NAME

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

SYNOPSIS

       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

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DESCRIPTION

       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.

API

       ::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.

   HIGHLIGHT CALLBACK
       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.

BUGS, IDEAS, FEEDBACK

       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.

KEYWORDS

       canvas, enter callback, highlighting, leave callback

tklib                                                  0.1                                canvas::highlight(3tk)