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  Does the `canvas` have a `see` method?
 The `canvas` lacks a `see` method like that available in the `text` or
`listbox` widgets.  The following code provides the equivalent
functionality for a canvas:

## "see" method alternative for canvas
## Aligns the named item as best it can in the middle of the screen
## Behavior depends on whether -scrollregion is set
## c    - a canvas widget
## item - a canvas tagOrId
proc canvas_see {c item} {
    set box [$c bbox $item]
    if {![llength $box]} return
    if {![llength [$c cget -scrollregion]]} {
	## People really should set -scrollregion you know...
	foreach {x y x1 y1} $box {
	    set x [expr {round(2.5*($x1+$x)/[winfo width $c])}]
	    set y [expr {round(2.5*($y1+$y)/[winfo height $c])}]
	$c xview moveto 0
	$c yview moveto 0
	$c xview scroll $x units
	$c yview scroll $y units
    } else {
	## If -scrollregion is set properly, use this
	foreach {x y x1 y1} $box {top btm} [$c yview]  {left right} [$c xview] {p q xmax ymax}  [$c cget -scrollregion] {
	    set xpos [expr {(($x1+$x)/2.0)/$xmax - ($right-$left)/2.0}]
	    set ypos [expr {(($y1+$y)/2.0)/$ymax - ($btm-$top)/2.0}]
	$c xview moveto $xpos
	$c yview moveto $ypos