TurtleWindow             Defines a Graphics Window for the Turtle

 TurtleWindow(CX,CY,Width,Height : Integer);                          [TG/TP]

    Defines the current graphics window in terms of turtle coordinates.
    Turtle coordinates always place (0,0) at the center of the current
    window. The pixel location (CX, CY) will be the point at which the
    turtle coordinate (0,0) will be located. The Width parameter specifies
    the width of the turtle window in pixels, while the Height parameter
    specifies the height of the turtle window in pixels.

           CX,CY    Turtle coordinate (0,0); center of window in pixels.

           Width    Width of window in pixels.

          Height    Height of window in pixels.

          Notes:    The default Turtle Window when entering a graphics
                    mode is the entire screen. The parameter values for
                    these windows are defined below:

              Mode       CX    CY   Width   Height    X-Range      Y-Range
           ---------------------------------------------------------------
           320 x 200    159    99    320     200     -159..160    -99..100
           640 x 200    319    99    640     200     -319..320    -99..100

                    When a window is set (using TurtleWindow, Window, or
                    GraphWindow), the turtle is initialized to the home
                    position and heading. Changing the display mode alsos
                    reset the window to the entire screen.

                    Turtle graphics operate using turtle coordinates. The
                    center of the turtle window is (0,0), while positive
                    values move to the right (X-range) and upwards (Y-
                    range), while negative values move to the left (X-
                    range) and downwards (Y-range).

                    The turtle can be moved outside of the active window,
                    but drawings outside of the active window will be
                    ignored.

  -------------------------------- Example ---------------------------------

           TurtleWindow(79,49,160,100);             { upper left quadrant }