Clips given source bounds and dest position.

procedure ClipCopyBounds(var SrcX: LongInt; 
                         var SrcY: LongInt; 
                         var Width: LongInt; 
                         var Height: LongInt; 
                         var DstX: LongInt; 
                         var DstY: LongInt; 
                         SrcImageWidth: LongInt; 
                         SrcImageHeight: LongInt; 
                         const DstClip: TRect);

ImagingUtility (at line 278)

It is used by various CopyRect functions that copy rect from one image to another. It handles clipping the same way as Win32 BitBlt function.