Canvas balloon help
Richard Suchenwirth 2005-08-16 - A colleague asked whether the Tk canvas has balloon help (little yellow windows showing some text) built-in.
I said no, but it'll be easy to make them. It turned out that there's some pitfalls, though: deleting a cballoon caused an <Enter> event on the underlying item, if the cursor was on the balloon, leading to a tight make-delete loop which hung the demo app. Delaying the deletion by a millisecond helped.
Here is the code:
package require Tk
proc cballoon {w tag text} {
$w bind $tag <Enter> [list cballoon'make $w $text]
$w bind all <Leave> [list after 1 $w delete cballoon]
}
proc cballoon'make {w text} {
foreach {- - x y} [$w bbox current] break
if [info exists y] {
set id [$w create text $x $y -text $text -tag cballoon]
foreach {x0 y0 x1 y1} [$w bbox $id] break
$w create rect $x0 $y0 $x1 $y1 -fill lightyellow -tag cballoon
$w raise $id
}
}
#---------------------------------------------------- Test
pack [canvas .c]
set id [.c create oval 10 10 110 110 -fill red]
cballoon .c $id "This is a red oval"
.c create rect 130 30 190 90 -fill blue -tag rect
cballoon .c rect "This is\na blue square"
bind . <Escape> {exec wish $argv0 &; exit}tklib now has a tooltip implementation that also supports items on a canvas. The code works 'as is' against zinc canvases as well.