hdc (HDC) - input

Device context handle.

hrgn (HRGN) - input

Region handle.

When NULL, the clip region is set to clipping (the initial state).

phrgnOld (PHRGN) - output

Pointer to previously selected region handle. If this is a NULL handle, there was no clip region.

pInstance (PVOID) - input

Pointer to instance data.

lFunction (ULONG) - input

High-order WORD=flags; low-order WORD=NGreSelectClipRegion.

rc (LONG) - returns

Return codes.

This function returns an integer (lComplexity) indicating the complexity of the DC region:

RGN_ERROR

Error
RGN_NULL
Null region
RGN_RECT
Rectangular region
RGN_COMPLEX
Complex region (more than 1 rectangle)
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_DEV_FUNC_NOT_INSTALLED PMERR_HDC_BUSY
PMERR_HRGN_BUSY
PMERR_INSUFFICIENT_MEMORY
PMERR_INV_COORDINATE
PMERR_INV_HDC
PMERR_INV_HRGN
PMERR_INV_IN_AREA
PMERR_INV_IN_PATH
PMERR_INV_RECT
PMERR_INV_REGION_CONTROL
PMERR_REGION_IS_CLIP_REGION

Refer to the "Error Explanations" section in the Presentation Manager Programming Reference for further explanation.