32 bit DIB from 24 bit bitmap

[bitshifter420]

Hello, I have a Win32 GDI question...
I need a way to make a 32 bit DIB from a 24 bit bitmap.
I can load the bitmap with LoadImage but how to make it a 32 bit DIB?
Any help would be greatly appreciated...

[olivthill2]

When your image is loaded, then use GetDIBits() with the argument containing the BITMAPINFO structure indicating you want a 32-bit bitmap, i.e. with bi.bmiHeader.biBitCount = 32:

   BITMAPINFO bi;
...
   bi.bmiHeader.biSize = sizeof(bi.bmiHeader);
   bi.bmiHeader.biWidth = picture_width;
   bi.bmiHeader.biHeight = - picture_height;
   bi.bmiHeader.biPlanes = 1;
   bi.bmiHeader.biBitCount = 32;
   bi.bmiHeader.biCompression = BI_RGB;
   bi.bmiHeader.biSizeImage = bi.bmiHeader.biWidth * 4 * bi.bmiHeader.biHeight * -1 * sizeof(unsigned char);
   bi.bmiHeader.biClrUsed = 0;
   bi.bmiHeader.biClrImportant = 0;
...
   if (!GetDIBits(hdc_mem, hbm, 0, picture_height, DIBits, &bi, DIB_RGB_COLORS)) {
...

Google will probably give you more complete examples.

[bitshifter420]

Ok, i have come up with a simple solution.
This is how to create an offscreen buffer (DIB32)
and load a 24bit texture and make it DIB32 compatible.
It seems i dont need to set the bmiHeader.biSizeImage value? Just zero it?

   // First we need a device context that is compatible
   // with the desktop settings. (1024x768x32 on my PC)

   HDC BufferDC = CreateCompatibleDC(NULL);

   // Now we describle a format for the offscreen buffer.

   BITMAPINFO BufferInfo;
   ZeroMemory(&BufferInfo,sizeof(BITMAPINFO));
   BufferInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
   BufferInfo.bmiHeader.biWidth = GetSystemMetrics(SM_CXSCREEN);
   BufferInfo.bmiHeader.biHeight = GetSystemMetrics(SM_CYSCREEN);
   BufferInfo.bmiHeader.biPlanes = 1;
   BufferInfo.bmiHeader.biBitCount = 32;
   BufferInfo.bmiHeader.biCompression = BI_RGB;

   // Create a device independant bitmap for the offscreen buffer.

   HBITMAP BufferBitmap = CreateDIBSection(
      BufferDC,
      &BufferInfo,
      DIB_RGB_COLORS,
      (void**)&g_Buffer.first, // Store pointer to first pixel in this value.
      NULL,0); // No file mapping crap.

   // Describe the texture format.
   // Same as buffer format but with hardwired size.

   BITMAPINFO TextureInfo = BufferInfo;
   TextureInfo.bmiHeader.biWidth = 100;
   TextureInfo.bmiHeader.biHeight = 100;

   // Create device independant bitmap for texture.

   HBITMAP TextureBitmap = CreateDIBSection(
      BufferDC,
      &TextureInfo,
      DIB_RGB_COLORS,
      (void**)&g_Texture.first, // Store pointer to first pixel in this value.
      NULL,0); // No file mapping crap.

   // Load the 24bit image from file.

   HBITMAP hImage = (HBITMAP)LoadImage(
      NULL, // No HINSTANCE since its not a resource.
      "Image.bmp",
      IMAGE_BITMAP,
      TextureInfo.bmiHeader.biWidth,
      TextureInfo.bmiHeader.biHeight,
      LR_LOADFROMFILE);

   // Transfer the bitmap into the texture DIB.

   GetDIBits(
      BufferDC,
      hImage,
      0,                              // First scan line.
      TextureInfo.bmiHeader.biHeight, // Number of scan lines.
      g_Texture.first,                // Pointer to first pixel.
      &TextureInfo,                   // Address of BITMAPINFO with desired specs.
      DIB_RGB_COLORS);

   // Were done with the inage so...

   DeleteObject(hImage);

   // Select the buffer for rendering to.

   HBITMAP OldBitmap = (HBITMAP)SelectObject(BufferDC,BufferBitmap);

   // Dont forget to clean up later :)