SDLPollEvent

SDLPollEvent is a function in the Simple DirectMedia Layer (SDL) style event handling system used to retrieve the next event from the program’s event queue. It copies the event data into a user-provided event structure and removes that event from the queue, making it available to the application for processing.

Signature and behavior: The function is typically defined as int SDLPollEvent(SDL_Event* event). It returns 1 when an event was retrieved and 0 when the event queue is empty. SDLPollEvent is non-blocking; it does not wait for an event to arrive and will return immediately if no events are pending.

Usage: SDLPollEvent is commonly employed in the main loop to process input, window, and system events. A typical pattern is:

SDL_Event e;

while (SDLPollEvent(&e)) {

switch (e.type) {

case SDL_QUIT:

// handle quit

break;

case SDL_KEYDOWN:

// handle key press

break;

// handle other event types

}

}

In this context, the event object uses a union-like structure (such as SDL_Event) with type-specific fields, and event types correspond to constants like SDL_QUIT, SDL_KEYDOWN, and others.

Relation to the event system: SDLPollEvent relies on the library’s event subsystem being initialized (for example, after a call to the library’s initialization routines). The event queue is populated by the operating system or window system, and some environments require explicit pumping of events (via a function equivalent to SDLPumpEvents) before polling.

Limitations and considerations: SDLPollEvent is typically not thread-safe and is intended to be used from a single thread responsible for event handling. The queue size is finite, so long-running loops should ensure responsiveness by processing events regularly.

See also: SDL_PollEvent, SDL_WaitEvent, SDL_Event, SDL_PumpEvents, SDL_Init.