Legacy Document

Inside Macintosh: Imaging With QuickDraw /

Chapter 3 - QuickDraw Drawing / QuickDraw Drawing Reference

Routines / Creating and Managing Regions

XorRgn

To calculate the difference between the union and the intersection of two regions, use the XorRgn procedure.

PROCEDURE XorRgn (srcRgnA,srcRgnB,dstRgn: RgnHandle);

srcRgnA

A handle to the first of two regions to compare.

srcRgnB

A handle to the second of two regions to compare.

dstRgn

A handle to the region to hold the result.

DESCRIPTION

The XorRgn procedure calculates the difference between the union and the intersection of the regions whose handles you pass in the srcRgnA and srcRgnB parameters and places the result in the region whose handle you pass in the dstRgn parameter.

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

If the regions are coincident, XorRgn sets the destination region to the empty region defined by the rectangle (0,0,0,0).

SPECIAL CONSIDERATIONS

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

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