The PtInRegion function determines whether the specified point is inside the specified region.
BOOL PtInRegion(
| HRGN hrgn, | // handle of region | 
| int X, | // x-coordinate of point | 
| int Y | // y-coordinate of point | 
| ); | 
If the specified point is in the region, the return value is nonzero.
If the specified point is not in the region, the return value is zero.