The window whose callback to set.
The new callback, or null to remove the currently set callback.
The previously set callback, or null if no callback was set or the library had not been initialized.
@callback_signature
void function_name(GLFWwindow* window, int focused)
For more information about the callback parameters, see the function pointer type.
Errors: Possible errors include @ref GLFW_NOT_INITIALIZED.
This function must only be called from the main thread.
@sa @ref window_focus
Added in version 3.0.
Ingroup: window
Sets the focus callback for the specified window.
This function sets the focus callback of the specified window, which is called when the window gains or loses input focus.
After the focus callback is called for a window that lost input focus, synthetic key and mouse button release events will be generated for all such that had been pressed. For more information, see @ref glfwSetKeyCallback and @ref glfwSetMouseButtonCallback.