destroy all textures on window destruction and restore OpenGL objects when Android resumes the app

engine/canvas.cpp

@@ -364,3 +364,13 @@ bool ui::Canvas::create(int width, int height)
     m_mesh.create();
     return true;
 }
+
+void ui::Canvas::snapshot_save()
+{
+
+}
+
+void ui::Canvas::snapshot_restore()
+{
+
+};