This chapter forges ahead with a lot of things I haven’t discussed yet, such as collision detection and keyboard input, but the Tank War game that is created in this chapter will help you absorb all the information presented thus far. You'll see how you can use the graphics primitives you learned in Chapter 3 to create a complete game with support for two players. You will learn how to draw and move a tank around on the screen using nothing but simple pixel and rectangle drawing functions. You will learn how to look at the video screen to determine when a projectile strikes a tank or another object, how to read the keyboard, and how to process a game loop. The goal of this chapter is to show you that you can create an entire game using the meager resources provided thus far (in the form of the Allegro functions you have already learned) and to introduce some new functionality that will be covered in more detail in later chapters.
Here is a breakdown of the major topics in this chapter:
Moving the tanks
Detecting collisions
Understanding the complete source code
If this is your first foray into game programming, then Tank War is likely your very first game! There is always a lot of joy involved in seeing your first game running on the screen. In the mid-1980s I subscribed to several of the popular computer magazines, such as Family Computing and Compute!, which provided small program listings in the BASIC language, most often games. I can still remember some of the games I painstakingly typed in from the magazine using Microsoft GW-BASIC on my old Tandy 1000. The games never ran on the first try! I would often miss entire lines of code, even with the benefit of line numbers in the old style of BASIC.
Today there are fantastic development tools that quite often cost nothing and yet incorporate some of the most advanced compiler technology available. The Free Software Foundation (http://www.fsf.org) has done the world a wonderful service by inspiring and funding the development of free software. Perhaps the most significant contribution by the FSF is the GNU Compiler Collection, fondly known as GCC. Oddly enough, this very same compiler is used on both Windows and Linux platforms by the Dev-C++ and KDevelop tools, respectively. The format of structured and object-oriented code is much easier to read and follow than in the numbered lines of the past.
Tank War is a two-player game that is played on a single screen using a shared keyboard. The first player uses the W, A, S, and D keys to move his tank, and the spacebar to fire the main cannon on the tank. The second player uses the arrow keys for movement and the Enter key to fire. The game is shown in Figure 4.1.
The graphics in Tank War are created entirely with the vector functions you learned about in the previous chapter. Figure 4.2 shows the four angles of the tank that are drawn based on the tank's direction of travel.
The drawtank function is called from the main loop to draw each tank according to its current direction. The drawtank function looks like this:
void drawtank(int num)
{
int x = tanks[num].x;
int y = tanks[num].y;
int dir = tanks[num].dir;
//draw tank body and turret
rectfill(screen, x-11, y-11, x+11, y+11, tanks[num].color);
rectfill(screen, x-6, y-6, x+6, y+6, 7);
//draw the treads based on orientation
if (dir == 0 || dir == 2)
{
rectfill(screen, x-16, y-16, x-11, y+16, 8);
rectfill(screen, x+11, y-16, x+16, y+16, 8);
}
else
if (dir == 1 || dir == 3)
{
rectfill(screen, x-16, y-16, x+16, y-11, 8);
rectfill(screen, x-16, y+16, x+16, y+11, 8);
}
//draw the turret based on direction
switch (dir)
{
case 0:
rectfill(screen, x-1, y, x+1, y-16, 8);
break;
case 1:
rectfill(screen, x, y-1, x+16, y+1, 8);
break;
case 2:
rectfill(screen, x-1, y, x+1, y+16, 8);
break;
case 3:
rectfill(screen, x, y-1, x-16, y+1, 8);
break;
}
}Did you notice how the entire tank is constructed with rectfill statements? This is one example of improvisation where better technology is not available. For instance, bitmaps and sprites are not yet available because I haven't covered that subject yet, so this game actually draws the tank “sprite” used in the game. Don't underestimate the usefulness of rendered graphics to enhance a sprite-based game or to create a game entirely. To erase the tank, you simply call the erasetank function, which looks like this:
void erasetank(int num)
{
//calculate box to encompass the tank
int left = tanks[num].x - 17;
int top = tanks[num].y - 17;
int right = tanks[num].x + 17;
int bottom = tanks[num].y + 17;
//erase the tank
rectfill(screen, left, top, right, bottom, 0);
}The erasetank function is calculated based on the center of the tank (which is how the tank is drawn as well, from the center). Because the tank is 32 × 32 pixels in size, the erasetank function draws a black-filled rectangle a distance of 17 pixels in each direction from the center (for a total of 34 × 34 pixels, to include a small border around the tank, which helps to keep the tank from getting stuck in obstacles).
The projectiles fired from each tank are drawn as small rectangles (four pixels total) that move in the current direction the tank is facing until they strike the other tank, an object, or the edge of the screen. You can increase the size of the projectile by increasing the size in the updatebullet function (coming up next). To determine whether a “hit” has occurred, you use the getpixel function to “look” at the pixel on the screen right in front of the bullet. If that pixel is black (color 0 or RGB 0,0,0), then the bullet is moved another space. If that color is anything other than black, then it is a sure hit! The fireweapon function gets the bullet started in the right direction.
void fireweapon(int num)
{
int x = tanks[num].x;
int y = tanks[num].y;
//ready to fire again?
if (!bullets[num].alive)
{
bullets[num].alive = 1;
//fire bullet in direction tank is facing
switch (tanks[num].dir)
{
//north
case 0:
bullets[num].x = x;
bullets[num].y = y-22;
bullets[num].xspd = 0;
bullets[num].yspd = -BULLETSPEED;
break;
//east
case 1
bullets[num].x = x+22;
bullets[num].y = y;
bullets[num].xspd = BULLETSPEED;
bullets[num].yspd = 0;
break;
//south
case 2:
bullets[num].x = x;
bullets[num].y = y+22;
bullets[num].xspd = 0;
bullets[num].yspd = BULLETSPEED;
break;
//west
case 3:
bullets[num].x = x-22;
bullets[num].y = y;
bullets[num].xspd = -BULLETSPEED;
bullets[num].yspd = 0;
}
}
}The fireweapon function looks at the direction of the current tank to set the X and Y movement values for the bullet. Once it is set up, the bullet will move in that direction until it strikes something or reaches the edge of the screen. The important variable here is alive, which determines whether the bullet is moved accordingly using this updatebullet function:
void updatebullet(int num)
{
int x = bullets[num].x;
int y = bullets[num].y;
if (bullets[num].alive)
{
//erase bullet
rect(screen, x-1, y-1, x+1, y+1, 0);
//move bullet
bullets[num].x += bullets[num].xspd;
bullets[num].y += bullets[num].yspd;
x = bullets[num].x;
y = bullets[num].y;
//stay within the screen
if (x < 5 || x > SCREEN_W-5 || y < 20 || y > SCREEN_H-5)
{
bullets[num].alive = 0;
return;
}
//draw bullet
x = bullets[num].x;
y = bullets[num].y;
rect(screen, x-1, y-1, x+1, y+1, 14);
//look for a hit
if (getpixel(screen, bullets[num].x, bullets[num].y))
{
bullets[num].alive = 0;
explode(num, x, y);
}
//print the bullet's position
textprintf_ex(screen, font, SCREEN_W/2-50, 1, 2, 0,
"B1 %-3dx%-3d B2 %-3dx%-3d",
bullets[0].x, bullets[0].y,
bullets[1].x, bullets[1].y);
}
}To move the tank, each player uses the appropriate keys to move forward, backward, left, right, and a button to fire the weapon. The first player uses W, A, S, and D to move and the spacebar to fire, while player two uses the arrow keys to move and Enter to fire. The main loop looks for a key press and calls on the getinput function to see which button has been pressed. I will discuss keyboard input in a later chapter; for now all you need to be aware of is an array called key that stores the values of each key press.
void getinput()
{
//hit ESC to quit
if (key[KEY_ESC])
gameover = 1;
//WASD / SPACE keys control tank 1
if (key[KEY_W])
forward(0);
if (key[KEY_D])
turnright(0);
if (key[KEY_A])
turnleft(0);
if (key[KEY_S])
backward(0);
if (key[KEY_SPACE])
fireweapon(0);
//arrow / ENTER keys control tank 2
if (key[KEY_UP])
forward(1);
if (key[KEY_RIGHT])
turnright(1);
if (key[KEY_DOWN])
backward(1);
if (key[KEY_LEFT])
turnleft(1);
if (key[KEY_ENTER])
fireweapon(1);
//short delay after keypress
rest(10);
}I have already explained how the bullets use getpixel to determine when a collision has occurred (when the bullet hits a tank or obstacle). But what about collision detection when you are moving the tanks themselves? There are several obstacles on the battlefield to add a little strategy to the game; they offer a place to hide or maneuver around (or straight through if you blow up the obstacles). The clearpath function is used to determine whether the tank can move. The function checks the screen boundaries and obstacles on the screen to clear a path for the tank or prevent it from moving any further in that direction. The function also takes into account reverse motion because the tanks can move forward or backward. clearpath is a bit lengthy, so I'll leave it for the main code listing later in the chapter. The clearpath function calls the checkpath function to actually see whether the tank's pathway is clear for movement. (checkpath is called multiple times for each tank.)
int checkpath(int x1,int y1,int x2,int y2,int x3,int y3)
{
if (getpixel(screen, x1, y1) ||
getpixel(screen, x2, y2) ||
getpixel(screen, x3, y3))
return 1;
else
return 0;
}All that remains of the program are the logistical functions for setting up the screen, modifying the speed and direction of each tank, displaying the score, placing the random debris, and so on.
The code listing for Tank War is included here in its entirety. Despite having already shown you many of the functions in this program, I think it's important at this point to show you the entire listing in one fell swoop so there is no confusion. Of course you can open the Tank War project that is located on the CD-ROM that accompanies this book; look inside a folder called chapter04 for the complete project. If you are using some other operating system, you can still compile this code for your favorite compiler by typing it into your text editor and including the Allegro library—or simply copy the source code files into a new project folder and add them to your project.
The first code listing is for the header file, which includes the variables, structures, constants, and function prototypes for the game. You will want to add a new file to the project called tankwar.h. The main source code file (main.c) will try to include the header file by this filename. If you need help configuring your compiler to link to the Allegro game library, refer back to Chapter 2.
/////////////////////////////////////////////////////////////////////////
// Game Programming All In One, Third Edition
// Chapter 4 - Tank War Game
/////////////////////////////////////////////////////////////////////////
#ifndef _TANKWAR_H
#define _TANKWAR_H
#include "allegro.h"
//define some game constants
#define MODE GFX_AUTODETECT_WINDOWED
#define WIDTH 640
#define HEIGHT 480
#define BLOCKS 5
#define BLOCKSIZE 100
#define MAXSPEED 2
#define BULLETSPEED 10
#define TAN makecol(255,242,169)
#define CAMO makecol(64,142,66)
#define BURST makecol(255,189,73)
//define tank structure
struct tagTank
{
int x,y;
int dir,speed;
int color;
int score;
} tanks[2];
//define bullet structure
struct tagBullet
{
int x,y;
int alive;
int xspd,yspd;
} bullets[2];
int gameover = 0;
//function prototypes
void drawtank(int num);
void erasetank(int num);
void movetank(int num);
void explode(int num, int x, int y);
void updatebullet(int num);
int checkpath(int x1,int y1,int x2,int y2,int x3,int y3);
void clearpath(int num);
void fireweapon(int num);
void forward(int num);
void backward(int num);
void turnleft(int num);
void turnright(int num);
void getinput();
void setuptanks();
void score(int);
void print(const char *s, int c);
void setupdebris();
void setupscreen();
#endif
The primary source code file for Tank War includes the tankwar.h header file (which in turn includes allegro.h). Included in this code listing are all of the functions needed by the game in addition to the main function (containing the game loop). You can type this code as-is for whatever OS and IDE you are using; if you have included the Allegro library, it will run without issue. This game is wonderfully easy to get to work because it requires no bitmap files, uses no backgrounds, and simply draws directly to the primary screen buffer (which can be full-screen or windowed).
/////////////////////////////////////////////////////////////////////////
// Game Programming All In One, Third Edition
// Chapter 4 - Tank War Game
/////////////////////////////////////////////////////////////////////////
#include "tankwar.h"
/////////////////////////////////////////////////////////////////////////
// drawtank function
// construct the tank using drawing functions
/////////////////////////////////////////////////////////////////////////
void drawtank(int num)
{
int x = tanks[num].x;
int y = tanks[num].y;
int dir = tanks[num].dir;
//draw tank body and turret
rectfill(screen, x-11, y-11, x+11, y+11, tanks[num].color);
rectfill(screen, x-6, y-6, x+6, y+6, 7);
//draw the treads based on orientation
if (dir == 0 || dir == 2)
{
rectfill(screen, x-16, y-16, x-11, y+16, 8);
rectfill(screen, x+11, y-16, x+16, y+16, 8);
}
else
if (dir == 1 || dir == 3)
{
rectfill(screen, x-16, y-16, x+16, y-11, 8);
rectfill(screen, x-16, y+16, x+16, y+11, 8);
}
//draw the turret based on direction
switch (dir)
{
case 0:
rectfill(screen, x-1, y, x+1, y-16, 8);
break;
case 1:
rectfill(screen, x, y-1, x+16, y+1, 8);
break;
case 2:
rectfill(screen, x-1, y, x+1, y+16, 8);
break;
case 3:
rectfill(screen, x, y-1, x-16, y+1, 8);
break;
}
}
/////////////////////////////////////////////////////////////////////////
// erasetank function
// erase the tank using rectfill
/////////////////////////////////////////////////////////////////////////
void erasetank(int num)
{
//calculate box to encompass the tank
int left = tanks[num].x - 17;
int top = tanks[num].y - 17;
int right = tanks[num].x + 17;
int bottom = tanks[num].y + 17;
//erase the tank
rectfill(screen, left, top, right, bottom, 0);
}
/////////////////////////////////////////////////////////////////////////
// movetank function
// move the tank in the current direction
/////////////////////////////////////////////////////////////////////////
void movetank(int num)
{
int dir = tanks[num].dir;
int speed = tanks[num].speed;
//update tank position based on direction
switch(dir)
{
case 0:
tanks[num].y -= speed;
break;
case 1:
tanks[num].x += speed;
break;
case 2:
tanks[num].y += speed;
break;
case 3:
tanks[num].x -= speed;
}
//keep tank inside the screen
if (tanks[num].x > SCREEN_W-22)
{
tanks[num].x = SCREEN_W-22;
tanks[num].speed = 0;
}
if (tanks[num].x < 22)
{
tanks[num].x = 22;
tanks[num].speed = 0;
}
if (tanks[num].y > SCREEN_H-22)
{
tanks[num].y = SCREEN_H-22;
tanks[num].speed = 0;
}
if (tanks[num].y < 22)
{
tanks[num].y = 22;
tanks[num].speed = 0;
}
}
/////////////////////////////////////////////////////////////////////////
// explode function
// display random boxes to simulate an explosion
/////////////////////////////////////////////////////////////////////////
void explode(int num, int x, int y)
{
int n;
//retrieve location of enemy tank
int tx = tanks[!num].x;
int ty = tanks[!num].y;
//is bullet inside the boundary of the enemy tank?
if (x > tx-16 && x < tx+16 && y > ty-16 && y < ty+16)
score(num);
//draw some random circles for the "explosion"
for (n = 0; n < 10; n++)
{
rectfill(screen, x-16, y-16, x+16, y+16, rand() % 16);
rest(1);
}
//clear the area of debris
rectfill(screen, x-16, y-16, x+16, y+16, 0);
}
/////////////////////////////////////////////////////////////////////////
// updatebullet function
// update the position of a bullet
/////////////////////////////////////////////////////////////////////////
void updatebullet(int num)
{
int x = bullets[num].x;
int y = bullets[num].y;
if (bullets[num].alive)
{
//erase bullet
rect(screen, x-1, y-1, x+1, y+1, 0);
//move bullet
bullets[num].x += bullets[num].xspd;
bullets[num].y += bullets[num].yspd;
x = bullets[num].x;
y = bullets[num].y;
//stay within the screen
if (x < 5 || x > SCREEN_W-5 || y < 20 || y > SCREEN_H-5)
{
bullets[num].alive = 0;
return;
}
//draw bullet
x = bullets[num].x;
y = bullets[num].y;
rect(screen, x-1, y-1, x+1, y+1, 14);
//look for a hit
if (getpixel(screen, bullets[num].x, bullets[num].y))
{
bullets[num].alive = 0;
explode(num, x, y);
}
//print the bullet's position
textprintf_ex(screen, font, SCREEN_W/2-50, 1, 2, 0,
"B1 %-3dx%-3d B2 %-3dx%-3d",
bullets[0].x, bullets[0].y,
bullets[1].x, bullets[1].y);
}
}
/////////////////////////////////////////////////////////////////////////
// checkpath function
// check to see if a point on the screen is black
/////////////////////////////////////////////////////////////////////////
int checkpath(int x1,int y1,int x2,int y2,int x3,int y3)
{
if (getpixel(screen, x1, y1) ||
getpixel(screen, x2, y2) ||
getpixel(screen, x3, y3))
return 1;
else
return 0;
}
/////////////////////////////////////////////////////////////////////////
// clearpath function
// verify that the tank can move in the current direction
/////////////////////////////////////////////////////////////////////////
void clearpath(int num)
{
//shortcut vars
int dir = tanks[num].dir;
int speed = tanks[num].speed;
int x = tanks[num].x;
int y = tanks[num].y;
switch(dir)
{
//check pixels north
case 0:
if (speed > 0)
{
if (checkpath(x-16, y-20, x, y-20, x+16, y-20))
tanks[num].speed = 0;
}
else
//if reverse dir, check south
if (checkpath(x-16, y+20, x, y+20, x+16, y+20))
tanks[num].speed = 0;
break;
//check pixels east
case 1:
if (speed > 0)
{
if (checkpath(x+20, y-16, x+20, y, x+20, y+16))
tanks[num].speed = 0;
}
else
//if reverse dir, check west
if (checkpath(x-20, y-16, x-20, y, x-20, y+16))
tanks[num].speed = 0;
break;
//check pixels south
case 2:
if (speed > 0)
{
if (checkpath(x-16, y+20, x, y+20, x+16, y+20))
tanks[num].speed = 0;
}
else
//if reverse dir, check north
if (checkpath(x-16, y-20, x, y-20, x+16, y-20))
tanks[num].speed = 0;
break;
//check pixels west
case 3:
if (speed > 0)
{
if (checkpath(x-20, y-16, x-20, y, x-20, y+16))
tanks[num].speed = 0;
}
else
//if reverse dir, check east
if (checkpath(x+20, y-16, x+20, y, x+20, y+16))
tanks[num].speed = 0;
break;
}
}
/////////////////////////////////////////////////////////////////////////
// fireweapon function
// configure a bullet's direction and speed and activate it
/////////////////////////////////////////////////////////////////////////
void fireweapon(int num)
{
int x = tanks[num].x;
int y = tanks[num].y;
//ready to fire again?
if (!bullets[num].alive)
{
bullets[num].alive = 1;
//fire bullet in direction tank is facing
switch (tanks[num].dir)
{
//north
case 0:
bullets[num].x = x;
bullets[num].y = y-22;
bullets[num].xspd = 0;
bullets[num].yspd = -BULLETSPEED;
break;
//east
case 1:
bullets[num].x = x+22;
bullets[num].y = y;
bullets[num].xspd = BULLETSPEED;
bullets[num].yspd = 0;
break;
//south
case 2:
bullets[num].x = x;
bullets[num].y = y+22;
bullets[num].xspd = 0;
bullets[num].yspd = BULLETSPEED;
break;
//west
case 3:
bullets[num].x = x-22;
bullets[num].y = y;
bullets[num].xspd = -BULLETSPEED;
bullets[num].yspd = 0;
}
}
}
/////////////////////////////////////////////////////////////////////////
// forward function
// increase the tank's speed
/////////////////////////////////////////////////////////////////////////
void forward(int num)
{
tanks[num].speed++;
if (tanks[num].speed > MAXSPEED)
tanks[num].speed = MAXSPEED;
}
/////////////////////////////////////////////////////////////////////////
// backward function
// decrease the tank's speed
/////////////////////////////////////////////////////////////////////////
void backward(int num)
{
tanks[num].speed--;
if (tanks[num].speed < -MAXSPEED)
tanks[num].speed = -MAXSPEED;
}
/////////////////////////////////////////////////////////////////////////
// turnleft function
// rotate the tank counter-clockwise
/////////////////////////////////////////////////////////////////////////
void turnleft(int num)
{
tanks[num].dir--;
if (tanks[num].dir < 0)
tanks[num].dir = 3;
}
/////////////////////////////////////////////////////////////////////////
// turnright function
// rotate the tank clockwise
/////////////////////////////////////////////////////////////////////////
void turnright(int num)
{
tanks[num].dir++;
if (tanks[num].dir > 3)
tanks[num].dir = 0;
}
/////////////////////////////////////////////////////////////////////////
// getinput function
// check for player input keys (2 player support)
/////////////////////////////////////////////////////////////////////////
void getinput()
{
//hit ESC to quit
if (key[KEY_ESC])
gameover = 1;
//WASD / SPACE keys control tank 1
if (key[KEY_W])
forward(0);
if (key[KEY_D])
turnright(0);
if (key[KEY_A])
turnleft(0);
if (key[KEY_S])
backward(0);
if (key[KEY_SPACE])
fireweapon(0);
//arrow / ENTER keys control tank 2
if (key[KEY_UP])
forward(1);
if (key[KEY_RIGHT])
turnright(1);
if (key[KEY_DOWN])
backward(1);
if (key[KEY_LEFT])
turnleft(1);
if (key[KEY_ENTER])
fireweapon(1);
//short delay after keypress
rest(10);
}
/////////////////////////////////////////////////////////////////////////
// score function
// add a point to the specified player's score
/////////////////////////////////////////////////////////////////////////
void score(int player)
{
//update score
int points = ++tanks[player].score;
//display score
textprintf_ex(screen, font, SCREEN_W-70*(player+1), 1, BURST, 0,
"P%d: %d", player+1, points);
}
/////////////////////////////////////////////////////////////////////////
// setuptanks function
// set up the starting condition of each tank
/////////////////////////////////////////////////////////////////////////
void setuptanks()
{
//player 1
tanks[0].x = 30;
tanks[0].y = 40;
tanks[0].dir = 1;
tanks[0].speed = 0;
tanks[0].color = 9;
tanks[0].score = 0;
//player 2
tanks[1].x = SCREEN_W-30;
tanks[1].y = SCREEN_H-30;
tanks[1].dir = 3;
tanks[1].speed = 0;
tanks[1].color = 12;
tanks[1].score = 0;
}
/////////////////////////////////////////////////////////////////////////
// setupdebris function
// set up the debris on the battlefield
/////////////////////////////////////////////////////////////////////////
void setupdebris()
{
int n,x,y,size,color;
//fill the battlefield with random debris
for (n = 0; n < BLOCKS; n++)
{
x = BLOCKSIZE + rand() % (SCREEN_W-BLOCKSIZE*2);
y = BLOCKSIZE + rand() % (SCREEN_H-BLOCKSIZE*2);
size = (10 + rand() % BLOCKSIZE)/2;
color = makecol(rand()%255, rand()%255, rand()%255);
rectfill(screen, x-size, y-size, x+size, y+size, color);
}
}
/////////////////////////////////////////////////////////////////////////
// setupscreen function
// set up the graphics mode and game screen
/////////////////////////////////////////////////////////////////////////
void setupscreen()
{
//set video mode
int ret = set_gfx_mode(MODE, WIDTH, HEIGHT, 0, 0);
if (ret != 0) {
allegro_message(allegro_error);
return;
}
//print title
textprintf_ex(screen, font, 1, 1, BURST, 0,
"Tank War - %dx%d", SCREEN_W, SCREEN_H);
//draw screen border
rect(screen, 0, 12, SCREEN_W-1, SCREEN_H-1, TAN);
rect(screen, 1, 13, SCREEN_W-2, SCREEN_H-2, TAN);
}
/////////////////////////////////////////////////////////////////////////
// main function
// start point of the program
/////////////////////////////////////////////////////////////////////////
int main(void)
{
//initialize everything
allegro_init();
install_keyboard();
install_timer();
srand(time(NULL));
setupscreen();
setupdebris();
setuptanks();
//game loop
while(!gameover)
{
//erase the tanks
erasetank(0);
erasetank(1);
//check for collisions
clearpath(0);
clearpath(1);
//move the tanks
movetank(0);
movetank(1);
//draw the tanks
drawtank(0);
drawtank(1);
//update the bullets
updatebullet(0);
updatebullet(1);
//check for keypresses
if (keypressed())
getinput();
//slow the game down (adjust as necessary)
rest(30);
}
//end program
allegro_exit();
return 0;
}
END_OF_MAIN()Congratulations on completing your first game with Allegro! It has been a short journey thus far—we're only in the fourth chapter of the book. Contrast this with the enormous amount of information that would have been required in advance to compile even a simple game, such as Tank War, using standard graphics libraries, such as DirectX or SVGAlib! It would have taken this amount of source code just to set up the screen and prepare the program for the actual game. That is where Allegro truly shines—by abstracting the logistical issues into a common set of library functions that work regardless of the underlying operating system.
This isn't the end of Tank War! We'll be improving the game many more times as you learn more tricks with each new chapter. By the time you're finished, the game will feature a scrolling background, a tile-based battlefield, sound effects. . . the whole works!
You can find the answers to this chapter quiz in Appendix A, “Chapter Quiz Answers.”