Apple II
Technical Notes
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                                                  Developer Technical Support


Apple IIGS
#10:    InvalRgn Twist

Revised by:    Steven Glass                                     November 1988
Written by:    Guillermo Ortiz                                     April 1987

InvalRgn(RgnHandle) accumulates the region to which RgnHandle points into the 
update region of the current window's port; in the process, it makes the 
region global, thus causing problems if later calls expect the region to still 
be local.
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The region you pass to InvalRgn is local to the window to which it is related; 
however, InvalRgn returns the region in global coordinates.  To preserve the 
original region for your use after the call to InvalRgn, you should duplicate 
it and use the copy to make the call then dispose of the copy when InvalRgn 
returns.  The following example demonstrates the process:

    void MyInvalReg(RegHandle)

    handle RegHandle;
    {
    handle AuxHandle;

    AuxHandle = NewRgn();            /* create room */
    CopyRgn(RegHandle,AuxHandle);    /* make a copy  */
    InvalRgn(AuxHandle);             /* do it with the copy */
    DisposeRgn(AuxHandle);           /* now get rid of it! */
    }


Further Reference
o    Apple IIGS Toolbox Reference, Volume 2

