proc wheelEvent { x y delta } {

    # Find out what's the widget we're on
    set act 0
    set widget [winfo containing $x $y]

    if {$widget != ""} {
        # Make sure we've got a vertical scrollbar for this widget
        if {[catch "$widget cget -yscrollcommand" cmd]} return

        if {$cmd != ""} {
            # Find out the scrollbar widget we're using
            set scroller [lindex $cmd 0]

            # Make sure we act
            set act 1
        }
    }

    if {$act == 1} {
        # Now we know we have to process the wheel mouse event
        set xy [$widget yview]
        set factor [expr [lindex $xy 1]-[lindex $xy 0]]

        # Make sure we activate the scrollbar's command
        set cmd "[$scroller cget -command] scroll [expr -int($delta/(120*$factor))] units"
        eval $cmd
    }
}

bind all <MouseWheel> "+wheelEvent %X %Y %D"