将C++对象方法作为SDL_EventFilter传递

您收到该错误是因为该语言不知道如何访问要调用该方法的类的正确实例。

您可以将 Game：：OnResize 替换为 Game 类之外的自由浮动函数，该函数可以访问指向游戏实例的指针，沿 SDL 事件数据转发，也可以在 Game 类中使用静态方法。

如果你想把它全部保留在你的类中（就像我倾向于做的那样），你可以将 Game：：OnResize 替换为一个静态方法，该方法可以访问指向你的游戏的指针，然后创建一个新的非静态方法来实际执行事件的处理。然后，静态方法可以将事件转发到非静态方法。

喜欢这个：

// =========================================================================
// game.h
// =========================================================================

class Game
{
    public:
    
        // public stuff...
        
    private:
    
        // private stuff...
        
        // replace OnResize with this:
        static int OnSDLEvent(void *data, SDL_Event *event);
        
        // new function:
        int HandleSDLEvent(void *data, SDL_Event *event);
};

// =========================================================================
// game.cpp
// =========================================================================

// somewhere at the top...
Game *g_Game{}; // global pointer to the game, only in this file

Game::Game()
{
    // let's make g_Game point to our actual game instance
    // in your game's constructor.

    // or it could be in Game::SetupSDL() or wherever...
    // it just needs to happen before adding your event watch.

    // this is so the static method has an instance to work with.
    g_Game = this;
}


// here's the static method that gets called by SDL
int Game::OnSDLEvent(void *data, SDL_Event *event)
{
    // just pass along the event data.
    return g_Game->HandleSDLEvent(data, event);
}

// and here's where you actually handle the event!
int Game::HandleSDLEvent(void *data, SDL_Event *event)
{
    if (event->type == SDL_WINDOWEVENT && event->window.event == SDL_WINDOWEVENT_RESIZED)
    {
        SetScale();
        states[state]->OnResize(*this);
    }
    return 0;
}

// finally, feed SDL with our static method we created
bool Game::SetupSDL()
{
    // setup code here...

    // now we pass in our static method
    SDL_AddEventWatch(OnSDLEvent, window);

    // etc.
}

问题：

为了向 SDL_AddEventWatch 注册事件回调，
您需要以函数的形式提供类型为 SDL_EventFilter：

int (*SDL_EventFilter)(void *userdata, SDL_Event *event);

这应该是一个自由函数，或者是一个类的静态方法。它不能是非静态方法，因为此类方法需要实例（指针）才能调用。Gamethis

解决方案：

为了使用非静态方法作为回调，您可以利用该参数作为上下文。userdata

注册事件处理程序时，将 （即 ） 与静态方法一起传递：thisGame*userdata

static int Game::OnResizeEventCallback(void *userdata, SDL_Event *event);  // see implementation below

// ...

//---------------------------------------vvvvv-
SDL_AddEventWatch(OnResizeEventCallback, this);

然后当你得到回调时，转换回 ，并调用非静态方法：userdataGame*

static int Game::OnResizeEventCallback(void *userdata, SDL_Event *event)
{
    // Retrieve your instance:
    Game* pThis = reinterpret_cast<Game*>(userdata);
    // Call your non-static method with it:
    pThis->OnResize(event);
}