Combine StretchBlt and TransparentBlt properly, so transparent bitmap can be created properly - c++

Question

INTRODUCTION AND RELEVANT INFORMATION:
Recently, I have asked, here in SO, a question about scaling a bitmap properly, so it can keep the quality of the picture:
Bitmap loses quality when stretched/shrinked on buttons background.
I have tried to employ a suggestion made in a comment, to use `StretchBlt, so I have made a small demo program.
It did improve the bitmaps sharpness, after I have set stretch mode to BLACKONWHITE.
I would like to try to make the portion of the bitmap, with the certain color-say black for example, transparent.
I have used TransparentBlt before, but I don't know how to do it now.
PROBLEM:
In order to preserve the sharpness of the picture, I need to StretchBlt it in the memory DC, with stretch mode being BLACKONWHITE.
The problem is that I do not know how to Blt it transparently into main window's DC.
Here is a code snippet from the demo app:
case WM_PAINT:
{
// main window's DC
hdc = BeginPaint(hWnd, &ps);
// main window's client rectangle
RECT r;
GetClientRect( hWnd, &r );
// memory DC for double buffering
HDC MemDC = CreateCompatibleDC( hdc );
// fill it with test brush
FillRect( MemDC, &r, (HBRUSH)GetStockObject( GRAY_BRUSH ) );
// select loaded bitmap into memory DC
HBITMAP old = (HBITMAP)SelectObject( MemDC, bmp );
// get bitmaps dimensions
BITMAP b;
GetObject( bmp, sizeof(BITMAP), &b );
// needed to preserve bitmap's sharpness
SetStretchBltMode( hdc, BLACKONWHITE );
StretchBlt( hdc, 0, 0, r.right - r.left, r.bottom - r.top,
MemDC, 0, 0, b.bmWidth, b.bmHeight, SRCCOPY );
/* TransparentBlt( ... ); call should go here,
so I can make portion of the bitmap transparent,
in order for the gray brush can be seen */
// cleanup
SelectObject( MemDC, old );
DeleteDC(MemDC);
EndPaint(hWnd, &ps);
}
return 0L;
break;
QUESTION:
How to modify the above code, so a bitmap can be transparent, in order for test brush to be seen ?
The original image is bellow.
I just need to use TransparentBlt( ..., RGB( 0, 0, 0 ) ); to make it transparent in black areas.
The example picture that shows result:
MY EFFORTS:
Browsing through Internet, I have found only simple tutorials, regarding double buffering.
I haven't found anything like this, but to be honest, I am inexperienced in WIN32 API, so I don't know how to phrase the question properly, in order to get better search results.
If further information is required, ask for it and I will supply it.
It is omitted to keep the question short.

Answer 1

You Need to create a mask use specific raster operations to copy only the Pixels were the mask is defined.
http://www.winprog.org/tutorial/transparency.html
The next code is MFC, but you can easily extract and convert the MFC objects into the Standard GDI operations.
http://www.codeproject.com/Articles/703/Drawing-Transparent-Bitmap-with-ease-with-on-the-f