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intro(BLT 2.4)							intro(BLT 2.4)


NAME    [Toc]    [Back]

       BLT - Introduction to the BLT library

DESCRIPTION    [Toc]    [Back]

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

COMMANDS    [Toc]    [Back]

       The following commands are  added  to  the  interpreter	from  the  BLT

       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 ycoordinate
 values designate the magnitude.  The barchart
		      widget  has  of  several	components;  coordinate  axes,
		      crosshairs, a legend, and a collection of  elements  and

       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

       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    [Toc]    [Back]

       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.


       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    [Toc]    [Back]

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

KEYWORDS    [Toc]    [Back]


								intro(BLT 2.4)
[ Back ]
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