[SDL] Converting an SDL_Surface to BMP format in memory

[Phase GmbH]

Hi Erik,

in my Windows programs I use the follwing code:

If the Image is 8 Bit Black and White:

if( bitmapWidth%4)
   padding_bytes=4- (bitmapWidth%4);  // the width bytes  must aways fit 
DWORD units
else
  padding_bytes=0;

filesize   = sizeof(BITMAPFILEHEADER)     +
                     sizeof(BITMAPINFOHEADER)     +
                     256 * sizeof(RGBQUAD)        +
                     (bitmapWidth+padding_bytes)*bitmapHeight;

If RGB:

if( (bitmapWidth*3)%4)
   padding_bytes=4- (bitmapWidth%4);  // the width bytes must aways fit 
DWORD units
else
  padding_bytes=0;

filesize   = sizeof(BITMAPFILEHEADER)     +
                     sizeof(BITMAPINFOHEADER)     +
                     bitmapHeight*(bitmapWidth*3 + padding_bytes);

Hope this helps.

Chris
----- Original Message ----- 
From: "E. Wing" <ewmailing at gmail.com>
Newsgroups: gmane.comp.lib.sdl
Sent: Saturday, June 10, 2006 5:31 PM
Subject: Converting an SDL_Surface to BMP format in memory


>I just picked up Sam's old clipboard demo "scrap". For copying images
> to the clipboard, it seems that SDL_surfaces are converted to BMPs and
> then are serialized into char* buffers so they can be passed through
> the API.
>
> The demo code does this by calling SDL_SaveBMP on the SDL_Surface and
> writes a temporary file. Then the file is read back in directly into a
> char* buffer using fread().
>
> I was wondering how to accomplish this without writing to the file
> system. I was thinking of using RWops for this like so:
>
> // Contents of the image_surface are converted to BMP and placed in 
> scrap_buffer
> SDL_SaveBMP_RW(image_surface, SDL_RWFromMem(scrap_buffer, scraplen), 1);
>
> But I think I have a problem with this because I think I need to make
> sure the buffer is large enough to hold the BMP. But I don't know the
> size should be.
>
> Assuming this is the right approach, is there a safe way I can
> determine the size the buffer needs to be?
>
> I'm thinking along the lines of:
>
> scraplen = image->h * image->pitch * image->format->BytesPerPixel +
> max_header_bytes
>
> Does this look reasonable? Can somebody tell me what the magic number
> for max_header_bytes should be for SDL_SaveBMP_RW?
>
> Thanks,
> Eric