window's size change after glfwPollEvents() 

void glfwPollEvents(void) 
Description
This function is used for polling for events, such as user input and window resize events. Upon calling
this function, all window states, keyboard states and mouse states are updated. If any related callback
functions are registered, these are called during the call to glfwPollEvents.

i think is resize event, but not find anything.