通過成員 Function 到 glfwSet*Callback

Question

我正在嘗試設置一個“事件接收器”class 以將 GLFW 回調包裝到 class 用戶可以繼承但在將基類成員 ZC1C425268E68385D1AB5074C17A94F1 傳遞到 GLFWW17A94F1 函數時遇到問題。

#include <GLFW/glfw3.h>

//
//
//  Event Receiver Framework

enum EventTypes {
    Keyboard = 1,
    Mouse = 2
};

struct Event {
    EventTypes Action;
    //  Other Event Related Values
};

class EventReceiver {
    void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods) {
        Event NewEvent;
        NewEvent.Action = EventTypes::Keyboard;
        OnEvent(NewEvent);
    }

public:
    virtual void OnEvent(Event& NewEvent) = 0;
};

//
//
//  Application Framework

class MyApplication {
    GLFWwindow* window;
public:
    void SetEventReceiver(EventReceiver* EventHandler) {
        glfwSetKeyCallback(window, &EventHandler->key_callback);
    }

};

//
//  
//  User-Defined Event Receiver

class MyEventReceiver : public EventReceiver {
public:
    void OnEvent(Event& NewEvent) {
        if (NewEvent.Action == EventTypes::Keyboard) {
            //  Custom Event Actions
        }
        else if (NewEvent.Action == EventTypes::Mouse) {
            //  Custom Event Actions
        }
    }
};

//
//
//  Main

int main() {
    MyEventReceiver _Events;
    MyApplication _App;
    _App.SetEventReceiver(&_Events);
    //
    //  Do logic
    //
    return 0;
}

這實質上提供了一個帶有純虛函數的基類，供用戶繼承和覆蓋，以便為事件發生時提供自己的邏輯。 用戶定義的子類旨在傳遞到更大的“應用程序框架”class 中，它會進行必要的調用以設置 GLFW 回調函數。

Of course you cannot pass a member function as a function argument expecting a c-style-function because you must provide access to the class instance, or in other words, you have to provide the class instance so the member function being called knows what object用作“this 指針”。

對於 GLFW 中的 'glfwSet*Callback' 函數，我不確定如何做到這一點。

Answer 1

只有 static 成員函數可以在 GLFW 中像這樣使用，相反，您可以使用 glfwGetWindowUserPointer 和 glfwSetWindowUserPointer 來提供對底層 class ZA8CFDE6331BD59EB2AC966F8911ZC4 的訪問。

#include <GLFW/glfw3.h>

//
//
//  Event Receiver Framework

enum EventTypes {
    Keyboard = 1,
    Mouse = 2
};

struct Event {
    EventTypes Action;
    //  Other Event Related Values
};


class EventReceiver {
    static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods) {
        Event NewEvent;
        NewEvent.Action = EventTypes::Keyboard;
        static_cast<EventReceiver*>(glfwGetWindowUserPointer(window))->OnEvent(NewEvent);
    }

public:
    virtual void OnEvent(Event& NewEvent) = 0;
    friend class MyApplication;
};

//
//
//  Application Framework

class MyApplication {
    GLFWwindow* window;
public:
    void SetEventReceiver(EventReceiver* EventHandler) {
        glfwSetWindowUserPointer(window, EventHandler);
        glfwSetKeyCallback(window, &EventReceiver::key_callback);
    }

};

//
//  
//  User-Defined Event Receiver

class MyEventReceiver : public EventReceiver {
public:
    void OnEvent(Event& NewEvent) {
        if (NewEvent.Action == EventTypes::Keyboard) {
            //  Custom Event Actions
        }
        else if (NewEvent.Action == EventTypes::Mouse) {
            //  Custom Event Actions
        }
    }
};

//
//
//  Main

int main() {
    MyEventReceiver _Events;
    MyApplication _App;
    _App.SetEventReceiver(&_Events);
    //
    //  Do logic
    //
    return 0;
}