|Microsoft DirectX 9.0|
The CountPrefixBits method calculates the number of zero bits at the start of a specified bit field.
DWORD CountPrefixBits( const DWORD Field );
Specifies a bit field as a DWORD value.
Returns the number of zero bits that occur before the first 1 bit, or 0x80000000 if all bits are zero.
This method is useful for working with color masks in VIDEOINFO structures.