Legacy Document

Inside Macintosh: Imaging With QuickDraw /

Chapter 3 - QuickDraw Drawing / QuickDraw Drawing Reference

Routines / Creating and Managing Regions

UnionRgn

To calculate the union of two regions, use the UnionRgn procedure.

PROCEDURE UnionRgn (srcRgnA,srcRgnB,dstRgn:\xDDRgnHandle);

srcRgnA

A handle to the first of two regions whose union is to be determined.

srcRgnB

A handle to the second of two regions whose union is to be determined.

dstRgn

A handle to the region to hold the resulting union area.

DESCRIPTION

The UnionRgn procedure calculates the union of the two regions whose handles you pass in the srcRgnA and srcRgnB parameters, and it places the union in the region whose handle you pass in the dstRgn parameter. If both regions are empty, UnionRgn sets the destination to the empty region defined by the rectangle (0,0,0,0).

The UnionRgn procedure does not create the destination region; you must have already allocated memory for it by using the NewRgn function.

The destination region may be one of the source regions, if desired.

SPECIAL CONSIDERATIONS

The UnionRgn procedure may temporarily use heap space that's twice the size of the two input regions.

The UnionRgn procedure may move or purge memory blocks in the application heap. Your application should not call this procedure at interrupt time.