Snippet for allegro 4 game engine to create a basic 2d game

snippet.c

/*
 * snippet.c
 * 
 * Copyright (C) 2015, 2016 Lukas Himsel <lukas.himsel@web.de>
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * 
 */

#include <stdio.h>
#include <allegro.h>
#include <pthread.h>

#define NUM_THREADS 2
#define WIDTH  1920U
#define HEIGHT 1080U

#define WINDOWED 1
/* Activate WINDOWED, if you want a window, not fullscreen! */

BITMAP *buffer;
BITMAP *cursor; //mouse cursor
int content_loaded=0;

static int rungame(void);
static void* loading_screen(void *arg); //called as thread
static void* load_contents(void *arg);  //called as thread
static void update(void);
static int init(void);
static int double_buffering_init(void); //used by init()
static void exit_error(void);

int main(int argc, char *argv[]){
	int rc;
    void *status[NUM_THREADS];
	pthread_t threads[NUM_THREADS];
	
	/* init */
	if(init()){
		return 1;
	}
	
	/* content thread */
	rc=pthread_create(&threads[0], NULL, loading_screen, (void *)0);
	rc=pthread_create(&threads[1], NULL, load_contents, (void *)0);
	
	if(rc){
		exit_error();
	}
	
    rc=pthread_join(theads[0], &status[0]);
    rc=pthread_join(threads[1], &status[1]);
    
	/* game action */
	if(rungame()){
		return 1;
	}
	
	/* exit */
	destroy_bitmap(cursor);
	destroy_bitmap(buffer);
	allegro_exit();
	pthread_exit(NULL);
}
END_OF_MAIN();


/* Game action-part */
static int rungame(){
	int k;
	while(!key[KEY_ESC]){
		clear(buffer);// clear complete buffer
		
		/* print */
		textprintf_ex(buffer,font,(SCREEN_W / 2 -30),(SCREEN_H / 2 -30),makecol(255,0,0),makecol(0,0,0),"HELLO WORLD!");
		
		/* draw mouse cursor */
		draw_sprite(buffer,cursor,mouse_x,mouse_y);
		
		/* events */
		// mouse
		if((mouse_b&1)==1){ // left mouse button
		}
		if((mouse_b&2)==2){ // right mouse button
		}
		//key
		if(k=readkey()){
			switch(k){
				//case 'W':
				case KEY_UP:
				break;
				
				//case 'A':
				case KEY_LEFT:
				break;
				
				//case 'S':
				case KEY_DOWN:
				break;
				
				//case 'D':
				case KEY_RIGHT:
				break;
				
				case KEY_ENTER:
				break;
			}
		}
		
		
		update();// update screen
	}
	return 0;
}

static void* loading_screen(void *arg){
	BITMAP *backgd;
	backgd = load_bitmap("<loading screen.bmp>", NULL);
	
	while(content_loaded==0){
		clear(buffer);
		draw_sprite(buffer,backgd,0,0);
		update();
	}
	
	destroy_bitmap(backgd);
	pthread_exit(NULL);
}

static void* load_contents(void *arg){
	
	/* 
	 * loading contents like bitmaps, samples, etc.
	 * The content has to be declared globally.
	 */
	cursor = load_bitmap("<cursor.bmp>", NULL);
	
	content_loaded=1;
	pthread_exit(NULL);
}

static void update(){
	blit(buffer, screen, 0, 0, 0, 0, SCREEN_W, SCREEN_H);
}

static int init(){
	
	allegro_init();
	install_keyboard();
	install_mouse();
	install_sound(DIGI_AUTODETECT,MIDI_AUTODETECT,NULL);
	set_color_depth(32);
	
#ifndef WINDOWED
	set_gfx_mode(GFX_AUTODETECT, WIDTH, HEIGHT, 0, 0);
#else
	set_gfx_mode(GFX_AUTODETECT_WINDOWED, WIDTH, HEIGHT, 0, 0);
#endif

	set_window_title("<title>");
	
	if (double_buffering_init()){
		exit_error();
	}
	
	return 0;
}

static int double_buffering_init(){
	buffer = create_bitmap(SCREEN_W, SCREEN_H);
	if(!buffer)
		return 1;
	return 0;
}

static void exit_error(){
	set_gfx_mode(GFX_TEXT,0,0,0,0);
	destroy_bitmap(buffer);
	destroy_bitmap(cursor);
	printf("Program crashed");
	exit(1);
}