_gtRectSize()
 Determine the buffer size needed to save a specified screen region
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 C Prototype

     #include "gt.api"
     ERRCODE _gtRectSize(
                          USHORT  uiTop,
                          USHORT  uiLeft,
                          USHORT  uiBottom,
                          USHORT  uiRight,
                          USHORTP uipBuffSize
                        )

 Arguments

     uiTop, uiLeft, uiBottom, and uiRight define the coordinates
     of the rectangular region to be calculated.  If all coordinates are
     NULL, the entire display region is used.

     uipBuffSize is the size of the buffer needed to contain the
     specified region.

 Returns

     _gtRectSize() returns zero if successful.  Any other value indicates an
     error.

 Description

     _gtRectSize() analyzes the specified screen region, determines the
     buffer size needed to save it, and saves the buffer size as a numeric
     value.

 Examples

     .  This example uses _gtRectSize() to calculate the memory needed
        by _xvalloc() (see the "Virtual Memory API Reference" chapter of this
        guide) to properly save the screen buffer:

        #include "gt.api"
        #include "vm.api"
        .
        .
        .
           BYTEP    psBuff;
           USHORT   uiBuffSize;
           HANDLE   hVM;

           _gtRectSize( 1, 1, 10, 25, &uiBuffSize );

           hVM      = _xvalloc( uiBuffSize, 0 );
           scrBuff  = _xvlock( hVM );
           _gtSave( 1, 1, 10, 25, fpBuff );   // Save area under rect
           .
           . <manipulate screen>
           .
           _gtRest( 1, 1, 10, 25, fpBuff );   // Restore screen

           _xvunlock( hVM );

           _xvfree( hVM );
        .
        .
        .

 Files  Library is CLIPPER.LIB, header file is Gt.api.