plucky (3) canvas::highlight.3tk.gz

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