creating CBitmap from byte values 1

[cisotta]

I'm trying to create a 256 graylevel CBitmap object, having the pixel values retrieved from a BYTE array.
I think I have to setup a BITMAPINFO structure, define the palette and then allocate the CBitmap object and set the bit values, but I can't manage with the palette definition stuff.

This is my code:

BITMAPINFO bmInfo;
BITMAPINFOHEADER &bmInfohdr = (BITMAPINFOHEADER)bmInfo.bmiHeader;

bmInfohdr.biSize = 40 + 255; //I think it's not of use
bmInfohdr.biWidth = x;
bmInfohdr.biHeight = y;
bmInfohdr.biPlanes=1;
bmInfohdr.biBitCount=8;
bmInfohdr.biCompression=0;
bmInfohdr.biSizeImage=0;
bmInfohdr.biXPelsPerMeter = 0;
bmInfohdr.biYPelsPerMeter = 0;
bmInfohdr.biClrUsed = 0;
bmInfohdr.biClrImportant = 0;

// should I allocate memory further than the
// bmColors[1]?? anyway the compiler gives an
// error for type mismatch!
//bmInfo.bmiColors = (RGBQUAD *)
malloc(sizeof(RGBQUAD) * 256);

// here I define the 256 graylevel palette
for (int i=0; i<256; i++)
{
bmInfo.bmiColors.rgbRed = i;
bmInfo.bmiColors.rgbGreen = i;
bmInfo.bmiColors.rgbBlue = i;
}


BYTE *matrix;
matrix = (BYTE*)malloc(size*sizeof(BYTE));
// here I put the BYTE values of the pixels

CDC *pdcDest = this->GetDC();

HBITMAP hBmp = CreateDIBitmap( pdcDest->m_hDC,
&bmInfohdr,
CBM_INIT,
matrix,
&bmInfo,
DIB_RGB_COLORS);
m_bmpBitmap.Attach( hBmp );


But when I load the m_bmpBitmap to screen, it's empty!
Can someone help me?
thanks,
francesco

 

[teriviret]

One problem is on the very first line:

BITMAPINFO bmInfo;

This only leaves space for 1 entry in the palette. Instead, allocate a larger chunk of memory like this:

char chunk [sizeof (BITMAPINFOHEADER) + sizeof (RGBQUAD) * 256];
BITMAPINFO &bmInfo = * (BITMAPINFO *) &chunk [0];

There might be other bugs in your code but this one practically leaped off the screen at me.