hdc (HDC) - input

Device context handle.

hrgn (HRGN) - input

Region handle.

pptlPoint (PPOINTL) - input

Pointer to (x, y) point specified in device coordinates.

pInstance (PVOID) - input

Pointer to instance data.

lFunction (ULONG) - input

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

rc (LONG) - returns

Return codes.

This function returns an integer (lInside) indicating whether the point is inside the region:

RGN_ERROR

Error
PRGN_INSIDE
In region
PRGN_OUTSIDE
Not in region.
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_HRGN_BUSY PMERR_INV_COORDINATE
PMERR_INV_HRGN
PMERR_INV_RECT
PMERR_REGION_IS_CLIP_REGION

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