Re: Operate only on the visible lines in a text window

* Shaun Deacon <sdeacon@us.socionext.com>
| The obvious solution to me is to just highlight the currently visible
| lines (or a range of lines spanning the current view - say 1000 or so)
| and when the user scrolls the window, highlight the new set of lines.

>

| Suggestions on the best way to find the indexes for the currently
| visible lines when the widget has been scrolled would be great.

>

| Can someone please point me in the right direction ?
 You could try 'text yview' and derive the displayed lines from that:
      grid [text .t -yscrollcommand {recalc {.s set}}] -sticky ewns -row 0 -column 0
     grid [scrollbar .s -command {recalc {.t yview}} -orient vertical] -sticky ns -row 0 -column 1
     grid [label .l] - -sticky ewns
     grid rowconfigure . 0 -weight 1
     grid columnconfigure . 0 -weight 1
     for {set l 1} {$l < 1000} {incr l} {
         .t insert end "Line $l\n"
     }
      proc recalc {cmd args} {
         # scroll if required
         if {$cmd ne ""} {
             {*}$cmd {*}$args
         }
         # Determine the visible range
         lassign [.t yview] start end
         # Get line count
         set lines [lindex [split [.t index end] "."] 0]
         # Get first and last line displayed.
         # Here you need to determine what to do with the partially displayed lines
         set first [format %.1f [expr {$start*$lines+1}]]
         set last [format %.1f [expr {$end*$lines}]]
                  .l configure -text "visible Lines $first ... $last"
     }
     bind . <Configure> [list recalc ""]
 HTH
R'