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Window resize events resize_w, resize_h ... values stored in the resize structure's resize_w and resize_h. When an + SDL_VIDEORESIZE is received the window should be resized to the new dimensions using SDL_SetVideoMode.
SDL_RESIZABLE Create a resizable window. When the window is resized by the user a SDL_VIDEORESIZE event is generated and SDL::Video::set_video_mode can be called again with the new size.