font configure

font configure fontname ?option? ?value option value ...?

Query or modify the desired attributes for the named font called fontname. If no option is specified, returns a list describing all the options and their values for fontname. If a single option is specified with no value, then returns the current value of that attribute. If one or more option-value pairs are specified, then the command modifies the given named font to have the given values; in this case, all widgets using that font will redisplay themselves using the new attributes for the font. See FONT OPTIONS for a list of the possible attributes.

[Anon] Here's a simple demo of using "font configure" to animate(*) some text by simply increasing its size.

  proc every {ms body} {
        eval $body
        after $ms [info level 0]

  proc pick { l } {
        return [lindex $l [expr {int( [llength $l] * rand() )}]]

  proc randColor {} {
        set h {0 1 2 3 4 5 6 7 8 9 a b c d e f}
        return "#[pick $h][pick $h][pick $h][pick $h][pick $h][pick $h]"

  proc biggen_font { cur_size max_size N } {
        if {$cur_size > $max_size} {
                if {[incr N -1] < 0} return
                after 3000 [list update_config $N]
        } else {
                font configure randfont -size [incr cur_size 2]
                after 40 [list biggen_font $cur_size $max_size $N]

  proc update_config { N } {
        if {[winfo exists .w]} {
                set cur_size 2
                font configure randfont \
                        -underline [pick {0 1}] \
                        -family [pick [font families]] \
                        -weight [pick {normal bold}] \
                        -slant [pick {roman italic}] \
                        -size $cur_size

                wm title .w [font configure randfont -family]
                set col [randColor]
                .w.f   configure -bg $col
                .w.f.l configure -bg $col
                biggen_font $cur_size 150 $N

  wm withdraw .
  font create randfont
  set PERIOD [expr {25 * 60 * 1000}]

  every $PERIOD {
        if {![winfo exists .w]} {
                toplevel .w
                wm state .w zoomed ;# maximize window
                pack [frame .w.f] -fill both -expand true
                pack [label .w.f.l -font randfont -text " Stretch! "] \
                        -fill both -expand true -padx 20 -pady 20
                update_config 20

Question: how can one use font configure to change Tk core widget fonts? Answer: see TIP 145 for details

See also