Basic game loops in Raylib, SDL2 and Allegro5

allegro5_basic_game_loop.c

#include <allegro5/allegro5.h>
#include <allegro5/allegro_primitives.h>
#include <stdio.h>
#include <stdlib.h>

#define WIN_WIDTH_PX (800)
#define WIN_HEIGHT_PX (800)
#define FPS (60.0f)

static void Initialize();
static void Terminate();
static void Draw();
static void Update(double dt, ALLEGRO_EVENT *ev);
static bool IsRunning();

static ALLEGRO_DISPLAY *display = NULL;
static ALLEGRO_EVENT_QUEUE *eq = NULL;
static ALLEGRO_TIMER *timer = NULL;
static bool redraw = true;
static bool doexit = false;

void UpdateCustom(double dt);
void DrawCustom(void);

int main() {
  double timeNow = 0.0, prevTime = 0.0, dt = 0.0;
  ALLEGRO_EVENT ev;

  Initialize();

  while (IsRunning()) {
    al_wait_for_event(eq, &ev);
    timeNow = al_get_time();
    dt = timeNow - prevTime;

    Update(dt, &ev);
    Draw();

    prevTime = timeNow;
  }

  Terminate();
  return 0;
}
static void Initialize() {
  time_t t;
  srand(time(&t));

  if (!al_init()) {
    fprintf(stderr, "ERROR: Failed to initialize allegro!\n");
    goto init_fail;
  }

  if (!al_init_primitives_addon()) {
    fprintf(stderr, "ERROR: Failed to load primitives addon!\n");
    goto prim_addon_fail;
  }

  timer = al_create_timer(1.0 / FPS);
  if (!timer) {
    fprintf(stderr, "ERROR: Failed to create timer!\n");
    goto timer_fail;
  }

  display = al_create_display(WIN_WIDTH_PX, WIN_HEIGHT_PX);
  if (!display) {
    fprintf(stderr, "ERROR: Failed to create display!\n");
    goto disp_fail;
  }

  eq = al_create_event_queue();
  if (!eq) {
    fprintf(stderr, "ERROR: Failed to create event queue!\n");
    goto eq_fail;
  }

  al_register_event_source(eq, al_get_display_event_source(display));
  al_register_event_source(eq, al_get_timer_event_source(timer));

  al_set_window_title(display, "Test");
  al_start_timer(timer);

  return;

eq_fail:
disp_fail:
  al_destroy_timer(timer);
timer_fail:
prim_addon_fail:
init_fail:
  exit(1);
}

static void Terminate() {
  al_destroy_event_queue(eq);
  al_destroy_display(display);
  al_destroy_timer(timer);
}

static void Draw() {
  if (redraw && al_is_event_queue_empty(eq)) {
    redraw = false;
    al_clear_to_color(al_map_rgb(0x30, 0x34, 0x3f));
    DrawCustom();
    al_flip_display();
  }
}

static void Update(double dt, ALLEGRO_EVENT *ev) {
  static double updateTimer = 0.0;
  if (ev->type == ALLEGRO_EVENT_DISPLAY_CLOSE) {
    doexit = true;
    return;
  } else if (ev->type == ALLEGRO_EVENT_TIMER) {
    redraw = true;
  }
  UpdateCustom(dt);
}

static bool IsRunning() { return !doexit; }

void UpdateCustom(double dt) {}
void DrawCustom(void) {}

raylib_basic_game_loop.c

//
// Basic Game Loop
//
// Engine/Framework: Raylib (https://www.raylib.com)
//

#include <stdbool.h>
#include "raylib.h"

#define WIN_WIDTH_PX (800)   // Main window width in pixels
#define WIN_HEIGHT_PX (640)  // Main window height in pixels

void GameInitialize();
void GameTerminate();
void GameDraw();
void GameProcessInput();
void GameUpdate();
bool IsGameRunning();

int main() {
  GameInitialize();

  while (IsGameRunning()) {
    GameProcessInput();
    GameUpdate();
    GameDraw();
  }

  GameTerminate();
  return 0;
}

void GameInitialize() {
  SetTargetFPS(60);
  InitWindow(WIN_WIDTH_PX, WIN_HEIGHT_PX,
             "Polyengine Gamedev: Basic Game Loop: Raylib");
}

void GameTerminate() { CloseWindow(); }

void GameDraw() {
  BeginDrawing();
  ClearBackground(GetColor(0xbedecaff));
  EndDrawing();
}

void GameProcessInput() {}

void GameUpdate() {}

bool IsGameRunning() { return !WindowShouldClose(); }

sdl2_basic_game_loop.c

//
// Basic Game Loop
//
// Engine/Framework: Simple DirectMedia Layer - SDL (https://libsdl.org)
//

#include <stdbool.h>
#include <stdio.h>
#include "SDL.h"

#define WIN_WIDTH_PX (800)   // Main window width in pixels
#define WIN_HEIGHT_PX (640)  // Main window height in pixels

void GameInitialize();
void GameTerminate();
void GameDraw();
void GameProcessInput();
void GameUpdate();
bool IsGameRunning();

SDL_Window *gWin = NULL;
SDL_Renderer *gRen = NULL;
bool gQuit = false;

int main(int argc, char *argv[]) {
  GameInitialize();

  while (IsGameRunning()) {
    GameProcessInput();
    GameUpdate();
    GameDraw();
  }

  GameTerminate();
  return 0;
}

void GameInitialize() {
  SDL_Init(SDL_INIT_VIDEO);
  gWin = SDL_CreateWindow("Polyengine Gamedev: Basic Game Loop: SDL2",
                          SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
                          WIN_WIDTH_PX, WIN_HEIGHT_PX, SDL_WINDOW_SHOWN);
  gRen = SDL_CreateRenderer(
      gWin, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
}

void GameTerminate() {
  SDL_DestroyWindow(gWin);
  SDL_Quit();
}

void GameDraw() {
  SDL_SetRenderDrawColor(gRen, 0xbe, 0xde, 0xca, 0xff);
  SDL_RenderClear(gRen);
  SDL_RenderPresent(gRen);
}

void GameProcessInput() {
  SDL_Event e;
  while (SDL_PollEvent(&e) != 0) {
    if (e.type == SDL_QUIT) {
      gQuit = true;
    }
  }
}

void GameUpdate() {}

bool IsGameRunning() { return !gQuit; }