| DirectX SDK | 
The RGBA_GETALPHA macro retrieves the alpha component of an RGBA D3DCOLOR value.
RGBA_GETALPHA(rgb) ((rgb) >> 24)
Returns the alpha component.
  Windows NT/2000: Requires Windows NT 4.0 SP3 or later.
  Windows 95/98: Requires Windows 95 or later. Available as a redistributable for Windows 95.
  Windows CE: Unsupported.
  Version: Requires DirectX 2.0 or later.
  Header: Declared in d3dtypes.h.