'''[https://www.tcl.tk/man/tcl/TkCmd/label.htm%|%label]''', a [Tk] command, creates and manipulate label (text or image) [widget]s


** See Also **

   [ttk::label]:   a [ttk]-themed label

   [label selection]:   

   [label wrapping]:   

   [labelled line]:   

   [message]:   a multiline, label-like widget that supports wrapping.

   [vertical labels]:   

   label widget in [Tix]:   

   

** Documentation **

   [https://www.tcl.tk/man/tcl/TkCmd/label.htm%|%official reference]:   



** Description **

labels ''can'' show multiple lines, if their text includes newlines; they even have the -justify option.



** Composite Labels **

'''Composite labels:''' A text label can hold either a constant text or a reference to a textvariable from which it is updated. Occasionally one wants both mixed, for instance to display "Distance from $from to $to: $mi miles", and auto-updated when one of those variables changes. The following code can help:

======
proc compositelabel {w contents} {
    frame $w
    set n 0
    foreach i $contents {
        set w1 [label $w.[incr n]]
        if [regexp {^[$](.+)} $i -> varname] {
            $w1 configure -textvar ::$varname
        } else {
            $w1 configure -text $i
        }
    }
    eval pack [winfo children $w] -side left
}
# usage example:
compositelabel .dist {Distance from $from to $to is $m miles}
======

[RS]: Make sure that the second argument is braced - the dollar signs are not to be seen by the Tcl parser, but rather used to indicate the following is the name of a global variable, not a text constant...

[DKF]: The other notion of composite label, that of a label that holds both picture and text, is also supported by Tk from 8.4 onwards.



** Selectable labels **

[Bryan Oakley] wrote in [comp.lang.tcl]:
''Here's a quick hack. Caveat emptor: this example has
hard-coded color names that probably only work on windows. But if you are on unix (or even on windows...) pick any colors that you want:''

======
bind Label <1> {focus %W}

bind Label <FocusIn> {
    %W configure -background SystemHighlight -foreground SystemHighlightText
}
bind Label <FocusOut> {
    %W configure -background SystemButtonFace -foreground SystemButtonText
}
bind Label <Control-c> {
    clipboard clear
    clipboard append [%W cget -text]
}
======

See also [label selection].



** Geometry **

Among the benefits of Tk is that its programming model encourages
"intelligent" displays, and specifically those with modestly dynamic
labeling.  Run-time context might call for a change in the text of a
[button] (an alternation between "Stop" and "Re-start", for example) or
label.  The one technical problem that immediately arises with most
such improvements is changes in widget size.  [Bryan Oakley] posted a
brief explanation of the usual idiom for these situations:
"Put it in a frame, and force the frame to a specific height [[or width]]
is one way of doing it. Read up on 'pack propagate', or 'grid
propagate' to see how you can keep children from causing their
parent[[s]] to resize."

Incidentally, [BLT] enjoys a wealth of geometry configurations which help
with these tasks.

----

[RS] just specifies a sufficient width for [label]s with changing content, which turns off the resizing.

----

[MG] 2004-04-20: A small proc that I wrote and thought I'd share, although I don't think it has a huge range of uses. Given a label widget as its only argument, it works out from the -width option, and the -font being used in the widget, how many pixels the -wraplength needs to be to stop the text overflowing.

======
proc calcWrap {w} {
    set font [$w cget -font]
    set x [font measure $font -displayof $w [string repeat 0 [$w cget -width]]]
};# calcWrap
======


**  Focus **

On [Microsoft Windows%|%Windows] (Xp, 8), the ''-highlight...'' options don't seem to work. [Schelte Bron] postulated that this is because on Windows, the highlight is inside a widget instead of around it.  One workaround is to manipulate ''-foreground'' or ''-background'' instead.

----

[MGS]: I have combined the code in [label wrapping] and [label selection] and created a package which you can find in the Links section at [Mark G. Saye].


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