How to make text blinking without blocking the whole program in C++ Allegro?

Question

bool running = true;

int width = al_get_display_width(display);
while (running) {

for (;;) {
    al_clear_to_color(al_map_rgb(255, 255, 255));
    al_draw_bitmap(bitmap, 0, 0, 0);
    al_draw_text(font, al_map_rgb(0, 0, 0), 760, 375, 0, "Play (Spacebar)");
    al_flip_display();
    al_rest(1.5);

    al_clear_to_color(al_map_rgb(255, 255, 255));
    al_draw_bitmap(bitmap, 0, 0, 0);
    al_flip_display();
    al_rest(0.5);
}

ALLEGRO_EVENT event;
al_wait_for_event(queue, &event);
if (event.type == ALLEGRO_EVENT_DISPLAY_CLOSE) {
    running = false;
}
}

As you can see I have this endless loop which blocks the whole program in order for the text to blink. The question is how do I do the blinking so the others things keep working like the event which follows up (it's here for the window to close, when the user clicks X)

Use some kind of timer and draw the blink effect when that timer expires, at all other times do whatever it is your program does. — SoronelHaetir, Jan 12 '18 at 20:54

score 1 · Answer 1 · edited Jan 12 '18 at 21:20

1

Outside your main loop:

Create timer: timer = al_create_timer(...);
Create event queue: event_queue = al_create_event_queue();
At the top within your main loop:

al_wait_for_event(event_queue, &ev);

if (ev.type == ALLEGRO_EVENT_TIMER)
{
// do your blinking stuff here
}

edited Jan 12 '18 at 21:20

Mooing Duck

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answered Jan 12 '18 at 21:09

StPiere

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Emil Laine · Accepted Answer · 2018-01-15T09:17:36.873

1

The best way is to check which state (blink on or off) to draw when drawing the text. This can be derived from the current time. Something like:

while (running) {
    al_clear_to_color(al_map_rgb(255, 255, 255));
    al_draw_bitmap(bitmap, 0, 0, 0);

    if (fmod(al_get_time(), 2) < 1.5) { // Show the text for 1.5 seconds every 2 seconds.
        al_draw_text(font, al_map_rgb(0, 0, 0), 760, 375, 0, "Play (Spacebar)");
    }

    al_flip_display();

    // Handle events in a non-blocking way, for example
    // using al_get_next_event (not al_wait_for_event).
}

edited Jan 15 '18 at 09:17

answered Jan 12 '18 at 21:33

Emil Laine

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157

I understand what you mean, and that's what the code looks like now: bool running = true; while (running) { al_clear_to_color(al_map_rgb(255, 255, 255)); al_draw_bitmap(bitmap, 0, 0, 0); if (fmod(al_get_time(), 2) < 1.5) { // Show the text for 1.5 seconds every 2 seconds. al_draw_text(font, al_map_rgb(0, 0, 0), 760, 375, 0, "Play (Spacebar)"); } al_flip_display(); ALLEGRO_EVENT event; al_wait_for_event(event_queue, &event); if (event.type == ALLEGRO_EVENT_DISPLAY_CLOSE) { running = false; } } Surprisingly, it does not work! – John Jan 14 '18 at 17:26
As the text does not blink – John Jan 14 '18 at 17:26
Changed this line: if (event.type == ALLEGRO_EVENT_DISPLAY_CLOSE) to if (event.type != ALLEGRO_EVENT_DISPLAY_CLOSE) and now when I quickly click the exit button the text is blinking! – John Jan 14 '18 at 17:28
There's some weird behaviour with this event. Do you know why? – John Jan 14 '18 at 17:29
Ah yes, I didn't notice you had `al_wait_for_event`. This way of blinking expects the drawing to happen continuously so it can redraw when the blink state changes, but `al_wait_for_event` stops the execution until an event has occurred. Try `al_wait_for_event_timed` with a small enough value for the `secs` argument, or `al_get_next_event` to have no waiting happen at all. – Emil Laine Jan 14 '18 at 18:05

How to make text blinking without blocking the whole program in C++ Allegro?

2 Answers2