KBK: Here's a little hack that I've been using for a couple of years but never bothered to post. Given a scrollbar that's managed by the grid command, it arranges for it to appear and disappear when the content of the widget being scrolled demands it.

Following the script is a demo script that uses it. Try launching it and then resizing the window.

---

 #----------------------------------------------------------------------
 #
 # autoscroll.tcl --
 #
 #       Package to create scroll bars that automatically appear when
 #       a window is too small to display its content.
 #
 #----------------------------------------------------------------------
 
 package provide autoscroll 1.0
 
 namespace eval autoscroll {
     namespace export autoscroll
 
     bind Autoscroll <Delete> [namespace code [list delete %W]]
     bind Autoscroll <Map> [namespace code [list map %W]]
 }
 
 #----------------------------------------------------------------------
 #
 # autoscroll::autoscroll --
 #
 #       Create a scroll bar that disappears when it is not needed, and
 #       reappears when it is.
 #
 # Parameters:
 #       w    -- Path name of the scroll bar, which should already
 #               exist and have its geometry managed by the gridder.
 #
 # Results:
 #       None.
 #
 # Side effects:
 #       The widget command is renamed, so that the 'set' command can
 #       be intercepted and determine whether the widget should appear.
 #       In addition, the 'Autoscroll' bind tag is added to the widget,
 #       so that the <Destroy> event can be intercepted.
 #
 # Notes:
 #       It is an error to change the widget's gridding after
 #       calling 'autoscroll' on it.
 #
 #----------------------------------------------------------------------
 
 proc autoscroll::autoscroll { w } {
 
     variable grid
     variable needed
 
     rename $w [namespace current]::renamed$w
 
     proc ::$w {args} "
         return \[eval \[list autoscroll::widgetCommand $w\] \$args\]
     "
 
     set i [grid info $w]
     if { [string match {} $i] } {
         error "$w is not gridded"
     }
     set grid($w) $i
     set needed($w) 1
     
     bindtags $w [linsert [bindtags $w] 1 Autoscroll]
 
     eval [list ::$w set] [renamed$w get]
 
     return
 }
 
 #----------------------------------------------------------------------
 #
 # autoscroll::widgetCommand --
 #
 #       Widget command on an 'autoscroll' scrollbar
 #
 # Parameters:
 #       w       -- Path name of the scroll bar
 #       command -- Widget command being executed
 #       args    -- Arguments to the commane
 #
 # Results:
 #       Returns whatever the widget command returns
 #
 # Side effects:
 #       Has whatever side effects the widget command has.  In
 #       addition, the 'set' widget command is handled specially,
 #       by setting/unsetting the 'needed' flag and gridding/ungridding
 #       the scroll bar according to whether it is required.
 #
 #----------------------------------------------------------------------
 
 proc autoscroll::widgetCommand { w command args } {
 
     variable grid
     variable needed
 
     switch -exact -- $command {
         set {
             foreach { min max } $args {}
             if { $min <= 0 && $max >= 1 } {
                 if { [info exists needed($w)] } {
                     unset needed($w)
                     grid forget $w
                 }
             } else {
                 if { ! [info exists needed($w)] } {
                     set needed($w) {}
                     eval [list grid $w] $grid($w)
                 }
             }
         }
     }
 
     return [eval [list renamed$w $command] $args]
 }
 
 #----------------------------------------------------------------------
 #
 # autoscroll::delete --
 #
 #       Delete an automatic scroll bar
 #
 # Parameters:
 #       w -- Path name of the scroll bar
 #
 # Results:
 #       None.
 #
 # Side effects:
 #       Cleans up internal memory.
 #
 #----------------------------------------------------------------------
 
 proc autoscroll::delete { w } {
     variable grid
     variable needed
 
     catch { unset grid($w) }
     catch { unset needed($w) }
     catch { rename renamed$w {} }
 
     return
 }
 
 #----------------------------------------------------------------------
 #
 # autoscroll::map --
 #
 #       Callback executed when an automatic scroll bar is mapped.
 #
 # Parameters:
 #       w -- Path name of the scroll bar.
 #
 # Results:
 #       None.
 #
 # Side effects:
 #       Geometry of the scroll bar's top-level window is constrained.
 #
 # This procedure keeps the top-level window associated with an
 # automatic scroll bar from being resized automatically after the
 # scroll bar is mapped.  This effect avoids a potential endless loop
 # in the case where the resize of the top-level window resizes the
 # widget being scrolled, causing the scroll bar no longer to be needed.
 #
 #----------------------------------------------------------------------
 
 proc autoscroll::map { w } {
     wm geometry [winfo toplevel $w] \
             [wm geometry [winfo toplevel $w]]
 }

----

As promised, here's a demo script:

[RBR] I left the URL, but this ref was annoyingly asking for a login every time I view the page. http://www.lucidway.org/Marty/Tcl/TclWikiImages/950.gif

----

 # remove the following line if autoscroll is on the package path
 source autoscroll.tcl
 
 package require autoscroll
 namespace import ::autoscroll::autoscroll
 
 text .t -width 40 -height 24 \
     -yscrollcommand [list .y set] -xscrollcommand [list .x set] \
     -font {Courier 12} -wrap none
 scrollbar .y -orient vertical -command [list .t yview]
 scrollbar .x -orient horizontal -command [list .t xview]
 
 grid .t -row 0 -column 1 -sticky nsew
 grid .y -row 0 -sticky ns \
     -column 2; # change to -column 0 for left-handers
 grid .x -row 1 -column 1 -sticky ew
 
 grid columnconfigure . 1 -weight 1
 grid rowconfigure . 0 -weight 1
 
 autoscroll .x
 autoscroll .y
 
 for { set i 0 } { $i < 26 } { incr i } {
     .t insert end {This widget contains a lot of text, doesn't it?}
     .t insert end \n
 }

---

JE Here's another way to do it:

    proc sbset {sb first last} {
        if {$first <= 0 && $last >= 1} {
            grid remove $sb
        } else {
            grid $sb
        }
        $sb set $first $last
    }

Usage:

    $scrollee configure -xscrollcommand [list sbset $hsb] -yscrollcommand [list sbset $vsb]

FW notes that this is a little less aesthetically necessary on Windows anymore since as of a recent 8.4 release (I don't remember which) scrollbars that aren't needed on Windows appear grayed-out, or disabled, rather than the elevator taking up the whole bar, which is nonstandard and actually caused the scrollbar to freeze under certain conditions in XP.

AF some windows apps use this behavior. most notably explorer.

---

MHo: 2008-04-09: Can someone please confirm that autoscroll doesn't work with ttk::scrollbar?

MSH: No, but I can confirm that it does work with ttk::scrollbar, I do not however use it with the automatic renamed scrollbars but

  ttk::scrollbar $fr.scrolly -orient v -command "$w yview"
  ::autoscroll::autoscroll $fr.scrolly

I had shimmering problems with using BWidget's ScrolledWindow which I do not see with autoscroll.

---

GJSI noticed a shimmering problem with autoscroll and a text widget. This code should explain what I mean.

package require Tk
package require autoscroll

#create a text widget with scroll bars
text .t -xscrollcommand [list .x set] -yscrollcommand [list .y set] -wrap word -background white -foreground black
scrollbar .y -command [list .t yview]
scrollbar .x -command [list .t xview] -orient horizontal

#show it
grid .t .y -sticky nswe
grid .x -sticky nswe
grid columnconfigure . 0 -weight 1
grid rowconfigure . 0 -weight 1

#autoscroll the bars
autoscroll::autoscroll .x
autoscroll::autoscroll .y

#text tags
.t tag configure title -font "courier 20" -foreground blue -justify center
.t tag configure normal -font "courier 14"
.t tag configure code -font "courier 14" -wrap none -foreground red

#add some text
.t insert end "Shimmering with autoscroll" title
.t insert end "\nI have noticed that when a text widget is created with auto scrollbars it will shimmer. " normal
.t insert end "To see this for yourself make this window narrower until the bottom scrollbar appears. " normal
.t insert end "Then, start making it shorter until the text that is not word wrapped goes under the scrollbar. " normal
.t insert end "\n" normal "The Code" title "\n" normal

#list the code in this file
set f [open [info script] r]
while {![eof $f]} {
        gets $f l
        if {$l eq "#-"} {break}
        .t insert end $l code \n code
}
close $f
#-
#add some more text
.t insert end "\n" normal "My Theory" title "\n" normal
.t insert end "When ever unwrapped text is behind the scroll bar the text widget calls \".x set 0.0 1.0\"" normal
.t insert end ", which causes the scrollbar to be removed by the autoscroll package. " normal
.t insert end "Once the scrollbar is no longer visible, the unwrapped text is visible causing the " normal
.t insert end "text widget to call \".x set\" with values other than \"0.0\" and \"1.0\"." normal
.t insert end "At this point the autoscroll package displays the scrollbar, hiding the unwrapped text." normal
.t insert end "Wash, rinse, and repeat." normal

I am using Vista64 with ActiveTcl 8.6b1.1 and autoscroll 1.1.