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intro(n)		     BLT Built-In Commands		      intro(n)


       BLT - Introduction to the BLT library

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

       The following commands are added	to the interpreter from	 the  BLT  li-

       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 win-
		      dow with an optional legend and annotations.   It	has of
		      several components; coordinate axes, crosshairs, a  leg-
		      end, and a collection of elements	and tags.

       barchart	      A	barchart widget.  Plots	two-variable data as rectangu-
		      lar 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

       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  im-
		      ages (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 tk-
		      wait  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  pro-
		      vides  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  bit-
		      map'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	appli-
		      cation.  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	debug-
		      ging Tcl code.  Displays each Tcl	command	before and af-
		      ter  substitution	 along its level in the	interpreter on
		      standard error.

       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 contain-
		      ing 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	appli-
		      cation. 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 applica-
		      tions  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 ar-
		      ray 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 com-

	      package require BLT

       from your Tcl script.

       Send bug	reports, requests, suggestions,	etc. to


BLT				      2.5			      intro(n)


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