This
function returns the handle of the clip region:
hrgn
Region handle
NULL
Null handle (no region selected)
HRGN_ERROR
Error
Possible
Errors Detected: When an error is detected, the handling routine must
call WinSetErrorInfo to post the condition. Error codes for conditions that
the handling routine is expected to check include:
PMERR_HDC_BUSY PMERR_INV_HDC
Refer
to the "Error Explanations" section in the Presentation Manager Programming
Reference for further explanation.