Updated 2018-06-04 13:58:41 by APE ▲

willdye On 2005-08-12, dkf posted some example code on the Tcl'ers chat, for the benefit of a new person who was asking basic questions about things like the canvas widget. The code below is derived from dkf's original example code. It should create a small display of several rooms. As the mouse moves into a room, an <Enter> event should be triggered, and the name of the room should appear in a label. As the mouse moves out of the room, a <Leave> event should be triggered, and the label should be blanked out.
 # Example of using 'bind' to trigger procs on <Enter> and <Leave> events.
 proc makeRoom {widget name polyCoords} {
     set id [$widget create poly $polyCoords -fill white -outline black]
     $widget bind $id <Enter> [list enterRoom $widget $id $name]
     $widget bind $id <Leave> [list leaveRoom $widget $id]
     $widget scale $id 0 0 20 20 }
 proc enterRoom {widget id name} {
     $widget itemconfigure Title -text $name
     $widget itemconfigure $id -fill yellow }
 proc leaveRoom {widget id} {
     $widget itemconfigure Title -text ""
     $widget itemconfigure $id -fill white }
 proc start {widget} {
     destroy $widget ; pack [canvas $widget -background white]
     makeRoom $widget "Bedroom" {1 1 4 1 4 3 1 3}
     makeRoom $widget "Kitchen" {5 1 9 1 9 3 5 3}
     makeRoom $widget "Hallway" {4 1 5 1 5 3 9 3 9 4 1 4 1 3 4 3}
     makeRoom $widget "Recroom" {9 4 9 9 1 7 1 4}
     $widget create text 40 10 -tag Title }
 start .c

This example is nearly equivalent, but even shorter, albeit at the expense of being less general, and binding to compound inline commands.
 # This is an example of binding compound, inline commands to mouse events.
 # Note that the use of double quotes here is considered dangerous.  It allows
 # $id and $name to be dereferenced, but in non-trival code the subtleties of
 # quoting and substitution are such that it's generally much better to bind
 # to procedure calls such as: .c bind $id <Enter> [list entry_proc $id $name]
 proc create_room {name coordinates} {
     set id [.c create polygon $coordinates -fill white -outline black]
     .c scale $id 0 0 29 20
     .c bind $id <Enter> ".c itemconfig $id -fill yellow; .l config -text $name"
     .c bind $id <Leave> ".c itemconfig $id -fill white;  .l config -text {}" }
 destroy .c .l
 pack [label  .l -background white] -fill x
 pack [canvas .c -background white]
 create_room "Bedroom" {1 1 4 1 4 3 1 3}
 create_room "Kitchen" {5 1 9 1 9 3 5 3}
 create_room "Hallway" {4 1 5 1 5 3 9 3 9 4 1 4 1 3 4 3}
 create_room "Recroom" {9 4 9 9 1 7 1 4}

APE 04/06/2018 Hereafter a slightly different version which make use of tags (and also removes the tag current for display) :
proc create_room {name coordinates} {
     set id [.c create polygon $coordinates -fill white -outline black -tags "room $name"]
     .c scale $id 0 0 29 20
 }
 destroy .c .l
 pack [label  .l -background white] -fill x
 pack [canvas .c -background white]
 create_room "Bedroom" {1 1 4 1 4 3 1 3}
 create_room "Kitchen" {5 1 9 1 9 3 5 3}
 create_room "Hallway" {4 1 5 1 5 3 9 3 9 4 1 4 1 3 4 3}
 create_room "Recroom" {9 4 9 9 1 7 1 4}

 .c bind room <Enter> {.c itemconfig current -fill yellow; .l config -text [string map {current "" room ""} [.c gettags current]]}
 .c bind room <Leave> {.c itemconfig current -fill white;  .l config -text ""}

Category ExampleCategory GraphicsCategory GUI