coyote: CGPIXMAPWINDOW__DEFINE

Description
This is the "object" behind cgPixmap. It is a subclassed cgCmdWindow object
and behaves almost identically, except that normally the draw widget at the
heart of the window is invisible. That is, it is a pixmap.
Default properties of the object can be controled with cgWindow_SetDefs and cgControl,
as with cgWindow. Be sure to delete the pixmap object when you are done with it, by
using (for example) cgDelete.
Categories
Graphics
Author
FANNING SOFTWARE CONSULTING::
   David W. Fanning 
   1645 Sheely Drive
   Fort Collins, CO 80526 USA
   Phone: 970-221-0438
   E-mail: david@idlcoyote.com
   Coyote's Guide to IDL Programming: http://www.idlcoyote.com
Copyright
Copyright (c) 2012, Fanning Software Consulting, Inc.
History
Change History::
   Created from cgCmdWindow, 7 February 2012. DWF.
   Problem with the ASPECT keyword, which should have been named WASPECT. 7 Oct 2012. DWF.
   Added WDestroyObjects keyword to destroy objects parameters, if needed. 11 November 2012. DWF.
   Confusion trying to change WBackground keyword to Background. Changed it back. Identical to ASPECT
      problem described above. 18 Jan 2013. DWF.
 method initializes the pixmap object.
Params
class: out, optional, type=struct
    The object class structure definition. Occasionally useful.
Keywords
visible: in, optional, type=boolean
   Set this keyword to make the pixmap visible.
_extra: in, optional
   Any keywords appropriate for the SetProperty method of the superclass object.
definition module for the cgPixmapWindow object