int glfwGetKey(long window, int key);

콜백과의 차이 (중요)

1) 이벤트 콜백 (Key callback)

glfwSetKeyCallback(window, (win, key, scancode, action, mods) -> {
    if (action == GLFW_PRESS) {
        System.out.println("Pressed: " + key);
    }
});

2) glfwGetKey (현재 상태 polling 방식)

if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS) { ... }