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Vsync-Dependent Game Loop
DragonDePlatino
Member #16,608
December 2016

I recently started C programming so I decided to check out allegro 5. I've statically linked everything and confirmed allegro is correctly installed by running some examples.

I want to create a simple game loop tied to vsync but I cannot do so. I've tried every combination of these I can think of but it always crashes the moment an event is found. I've tried debugging but it fails with [Inferior 1 (process 2552) exited with code 03] every time I try to add an event loop.

To be clear I do not want delta time, I do not want to use timers and I do not want to pause my program's execution to wait for events. I want an SDL-style event loop where I continually render at 60 FPS regardless if there are any events in the queue. I've done this in the past with SDL 2.0, SFML and CSFML but I cannot do it with allegro.

#SelectExpand
1#include <allegro5/allegro.h> 2#include <stdio.h> 3 4static ALLEGRO_DISPLAY* display; 5static ALLEGRO_EVENT_QUEUE* window_queue; 6 7static void init(void); 8static void quit(void); 9static void loop(void); 10 11int main(void) 12{ 13 init(); 14 loop(); 15 quit(); 16} 17 18void init(void) { 19 if (!al_init()) { 20 puts("Failed to initialize allegro!"); 21 exit(1); 22 } 23 24 al_set_new_display_option(ALLEGRO_VSYNC, 1, ALLEGRO_REQUIRE); 25 display = al_create_display(640, 480); 26 if (!display) { 27 puts("Failed to create display!"); 28 exit(1); 29 } 30 31 window_queue = al_create_event_queue(); 32 if (!window_queue) { 33 puts("Failed to create event queue!"); 34 al_destroy_display(display); 35 exit(1); 36 } 37 al_register_event_source(window_queue, al_get_display_event_source(display)); 38} 39 40void quit(void) { 41 al_destroy_display(display); 42 al_destroy_event_queue(window_queue); 43} 44 45void loop(void) { 46 bool window_open = true; 47 ALLEGRO_EVENT* event = NULL; 48 int value = 0; 49 50 while (window_open) { 51 while (al_get_next_event(window_queue, event)) { 52 if (event->type == ALLEGRO_EVENT_DISPLAY_CLOSE) { 53 window_open = false; 54 } 55 } 56 57 value = (value + 1) % 256; 58 al_clear_to_color(al_map_rgb(value, value, value)); 59 al_flip_display(); 60 } 61}

And yes, I am aware that my game's speed will be tied to framerate and that the game will not even boot if the user does not have vsync.

Edgar Reynaldo
Member #8,592
May 2007
avatar

DragonDePlatino
Member #16,608
December 2016

Hey, I got it working! Keyboard input too! Thanks for your help. ;D

#SelectExpand
1#include <allegro5/allegro.h> 2#include <stdio.h> 3 4static ALLEGRO_DISPLAY* display; 5static ALLEGRO_EVENT_QUEUE* event_queue; 6 7static void init(void); 8static void quit(void); 9static void loop(void); 10 11int main(void) 12{ 13 init(); 14 loop(); 15 quit(); 16} 17 18void init(void) { 19 if (!al_init()) { 20 puts("Failed to initialize allegro!"); 21 exit(1); 22 } 23 24 if(!al_install_keyboard()) { 25 puts("Failed to initialize keyboard!"); 26 exit(1); 27 } 28 29 al_set_new_display_option(ALLEGRO_VSYNC, 1, ALLEGRO_REQUIRE); 30 display = al_create_display(640, 480); 31 if (!display) { 32 puts("Failed to create display!"); 33 exit(1); 34 } 35 36 event_queue = al_create_event_queue(); 37 if (!event_queue) { 38 puts("Failed to create event queue!"); 39 al_destroy_display(display); 40 exit(1); 41 } 42 al_register_event_source(event_queue, al_get_display_event_source(display)); 43 al_register_event_source(event_queue, al_get_keyboard_event_source()); 44} 45 46void quit(void) { 47 al_destroy_display(display); 48 al_destroy_event_queue(event_queue); 49} 50 51void loop(void) { 52 bool window_open = true; 53 ALLEGRO_EVENT event; 54 int value = 0; 55 56 while (window_open) { 57 while (al_get_next_event(event_queue, &event)) { 58 if (event.type == ALLEGRO_EVENT_DISPLAY_CLOSE) { 59 window_open = false; 60 } else if (event.type == ALLEGRO_EVENT_KEY_DOWN) { 61 switch (event.keyboard.keycode) { 62 case ALLEGRO_KEY_ESCAPE: 63 window_open = false; 64 } 65 } 66 } 67 68 value = (value + 1) % 256; 69 al_clear_to_color(al_map_rgb(value, value, value)); 70 al_flip_display(); 71 } 72}

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