Consequences of Not Calling SDL_PollEvent()
or SDL_PumpEvents()
in SDL2
What happens if I don't call SDL_PollEvent()
or SDL_PumpEvents()
in my loop?
If you forget to call either SDL_PollEvent()
or SDL_PumpEvents()
within each iteration of your main application loop, your SDL application will quickly become unresponsive.
Why Event Processing is Crucial
SDL needs to regularly communicate with the underlying operating system (OS) to receive information about user input (like mouse movements, clicks, key presses) and window events (like the user trying to close the window, resizing it, or minimizing it).
Functions like SDL_PumpEvents()
and SDL_PollEvent()
are the mechanisms through which SDL performs this communication. They check for new messages or events from the OS, update SDL's internal state (e.g., the current position of the mouse, the state of keyboard keys), and populate SDL's internal event queue.
Consequences of Omission
Without these calls, several problems arise:
- No Event Updates: SDL's internal event queue will not be updated with new events from the OS.
- Window Unresponsiveness: The application window will stop responding to user interactions. Clicking the close button, resizing, or minimizing won't work as expected because the OS messages triggering these actions are never processed by SDL.
- OS Intervention: The operating system will likely detect that your application isn't processing its messages. On Windows, this often leads to the window title bar appending "(Not Responding)" and the window potentially graying out. On macOS, you might see the "spinning beach ball" cursor. On Linux, the window manager might offer to force-quit the application.
- Input State Stagnation: Functions that rely on SDL's internal state reflecting the latest input (like
SDL_GetMouseState()
orSDL_GetKeyboardState()
) will not be updated. They will perpetually report the state from the last time events were processed.
In this example, the window will likely appear, but it won't respond to clicking the close button or any other interaction after the first pass through the event loop (if there were any initial events). The SDL_Delay
prevents it from consuming all CPU, but the application remains effectively frozen from the user's perspective.
Always ensure that every iteration of your main loop includes a call to SDL_PumpEvents()
or a loop that calls SDL_PollEvent()
until it returns false.
Implementing an Application Loop
Step-by-step guide on creating the SDL2 application and event loops for interactive games