...

void engine_handle_cmd(struct android_app* app, int32_t cmd)
{
     MySettings* pMySettings = (MySettings*)app->userData;

     switch (cmd) {

          case APP_CMD_INIT_WINDOW:
          pMySettings->m_MyGame.OnCreateWindow(app->window);
               break;

          case APP_CMD_TERM_WINDOW:
               pMySettings->m_MyGame.OnCloseWindow();
               break;

               case APP_CMD_WINDOW_RESIZED:
               pMySettings->m_MyGame.OnResizeWindow(app->window);
               break;

          ...
     }
}

...

class MyGame
{
     ...

     public: void OnResizeWindow(ANativeWindow* pWindow)
     {
          int w = ANativeWindow_getWidth(pWindow);
          int h = ANativeWindow_getHeight(pWindow);
          m_Graphic.SetViewport_WidthHeight(w, h);
     }

     ...
}

...

void MyGraphic::SetViewport_WidthHeight(int w, int h)
{
     glViewport(0, 0, width, height); // OpenGL function
     m_Width = w;
     m_Height = h;
}

...

class MyGraphic
{
     ...

     public:
     void SetViewport_WidthHeight(int w, int h);

     ...
}