Here's the newgroup message that introduced Canvas Buttons.
Rick Hedin wrote:
> We have come to a place where it seems desireable to have lightweight
> widgets within a canvas. The Java folks are all excited about lightweight
> widgets that share a single window, and Swing, and whatnot. Has similar
> work been done within Tcl?
You can do a lot by tagging groups of canvas items and binding to their
tags. The enclosed code, for instance, creates canvas items that look
and act a lot like buttons.
The idea of making Tk widgets themselves leaner has also been pursued.
The TkGS project is trying to do it. There's information on that at
http://www.purl.org/net/bonnet/Tcl/TkGS/
and http://www.sourceforge.net/projects/tkgs/
--
Kevin KENNY GE Corporate R&D, Niskayuna, New York, USAHere's the code for Canvas Buttons.
# ----------------------------------------------------------------------
#
# cbutton.tcl --
#
# Example of how to provide button-like behavior on canvas
# items. (Posted on comp.lang.tcl by Kevin Kenny)
set ::RCSID([info script]) \
{$Id: 1383,v 1.3 2006-09-24 06:00:06 jcw Exp $}
package provide canvasbutton 1.0
namespace eval canvasbutton {
# nexttag - Next unique tag number for a "button" being
# created
variable nexttag 0
# command - command(tag#) contains the command to execute when
# a "button" is selected.
variable command
# cursor - cursor(pathName) contains the (saved) cursor
# symbol of the widget when the pointer is in
# a "button"
variable cursor
# enteredButton - contains the tag number of the button
# containing the pointer.
variable enteredButton {}
# pressedButton - contains the tag number of the "button"
# in which the mouse button was pressed
variable pressedButton {}
namespace export canvasbutton
}
# ----------------------------------------------------------------------
#
# canvasbutton::canvasbutton --
#
# Create a button-like object on a canvas.
#
# Parameters:
# w Path name of the canvas
# x0 Canvas X co-ordinate of left edge
# y0 Canvas Y co-ordinate of top edge
# x1 Canvas X co-ordinate of right edge
# y1 Canvas Y co-ordinate of bottom edge
# text Text to display in the button
# cmd Command to execute when the button is selected.
#
# Results:
# Unique canvas tag assigned to the items that make
# up the button.
#
# Side effects:
# A rectangle and a text item are created in the canvas,
# and bindings are established to give them button-like
# behavior.
#
#----------------------------------------------------------------------
proc canvasbutton::canvasbutton {w x0 y0 x1 y1 text cmd} {
variable nexttag
variable command
set btag [list canvasb# [incr nexttag]]
set command($btag) $cmd
$w create rectangle $x0 $y0 $x1 $y1 \
-fill white -outline black -width 1 \
-tags [list canvasb $btag [linsert $btag end frame]]
set x [expr { ($x0+$x1) / 2 }]
set y [expr { ($y0+$y1) / 2 }]
$w create text $x $y -anchor center -justify center \
-text $text \
-tags [list canvasb $btag [linsert $btag end text]]
$w bind canvasb <Enter> [list [namespace current]::enter %W]
$w bind canvasb <Leave> [list [namespace current]::leave %W]
$w bind canvasb <ButtonPress-1> \
[list [namespace current]::press %W]
$w bind canvasb <ButtonRelease-1> \
[list [namespace current]::release %W]
return $btag
}
# ----------------------------------------------------------------------
#
# canvasbutton::enter --
#
# Process the <Enter> event on a canvas-button.
#
# Parameters:
# w Path name of the canvas
#
# Results:
# None.
#
# Side effects:
# When the mouse pointer is in a button, the button is
# highlighted with a broad outline and the cursor
# symbol changes to an arrow. When the active button
# is pressed, it is highlighted in green.
#
# ----------------------------------------------------------------------
proc canvasbutton::enter {w} {
variable enteredButton
variable pressedButton
variable cursor
set enteredButton [findBtag $w]
set frame [linsert $enteredButton end frame]
set cursor($w) [$w cget -cursor]
$w configure -cursor arrow
$w itemconfigure $frame -width 3
if {![string compare $enteredButton $pressedButton]} {
$w itemconfigure $frame -fill green
}
}
# ----------------------------------------------------------------------
#
# canvasbutton::leave --
#
# Process the <Leave> event on a canvas-button.
#
# Parameters:
# w Path name of the canvas
#
# Results:
# None.
#
# Side effects:
# Reverts the cursor symbol, the border width
# if needed, the highlight color of the button.
#
# ----------------------------------------------------------------------
proc canvasbutton::leave {w} {
variable enteredButton
variable pressedButton
variable cursor
if {[string compare $enteredButton {}]} {
set btag [findBtag $w]
set frame [linsert $btag end frame]
$w itemconfigure $frame -width 1
$w configure -cursor $cursor($w)
unset cursor($w)
if {![string compare $btag $pressedButton]} {
$w itemconfigure $frame -fill white
}
set enteredButton {}
}
return
}
# ----------------------------------------------------------------------
#
# canvasbutton::press --
#
# Process the <ButtonPress-1> event on a canvas-button.
#
# Parameters:
# w Path name of the canvas
#
# Results:
# None.
#
# Side effects:
# Highlights the selected button in green.
#
# ----------------------------------------------------------------------
proc canvasbutton::press {w} {
variable pressedButton
set pressedButton [findBtag $w]
$w itemconfigure [linsert $pressedButton end frame] \
-fill green
return
}
# ----------------------------------------------------------------------
#
# canvasbutton::release --
#
# Process the <ButtonRelease-1> event on a canvas-button.
#
# Parameters:
# w Path name of the canvas
#
# Results:
# None.
#
# Side effects:
# Reverts the highlight color on the button. If the
# mouse has not left the button, invokes the button's
# command.
#
# ----------------------------------------------------------------------
proc canvasbutton::release {w} {
variable enteredButton
variable pressedButton
variable command
set pressedButtonWas $pressedButton
set pressedButton {}
$w itemconfigure [linsert $pressedButtonWas end frame] \
-fill white
if {![string compare $enteredButton $pressedButtonWas]} {
uplevel #0 $command($pressedButtonWas)
}
return
}
# ----------------------------------------------------------------------
#
# canvasbutton::btag --
#
# Locate the unique tag of a canvas-button
#
# Parameters:
# w Path name of the canvas
#
# Results:
# Button tag, or the null string if the current
# item is not a canvas-button
#
# Side effects:
# Searches the tag list of the current canvas item
# for a tag that begins with the string, `canvasb#',
# and returns the first two elements of the tag
# interpreted as a Tcl list.
#
# ----------------------------------------------------------------------
proc canvasbutton::findBtag {w} {
foreach tag [$w itemcget current -tags] {
if {[regexp {^canvasb#} [lindex $tag 0]]} {
return [lrange $tag 0 1]
}
}
return {}
}
if {![string compare $argv0 [info script]]} {
grid [canvas .c -width 300 -height 200 -cursor crosshair]
namespace import canvasbutton::*
.c create text 150 150 -anchor n -tags label \
-font {Helvetica 10 bold}
canvasbutton .c 10 60 90 140 "First\nButton" {
.c itemconfigure label -text One
}
canvasbutton .c 110 60 190 140 "Second\nButton" {
.c itemconfigure label -text Two
}
canvasbutton .c 210 60 290 140 "Third\nButton" {
.c itemconfigure label -text Three
}
canvasbutton .c 240 160 290 190 "Quit" exit
}Here's a link to a version of Canvas Buttons where you can watch the button depress when you click it, and spring back when you release it.
See also: