Modes of Operation¶

A mode of operation specifies how Céu-SDL captures events from the environment (e.g., key presses) and redirects them to the Céu application.

Céu-SDL supports polling, waiting, and frame-based modes of operation.

Each mode of operation uses a different compilation flag:

$ make CEU_ARGS="-DCEU_SDL_MODE_POLLING"  CEU_SRC=<path-to-ceu-application>
$ make CEU_ARGS="-DCEU_SDL_MODE_WAITING"  CEU_SRC=<path-to-ceu-application>
$ make CEU_ARGS="-DCEU_SDL_MODE_FRAME=33" CEU_SRC=<path-to-ceu-application>

The frame-based mode also requires the desired period of the frame (in milliseconds).

The frame-based mode is the default mode of operation and is preset to 33 milliseconds.

The modes of operation are implemented in C and are part of Céu-SDL. Each mode is described in pseudo-code as follows.

Polling¶

The polling mode of Céu-SDL continually checks for SDL input events in an infinite loop:

int main (void) {
    ceu_start();
    while (<program-is-running>) {
        if (SDL_PollEvent(<...>)) {
            ceu_input(CEU_INPUT__*, <...>);     /* input SDL_QUIT, SDL_KEY*, SDL_MOUSE*, etc */
        }
        ceu_input(CEU_INPUT__NONE, <time>);     /* input async and timer */
        ceu_input(CEU_INPUT_SDL_REDRAW, <...>); /* input SDL_REDRAW after every input */
    }
    ceu_stop();
    return <program-escape-value>;
}

The inputs are polled on each loop iteration and changes are notified to the Céu application through ceu_input calls.

The polling mode uses 100% of the CPU time.

Waiting¶

The waiting mode of Céu-SDL continually waits for SDL input events in an infinite loop:

int main (void) {
    ceu_start();
    while (<program-is-running>) {
        int timeout = (<program-has-pending-async>) ? 0 : <next-timer-in-ms>;
        if (SDL_WaitEventTimeout(<...>, timeout);
            ceu_input(CEU_INPUT__*, <...>);     /* input SDL_QUIT, SDL_KEY*, SDL_MOUSE*, etc */
        }
        ceu_input(CEU_INPUT__NONE, <time>);     /* input async and timer */
        ceu_input(CEU_INPUT_SDL_REDRAW, <...>); /* input SDL_REDRAW after every input */
    }
    ceu_stop();
    return <program-escape-value>;
}

The inputs are polled on each loop iteration and changes are notified to the Céu application through ceu_input calls.

Frame¶

The frame-based mode of Céu-SDL continually waits for SDL input events in an infinite loop. The waiting period is limited to the next frame period:

int main (void) {
    ceu_start();
    while (<program-is-running>) {
        int timeout = (<program-has-pending-async>) ?
                        0 : MIN(<next-timer-in-ms>,<next-frame-in-ms>);
        if (<next-frame-expired>) {
            ceu_input(CEU_INPUT_SDL_DT, CEU_SDL_MODE_FRAME);
        }
        if (SDL_WaitEventTimeout(<...>, timeout);
            ceu_input(CEU_INPUT__*, <...>);     /* input SDL_QUIT, SDL_KEY*, SDL_MOUSE*, etc */
        }
        ceu_input(CEU_INPUT__NONE, <time>);     /* input async and timer */
        ceu_input(CEU_INPUT_SDL_REDRAW, <...>); /* input SDL_REDRAW after every input */
    }
    ceu_stop();
    return <program-escape-value>;
}

The inputs are polled on each loop iteration and changes are notified to the Céu application through ceu_input calls.

The frame-based mode also provides the CEU_SDL_DT input, which is notified after each frame period expires.