3D Game Programming with a Virtual Computer

This chapter is from the book

Tricks of the 3D Game Programming Gurus-Advanced 3D Graphics and Rasterization

Learn More Buy

This chapter is from the book

This chapter is from the book 

Tricks of the 3D Game Programming Gurus-Advanced 3D Graphics and Rasterization

Learn More Buy

The T3DLIB Game Console

At this point, I have another dilemma brewing. I want to show you the generic Windows Game Console prototype we are going to use to shell our games. However, within it are calls to the API. Should I show you the library function API now, or should I wait? Well, I'm in a top-down mood right now, and because you are an intermediate or advanced game programmer, I think you can handle waiting. If there is anything that you can't follow, simply take a peek at the Library API listings and descriptions.

T3DLIB System Overview

Based on our discussion of the virtual computer design, our goal is to abstract the Win32/DirectX model into a very simple double-buffered graphics system that we can access along with support for input and sound. Along the lines of this goal, I have created what's called the T3D Game Console. The Game Console is really the first step in creating the virtual computer interface. Before we can get into DirectX, input, and sound, first we have to remove Windows from the equation. How I'm going to do this is by creating a template, or Game Console as I call it, around Windows, so that from our point of view, a Windows application looks like a standard DOS/Unix application with a main() and that's it.

What we're going to do is build up the Game Console layer by layer until we have our virtual computer. Let's first start with removing Windows from the equation as best we can.

The Basic Game Console

The first iteration of the Game Console should perform the following tasks:

1. Open a window.

2. Call a user-defined initialization function: Game_Init().

3. Enter into the main Windows event loop, process any messages for you, and return.

4. Call a user-defined "main" work function Game_Main() that performs one cycle of game logic and then returns.

5. Loop to step 3 until the user kills the application.

6. Call a user-defined shutdown function Game_Shutdown() that cleans up.

Figure 3.7 depicts the flow diagram of the Game Console. You will notice that I have decided to call the initialization, runtime, and shutdown functions Game_Init(), Game_Main(), and Game_Shutdown(), respectively.

If we can implement a shell program that performs the functionality of steps 1 through 6, we can completely forget about Windows and focus on the functions Game_Init(), Game_Main(), and Game_Shutdown() only. First, let's prototype out the three functions with some generic interfaces:

// game console
int Game_Init(void *parms=NULL);
int Game_Shutdown(void *parms=NULL);
int Game_Main(void *parms=NULL);

Figure 3.7 The control flow of the Game Console.

Not much to them, huh? Basically, I have written them so you can (if you want) send a structure to the functions, but I find I never use the feature. In any case, with that in mind, we need to write a Windows program shell program that does the following:

1. Creates a Windows class and registers the class.

2. Creates a window.

3. Has an event loop and a WinProc() that handles the basic messages WM_CREATE, WM_PAINT, and WM_DESTROY.

4. Before the event loop is called, a call to Game_Init() is called, so you can do your initialization here.

5. During the event loop, Game_Main() is called each cycle, so your game can process and run.

6. When the Window is terminated, a call to Game_Shutdown() is made, so you can clean up.

The following is a T3DCONSOLEALPHA1.CPP from the CD, a complete Windows program that does all of these steps. I have highlighted the function calls to our worker functions:

// T3DCONSOLEALPHA1.CPP - First alpha iteration of game console

// INCLUDES ///////////////////////////////////////////////

#define WIN32_LEAN_AND_MEAN

#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>


// DEFINES ////////////////////////////////////////////////

// defines for windows interface
#define WINDOW_CLASS_NAME "WIN3DCLASS" // class name
#define WINDOW_TITLE  "T3D Graphics Console Alpha 1.0"
#define WINDOW_WIDTH  320 // size of window
#define WINDOW_HEIGHT  240

// 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)

// 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
char buffer[256];     // used to print text


// 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);

  // 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 stucture
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 test to see if WINDOWED_APP is
// true to select the appropriate window flags
if (!(hwnd = CreateWindow(WINDOW_CLASS_NAME, // class
    WINDOW_TITLE,  // title
       WS_OVERLAPPED | WS_SYSMENU | WS_CAPTION,
    0,0,  // x,y
    WINDOW_WIDTH, // width
       WINDOW_HEIGHT, // height
    NULL,  // handle to parent
    NULL,  // handle to menu
    hinstance,// instance
    NULL))) // creation parms
return(0);

// save the window handle and instance in a global
main_window_handle = hwnd;
main_instance  = hinstance;

// make sure window is visible
ShowWindow(main_window_handle, SW_SHOW);

// 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();

// return to Windows like this
return(msg.wParam);

} // end WinMain

// T3D II 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

//////////////////////////////////////////////////////////

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!

// game logic here...

// check if user is trying to exit
if (KEY_DOWN(VK_ESCAPE))
 {
 PostMessage(main_window_handle, WM_DESTROY,0,0);
 } // end if

// return success
return(1);

} // end Game_Main

The name of the source code on the CD is T3DCONSOLEALPHA1.CPP, and the executable is, of course, T3DCONSOLEALPHA1.EXE. If you run the .EXE, all you will see is the image in Figure 3.8—basically a little window with nothing happening. However, behind the scenes a lot is really going on: a window was created, Game_Init() was called, and Game_Main() is being called over and over each event cycle. Finally, when you close the window, Game_Shutdown() is called.

Figure 3.8 Alpha game console T3DCONSOLEALPHA1.EXE in action.

So all you need to do is put your entire game functionality within those three functions. That's all there is to it—we have abstracted a Windows application to three function calls, and everything else is done for us.

Based on this first version of the Game Console, we have all the Windows functionality that we need. Now we need the DirectX interface that emulates our virtual computer for us and gives us the basic double-buffered graphics system with sound and input capabilities. At this point, we could dive right in and take a look at the final Game Console that does all this, but I think it's a better idea to take a look at the API that I am going to use to build it up. Now remember, you don't need to completely understand the API and all the functions. Simply take a look at all of them and their associated explanations and examples.

After you have reviewed the tools that we will use to build the final Game Console, we will take the T3DGAMECONSOLEALPHA1.CPP file and add to it in various areas, so that the results are the final virtual computer interface that we need. Then we will use this "template" as a starting point for all the demos and games in the book. Additionally, before ending the chapter, I will give a number of examples that show how to use the T3DLIB's graphics, sound, and input abilities. Alrighty then, let's move on to the three subsystems that make up the T3DLIB game engine from the first Tricks.