Loading and blitting bitmaps

Loading and blitting bitmaps
by Matthew Allen
MXF Entertainment
updated: 2/12/00

I'll just rape this tutorial from a few posts I made on GameDev.net. Ya know, GameDev kicks ass! For more bitmap blitting and loading functions, look at the notTETRIS source.

The files ddutil.cpp and ddutil.h can be found here.

Words of wisdom:

posted November 04, 1999 09:23 PM

Ok, so you have DirectDraw set up and you want to load a bitmap and display it on the screen, right? It's really easy, there's only a couple of steps you need to follow:

Create a surface for the bitmap.
Load the bitmap into the surface.
Blit the bitmap onto the back buffer.
Flip the back buffer to the primary surface. (you can do this, right?)

1. and 2.
Luckily, Microsoft made a function that creates an offscreen surface and loads a bitmap into it: DDLoadBitmap(). To use this, though, you need to get the files "ddutil.cpp" and "ddutil.h" from the DirectDraw SDK. If you don't have them and want em, I can send them to you.

Now, after you've included the ddutil.h file, call DDLoadBitmap() like this:


LPDIRECTDRAWSURFACE4 lpDDSBitmap = NULL;

if ( ( lpDDSBitmap = DDLoadBitmap( lpDD, "bitmap.bmp", 0, 0) ) == NULL )
   return FALSE;

Now the bitmap is loaded into lpDDSBitmap!

3.
To blit the bitmap onto the back buffer, call BltFast():


RECT rcFrom;
rcFrom.left = 0;
rcFrom.top = 0;
rcFrom.right = BITMAP_WIDTH;
rcFrom.bottom = BITMAP_HEIGHT;

if ( FAILED( lpDDSBack->BltFast( 0, 0, lpDDSBitmap, &rcFrom, DDBLTFAST_WAIT ) ) )
   return FALSE;

What the DDLoadBitmap() function does is creates a HBITMAP and a DirectDraw sufrace, uses a Windows function (LoadImage()) to load the bitmap from a resource or a file into the HBITMAP, then blits the bitmap from the HBITMAP to the DirectDraw Surface using another Windows function (StretchBlt()).

If you need any more help, send me and email or post to this thread.

I would suggest that you look over the function really well before you use it so you know what it's doing...

posted November 08, 1999 02:44 PM

To make a couple of back buffers, you have to make the primary surface with the "two back buffers" flag:


// You have to zero the memory so random bits that were in the memory
// where the variable was created won't mess up the things up.
ZeroMemory( &ddsd, sizeof( ddsd ) );

// This is so the functions know how big the ddsd variable is.
ddsd.dwSize = sizeof( ddsd );

// The DDSD_CAPS flag lets DirectDraw know that the ddsd.ddsCaps.dwCaps
// variable is being used. DDSD_BACKBUFFERCOUNT lets the program know
// that the ddsd.dwBackBufferCount variable is valid (and that there
// will be back buffers to this surface).
ddsd.dwFlags = DDSD_CAPS | DDSD_BACKBUFFERCOUNT;

// DDSCAPS_PRIMARYSURFACE: lets DirectDraw know that this is the primary
// surface. DDSCAPS_FLIP: it can be flipped (back buffers can be used).
// DDSCAPS_COMPLEX: the surface has backbuffers, so it's complex.
ddsd.ddsCaps.dwCaps = DDSCAPS_PRIMARYSURFACE | DDSCAPS_FLIP | DDSCAPS_COMPLEX;
ddsd.dwBackBufferCount = 2;

// Create the primary surface.
if ( FAILED( lpDD->CreateSurface( &ddsd, &lpDDSPrimary, NULL ) ) )
   return FALSE;

Now the primary surface has been created with two back buffers, but you need to call GetAttachedSurface() to actually be able to access the back buffer:


// Again, make sure the memory is cleared.
ZeroMemory( &ddscaps, sizeof( ddscaps ) );

// The surface being created is a back buffer.
ddscaps.dwCaps = DDSCAPS_BACKBUFFER;

// Get the back buffer!
if ( FAILED( lpDDSPrimary->GetAttachedSurface( &ddscaps, &lpDDSBack ) ) )
   return FALSE;

You have to call GetAttachedSurface instead of CreatSurface because the back buffer has to be "a part of" another surface. DirectDraw needs to know which surface each backbuffer belongs to.
You really ahve two back buffers (dwBackBufferCount) but you only need to draw onto one of them. The other one is kindof a "middlebuffer". This is how it works: you write to the back buffer, call "flip", the back buffer goes to the middlebuffer, call flip again and the middle buffer goes to the primary surface. This may seem slower, but it really speeds things up. Read the part in Inside DirectX about back buffers.

Now that you have a back buffer and a primary surface, what you need to do is:

create another surface
load a bitmap into it
blit that onto the back buffer
4. flip the surfaces

I could send you a file that came with the directx SDK, ddutil.cpp, that create a surface and loads a bitmap into it. So, you call that and then blit that onto the back buffer with BltFast(), a DirectDraw function (look at the help file). After that, call Flip() (also, look at the help file).

You should have it call BltFast() and Flip() in a loop, say in WinMain() after it processes a message.

I really hope that is what you wanted because it took a damn long time to write.

If it doesn't help, post back here. Or I suppose you could get on ICQ...

posted November 08, 1999 02:51 PM

Here's some code to grind on:


int PASCAL WinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow )
{
   // This stores the messages that Windows sends the program.
   MSG message;

   // Init the system stuff.
   if ( sys_Init( hInstance, nCmdShow ) == FALSE )
      return FALSE;

   // Get, Translate, and Dispatch the messages that Windows give the program.
   while ( TRUE )
   {
      // Process All Pending Window Messages
      while ( PeekMessage( &message, NULL, 0, 0, PM_NOREMOVE ) == TRUE )
      {
         if ( GetMessage( &message, NULL, 0, 0 ) )
         {
            TranslateMessage( &message );
            DispatchMessage( &message );
         }
         else
            return TRUE;
      }

      // Blit to the back buffer. xTo and yTo are where it's blitted to.
      // It blits the whole lpDDSBitmap surface.
      int xTo = 0, yTo = 0;
      if ( FAILED( lpDDSBack->BltFast( xTo, yTo, lpDDSBitmap, NULL, DDBLTFAST_WAIT ) ) )
         return FALSE;

      // Flip the surface. This makes the back buffer the primary surface and vice versa.
      if ( FAILED( lpDDSPrimary->Flip( NULL, DDFLIP_WAIT ) ) )
         return FALSE;
   } 

   return message.wParam;
}

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Date this article was posted to GameDev.net: 7/5/2000
(Note that this date does not necessarily correspond to the date the article was written)

See Also:
DirectDraw