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An Example: FreakOutBefore we both lose our minds with all this talk about Windows, DirectX, and 3D graphics, I would like to take a pause and show you a complete game—albeit a simple one, but a game nonetheless. This way you can see a real game loop and some graphics calls, and take a shot at compilation. Sound good? Alrighty, then! The problem is, we're only on Chapter 1. It's not like I can use stuff from later chapters…that would be cheating, right? So what I've decided to do is get you used to using black box APIs for game programming. Based on that requirement, I asked, "What are the absolute minimum requirements for creating a 2D Breakout-like game?" All we really need is the following functionality:
So I created a library called BLACKBOX.CPP|H. Within it is a DirectX (DirectDraw only) set of functions, along with support code that implements the required functionality. The beauty is, you don't need to look at the code; you just have to use the functions, based on their prototypes, and make sure to link with BLACKBOX.CPP|H to make an .EXE. Based on the BLACKBOX library, I wrote a game called FreakOut that demonstrates a number of the concepts that we have discussed in this chapter. FreakOut contains all the major components of a real game, including a game loop, scoring, levels, and even a little baby physics model for the ball. And I do mean baby! Figure 1.9 is a screenshot of the game in action. Granted, it's not Arkanoid, but it's not bad for four hours of work! Figure 1.9. A screenshot of FreakOut.
Before I show you the source code to the game, I want you to take a look at how the project and its various components fit together. Refer to Figure 1.10. Figure 1.10. The structure of FreakOut.
As you can see from the figure, the game is composed of the following files:
So, to compile, you need to include in your project the source files BLACKBOX.CPP and FREAKOUT.CPP, link to the library DDRAW.LIB, and make sure that BLACKBOX.H is in the search path or the working directory where you are compiling so that the compiler can find it. Now that we have that all straight, let's take a look at the BLACKBOX.H header file and see what the functions are within it. Listing 1.2 BLACKBOX.H Header File
// BLACKBOX.H - Header file for demo game engine library
// watch for multiple inclusions
#ifndef BLACKBOX
#define BLACKBOX
// DEFINES ////////////////////////////////////////////////////
// default screen size
#define SCREEN_WIDTH 640 // size of screen
#define SCREEN_HEIGHT 480
#define SCREEN_BPP 8 // bits per pixel
#define MAX_COLORS 256 // maximum colors
// MACROS /////////////////////////////////////////////////////
// these read the keyboard asynchronously
#define KEY_DOWN(vk_code) ((GetAsyncKeyState(vk_code) & 0x8000) ? 1 : 0)
#define KEY_UP(vk_code) ((GetAsyncKeyState(vk_code) & 0x8000) ? 0 : 1)
// initializes a direct draw struct
#define DD_INIT_STRUCT(ddstruct) {memset(&ddstruct,0,sizeof(ddstruct));
ddstruct.dwSize=sizeof(ddstruct); }
// TYPES //////////////////////////////////////////////////////
// basic unsigned types
typedef unsigned short USHORT;
typedef unsigned short WORD;
typedef unsigned char UCHAR;
typedef unsigned char BYTE;
// EXTERNALS //////////////////////////////////////////////////
extern LPDIRECTDRAW7 lpdd; // dd object
extern LPDIRECTDRAWSURFACE7 lpddsprimary; // dd primary surface
extern LPDIRECTDRAWSURFACE7 lpddsback; // dd back surface
extern LPDIRECTDRAWPALETTE lpddpal; // a pointer dd palette
extern LPDIRECTDRAWCLIPPER lpddclipper; // dd clipper
extern PALETTEENTRY palette[256]; // color palette
extern PALETTEENTRY save_palette[256]; // used to save palettes
extern DDSURFACEDESC2 ddsd; // a ddraw surface description struct
extern DDBLTFX ddbltfx; // used to fill
extern DDSCAPS2 ddscaps; // a ddraw surface capabilities struct
extern HRESULT ddrval; // result back from dd calls
extern DWORD start_clock_count; // used for timing
// these defined the general clipping rectangle
extern int min_clip_x, // clipping rectangle
max_clip_x,
min_clip_y,
max_clip_y;
// these are overwritten globally by DD_Init()
extern int screen_width, // width of screen
screen_height, // height of screen
screen_bpp; // bits per pixel
// PROTOTYPES /////////////////////////////////////////////////
// DirectDraw functions
int DD_Init(int width, int height, int bpp);
int DD_Shutdown(void);
LPDIRECTDRAWCLIPPER DD_Attach_Clipper(LPDIRECTDRAWSURFACE7 lpdds,
int num_rects, LPRECT clip_list);
int DD_Flip(void);
int DD_Fill_Surface(LPDIRECTDRAWSURFACE7 lpdds,int color);
// general utility functions
DWORD Start_Clock(void);
DWORD Get_Clock(void);
DWORD Wait_Clock(DWORD count);
// graphics functions
int Draw_Rectangle(int x1, int y1, int x2, int y2,
int color,LPDIRECTDRAWSURFACE7 lpdds=lpddsback);
// gdi functions
int Draw_Text_GDI(char *text, int x,int y,COLORREF color,
LPDIRECTDRAWSURFACE7 lpdds=lpddsback);
int Draw_Text_GDI(char *text, int x,int y,int color,
LPDIRECTDRAWSURFACE7 lpdds=lpddsback);
#endif
Now, don't waste too much time straining your brain on the code and what all those weird global variables are. Rather, just look at the functions themselves. As you can see, there are functions to do everything that we needed for our little graphics interface. Based on that and a minimum Win32 application (the less Windows programming I have to do, the better), I have created the game FREAKOUT.CPP, which is shown in Listing 1.3. Take a good look at it, especially the main game loop and the calls to the game processing functions. Listing 1.3 The Source File FREAKOUT.CPP// INCLUDES /////////////////////////////////////////////////// #define WIN32_LEAN_AND_MEAN // include all macros #define INITGUID // include all GUIDs #include <windows.h> // include important windows stuff #include <windowsx.h> #include <mmsystem.h> #include <iostream.h> // include important C/C++ stuff #include <conio.h> #include <stdlib.h> #include <malloc.h> #include <memory.h> #include <string.h> #include <stdarg.h> #include <stdio.h> #include <math.h> #include <io.h> #include <fcntl.h> #include <ddraw.h> // directX includes #include "blackbox.h" // game library includes // DEFINES //////////////////////////////////////////////////// // defines for windows #define WINDOW_CLASS_NAME "WIN3DCLASS" // class name #define WINDOW_WIDTH 640 // size of window #define WINDOW_HEIGHT 480 // states for game loop #define GAME_STATE_INIT 0 #define GAME_STATE_START_LEVEL 1 #define GAME_STATE_RUN 2 #define GAME_STATE_SHUTDOWN 3 #define GAME_STATE_EXIT 4 // block defines #define NUM_BLOCK_ROWS 6 #define NUM_BLOCK_COLUMNS 8 #define BLOCK_WIDTH 64 #define BLOCK_HEIGHT 16 #define BLOCK_ORIGIN_X 8 #define BLOCK_ORIGIN_Y 8 #define BLOCK_X_GAP 80 #define BLOCK_Y_GAP 32 // paddle defines #define PADDLE_START_X (SCREEN_WIDTH/2 - 16) #define PADDLE_START_Y (SCREEN_HEIGHT - 32); #define PADDLE_WIDTH 32 #define PADDLE_HEIGHT 8 #define PADDLE_COLOR 191 // ball defines #define BALL_START_Y (SCREEN_HEIGHT/2) #define BALL_SIZE 4 // PROTOTYPES ///////////////////////////////////////////////// // game console int Game_Init(void *parms=NULL); int Game_Shutdown(void *parms=NULL); int Game_Main(void *parms=NULL); // GLOBALS //////////////////////////////////////////////////// HWND main_window_handle = NULL; // save the window handle HINSTANCE main_instance = NULL; // save the instance int game_state = GAME_STATE_INIT; // starting state int paddle_x = 0, paddle_y = 0; // tracks position of paddle int ball_x = 0, ball_y = 0; // tracks position of ball int ball_dx = 0, ball_dy = 0; // velocity of ball int score = 0; // the score int level = 1; // the current level int blocks_hit = 0; // tracks number of blocks hit // this contains the game grid data UCHAR blocks[NUM_BLOCK_ROWS][NUM_BLOCK_COLUMNS]; // FUNCTIONS ////////////////////////////////////////////////// LRESULT CALLBACK WindowProc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam) { // this is the main message handler of the system PAINTSTRUCT ps; // used in WM_PAINT HDC hdc; // handle to a device context // what is the message switch(msg) { case WM_CREATE: { // do initialization stuff here return(0); } break; case WM_PAINT: { // start painting hdc = BeginPaint(hwnd,&ps); // the window is now validated // end painting EndPaint(hwnd,&ps); return(0); } break; case WM_DESTROY: { // kill the application PostQuitMessage(0); return(0); } break; default:break; } // end switch // process any messages that we didn't take care of return (DefWindowProc(hwnd, msg, wparam, lparam)); } // end WinProc // WINMAIN //////////////////////////////////////////////////// int WINAPI WinMain(HINSTANCE hinstance, HINSTANCE hprevinstance, LPSTR lpcmdline, int ncmdshow) { // this is the winmain function WNDCLASS winclass; // this will hold the class we create HWND hwnd; // generic window handle MSG msg; // generic message HDC hdc; // generic dc PAINTSTRUCT ps; // generic paintstruct // first fill in the window class structure winclass.style = CS_DBLCLKS | CS_OWNDC | CS_HREDRAW | CS_VREDRAW; winclass.lpfnWndProc = WindowProc; winclass.cbClsExtra = 0; winclass.cbWndExtra = 0; winclass.hInstance = hinstance; winclass.hIcon = LoadIcon(NULL, IDI_APPLICATION); winclass.hCursor = LoadCursor(NULL, IDC_ARROW); winclass.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH); winclass.lpszMenuName = NULL; winclass.lpszClassName = WINDOW_CLASS_NAME; // register the window class if (!RegisterClass(&winclass)) return(0); // create the window, note the use of WS_POPUP if (!(hwnd = CreateWindow(WINDOW_CLASS_NAME, // class "WIN3D Game Console", // title WS_POPUP | WS_VISIBLE, 0,0, // initial x,y GetSystemMetrics(SM_CXSCREEN), // initial width GetSystemMetrics(SM_CYSCREEN), // initial height NULL, // handle to parent NULL, // handle to menu hinstance, // instance NULL))) // creation parms return(0); // hide mouse ShowCursor(FALSE); // save the window handle and instance in a global main_window_handle = hwnd; main_instance = hinstance; // perform all game console specific initialization Game_Init(); // enter main event loop while(1) { if (PeekMessage(&msg,NULL,0,0,PM_REMOVE)) { // test if this is a quit if (msg.message == WM_QUIT) break; // translate any accelerator keys TranslateMessage(&msg); // send the message to the window proc DispatchMessage(&msg); } // end if // main game processing goes here Game_Main(); } // end while // shutdown game and release all resources Game_Shutdown(); // show mouse ShowCursor(TRUE); // return to Windows like this return(msg.wParam); } // end WinMain // T3DX GAME PROGRAMMING CONSOLE FUNCTIONS //////////////////// int Game_Init(void *parms) { // this function is where you do all the initialization // for your game // return success return(1); } // end Game_Init /////////////////////////////////////////////////////////////// int Game_Shutdown(void *parms) { // this function is where you shutdown your game and // release all resources that you allocated // return success return(1); } // end Game_Shutdown /////////////////////////////////////////////////////////////// void Init_Blocks(void) { // initialize the block field for (int row=0; row < NUM_BLOCK_ROWS; row++) for (int col=0; col < NUM_BLOCK_COLUMNS; col++) blocks[row][col] = row*16+col*3+16; } // end Init_Blocks /////////////////////////////////////////////////////////////// void Draw_Blocks(void) { // this function draws all the blocks in row major form int x1 = BLOCK_ORIGIN_X, // used to track current position y1 = BLOCK_ORIGIN_Y; // draw all the blocks for (int row=0; row < NUM_BLOCK_ROWS; row++) { // reset column position x1 = BLOCK_ORIGIN_X; // draw this row of blocks for (int col=0; col < NUM_BLOCK_COLUMNS; col++) { // draw next block (if there is one) if (blocks[row][col]!=0) { // draw block Draw_Rectangle(x1-4,y1+4, x1+BLOCK_WIDTH-4,y1+BLOCK_HEIGHT+4,0); Draw_Rectangle(x1,y1,x1+BLOCK_WIDTH, y1+BLOCK_HEIGHT,blocks[row][col]); } // end if // advance column position x1+=BLOCK_X_GAP; } // end for col // advance to next row position y1+=BLOCK_Y_GAP; } // end for row } // end Draw_Blocks /////////////////////////////////////////////////////////////// void Process_Ball(void) { // this function tests if the ball has hit a block or the paddle // if so, the ball is bounced and the block is removed from // the playfield note: very cheesy collision algorithm :) // first test for ball block collisions // the algorithm basically tests the ball against each // block's bounding box this is inefficient, but easy to // implement, later we'll see a better way int x1 = BLOCK_ORIGIN_X, // current rendering position y1 = BLOCK_ORIGIN_Y; int ball_cx = ball_x+(BALL_SIZE/2), // computer center of ball ball_cy = ball_y+(BALL_SIZE/2); // test of the ball has hit the paddle if (ball_y > (SCREEN_HEIGHT/2) && ball_dy > 0) { // extract leading edge of ball int x = ball_x+(BALL_SIZE/2); int y = ball_y+(BALL_SIZE/2); // test for collision with paddle if ((x >= paddle_x && x <= paddle_x+PADDLE_WIDTH) && (y >= paddle_y && y <= paddle_y+PADDLE_HEIGHT)) { // reflect ball ball_dy=-ball_dy; // push ball out of paddle since it made contact ball_y+=ball_dy; // add a little english to ball based on motion of paddle if (KEY_DOWN(VK_RIGHT)) ball_dx-=(rand()%3); else if (KEY_DOWN(VK_LEFT)) ball_dx+=(rand()%3); else ball_dx+=(-1+rand()%3); // test if there are no blocks, if so send a message // to game loop to start another level if (blocks_hit >= (NUM_BLOCK_ROWS*NUM_BLOCK_COLUMNS)) { game_state = GAME_STATE_START_LEVEL; level++; } // end if // make a little noise MessageBeep(MB_OK); // return return; } // end if } // end if // now scan thru all the blocks and see if ball hit blocks for (int row=0; row < NUM_BLOCK_ROWS; row++) { // reset column position x1 = BLOCK_ORIGIN_X; // scan this row of blocks for (int col=0; col < NUM_BLOCK_COLUMNS; col++) { // if there is a block here then test it against ball if (blocks[row][col]!=0) { // test ball against bounding box of block if ((ball_cx > x1) && (ball_cx < x1+BLOCK_WIDTH) && (ball_cy > y1) && (ball_cy < y1+BLOCK_HEIGHT)) { // remove the block blocks[row][col] = 0; // increment global block counter, so we know // when to start another level up blocks_hit++; // bounce the ball ball_dy=-ball_dy; // add a little english ball_dx+=(-1+rand()%3); // make a little noise MessageBeep(MB_OK); // add some points score+=5*(level+(abs(ball_dx))); // that's it -- no more block return; } // end if } // end if // advance column position x1+=BLOCK_X_GAP; } // end for col // advance to next row position y1+=BLOCK_Y_GAP; } // end for row } // end Process_Ball /////////////////////////////////////////////////////////////// int Game_Main(void *parms) { // this is the workhorse of your game it will be called // continuously in real-time this is like main() in C // all the calls for your game go here! char buffer[80]; // used to print text // what state is the game in? if (game_state == GAME_STATE_INIT) { // initialize everything here graphics DD_Init(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP); // seed the random number generator // so game is different each play srand(Start_Clock()); // set the paddle position here to the middle bottom paddle_x = PADDLE_START_X; paddle_y = PADDLE_START_Y; // set ball position and velocity ball_x = 8+rand()%(SCREEN_WIDTH-16); ball_y = BALL_START_Y; ball_dx = -4 + rand()%(8+1); ball_dy = 6 + rand()%2; // transition to start level state game_state = GAME_STATE_START_LEVEL; } // end if //////////////////////////////////////////////////////////////// else if (game_state == GAME_STATE_START_LEVEL) { // get a new level ready to run // initialize the blocks Init_Blocks(); // reset block counter blocks_hit = 0; // transition to run state game_state = GAME_STATE_RUN; } // end if /////////////////////////////////////////////////////////////// else if (game_state == GAME_STATE_RUN) { // start the timing clock Start_Clock(); // clear drawing surface for the next frame of animation Draw_Rectangle(0,0,SCREEN_WIDTH-1, SCREEN_HEIGHT-1,200); // move the paddle if (KEY_DOWN(VK_RIGHT)) { // move paddle to right paddle_x+=8; // make sure paddle doesn't go off screen if (paddle_x > (SCREEN_WIDTH-PADDLE_WIDTH)) paddle_x = SCREEN_WIDTH-PADDLE_WIDTH; } // end if else if (KEY_DOWN(VK_LEFT)) { // move paddle to right paddle_x-=8; // make sure paddle doesn't go off screen if (paddle_x < 0) paddle_x = 0; } // end if // draw blocks Draw_Blocks(); // move the ball ball_x+=ball_dx; ball_y+=ball_dy; // keep ball on screen, if the ball hits the edge of // screen then bounce it by reflecting its velocity if (ball_x > (SCREEN_WIDTH - BALL_SIZE) || ball_x < 0) { // reflect x-axis velocity ball_dx=-ball_dx; // update position ball_x+=ball_dx; } // end if // now y-axis if (ball_y < 0) { // reflect y-axis velocity ball_dy=-ball_dy; // update position ball_y+=ball_dy; } // end if else // penalize player for missing the ball if (ball_y > (SCREEN_HEIGHT - BALL_SIZE)) { // reflect y-axis velocity ball_dy=-ball_dy; // update position ball_y+=ball_dy; // minus the score score-=100; } // end if // next watch out for ball velocity getting out of hand if (ball_dx > 8) ball_dx = 8; else if (ball_dx < -8) ball_dx = -8; // test if ball hit any blocks or the paddle Process_Ball(); // draw the paddle and shadow Draw_Rectangle(paddle_x-8, paddle_y+8, paddle_x+PADDLE_WIDTH-8, paddle_y+PADDLE_HEIGHT+8,0); Draw_Rectangle(paddle_x, paddle_y, paddle_x+PADDLE_WIDTH, paddle_y+PADDLE_HEIGHT,PADDLE_COLOR); // draw the ball Draw_Rectangle(ball_x-4, ball_y+4, ball_x+BALL_SIZE-4, ball_y+BALL_SIZE+4, 0); Draw_Rectangle(ball_x, ball_y, ball_x+BALL_SIZE, ball_y+BALL_SIZE, 255); // draw the info sprintf(buffer,"F R E A K O U T Score %d // Level %d",score,level); Draw_Text_GDI(buffer, 8,SCREEN_HEIGHT-16, 127); // flip the surfaces DD_Flip(); // sync to 33ish fps Wait_Clock(30); // check if user is trying to exit if (KEY_DOWN(VK_ESCAPE)) { // send message to windows to exit PostMessage(main_window_handle, WM_DESTROY,0,0); // set exit state game_state = GAME_STATE_SHUTDOWN; } // end if } // end if /////////////////////////////////////////////////////////////// else if (game_state == GAME_STATE_SHUTDOWN) { // in this state shut everything down and release resources DD_Shutdown(); // switch to exit state game_state = GAME_STATE_EXIT; } // end if // return success return(1); } // end Game_Main Cool, huh? That's the entire Win32/DirectX game. Well, almost. There are a few hundred lines of code in the BLACKBOX.CPP source file, but we'll just pretend that it's like DirectX and someone else wrote it (me!). Anyway, let's take a quick look at the contents of Listing 1.3. Basically, Windows needs to have what's called an event loop. This is standard for all Windows programs since Windows is, for the most part, event-driven. However, games aren't event-driven; they run at all times, whether the user does something or not. So we need to at least support a minimum event loop to make Windows happy. The code that implements this is in WinMain()—jeez, that's a surprise, huh? WinMain() is the main entry point for all Windows programs, just like main() is the entry point for all DOS/Unix programs (please wash your mouth out if you said "Unix" out loud). In any case, the WinMain() for FreakOut creates a window and then enters right into the event loop. If Windows needs to do something, it does so. When all the basic event handling is over, Game_Main() is called. This is where the real action occurs for our game. If you wanted to, you could loop in Game_Main() forever, never releasing it back to the main event loop in WinMain(). But this would be bad because Windows would never receive any messages and you would starve the system. Alas, what we need to do is perform one frame of animation and logic and then return back to WinMain(). This way, Windows will continue to function and process messages. If this all sounds a little hocus-pocus, don't worry—it gets worse in the next chapter <BG>. Once in Game_Main(), the logic for FreakOut is executed. The game image is rendered into an offscreen workspace and then finally shown on the display at the end of the loop via the DD_FLIP() call. So what I want you to do is take a look at all the game states and try to follow each section of the game loop and what it does. To play the game, simply click on FREAKOUT.EXE. The program will launch immediately. The controls are
Also, there's a 100-point penalty if you miss the ball, so watch it! When you feel comfortable with the game code and gameplay, try modifying the game and making changes to it. You could add different background colors (0–255 are valid colors), more balls, a paddle that changes size, and more sound effects (which I'm making right now with the Win32 API MessageBeep() function).  |
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