This is my answer to my own question originally posted in [http://wiki.tcl.tk/29226%|%Ask-11%|%].

The problem was in handling large numbers of independent items on a dragable background. I was not asking for help because I could ''not'' do it - rather I was concerned about performance and so was interested in which way was ''best''.

Here is the original post:

I am curious about a particular GUI feature. I could (and may yet!) answer the question by spending many hours writing test code for many different versions - but I thought that I would ask the experts first.
I am thinking of a scrolling viewport containing a large number of independent, simple items. ''Large'' is a subjective term, but certainly hundreds - possibly thousands. As far as I can tell there are several different approaches which could be taken:
   1. Viewport is a frame, items are normal widgets (labels/frames etc.) placed upon it.
   2. Viewport is a canvas, items are normal widgets (labels/frames etc.) placed upon it.
   3. Viewport is a canvas, items are normal widgets (labels/frames etc.) added not with place but with the 'canvas create window' command.
   4. Viewport is a canvas, items are canvas text/shape etc. drawn upon it.
(Actually there are possibly 6 options - since for both 3 and 4 the scrolling could be accomplished in either of two ways: the canvas specific 'scan mark'/'scan dragto' and the generic 'place config' to move the container).
I am confident that given enough time I could code all of these successfully, however I was wondering which would be faster? Given that frame seems like a more 'lightweight' widget than canvas I am naïvely assuming that option 1 would be best - however I know that considerable effort has gone into making the canvas very efficient...
Does anyone know the answer - before I spend all weekend coding five wrong answers in order to find the right one?
Many thanks, RJH.

RJH: 22 Jan 2014: I found the time to test all of these myself and was amazed at the difference between certain cases. I'll tidy the code ans post here if anyone is interested?
[AM] Please do: make a separate page for that and use a suitable set of categories. Even if no one is interested right now, that may change in the near future. And it is probably a good exercise as well ;).
----

... and here is my testbed. I was amazed to find that 'canvas create window' was so slow when dragging the viewport. It turned out not to be as onerous a task as I expected, the testbed took shape in few hours.

======
proc go "items container widgets drag" {
  destroy .background

  if {$container=="canvas"} {
    canvas .background -bg ivory -width 500 -height 500
    .background create text 0 0 -text CANVAS
  } else {frame .background -bg ivory -width 500 -height 500}

  if {$widgets=="place"} {
    proc make-item "x y text" {place [label .background.t-$text -text $text -bd 1 -relief solid -bg beige] -x $x -y $y}
  } elseif {$widgets=="window"} {
    proc make-item "x y text" {label .background.t-$text -text $text -bd 1 -relief solid -bg beige
                                .background create window $x $y -window .background.t-$text}
  } else {
    proc make-item "x y text" {set a [.background create text $x $y -text $text]
                               set b [.background create rectangle [.background bbox $a] -fill beige]
                               .background lower $b $a}
  }

  if {$drag=="canvas"} {
    # Dragging by the 'canvas scan mark/dragto' methods.
    proc start "x y" {.background scan mark $x $y
                      .background conf -cursor fleur}
    proc drag  "x y" {.background scan dragto $x $y 1}
  } else {
    # Dragging by moving the container.
    proc start "x y" {set ::dx $x; set ::dy $y}
    proc drag  "x y" {
      place conf .background -x [expr [winfo x .background] + $x - $::dx] -y [expr [winfo y .background] + $y - $::dy]
      .background conf -cursor fleur
    }
  }

  place .background -x 0 -y 0

  for {set i 0} {$i < $items} {incr i} {make-item [expr rand()*400] [expr rand()*400] "Item $i"}

  bind .background <ButtonPress-1>    {start %x %y}
  bind .background <B1-Motion>        {drag %x %y}
  bind .background <ButtonRelease-1>  {.background conf -cursor ""}
}

. conf -height 500 -width 500

toplevel .config
tk_optionMenu .config.canvas  ::container canvas frame
tk_optionMenu .config.drag    ::drag canvas container
tk_optionMenu .config.widgets ::widgets canvas window place
pack [entry .config.items -textvariable ::items ]
pack .config.canvas .config.widgets .config.drag
pack [button .config.go -command {go $::items $::container $::widgets $::drag} -text GO]
proc fixwidgets   args {if {$::widgets=="place"}   {set ::drag container}}
proc fixcontainer args {if {$::container=="frame"} {set ::widgets place}}
trace add variable ::widgets write fixwidgets
trace add variable ::container write fixcontainer
set items 100
======


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