给静态函数访问数据而不将数据作为参数传递

Question

我在我的C++应用程序中使用GLFW作为窗口,我正在尝试使用GLFW的回调来获取输入事件.例如,这是您获取关键事件的方式:

void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods){
    // Do something with event data.
}

int main(){
    // initialize window (I have no problems with this step)

    glfwSetKeyCallback(window, key_callback);
    // Now when a key is pressed in the window it will call this function.
}

问题:

在我的key_callback我想要使​​用在key_callback函数外声明的变量,因为我不能改变参数,key_callback我无法传递对变量的引用.

现在,在上面给出的例子中,我可以简单地宣布我的变量外int main()无一不key_callback和int main()将有机会获得该变量的同一个实例.

我想要的用途:

我希望有一个WindowWrapper创建和管理生命周期的类glfwWindow,这将包括设置事件回调.

WindowWrapper.h

// Includes
class WindowWrapper{
private:
    Centrum* g_centrum_;
    GLFWwindow* window_;
    std::thread thread_;
public:
    WindowWrapper();
    WindowWrapper(Centrum* g_centrum);
    ~WindowWrapper();
private:
    // Callbacks
    static void key_callback(
        GLFWwindow* window, int key, int scancode, int action, int mods
        );
};

WindowWrapper.cpp

WindowWrapper::WindowWrapper(Centrum* g_centrum){
    g_centrum_ = g_centrum;
    // Initialize window

    glfwSetKeyCallback(window_, key_callback); // Problems

    // Window loop and OpenGL stuff
}
WindowWrapper::~WindowWrapper(){
    thread_.join(); // Don't worry about this, it works but, I will make it safer.
    glfwDestroyWindow(window_);
    printf("WindowWrapper Completely Destructed!\n"); // For testing purposes
}

void WindowWrapper::key_callback(
    GLFWwindow* window, int key, int scancode, int action, int mods
    ){
    // This function is declared static in the class declaration.
    // And as a result I cannot use g_centrum_ since it is a non-static variable
    // Essentially I want to be able to access g_centrum_ from this function
    g_centrum_->input_eventmanager_->key_eventmanager_->
        TriggerKeyEvent(key, action, mods);
}

我认为这样做的第一种方法是传递一个引用g_centrum,但GLFW不会对回调的参数产生任何偏差.

我的第二次尝试是在构造函数中声明和定义回调,但你不能这样做.

我的第三个尝试是使g_centrum_静态,但我必须在构造函数之外给它引用,我不认为这是一个优雅的解决方案.

Answer 1

用于glfwSetWindowUserPointer()在注册回调之前将包装器指针关联到窗口.调用回调时,您可以使用glfwGetWindowUserPointer()它来检索它.GLFW文档中描述了这些API .

窗口用户指针

每个窗口具有可与设置用户指针glfwSetWindowUserPointer并取出与glfwGetWindowUserPointer.这可以用于您需要的任何目的,并且在窗口的整个生命周期内不会被GLFW修改.

例如,您可以在WindowWrapper构造函数中执行此操作:

WindowWrapper::WindowWrapper(Centrum* g_centrum){
    g_centrum_ = g_centrum;
    // Initialize window first
    ...
    // Now, associate the wrapper to the window
    glfwSetWindowUserPointer(window_, this);

    glfwSetKeyCallback(window_, key_callback); // Problems

    // Window loop and OpenGL stuff
}

然后,在你的回调中:

void WindowWrapper::key_callback(
    GLFWwindow* window, int key, int scancode, int action, int mods
    ){

    void *data = glfwGetWindowUserPointer(window);  
    WindowWrapper *w = static_cast<WindowWrapper *>(data);

    w->g_centrum_->input_eventmanager_->key_eventmanager_->
        TriggerKeyEvent(key, action, mods);
}