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 interpreter.

COMMANDS

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

       table          A table geometry manager for Tk.  You specify window  placements  as  table
                      row,column  positions  and  windows can also span multiple 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 components; coordinate axes,
                      crosshairs, a legend, 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-coordinate 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 variable, 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-coordinates) at a given set
                      of x-coordinates.

       bgexec         Like Tcl's exec command, bgexec runs a pipeline of  Unix  commands  in  the
                      background.  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  Unix  commands to finish while still handling 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  useful  for debugging Tcl code.
                      Displays each Tcl command before and after substitution along its level  in
                      the interpreter on standard error.

VARIABLES

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

       blt_library    This variable contains the name of a directory containing a library of  Tcl
                      scripts and other files related to BLT.  Currently, this directory contains
                      the drag&drop protocol 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
                      compatible  (i.e.  whenever  existing  applications and scripts may have to
                      change to work with the new release).  The minor version  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
                      command 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@siliconmetrics.com   or
       ghowlett@grandecom.net

KEYWORDS

       BLT