1 Language
                        GTVL\ Language Summary
    CHANGE          : Change some attributs of the plot
    CLEAR Arg       : Clear some (parts of) the plot or windows.
    COMPRESS        : Remove invisible parts of the plot.
    CREATE Arg      : Create directory, windows or LUTs
    DEVICE          : Open the graphic device
    DISPLAY         : List some parameters of the plot
    EXPORT File     : Save part of the plot to metacode file, for further use
    HARDCOPY        : Get a printed copy of the plot
    IMPORT File     : Insert an external plot into the current one
    LUT [arg]       : Change the color Look-Up-Table
    REPLICATE       : Copy a directory to another place
    ZOOM            : ZOOM or REFRESHES the plot (possibly in another window)

1 CHANGE
        [GTVL\]CHANGE Item SegName Value [Val2 [Val3]]

    Change some attribute of the Graphic Library. Three  items  concern  the
    current directory and active windows:
      - CHANGE DIRECTORY DirName [WinNum] change the  default  directory  to
        DirName,  and optionally the active window number to WinNum (instead
        of 0) within this directory.
      - CHANGE WINDOW WinNum [NOREFRESH|REFRESH] change  the  active  window
        number  to  WinNum,  and  optionally  change  its  automatic refresh
        behaviour.
      - CHANGE ZOOM NEW|CURRENT change the default ZOOM command behaviour.
      - CHANGE CLEAR  TREE|WHOLE  change  the  default  CLEAR  PLOT  command
        behaviour.

    Two items are image segment attributes:
      - CHANGE  SCALING  SegName  LIN|LOG  [Lcut  [Hcut]]  will  change  the
        transfer function for the specified image segment.
      - CHANGE BLANKING SegName BLACK |  WHITE  |  Colour  will  change  the
        colour  of blanked pixels (if any) in the displayed image. Colour is
        a colour value as in PENCIL command (1-8).

    Other items are general  segment  attributes:  WEIGHT,  DASHED,  COLOUR,
    DEPTH, VISIBILITY (ON or OFF). For these items, if SegName is a segment,
    only that segment is modified, but if it is a  directory,  all  segments
    attached to this directory are modified accordingly.

2 SEGMENT_NAMES

        The 'SegName' used in all the CHANGE commands is formed by  a  name,
    given  by  the  calling  high-level  program  (usually a reminder of the
    command used), followed by an unique, incremental, number.  To  refer  a
    particular    segment,    one    uses    the    full    name    (as   in
    CHANGE VISIBILITY CONTOUR:46 OFF). To refer to ALL the segments with the
    same  name,  omit  the  number (as in CHANGE VISIBILITY CONTOUR OFF). To
    refer to a range of segments, use a 'minus' sign in  the  range  (as  in
    CHANGE VISIBILITY CONTOUR:32-46 OFF). Segments names can be 'wildcarded'
    (an '*' can replace part of the beginning or  the  end  of  the  segment
    name, as in CHANGE VISIBILITY *TOUR OFF).

    Trick: A reverse range of segments (as in CLEAR SEGMENT 32-12) is valid.
    In  the  particular  case  of the above example, it is equivalent to the
    command CHANGE VISIBILITY 32-12 CLEAR wich in turns tries to delete  (as
    opposed  to  change  the  visibility) the segments (which is possible if
    segment 32 is the last segment plotted).

1 CLEAR
        CLEAR [Arg]

    CLEAR withous arguments clears the current plot and  ask  the  user  for
    confirmation.  In  non  interactive  session, it clears the plot without
    prompting.

    Please consult the following sections for the various CLEAR arguments:
2 ALPHA
         CLEAR ALPHA erases the alphanumeric screen alone, without affecting
    the  plot  on  old graphic terminals. Under X-Window, the graphic screen
    created by the 'DEVICE' command is raised up.
2 DIRECTORY
         CLEAR DIRECTORY [DirName] makes the named directory (or by  default
    the  current  directory)  invisible.  All the attached structure becomes
    invisible. Under X, the graphic screen is  updated,  elsewhere  use  the
    command ZOOM REFRESH to do it. Note that the directory is not destroyed:
    you can recover it by a CHANGE VISIBILITY command.
2 GRAPHIC
         CLEAR GRAPHIC lowers the graphic  windows,  popping  up  the  alpha
    screen (X window only).
2 PLOT
         CLEAR PLOT destroys the current tree or the whole plot, and  clears
    the  graphic screen accordingly. The default behaviour can be controlled
    by command CHANGE CLEAR.
2 SEGMENT
         CLEAR SEGMENT destroys the last graphic segment, i.e. the  part  of
    the  plot  corresponding  to  the  last  graphic  command.   Can be used
    repetitively. The Graphic screen is updated  under  X-Window,  elsewhere
    use command ZOOM REFRESH to do it.

    CLEAR SEGMENT SegName makes the named segment invisible.

    One can erase a range of graphic segments in a single command by  typing
    a  range  of  segment  numbers,  as  in  CLEAR SEGMENT 24-16. The use of
    reverse range (24-16) forces the graphic library to actually delete  the
    segment,  if  possible,  instead  of  making  it  invisible. See command
    GTVL\CHANGE for details.

2 TREE
         CLEAR TREE clears the current tree only, leaving all other parallel
    trees  intact.  All associated windows are destroyed, and the tree is is
    recreated empty, with a single attached window. If only one tree  exist,
    a CLEAR WHOLE is performed.
2 WHOLE
         CLEAR WHOLE destroys the whole  plot.  On  X-Window  displays,  all
    windows are destroyed, and a new window is recreated for the first tree.
    Other trees are destroyed.
2 WINDOW
         CLEAR WINDOW windownumber deletes the current  graphic  window  (if
    possible).  Only supported on multi-window displays (X-Window).

1 COMPRESS
        [GTVL\]COMPRESS

        Compress  the  internal  metacode,  by  removing  (definitely)   all
    invisible segments and directories.

1 CREATE
        [GTVL\]CREATE Argum Value

      - CREATE DIRECTORY PathName
        Create  a  new  directory.  PathName  syntax   follows   "Unix-like"
        pathnames, with the use of token '<' instead of '/'. Constructs like
        ..<DIR are valid.  To  create  a  new  top  directory  (called  e.g.
        NEWTOP), use the following syntax:
            CREATE DIRECTORY <NEWTOP
      - CREATE LUT
        Store the current Look Up Table into the internal  metacode.  Stored
        LUT  will be re-used for PostScript hardcopies, allowing to use more
        than one color palette on PostScript printout.
      - CREATE PENLUT
        Store the current pencil colors into the internal  metacode.  Stored
        pencil LUTs will be re-used for PostScript hardcopies, allowing more
        than 16 filled colors on the same printout.
      - CREATE WINDOW [BLACK|WHITE] [[NOREFRESH] [NAME Name] [/PIXEL Px Py]
        Create a new window with the corresponding attributs  of  background
        colour,   automatic   refresh  behaviour  and  Name.  Option  /PIXEL
        specifies the window size (in pixels); if not present, the cursor is
        used to define the zooming area.

1 DEVICE
        [GTVL\]DEVICE Dev_Type [Mode] [/OUTPUT Dev_Name]

    Directs graphic output to the graphics device of the specified type  and
    sets  default  values  for  the plot region location and device physical
    limits. The basic unit is 1 cm for hardcopies. All plots to  interactive
    devices  are made with some pre-computed factor to match the screen size
    to the Plot Page size, defined by command SET PLOT_PAGE (default size is
    an A4 format page, 30 by 21) .

    Use DEVICE ? to get the list of recognized graphics  devices  or  DEVICE
    type ? to get the list of modes on a given device.

    /OUTPUT Dev_Name  Allows you to direct the graphic output  to  something
    else  than your own terminal (TT:). Note that some specific devices will
    not support this  option:  this  is  currently  the  case  for  X-Window
    devices.

    Bitmap color is only available with DEVICE IMAGE on X-Window terminals.

1 DISPLAY
        [GTVL\]DISPLAY Item [Argument [s]] [/OUTPUT]

    List the internal parameters of the named item
      DISPLAY DIRECTORY  shows the working directory. Symbol  PWD  does  the
        same...
      DISPLAY SEGMENT  shows the attributes of segments attached to  current
        directory
      DISPLAY TREE      shows the directory tree from current point.
      DISPLAY  WINDOW  shows  the  list  of  windows  and  their  associated
        directories.
    etc... for other stuff to be added. Used for debugging mostly.

1 EXPORT
        [GTVL\]EXPORT FileName [DirName]

    Export the current (or specified) directory tree to an external metacode
    file  of  name FileName. The default extension is .meta, and these files
    have a different format than the old .vec files. The sub-plot can  later
    be  reincorporated  using  command  IMPORT.  This allows merging several
    plots together. This command does an implicit COMPRESS before saving the
    tree, so that invisible subtrees will be deleted.

1 HARDCOPY
        [GTVL\]HARDCOPY [File] [/DEVICE FirstName SecondName]
        [/PLOT Destination ] [/LANDSCAPE] [/PORTRAIT] [/EXACT]

    Creates (and optionally plots) a "hardcopy"  of the current  plot.   The
    plot  is not destroyed  and  can be appended later by new plot commands.
    The default behaviour is to scale the GreG PLOT_PAGE (centimeters)  into
    the  output  physical  page.   This  behaviour  can be overridden by the
    /EXACT option,  and  in  a  restricted  manner  by  the  /LANDSCAPE  and
    /PORTRAIT options.

    The /DEVICE option first argument specifies which type of  plotter  will
    be  used.  The same devices recognized by command DEVICE are allowed for
    this option. PrimaryName usually indicate the graphic protocol supported
    by the device, and SecondaryName a variant of this protocol. For example
                   HARDCOPY File /DEVICE PS COLOR
    is used to create a Postscript file with full color support.  The device
    First  and  Second  names  are  defined  in the file "GAG_TERMINAL" that
    describes, in binary format, the protocol and options  relative  to  all
    the  devices  locally  supported.  Changes  to this file are done by the
    system manager using the gtvdef program.

    The /PLOT option is used to force immediate plotting and, optionaly,  to
    control which plotter should be used. Plotter is the plotter name, which
    defaults to the content of the logical name "GAG_PLOTTER".  If  no  file
    name  was  specified  for  an  immediate  plotting, the metacode file is
    deleted after plot completion, otherwise it is kept.

    Default  type  and  destination  can  be  controlled  by  logical  names
    GAG_HARDCOPY   and   GAG_PLOTTER,   in   the   user,   local  or  global
    dictionnaries.

2 /DEVICE
        The /DEVICE option first argument specifies which  type  of  plotter
    will  be used. The same devices recognized by command DEVICE are allowed
    for this option. PrimaryName indicates the graphic protocol supported by
    the  device,  and  SecondaryName  a  variant of this protocol. Among the
    available device types are the following
       PS FAST         PostScript with hardware pen thickness handling
                       Clipping of wide pens may be inaccurate.
       PS GREY         PostScript with fixed greyscale transfer function for
                       bitmap. Clipping is accurate.
       PS COLOR        PostScript with user controlled color transfer
                       function. A greyscale with equivalent luminosity is
                       is used on non-color printers.

       EPS FAST, EPS GREY, EPS COLOR
                       As PS, but for "Encapsulated PostScript", in which
                       the BoundingBox is computed from the plot boundaries
                       rather than from the Plot Page size.

       HPGL            HPGL language for HP printers.

2 /LANDSCAPE
        The output plot will be in LANDSCAPE mode.   Not  available  on  all
    types of hardcopy devices.
2 /PORTRAIT
        The output plot will be in PORTRAIT mode. Not available on all types
    of hardcopy devices.
2 /EXACT
        The EXACT option is used to preserve the size of the plot (1  cm  in
    GreG = 1 cm of the plotter). Available only on PostScript devices

1 IMPORT
        [GTVL\]IMPORT File [DirName] [/PATH PathName]

    Insert an external metacode file (type .meta, not the old .vec files) at
    the specified PathName into the current plot. The directory name DirName
    is derived from the filename by default.

1 LUT
        [GTVL\]LUT Argum [/PEN]

    Modify the bitmap or pen look up table. Option /PEN indicates to  modify
    the  the  value  of  the  16 user-controlled pen colors (colors 8 to 23)
    rather than the bitmap look-up table.

    Possibles arguments are:
      - COLOR Load a default color table
      - WHITE Load a black and white color table  (White  background,  black
        sources)
      - BLACK Load a black and white color table  (Black  background,  white
        sources).
      - LUT Load the color table defined by an HSV color model. (HSV  stands
        for  HUE,  SATURATION and VALUE). There are three user-writeable SIC
        Variables of name HUE, SATURATION and VALUE, that  contain  the  HSV
        model  of  the  current LUT. These array's values can be manipulated
        using standard SIC mathematic functions to create new Lookup  Tables
        (see below).
      - Any other : "LUT Argum" will read Red Green  Blue  values  from  the
        formatted file named "Argum".

    The default argument is LUT. A convenient value for the HUE array is
      LET HUE[I] = 256-2*I !a "classical" color table from blue  to  red  as
        used in AIPS for example.
        Color contours can be obtained using variations around the following
        command:
      LET HUE[I] = 16*INT((256-2*I)|16)
        and so on with the most funny functions you may invent.
    CAUTION : the HUE is a real number between 0 and 360.0

    Note that a similar behaviour is defined for the  pen  colors  with  the
    arrays  P_HUE,  P_SATURATION  and P_VALUE (the colors of the 16 contour-
    filling pens), and for the BLANKING  color  (the  color  used  to  paint
    blanked  pixels  in  images),  with  the 3 reals B_HUE, B_SATURATION and
    B_VALUE.

2 /PEN
        Same behaviour as LUT, but will update the colors  of  the  16  pens
    used for contour-filling.

1 REPLICATE
        REPLICATE Dir1 Dir2

    Copy Dir1 subtree to Dir2 subtree. Not very useful now, but will  become
    interesting  when  shifting,  stretching, rotations, and user coordinate
    changes will be allowed for all segments.

1 ZOOM
        [GTVL\]ZOOM [Argument(s)] [/NEW] [/CURRENT] [/REGION]

    ZOOM can be used to modify the viewing window of the current plot.   The
    zooming does not affect the plot, but only the way it is displayed.
      - ZOOM X1 X2 Y1 Y2 Defines the viewing window by its corners
      - ZOOM OFF Turns off zooming, i.e. defines the viewing  window  to  be
        the plot page
      - ZOOM REFRESH Redraw the current plot (useful after CLEAR SEGMENT)

    Without arguments ZOOM calls the cursor to define a new viewing  window.
    This  new  window will be defined by its center (at the cursor position)
    and a zooming factor (by steps of 1.414) :
       Z    Increase the zooming factor
       -    Decrease it
       B    Display the viewing window boundaries
    These commands do not produce effective zooming, press the space bar
    to do it. Additional commands :
       A    Clear alphanumeric screen
       0    Display the whole plot page (ZOOM OFF).
            <Space> returns to previous zooming factor.
       E    Exits from the routine.
    For X11 displays, you may use the mouse buttons for the commands Z (left
    mouse  button),  <Space>  (middle  mouse  button),  and  E  (right mouse
    button).

    Option /NEW and /CURRENT can be used to  specified  whether  the  zoomed
    area appears in the special zoom window (/NEW) or in the original window
    (/CURRENT). Default behaviour is specified by  CHANGE  ZOOM  NEW|CURRENT
    command.
2 /REGION
        This option uses a different ZOOM cursor, a rectangular  area  drawn
    using  the midle button of the mouse. Clicking outside the area with the
    middle button will resize the rectangle. By keeping  the  middle  button
    pressed,  the  shape will follow the mouse. To drag the shape on another
    part of the screen, click with the middle button inside  the  shape  and
    keep  the button pressed while dragging the shape. Button 1 will perform
    the zoom (in an auxiliary zoom window), button 3 exits.
1 END