DOKK / manpages / debian 10 / tklib / canvas::highlight.3tk.en
canvas::highlight(3tk) Variations on a canvas canvas::highlight(3tk) 







canvas::highlight - Manage the highlighting of canvas items or
    item groups








package require Tcl 8.5


package require Tk 8.5


package require canvas::highlight ?0.1?


::canvas::highlight on canvas tagOrId
    cmd


::canvas::highlight off canvas
  tagOrId


{*}cmd on canvas item


{*}cmd off canvas clientdata












This package provides utility commands for setting up and tearing
    down of highlights for canvas items or item groups, the latter identified by
    a tag.









  
::canvas::highlight on canvas tagOrId
    cmd

  
This command sets up a general highlight, with the items of canvas
      canvas to highlight in this manner identified by tagOrId and
      the cmd prefix providing the implementation, i.e. the how to
      perform the highlight.
    
The signature of the command prefix is described later, in
        section Highlight callback.

    
The result of the command is the empty string.

    
Limitations:

  







  
[1]

  
When a highlight is active no other highlight can be activated. This means
      that nested highlights are not possible.

  
[2]

  
The system may break if a highlight is removed from within its highlight
      callback.







  
::canvas::highlight off canvas tagOrId

  
This command removes any highlight set on the items of canvas
      canvas identified by tagOrId.
    
The result of the command is the empty string.

  








The highlight callback is a command prefix invoked in the
    following two ways:



  
{*}cmd on canvas item

  
This form is invoked when the mouse has entered (one of) the item(s) the
      highlight was set up for. The callback now has to perform any
      reconfiguration necessary to highlight the item (group).
    
The result of the command can be anything. It is stored by the
        system as client information and passed unchanged to the un-highlight
        callback for its use. In this manner the highlight callback is able to
        maintain custom state from highlighting to un-highlighting.

    
Note that the callback does not have to maintain state, nor
        does it have to actually reconfigure the item (group). In the latter
        case the callback simply serves as easy enter/leave notification.

  

  
{*}cmd off canvas clientdata

  
This form is invoked when the mouse has left (one of) the item(s) of the
      currently active the highlight. The callback now has to perform any
      reconfiguration necessary to un-highlight the item (group).
    
The result of the command must be a boolean value with the
        usual value to be true. By returning false instead the
        callback can veto the removal of the highlight.

  












This document, and the package it describes, will undoubtedly
    contain bugs and other problems. Please report such in the category
    canvas of the Tklib Trackers
    [http://core.tcl.tk/tklib/reportlist]. Please also report any ideas for
    enhancements you may have for either package and/or documentation.








canvas, enter callback, highlighting, leave callback







  

    0.1
    canvas