NAME

       BLT - Introduction to the BLT library
_________________________________________________________________


DESCRIPTION

       BLT is a library of extensions to the Tk library.  It adds
       new commands and variables  to  the  application's  inter­
       preter.


COMMANDS

       The  following  commands are added to the interpreter from
       the BLT library:

       table          A table geometry manager for Tk.  You spec­
                      ify  window  placements as table row,column
                      positions and windows can also span  multi­
                      ple  rows  or  columns.   It  also has many
                      options for setting and/or bounding  window
                      sizes.

       graph          A  2D  plotting widget.  Plots two variable
                      data in a window with  an  optional  legend
                      and annotations.   It has of several compo­
                      nents; coordinate axes, crosshairs, a  leg­
                      end, and a collection of elements and tags.

       barchart       A barchart widget.  Plots two-variable data
                      as  rectangular  bars  in a window.  The x-
                      coordinate values designate the position of
                      the bar along the x-axis, while the y-coor­
                      dinate values designate the magnitude.  The
                      barchart  widget has of several components;
                      coordinate axes, crosshairs, a legend,  and
                      a collection of elements and tags.

       vector         Creates  a vector of floating point values.
                      The vector's components can be  manipulated
                      in  three  ways:  through a Tcl array vari­
                      able, a Tcl command, or the C API.

       spline         Computes a spline fitting  a  set  of  data
                      points  (x  and  y  vectors) and produces a
                      vector of the interpolated images  (y-coor­
                      dinates) at a given set of x-coordinates.

       bgexec         Like  Tcl's  exec  command,  bgexec  runs a
                      pipeline of  Unix  commands  in  the  back­
                      ground.   Unlike  exec,  the  output of the
                      last process is collected and a global  Tcl
                      variable   is   set  upon  its  completion.
                      bgexec can be used with tkwait to wait  for

                      dling expose events.   Intermediate  output
                      is  also  available  while  the pipeline is
                      active.

       busy           Creates  a  "busy  window"  which  prevents
                      user-interaction  when  an  application  is
                      busy.  The busy  window  also  provides  an
                      easy  way  to  have  temporary busy cursors
                      (such as a watch or hourglass).

       bitmap         Reads and writes bitmaps from Tcl.   New  X
                      bitmaps can be defined on-the-fly from Tcl,
                      obviating the need to  copy  around  bitmap
                      files.    Other   options  query  loaded  X
                      bitmap's dimensions and data.

       drag&drop      Provides a drag-and-drop facility  for  Tk.
                      Information (represented by a token window)
                      can be dragged to and from any  Tk  window,
                      including  those of another Tk application.
                      drag&drop acts as a coordinator,  directing
                      Tk send commands between (or within) TCL/Tk
                      applications.

       htext          A simple hypertext widget.   Combines  text
                      and  Tk  widgets  into a single scroll-able
                      window.  Tcl commands can be embedded  into
                      text,  which  are  invoked  as  the text is
                      parsed.  In addition,  Tk  widgets  can  be
                      appended to the window at the current point
                      in the text.  Htext can  be  also  used  to
                      create scrolled windows of Tk widgets.

       winop          Raise,  lower,  map,  or, unmap any window.
                      The raise and lower  functions  are  useful
                      for  stacking  windows above or below "busy
                      windows".

       watch          Arranges for Tcl procedures  to  be  called
                      before  and/or after the execution of every
                      Tcl command. This command may  be  used  in
                      the  logging,  profiling, or tracing of Tcl
                      code.

       bltdebug       A simple Tcl command tracing facility  use­
                      ful  for debugging Tcl code.  Displays each
                      Tcl command before and  after  substitution
                      along its level in the interpreter on stan­
                      dard error.


VARIABLES

       The following Tcl variables are either set or used by  BLT
       at various times in its execution:

                      tory containing a library  of  Tcl  scripts
                      and other files related to BLT.  Currently,
                      this directory contains the drag&drop  pro­
                      tocol  scripts  and  the  PostScript prolog
                      used by graph and barchart.  The  value  of
                      this variable is taken from the BLT_LIBRARY
                      environment variable,  if  one  exists,  or
                      else from a default value compiled into the
                      BLT library.

       blt_versions   This variable is set in the interpreter for
                      each  application.  It  is  an array of the
                      current version numbers for each of the BLT
                      commands  in  the  form major.minor.  Major
                      and minor are integers.  The major  version
                      number   increases   in  any  command  that
                      includes changes that are not backward com­
                      patible  (i.e.  whenever  existing applica­
                      tions and scripts may  have  to  change  to
                      work with the new release).  The minor ver­
                      sion number increases with each new release
                      of a command, except that it resets to zero
                      whenever the major version number  changes.
                      The array is indexed by the individual com­
                      mand name.


ADDING BLT TO YOUR APPLICATIONS

       It's easy to add BLT to an existing Tk  application.   BLT
       requires  no  patches or edits to the Tcl or Tk libraries.
       To add BLT, simply add the following code snippet to  your
       application's tkAppInit.c file.

              if (Blt_Init(interp) != TCL_OK) {
                  return TCL_ERROR;
              }

       Recompile  and  link  with  the BLT library (libBLT.a) and
       that's it.

       Alternately, you  can  dynamically  load  BLT,  simply  by
       invoking the command

              package require BLT

       from your Tcl script.


BUGS

       Send bug reports, requests, suggestions, etc. to gah@bell-
       labs.com or ghowlett@fast.net


KEYWORDS

       BLT


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