       The program tksipp is a Tk wish shell containing TSIPP and
       additional support for render to Tk photo images.

       During the rendering of a scene, events  will  be  handled
       via  the  Tk  update  mechanism.  The update period may be
       specified as an option to any of the  rendering  commands.
       The  unit of the update period is approximately the amount
       of time taken to render one pixel  in  an  average  scene.
       The  updates  themselves  occur at points in the rendering
       other than the direct rendering of the picture, this  time
       unit  is  just  a  guideline.  Specifying a smaller period
       makes an application more responsive, specifying a  larger
       period speeds the rendering.

       SIPP  commands  may not be used by events that occur while
       rendering, they will return an error if this is attempted.
       The SippInfo command may be used to determine if rendering
       is in progress.  An application  should  normally  disable
       any  widgets  that  might  invoke a command that result in
       SIPP commands being executed while a during rendering.  It
       is possible to abort a rendering in progress with the Sip-
       pAbortRender command.

       See the Tk photo image manual page for details in  how  to
       create  and manage Tk photo images.  Photo images may have
       images displayed on it with the SippRender or the SippCopy
       commands.   The  images  is  initialized to the background
       color at the start of the output.  Photo  images  have  no
       internal  background color, by default, they are transpar-
       ent.  I maybe desirable to set the background color of the
       widget  that  the  image is to be displayed on to be back-
       ground color that will be used during rendering.  The Sip-
       pColor command can be useful for this.
