Windows Game Programming for Dummies (2nd Edition)/WinGamProgFD.iso/pc/Source/GPCHAP11/PROG11_1.CPP

C/C++ Source or Header | 2002-04-27 | 23.5 KB | 822 lines

// PROG11_1.CPP - a demo of blitter objects (BOBS)
// creates an asteroid field

// INCLUDES ///////////////////////////////////////////////
#define WIN32_LEAN_AND_MEAN
#define INITGUID

#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

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

// defines for windows
#define WINDOW_CLASS_NAME "WINXCLASS"  // class name

#define WINDOW_WIDTH  800         // size of window
#define WINDOW_HEIGHT 600
#define SCREEN_WIDTH  800         // size of screen
#define SCREEN_HEIGHT 600
#define SCREEN_BPP    8           // bits per pixel

#define BITMAP_ID     0x4D42      // universal id for a bitmap

// defines for BOBs
#define BOB_STATE_DEAD     0      // this is a dead bob
#define BOB_STATE_ALIVE    1      // this is a live bob
#define BOB_STATE_LOADED   2      // the bob has been loaded

// defines for asteroids
#define NUM_ASTEROIDS      64     // number of active asteroids

// 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)

// this builds a 16 bit color value in 5.5.5 format (1-bit alpha mode)
#define _RGB16BIT555(r,g,b) ((b & 31) + ((g & 31) << 5) + ((r & 31) << 10))

// this builds a 16 bit color value in 5.6.5 format (green dominate mode)
#define _RGB16BIT565(r,g,b) ((b & 31) + ((g & 63) << 5) + ((r & 31) << 11))

// TYPES //////////////////////////////////////////////////

typedef unsigned short USHORT;
typedef unsigned short WORD;
typedef unsigned char  UCHAR;
typedef unsigned char  BYTE;

// container structure for bitmaps .BMP file
typedef struct BITMAP_FILE_TAG
        {
        BITMAPFILEHEADER bitmapfileheader;  // this contains the bitmapfile header
        BITMAPINFOHEADER bitmapinfoheader;  // this is all the info including the palette
        PALETTEENTRY     palette[256];      // we will store the palette here
        UCHAR            *buffer;           // this is a pointer to the data

        } BITMAP_FILE, *BITMAP_FILE_PTR;

// the blitter object structure BOB
typedef struct BITMAP_OBJ_TYP
        {
        int state; // the state of the object (general)
        int attr;  // attributes pertaining to the object (general)
        int x,y;   // position bitmap will be displayed at
        int xv,yv; // velocity of object
        int width, height; // the width and height of the bitmap
        LPDIRECTDRAWSURFACE7 image; // the bitmap surface itself

        } BITMAP_OBJ, *BITMAP_OBJ_PTR;

// PROTOTYPES /////////////////////////////////////////////

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

// bitmaps
int Load_Bitmap_File(BITMAP_FILE_PTR bitmap, char *filename);
int Unload_Bitmap_File(BITMAP_FILE_PTR bitmap);
int Flip_Bitmap(UCHAR *image, int bytes_per_line, int height);

// bobs
int Draw_BOB(BITMAP_OBJ_PTR bob,LPDIRECTDRAWSURFACE7 dest);
int Destroy_BOB(BITMAP_OBJ_PTR bob);
int Create_BOB(BITMAP_OBJ_PTR bob,int width, int height,int attr, int flags);
int Load_BOB(BITMAP_OBJ_PTR bob,BITMAP_FILE_PTR bitmap,int cx,int cy,int mode);

// GLOBALS ////////////////////////////////////////////////

HWND main_window_handle = NULL; // save the window handle
HINSTANCE main_instance = NULL; // save the instance
char buffer[80];                // used to print text

LPDIRECTDRAW7        lpdd         = NULL;  // dd object
LPDIRECTDRAWSURFACE7 lpddsprimary = NULL;  // dd primary surface
LPDIRECTDRAWSURFACE7 lpddsback    = NULL;  // dd back surface
LPDIRECTDRAWPALETTE  lpddpal      = NULL;  // a pointer to the created dd palette
PALETTEENTRY         palette[256];         // color palette
DDSURFACEDESC2       ddsd;                 // a direct draw surface description struct
DDBLTFX              ddbltfx;              // used to fill
DDSCAPS2             ddscaps;              // a direct draw surface capabilities struct
HRESULT              ddrval;               // result back from dd calls
UCHAR                *primary_buffer = NULL; // primary video buffer
UCHAR                *back_buffer    = NULL; // secondary back buffer
BITMAP_FILE          bitmap16bit,            // a 16 bit bitmap file
                     bitmap8bit;             // a 8 bit bitmap file

BITMAP_OBJ           asteroids[NUM_ASTEROIDS]; // asteroid field

// FUNCTIONS //////////////////////////////////////////////

int Load_Bitmap_File(BITMAP_FILE_PTR bitmap, char *filename)
{
// this function opens a bitmap file and loads the data into bitmap

int file_handle,  // the file handle
    index;        // looping index

UCHAR *temp_buffer = NULL; // used to convert 24 bit images to 16 bit
OFSTRUCT file_data;        // the file data information

// open the file if it exists
if ((file_handle = OpenFile(filename,&file_data,OF_READ))==-1)
   return(0);

// now load the bitmap file header
_lread(file_handle, &bitmap->bitmapfileheader,sizeof(BITMAPFILEHEADER));

// test if this is a bitmap file
if (bitmap->bitmapfileheader.bfType!=BITMAP_ID)
   {
   // close the file
   _lclose(file_handle);

   // return error
   return(0);
   } // end if

// now we know this is a bitmap, so read in all the sections

// first the bitmap infoheader

// now load the bitmap file header
_lread(file_handle, &bitmap->bitmapinfoheader,sizeof(BITMAPINFOHEADER));

// now load the color palette if there is one
if (bitmap->bitmapinfoheader.biBitCount == 8)
   {
   _lread(file_handle, &bitmap->palette,256*sizeof(PALETTEENTRY));

   // now set all the flags in the palette correctly and fix the reversed
   // BGR RGBQUAD data format
   for (index=0; index < 256; index++)
       {
       // reverse the red and green fields
       int temp_color = bitmap->palette[index].peRed;
       bitmap->palette[index].peRed  = bitmap->palette[index].peBlue;
       bitmap->palette[index].peBlue = temp_color;

       // always set the flags word to this
       bitmap->palette[index].peFlags = PC_NOCOLLAPSE;
       } // end for index

    } // end if

// finally the image data itself
_lseek(file_handle,-(int)(bitmap->bitmapinfoheader.biSizeImage),SEEK_END);

// now read in the image, if the image is 8 or 16 bit then simply read it
// but if its 24 bit then read it into a temporary area and then convert
// it to a 16 bit image

if (bitmap->bitmapinfoheader.biBitCount==8 || bitmap->bitmapinfoheader.biBitCount==16)
   {
   // allocate the memory for the image
   if (!(bitmap->buffer = (UCHAR *)malloc(bitmap->bitmapinfoheader.biSizeImage)))
      {
      // close the file
      _lclose(file_handle);

      // return error
      return(0);
      } // end if

   // now read it in
   _lread(file_handle,bitmap->buffer,bitmap->bitmapinfoheader.biSizeImage);

   } // end if
else
   {
   // this must be a 24 bit image, load it in and convert it to 16 bit
//   printf("\nconverting 24 bit image...");

   // allocate temporary buffer
   if (!(temp_buffer = (UCHAR *)malloc(bitmap->bitmapinfoheader.biSizeImage)))
      {
      // close the file
      _lclose(file_handle);

      // return error
      return(0);
      } // end if

   // allocate final 16 bit storage buffer
   if (!(bitmap->buffer=(UCHAR *)malloc(2*bitmap->bitmapinfoheader.biWidth*bitmap->bitmapinfoheader.biHeight)))
      {
      // close the file
      _lclose(file_handle);

      // release working buffer
      free(temp_buffer);

      // return error
      return(0);
      } // end if

   // now read it in
   _lread(file_handle,temp_buffer,bitmap->bitmapinfoheader.biSizeImage);

   // now convert each 24 bit RGB value into a 16 bit value
   for (index=0; index<bitmap->bitmapinfoheader.biWidth*bitmap->bitmapinfoheader.biHeight; index++)
       {
       // extract RGB components (note they are in memory BGR)
       // also, assume 5.6.5 format, so scale appropriately
       UCHAR red    = (temp_buffer[index*3 + 2] >> 3), // 5 bits
             green  = (temp_buffer[index*3 + 1] >> 2), // 6 bits, change to 3 for 5 bits
             blue   = (temp_buffer[index*3 + 0] >> 3); // 5 bits

       // build up 16 bit color word assume 5.6.5 format
       USHORT color = _RGB16BIT565(red,green,blue);

       // write color to buffer
       ((USHORT *)bitmap->buffer)[index] = color;

       } // end for index

   // finally write out the correct number of bits
   bitmap->bitmapinfoheader.biBitCount=16;

   } // end if

#if 0
// write the file info out
printf("\nfilename:%s \nsize=%d \nwidth=%d \nheight=%d \nbitsperpixel=%d \ncolors=%d \nimpcolors=%d",
        filename,
        bitmap->bitmapinfoheader.biSizeImage,
        bitmap->bitmapinfoheader.biWidth,
        bitmap->bitmapinfoheader.biHeight,
        bitmap->bitmapinfoheader.biBitCount,
        bitmap->bitmapinfoheader.biClrUsed,
        bitmap->bitmapinfoheader.biClrImportant);
#endif

// close the file
_lclose(file_handle);

// flip the bitmap
Flip_Bitmap(bitmap->buffer,
            bitmap->bitmapinfoheader.biWidth*(bitmap->bitmapinfoheader.biBitCount/8),
            bitmap->bitmapinfoheader.biHeight);

// return success
return(1);

} // end Load_Bitmap_File

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

int Unload_Bitmap_File(BITMAP_FILE_PTR bitmap)
{
// this function releases all memory associated with "bitmap"
if (bitmap->buffer)
   {
   // release memory
   free(bitmap->buffer);

   // reset pointer
   bitmap->buffer = NULL;

   } // end if

// return success
return(1);

} // end Unload_Bitmap_File

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

int Flip_Bitmap(UCHAR *image, int bytes_per_line, int height)
{
// this function is used to flip upside down .BMP images

UCHAR *buffer; // used to perform the image processing
int index;     // looping index

// allocate the temporary buffer
if (!(buffer = (UCHAR *)malloc(bytes_per_line*height)))
   return(0);

// copy image to work area
memcpy(buffer,image,bytes_per_line*height);

// flip vertically
for (index=0; index < height; index++)
    memcpy(&image[((height-1) - index)*bytes_per_line],
           &buffer[index*bytes_per_line], bytes_per_line);

// release the memory
free(buffer);

// return success
return(1);

} // end Flip_Bitmap

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

int Create_BOB(BITMAP_OBJ_PTR bob,    // the bob to create
               int width, int height, // size of bob
               int attr,              // attrs
               int flags = 0)         // memory flag
{
// Create the BOB object, note that all BOBs
// are created as offscreen surfaces in VRAM as the
// default, if you want to use system memory then
// set flags equal to DDSCAPS_SYSTEMMEMORY

DDSURFACEDESC2 ddsd; // used to create surface

// set state and attributes of BOB
bob->state = BOB_STATE_ALIVE;
bob->attr  = attr;
bob->image = NULL;

// set position and velocity to 0
bob->x = bob->y = bob->xv = bob->yv = 0;

// set to access caps, width, and height
memset(&ddsd,0,sizeof(ddsd));
ddsd.dwSize  = sizeof(ddsd);
ddsd.dwFlags = DDSD_CAPS | DDSD_WIDTH | DDSD_HEIGHT;

// set dimensions of the new bitmap surface
ddsd.dwWidth  = bob->width = width;
ddsd.dwHeight = bob->height = height;

// set surface to offscreen plain
ddsd.ddsCaps.dwCaps = DDSCAPS_OFFSCREENPLAIN | flags;

// create the surface
if (lpdd->CreateSurface(&ddsd,&(bob->image),NULL)!=DD_OK)
   return(0);

// set color key to color 0
DDCOLORKEY color_key; // used to set color key
color_key.dwColorSpaceLowValue  = 0;
color_key.dwColorSpaceHighValue = 0;

// now set the color key for source blitting
(bob->image)->SetColorKey(DDCKEY_SRCBLT, &color_key);

// return success
return(1);

} // end Create_BOB

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

int Destroy_BOB(BITMAP_OBJ_PTR bob)
{
// destroy the BOB, simply release the surface

if (bob->image)
   (bob->image)->Release();
else
   return(0);

// return success
return(1);

} // end Destroy_BOB

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

int Draw_BOB(BITMAP_OBJ_PTR bob,       // bob to draw
             LPDIRECTDRAWSURFACE7 dest) // surface to draw the bob on
{
// draw a bob at the x,y defined in the BOB
// on the destination surface defined in dest

RECT dest_rect,   // the destination rectangle
     source_rect; // the source rectangle

// fill in the destination rect
dest_rect.left   = bob->x;
dest_rect.top    = bob->y;
dest_rect.right  = bob->x+bob->width;
dest_rect.bottom = bob->y+bob->height;

// fill in the source rect
source_rect.left    = 0;
source_rect.top     = 0;
source_rect.right   = bob->width;
source_rect.bottom  = bob->height;

// blt to destination surface
dest->Blt(&dest_rect, bob->image,
          &source_rect,(DDBLT_WAIT | DDBLT_KEYSRC),
          NULL);

// return success
return(1);
} // end Draw_BOB

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

int Load_BOB(BITMAP_OBJ_PTR bob, // bob to load with data
             BITMAP_FILE_PTR bitmap, // bitmap to scan image data from
             int cx,int cy,   // cell or absolute pos. to scan image from
             int mode)    // if 0 then cx,cy is cell position, else
                          // cx,cy are absolute coords
{
// this function extracts a bitmap out of a bitmap file

UCHAR *source_ptr,   // working pointers
      *dest_ptr;

DDSURFACEDESC2 ddsd;  //  direct draw surface description

// test the mode of extraction, cell based or absolute
if (mode==0)
   {
   // re-compute x,y
   cx = cx*(bob->width+1) + 1;
   cy = cy*(bob->height+1) + 1;
   } // end if

// extract bitmap data
source_ptr = bitmap->buffer +
      cy*bitmap->bitmapinfoheader.biWidth+cx;

// get the addr to destination surface memory

// set size of the structure
ddsd.dwSize = sizeof(ddsd);

// lock the display surface
(bob->image)->Lock(NULL,
                   &ddsd,
                   DDLOCK_WAIT | DDLOCK_SURFACEMEMORYPTR,
                   NULL);

// assign a pointer to the memory surface for manipulation
dest_ptr = (UCHAR *)ddsd.lpSurface;

// iterate thru each scanline and copy bitmap
for (int index_y=0; index_y<bob->height; index_y++)
    {
    // copy next line of data to destination
    memcpy(dest_ptr, source_ptr,bob->width);

    // advance pointers
    dest_ptr   += (ddsd.lPitch);
    source_ptr += bitmap->bitmapinfoheader.biWidth;
    } // end for index_y

// unlock the surface
(bob->image)->Unlock(NULL);

// set state to loaded
bob->state |= BOB_STATE_LOADED;

// return success
return(1);

} // end Load_BOB

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

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)
{

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 use of WS_POPUP
if (!(hwnd = CreateWindow(WINDOW_CLASS_NAME, // class
                          "WinX Game Console",     // title
                          WS_POPUP | WS_VISIBLE,
                           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);

// hide the 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();

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

} // end WinMain

// WINX GAME PROGRAMMING CONSOLE FUNCTIONS ////////////////

int Game_Init(void *parms)
{
// this function is where you do all the initialization
// for your game

int index; // looping var

// create object and test for error
if (DirectDrawCreateEx(NULL, (void **)&lpdd, IID_IDirectDraw7, NULL)!=DD_OK)
   return(0);

// set cooperation level to windowed mode normal
if (lpdd->SetCooperativeLevel(main_window_handle,
           DDSCL_ALLOWMODEX | DDSCL_FULLSCREEN |
           DDSCL_EXCLUSIVE | DDSCL_ALLOWREBOOT)!=DD_OK)
    return(0);

// set the display mode
if (lpdd->SetDisplayMode(SCREEN_WIDTH,SCREEN_HEIGHT,SCREEN_BPP,0,0)!=DD_OK)
   return(0);

// Create the primary surface
memset(&ddsd,0,sizeof(ddsd));
ddsd.dwSize = sizeof(ddsd);
ddsd.dwFlags = DDSD_CAPS | DDSD_BACKBUFFERCOUNT;

// we need to let dd know that we want a complex
// flippable surface structure, set flags for that
ddsd.ddsCaps.dwCaps =
  DDSCAPS_PRIMARYSURFACE | DDSCAPS_FLIP | DDSCAPS_COMPLEX;

// set the backbuffer count to 1
ddsd.dwBackBufferCount = 1;

// create the primary surface
lpdd->CreateSurface(&ddsd,&lpddsprimary,NULL);

// query for the backbuffer i.e the secondary surface
ddscaps.dwCaps = DDSCAPS_BACKBUFFER;
lpddsprimary->GetAttachedSurface(&ddscaps,&lpddsback);

// create and attach palette

// create palette data
// first clear out all the entries, defensive programming
memset(palette,0,256*sizeof(PALETTEENTRY));

// create a R,G,B,GR gradient palette
for (index=0; index<256; index++)
    {
    palette[index].peRed = rand()%256;
    palette[index].peGreen = rand()%256;
    palette[index].peBlue = rand()%256;
    // set flags
    palette[index].peFlags = PC_NOCOLLAPSE;
    } // end for index

    palette[0].peRed = 0;
    palette[0].peGreen = 0;
    palette[0].peBlue =0;

// now create the palette object
if (lpdd->CreatePalette(DDPCAPS_8BIT | DDPCAPS_INITIALIZE | DDPCAPS_ALLOW256,
                         palette,&lpddpal,NULL)!=DD_OK)
   return(0);

// attach the palette to the primary
if (lpddsprimary->SetPalette(lpddpal)!=DD_OK)
   return(0);

// now load the 8 bit color bitmap
Load_Bitmap_File(&bitmap8bit, "ROCK8.BMP");

// now load the palette into the directdraw
lpddpal->SetEntries(0,0,256,bitmap8bit.palette);

// create BOBs
for (index=0; index<NUM_ASTEROIDS; index++)
    {
    // create the bob
    Create_BOB(&asteroids[index],64,64,0,DDSCAPS_SYSTEMMEMORY);

    // extract a bitmap image for the BOB from the large bitmap
    Load_BOB(&asteroids[index],&bitmap8bit,rand()%4,0,0);

    // set random position and velocity
    asteroids[index].x = rand()%SCREEN_WIDTH;
    asteroids[index].y = rand()%SCREEN_HEIGHT;

    asteroids[index].xv = -8 + rand()%16;
    asteroids[index].yv = -8 + rand()%16;

    } // end for index

// clear the primary and secondary surfaces
memset(&ddbltfx,0,sizeof(ddbltfx));
ddbltfx.dwSize = sizeof(ddbltfx);
ddbltfx.dwFillColor = 0;

lpddsprimary->Blt(NULL,NULL,NULL,DDBLT_COLORFILL | DDBLT_WAIT,&ddbltfx);
lpddsback->Blt(NULL,NULL,NULL,DDBLT_COLORFILL | DDBLT_WAIT,&ddbltfx);

// delete the bitmap
Unload_Bitmap_File(&bitmap8bit);

// 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

// delete bobs
for (int index=0; index<NUM_ASTEROIDS; index++)
    Destroy_BOB(&asteroids[index]);

// first release the secondary surface
if (lpddsback!=NULL)
   lpddsback->Release();

// now release the primary surface
if (lpddsprimary!=NULL)
   lpddsprimary->Release();

// release the directdraw object
if (lpdd!=NULL)
   lpdd->Release();

// 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 you game go here!
int index; // looping variable

// check of user is trying to exit
if (KEY_DOWN(VK_ESCAPE) || KEY_DOWN(VK_SPACE))
    PostMessage(main_window_handle, WM_DESTROY,0,0);

// clear secondary buffer
memset(&ddbltfx,0,sizeof(ddbltfx));
ddbltfx.dwSize = sizeof(ddbltfx);
ddbltfx.dwFillColor = 0;
lpddsback->Blt(NULL,NULL,NULL,DDBLT_COLORFILL | DDBLT_WAIT,&ddbltfx);

// move asteroids
for (index=0; index<NUM_ASTEROIDS; index++)
    {
    asteroids[index].x+=asteroids[index].xv;
    asteroids[index].y+=asteroids[index].yv;
    } // end for index

// check if asteroids are off screen boundaries
for (index=0; index<NUM_ASTEROIDS; index++)
    {
    // x bounds
    if (asteroids[index].x > SCREEN_WIDTH)
       asteroids[index].x = -asteroids[index].width;
    else
    if (asteroids[index].x < -asteroids[index].width)
        asteroids[index].x = SCREEN_WIDTH;

    // y bounds
    if (asteroids[index].y > SCREEN_HEIGHT)
        asteroids[index].y = -asteroids[index].height;
    else
    if (asteroids[index].y < -asteroids[index].height)
       asteroids[index].y = SCREEN_HEIGHT;
    } // end for index

// draw all asteroids
for (index=0; index<NUM_ASTEROIDS; index++)
     Draw_BOB(&asteroids[index], lpddsback);

// flip pages
while(lpddsprimary->Flip(NULL, DDFLIP_WAIT)!=DD_OK);

// slow things down
Sleep(30);

// return success
return(1);

} // end Game_Main