# Introduction to Tcl/Tk

### TraNese Christy

Approved for public release; distribution is unlimited.

Date approved: ????

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

Figure 1. 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

Figure 2. 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.

- 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

- 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

Figure 3. Procedure Example (1)

Figure 4. Procedure Example (2)

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:

Figure 5. Mged Defaults

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.