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