callbackfunction that will be called whenever the window system has lost the contents of a region of the onscreen buffer and the application should redraw it to repair the buffer.
callbackfunction that will be called for significant events relating to the given this framebuffer.
callbackwith this that will be called whenever the this framebuffer changes size.
callbackfunction that should be called whenever a swap buffers request (made using swap_buffers) for the given this completes.
user_datapair that were previously associated with this via add_resize_callback.