SDL2多窗口场景下顶部关闭按钮点击事件的处理疑问

Great question! This is a super common gotcha when working with multiple SDL2 windows—let’s break down exactly what’s happening and how to fix your event handling.

First, let’s set the record straight on event behavior:

• When you close the last remaining window in your app, SDL sends an SDL_QUIT event (this is the behavior you’re already familiar with).
• When you close one of multiple open windows, SDL does NOT fire an SDL_QUIT event—instead, it sends an SDL_WINDOWEVENT with the sub-type SDL_WINDOWEVENT_CLOSE.

Why Your SDL_WINDOWEVENT_CLOSE Capture Might Have Failed #

If you didn’t see this event triggering, it’s almost certainly an issue with how you structured your event loop. Here’s the correct way to catch and handle it:

Example Working Event Loop #

SDL_Event event;
bool running = true;
// Track your open windows (e.g., a vector or array of SDL_Window pointers)
std::vector<SDL_Window*> activeWindows;

while (running) {
    while (SDL_PollEvent(&event)) {
        switch (event.type) {
            case SDL_QUIT:
                running = false;
                break;
            case SDL_WINDOWEVENT:
                switch (event.window.event) {
                    case SDL_WINDOWEVENT_CLOSE:
                        // Get the specific window that triggered the close request
                        SDL_Window* closedWindow = SDL_GetWindowFromID(event.window.windowID);
                        if (closedWindow != nullptr) {
                            // Clean up the window
                            SDL_DestroyWindow(closedWindow);
                            // Remove it from our active window list
                            auto it = std::find(activeWindows.begin(), activeWindows.end(), closedWindow);
                            if (it != activeWindows.end()) {
                                activeWindows.erase(it);
                            }
                            // If no windows are left, trigger app exit
                            if (activeWindows.empty()) {
                                running = false;
                            }
                        }
                        break;
                    // Handle other window events (resize, focus loss, etc.) if needed
                    default:
                        break;
                }
                break;
            // Handle other event types (keyboard, mouse, etc.) here
            default:
                break;
        }
    }
    // Your app's update/render logic goes here
}

Key Details to Remember #

• Always check the window ID: event.window.windowID tells you exactly which window the user tried to close—critical for managing multiple windows correctly.
• SDL won’t destroy the window automatically: The SDL_WINDOWEVENT_CLOSE is just a notification. You have to call SDL_DestroyWindow() yourself to free up resources.
• Manual quit trigger: After destroying a window, you need to check if any windows are still open. If none remain, you’ll want to set your running flag to false or call SDL_Quit() directly.

Common Mistakes to Avoid #

• Forgetting to nest the SDL_WINDOWEVENT_CLOSE check inside the main SDL_WINDOWEVENT case—if you try to catch it at the top-level event switch, it will never fire.
• Not tracking active windows: Without a list of open windows, you can’t verify when you’ve closed the last one and need to exit the app.

内容的提问来源于stack exchange，提问作者Konrad