_DRAW_FRAMEBUFFER_BINDING, &fb0);
+    LOG("Default Framebuffer %d", fb0);
+}
+
+void App::async_start()
+{
+#if __OSX__
+    [osx_view async_lock];
+#elif __IOS__
+    [ios_view async_lock];
+#elif __ANDROID__
+    android_async_lock(and_engine);
+#endif
+}
+
+void App::async_update()
+{
+#if __IOS__
+    [ios_view->glview bindDrawable];
+#endif
+    redraw = true;
+    clear();
+    update(0);
+#if __OSX__
+    [osx_view async_swap];
+#elif __IOS__
+    [ios_view async_swap];
+#elif __ANDROID__
+    android_async_swap(and_engine);
+#endif
+}
+
+void App::async_end()
+{
+#if __OSX__
+    [osx_view async_unlock];
+#elif __IOS__
+    [ios_view async_unlock];
+#elif __ANDROID__
+    android_async_unlock(and_engine);
+#endif
 }
 
 void App::update(float dt)
@@ -155,6 +204,11 @@ void App::update(float dt)
         }
     };
     //glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
+#if __IOS__
+    [ios_view->glview bindDrawable];
+#else
+    glBindFramebuffer(GL_FRAMEBUFFER, 0);
+#endif
     glEnable(GL_SCISSOR_TEST);
     if (auto* main = layout[main_id])
         main->watch(observer);