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