Introduction to Tcl/Tk

TraNese Christy

What is Tcl/Tk?

Tool Command Language/ToolKit.
Tcl is an embeddable and extensible interpreted language.
Tk is a toolkit for building user interfaces.
Combined, they provide a programming system for development and use of GUI applications.

Benefits of Tcl/Tk

Ease of providing applications with a powerful scripting language
An excellent "glue language"
User convenience
Portability

Tcl/Tk-Based GUI for MGED

Tcl Syntax

A command is a list of words.
First word on the command line is the command name, any additional words are arguments.

      -- command [arg1 ... argn
      mged> puts "Hello World"
      Hello World

Words can be grouped with double quotes (" ") or curly braces ({}).
Commands are terminated with a newline or semicolon.

Variables

Variable names are case-sensitive.
Declarations are not necessary.
set varName [value]
Assigns value to the variable varName.

      mged> set day Friday

      Friday
      mged> set day
      Friday

      mged> set day 25

      25

Lists

An ordered set of strings
Specified with curly braces

      mged> set colors {red yellow green blue}
      red yellow green blue

Sometimes created with "list" command

      mged> set colors [list red yellow green blue]
      red yellow green blue

Can extract elements from the list using the "lindex" command (indices start at zero)

      mged> lindex {red yellow green blue} 2
     green

Arrays

Uses associative arrays
- -- Strings used to index the array elements

      mged> set profit(January) 1500
      1500

      mged> set profit(February) -200
      -200

    mged> set profit(January)
    1500

Special Characters

Dollar sign $

--Substitutes the value of the variable
Square brackets [ ]

-- Replaces contents with the result of evaluating the command
Backslash \

-- Allows special characters such as newlines, [, and $ to be inserted without being treated specially
Double quotes " "

-- Allows special characters to be processed normally
Curly braces {}

-- Disables special characters
Parentheses ()

-- Delimits key values in arrays
Hashmark #

-- At the beginning of a line, signifies a comment to follow

Special Character Examples

      mged> set name Elvis
      Elvis

      mged> puts "Hello name"
      Hello name

     mged> puts "Hello $name"
     Hello Elvis

      mged> set len [string length $name]
      5

-- string length $name returns 5
-- len gets the value 5

Special Character Examples (cont'd)

      mged> set price 1.41
      1.41
      mged> puts "Gasoline: \$ $price/gallon"
      Gasoline: $1.41/gallon
      mged> puts {Gasoline: \$ $price/gallon}
      Gasoline: \$ $price/gallon
      mged> set product 1; #This is a comment
      1

Special Character Conflicts

MGED traditional "name globbing" characters conflict with Tcl/Tk usage:
- -- MGED follows Unix shell filename patterns.
- -- Tcl/Tk has different interpretation of * and [].
Users can select which interpretation of special characters:
- .mgedrc: set MGED variable
- glob_compat_mode
- set glob_compat_mode 0 (for Tcl evaluation)
- set glob_compat_mode 1 (for object name matching)
- Menu: File->Preferences->Special Characters

Special Character Interpretation

Special Character Interpretation

Expressions

The exprcommand is used to evaluate math expressions.

      mged> expr 2 + 2

      4

      mged> expr (3 + 2) * 4

      20

      mged> in ball.s sph 0 0 0 [expr 3 + 4]

-- A sphere is created with a vertex (0,0,0) and a radius of 7.

Control Flow

      if {test} {body1} [else {body2}]

      mged> set temp 90

      90

      mged> if {$temp > 75} {

      puts "It's hot"

      } else {

      puts "It's moderate"

      }

      It's hot

Control Flow (cont'd)

      while {test} {body}

      mged> set time 3

      3

      mged> while {$time > 0} {

      puts "Time is $time"

      set time [expr $time - 1]

      }

Time is 3

Time is 2

Time is 1

Control Flow (cont'd)

      for{init} {test} {reinit} {body}
      for {set time 3} {$time > 0} {set time [expr $time - 1]} {puts "Time is $time"}

Time is 3

Time is 2

Time is 1

Control Flow (cont'd)

      foreach
      varList list{body}
      mged>
      foreach fruit {apples pears peaches} {
      puts "I like $fruit"}

I like apples

I like pears

I like peaches

      mged>
      foreach {key val} {sky blue grass green snow white} {
      puts "The $key is $val"
      }

The sky is blue

The grass is green

The snow is white

MGED Commands

     get
     obj[attr]
     Returns a list of the object's attributes. If attr is specified,
      only the value for that attribute is returned.
      mged>
      get foo.r
      comb region yes id 200 los 100 GIFTmater 2 rgb {100 100 100}
      mged>
      get foo.r rgb
      100 100 100
      mged>
      get foo.s
      ell V {0 0 0} A {4 0 0} B {0 4 0} C {0 0 4}

MGED Commands (cont'd)

adjust obj attr value[attr value]
- Modifies the object's attribute(s) by adjusting the value of the attribute(s) to the new value(s).
ls[-c -r -s]
- Without any options, lists every object in the database.
- With the "c" option, lists all nonhidden combinations; "r" option lists all nonhidden regions; and "s" option lists all nonhidden primitives.

MGED Examples

Task: Change the color of all regions to blue.


      mged>
      foreach region [ls -r] {
      adjust $region rgb {0 0 255}
      }

Task: Print all regions with nonzero air codes.

Task: Print all regions with nonzero air codes.


      mged>
      foreach reg [ls -r] {
      if {[get $reg air] != 0} {
      puts "$reg"
      }
      }

MGED Examples (cont'd)

Task: Print all objects with the inherit flag set.


      mged> foreach obj [ls -c] {
      if {[get $obj inherit] == "yes"} {
      puts "$obj"
      }
      }

Procedures

User-Defined commands
proc

      procName{args} {body}
      mged>
      proc add {x y} {
      set answer [expr $x + $y]
      return $answer
      }
      mged>add 123 456
      579

Create new MGED commands
Save in .mgedrc

Procedure Example

Procedure that generates a PART that encompasses two specified SPHs


    proc sph-part {sph1 sph2 newname} {
    foreach {vx1 vy1 vz1} [lindex [get $sph1 V] 0] {}
    foreach {vx2 vy2 vz2} [lindex [get $sph2 V] 0] {}
    foreach {ax1 ay1 az1} [lindex [get $sph1 A] 0] {}
    foreach {ax2 ay2 az2} [lindex [get $sph2 A] 0] {}
    set radius1 [expr sqrt($ax1*$ax1 + $ay1*$ay1 + $az1*$az1)]
    set radius2 [expr sqrt($ax2*$ax2 + $ay2*$ay2 + $az2*$az2)]
    set hx [expr $vx2-$vx1]
    set hy [expr $vy2-$vy1]
    set hz [expr $vz2-$vz1]
    in $newname part $vx1 $vy1 $vz1 $hx $hy $hz $radius1 $radius2
    }

Procedure Example (cont'd)

 mged>
sph-part s1.s s2.s part.s

The "source" Command

source fileName
- Reads and executes the file as a Tcl script.
Create the file with a text editor.
Reload the file with "source" changes are made.
The proc or the source command can be placed in .mgedrc.

MGED Defaults

Create the default .mgedrc from inside MGED:

MGED Customization

Placed in the file

.mgedrc

In local directory or home

############### MGEDRC_HEADER ###############

# You can modify the values below. However, if you want

# to add new lines, add them above the MGEDRC_HEADER.

# Note - it's not a good idea to set the same variables

# above the MGEDRC_HEADER that are set below (i.e., the last

# value set wins).

# Determines the maximum number of lines of

# output displayed in the command window

set mged_default(max_text_lines) 1000

[incr Tcl/Tk]

Object-oriented extension to Tcl.
Provides support to build large programs.
New applications in BRL-CAD are being written in [incr Tcl/Tk].

Useful References

Raines, Paul. Tcl/Tk Pocket Reference. O'Reilly & Associates, Inc., Sebastopol, CA, 1998.
Ousterhout, John K. Tcl and the Tk Toolkit. Addison-Wesley, Reading, MA, 1994.
Welch, Brent B. Practical Programming in Tcl and Tk, Second Edition. Prentice Hall, Upper Saddle River, NJ, 1997.