add vr_draw_ui method and make ui observer as method to be wildly available

src/app_vr.cpp

@@ -23,6 +23,23 @@ void App::vr_stop()
 #endif
 }
 
+void App::vr_draw_ui()
+{
+    if (auto* main = layout[main_id])
+        main->update(width, height, zoom);
+
+    uirtt.bindFramebuffer();
+    uirtt.clear();
+    glViewport(0, 0, uirtt.getWidth(), uirtt.getHeight());
+    glEnable(GL_SCISSOR_TEST);
+    auto observer = std::bind(&App::update_ui_observer, this, std::placeholders::_1);
+    for (int i = 1; i < layout[main_id]->m_children.size(); i++)
+        layout[main_id]->m_children[i]->watch(observer);
+    //msgbox->watch(observer);
+    glDisable(GL_SCISSOR_TEST);
+    uirtt.unbindFramebuffer();
+}
+
 void App::vr_draw(const glm::mat4& proj, const glm::mat4& camera, const glm::mat4& pose)
 {
     //glm::mat4 ortho_proj = glm::ortho(0.f, box.z, 0.f, box.w, -1000.f, 1000.f);