Text widget elision

if 0 {Richard Suchenwirth 2004-07-24 - Tk's text widget has since version 8.3 received an -elide feature which I hadn't tried yet. So in this weekend fun project, I experimented how to implement "folding" parts of a text content.

The command elidify adds buttons in a text widget wherever an open brace appears at end of line (the typical pattern for proc bodies). If such a button displays "-", clicking it will elide (hide) the braces and its contents; clicking a "+" button will make the braces and its contents reappear. This way one can "close" details one is not interested in, and see more of the grand picture instead.

Buttons have the advantage that they don't show up when you retrieve the text content, say for saving to a file. }

 proc elidify w {
    set from 1.0
    set id 0
    #-- remove previous elidify buttons (if you have no other embedded widgets)
    foreach i [winfo children $w] {
        $w tag config $i -elide 0
        $w tag delete $i
        destroy $i
    }
    while 1 {
        set here [$w search -regexp {\{$} $from end]
        if {$here eq ""} break
        set n 1
        while {![info complete [$w get $here "$here + $n chars"]]} {
            if {[incr n]>65536} break ;#-- avoid runanway loops on unbalanced braces
        }
        set there [$w index "$here + $n chars"]
        set b $w.[incr id]
        button $b -text - -command "eliToggle $b" -pady 0
        $w window create $here -window $b
        $w tag config $b -elide 0
        $w tag add    $b "$here + 1 char" "$there + 1 char"
        set from [$w index "$there + 2 chars"]
    }
    set id ;# returns the number of elidable sections
 }

# This procedure is called whenever a "folding" button is clicked

 proc eliToggle w {
    if {[$w cget -text] eq "-"} {
        $w config -text +
        [winfo parent $w] tag config $w -elide 1
    } else {
        $w config -text -
        [winfo parent $w] tag config $w -elide 0
    }
 }

if 0 {Let's now test the whole thing on its own source code:}

 pack [text .t -wrap word] -fill both -expand 1
 set fp [open [info script]]
 .t insert end [read $fp]
 close $fp
 elidify .t

sbron 14 Sept 2005: Now what if you want to extract the text as shown at a certain point, for instance for printing it. You can't use [.t get 1.0 end] because that will include the elide text.

In the Tcl Chatroom Pat Thoyts mentioned a quick and dirty method:

 .t tag add sel 1.0 end
 set text [selection get]
 .t tag remove sel 1.0 end

But this has the sometimes unwanted side effect of changing the clipboard contents.

Here's a method that doesn't have that disadvantage:

 proc gettext {w {start 1.0} {end end}} {
     $w tag add gettext $start $end
     foreach n [$w tag names] {
         set elide [$w tag cget $n -elide]
         if {$elide eq ""} continue
         foreach {n1 n2} [$w tag ranges $n] {
             if {$elide} {
                 $w tag remove gettext $n1 $n2
             } else {
                 $w tag add gettext $n1 $n2
             }
         }
     }
     $w tag remove gettext 1.0 $start $end end
     set rc ""
     foreach {n1 n2} [$w tag ranges gettext] {
         append rc [$w get $n1 $n2]
     }
     $w tag delete gettext
     return $rc
 }

Arts and crafts of Tcl-Tk programming Category Widget