[ lecture notes | CSC 397 | Pete Sanderson | Computer Science | SMSU ]

Origins
Tcl characteristics
Tk characteristics
Procedure for preparing demo
Hello world in Tcl/Tk with variations
Packing using geometry manager
The ExecLog example

Practical Programming in Tcl and Tk 2nd Edition, by Brent Welch
Scriptics ("The Tcl Platform Company") provides definitive Tcl web resource
Sun Microsystems also supports Tcl/Tk
MI/X is a free X server for Mac or Windows from MicroImages..

TCL = Tool Command Language

TK = Tool Kit

• Developed by Dr. John Ousterhout at UC Berkeley (later a Sun Distinguished Engineer; in 1998 formed Scriptics Corporation to market Tcl to industry)
• Developed as a tool for development of Sprite network OS at UCB.
• Developed for Unix/X environment
• Ported to Mac/Win95NT/OS2, and more??

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• Scripting language (like Perl or a shell language)
• Interpreted (like other scripting languages)
• syntax resembles Unix shell languages (and a bit of C)
• Interpreter (and thus language) can be extended to implement new commands
• Useful as 'glue' to combine existing programs in powerful ways

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• Extension to TCL
• Provides set of commands to create and manipulate widgets
• Gives application an event-driven control flow
• Widgets are associated with events (and thus can respond to them)
• GUI widgets are related in tree hierarchy with '.' as root (primary window) [ looks like file pathname except use '.' instead of '/']

A sampling of Tk widgets:

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MI/X is a free X server for Mac or Windows from MicroImages. As of October 1998, the Windows version is X11R5, the Mac version is X11R6. Thanks to Jeff Peck for providing this URL.

In the X world, server is local and client is remote. In the demo configuration, server runs on the Gateway (WinNT), client runs on csc.smsu.edu.

Procedure to run the demo is:

• On the Gateway, launch MI/X (assuming it has been installed).
• On the Gateway, telnet to CSC.
• On CSC, set the DISPLAY environment variable to point back to the Gateway, e.g. setenv DISPLAY joe.smsu.edu:0.0
• On CSC, run the xterm program in background, e.g. xterm &
• On Gateway MI/X window, CSC command shell window will appear.
• Subsequent interaction is through MI/X and its windows. MI/X default window manager is twm.
• Run Tcl/Tk programs through wish interpreter. e.g. wish hello.tcl

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• '.' is the parent frame
• '.hello' identifies button hello as child of '.' Button label is "Hello"
• the backslash ('\') indicates that specification continues on next line.
• '-command' specifies response when button pressed
• curly brackets are used to group a set of words.
• 'pack' places button into parent frame and displays

• widget names can be put into variables to facilitate single point control

• Widget attributes can be modified at runtime using config
• When Hello button is selected first time, its label changes to Goodbye and action changes to exit
• When button is selected second time, program exits.

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(chap 12 in Welch first edition, chap 20 in second edition)

• pack is a Tk "geometry manager" for arranging widgets
• The packer is constraint-based.
• manager uses one widget as parent (typically a frame) and arranges children (slaves) inside the parent
• widget must be managed (packed) to appear
• one constraint is "pack toward" (-side) direction: top, bottom, right, left
• Welch example shows two frames inside main frame, packed toward top.
  # Example 20-1
  # Two frames packed inside the main frame.
  #
  # Make the main window black
  . config -bg black
  # Create and pack two frames
  frame .one -width 40 -height 40 -bg white
  frame .two -width 100 -height 50 -bg grey50
  pack .one .two -side top
• Next Welch example shows hierarchy: pack buttons "toward left" inside frame, pack frames "toward top" inside parent frame. Pleasing arrangement.
  # Example 20-3
  # A horizontal stack inside a vertical stack.
  #
  frame .one -bg white
  frame .two -width 100 -height 50 -bg grey50
  # Create a row of buttons
  foreach b {alpha beta gamma} {
  button .one.$b -text $b
  pack .one.$b -side left
  }
  pack .one .two -side top
  Note visual constraints:
  - first frame size not specified so is just large enough to hold buttons.
  - Second frame size fixed.
  - Parent frame size not specified; just large enough for both children
• place is another Tk geometry manager that expects numerical specification of widget sizes and locations (relative or absolute).

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An interface for entering Unix commands into text entry field with output displayed in separate scrolling text window. Demonstrates a number of the techniques described above, and then some. Primary frame has two child frames: one contains the text entry field and two buttons ("Run it" and "Quit"); the other contains the text output window along with its scrollbar. This is example 19-1 from Welch second edition (example 11-1 from first edition).

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[ lecture notes | CSC 397 | Pete Sanderson | Computer Science | SMSU ]

Peter Sanderson ( pete@csc.smsu.edu )