This function sets the key callback of the specified window, which is called when a key is pressed, repeated or released.
The key functions deal with physical keys, with layout independent key tokens named after their values in the standard US keyboard layout. If you want to input text, use the character callback instead.
When a window loses input focus, it will generate synthetic key release events for all pressed keys. You can tell these events from user-generated events by the fact that the synthetic ones are generated after the focus loss event has been processed, i.e. after the window focus callback has been called.
The scancode of a key is specific to that platform or sometimes even to that machine. Scancodes are intended to allow users to bind keys that don't have a GLFW key token. Such keys have key set to GLFW_KEY_UNKNOWN, their state is not saved and so it cannot be queried with glfwGetKey.
Sometimes GLFW needs to generate synthetic key events, in which case the scancode may be zero.
$windowThe window whose callback to set.