Legacy Document

Inside Macintosh: Imaging With QuickDraw /

Chapter 3 - QuickDraw Drawing / QuickDraw Drawing Reference

Routines / Creating and Managing Regions

EmptyRgn

To determine whether a region is empty, use the EmptyRgn function.

FUNCTION EmptyRgn (rgn:\xDDRgnHandle):\xDDBoolean;

rgn

A handle to the region to test for emptiness.

DESCRIPTION

The EmptyRgn function returns TRUE if the region whose handle you pass in the rgn parameter is an empty region or FALSE if it is not.

SEE ALSO

The EmptyRgn function does not create an empty region. To create an empty region, you can perform any of the following operations:

• use the NewRgn function (described on page 3-83)
• pass the handle to an empty region to the CopyRgn procedure (described on page 3-86)
• pass an empty rectangle to either the SetRectRgn procedure (described on page 3-87) or the RectRgn procedure (described on page 3-88)
• call the CloseRgn procedure (described on page 3-85) without a previous call to the OpenRgn procedure
• call CloseRgn without performing any drawing after calling OpenRgn
• pass an empty region to the OffsetRgn procedure (described on page 3-89)
• pass an empty region or too large an inset to the InsetRgn procedure (described on page 3-89)
• pass two nonintersecting regions to the SectRgn procedure (described on page 3-90)
• pass two empty regions to the UnionRgn procedure (described on page 3-91)
• pass two identical or nonintersecting regions to the DiffRgn (described on page 3-92) or XorRgn (described on page 3-92) procedure