canvas::edit::points(n)     Variations on a canvas     canvas::edit::points(n)



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NAME
       canvas::edit::points - Editing a cloud of points on a canvas

SYNOPSIS
       package require Tcl  8.5

       package require Tk  8.5

       package require canvas::edit::points  ?0.1?

       ::canvas::edit points objectName canvas options...

       objectName destroy

       objectName enable

       objectName disable

       objectName active

       objectName add x y

       objectName clear

       createCmd canvas x y

       highlightCmd on canvas item

       highlightCmd off canvas state

       dataCmd add editorObj id x y

       dataCmd remove editorObj id

       dataCmd move start editorObj id

       dataCmd move delta editorObj id x y dx dy

       dataCmd move done editorObj id

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DESCRIPTION
       This package provides a class whose instances handle editing a cloud of
       point markers on a canvas. Instances can be configured with regard to
       the visual appearance of markers (regular, and highlighted). Note that
       instances do not store the edited points themselves, but delegate this
       to a configurable object.

CLASS API
       ::canvas::edit points objectName canvas options...
              This, the class command, creates and configures a new instance
              of a point cloud editor, named objectName. The instance will be
              connected to the specified canvas widget.

              The result of the command is the fully qualified name of the
              instance command.

              The options accepted here, and their values, are explained in
              the section Options.

INSTANCE API
       Instances of the point cloud editors provide the following API:

       objectName destroy
              This method destroys the point cloud editor and releases all its
              internal resources.

              Note that this operation does not destroy the items of the point
              markers the editor managed on the attached canvas, nor the
              canvas itself.

              The result of the method is an empty string.

       objectName enable
              This method activates editing of the point cloud on the canvas.
              This is the default after instance creation. A call is ignored
              if the editor is already active.

              The result of the method is an empty string.

              The complementary method is disable. The interogatory method for
              the current state is active.

       objectName disable
              This method disables editing of the point cloud on the canvas. A
              call is ignored if the editor is already disabled.

              The result of the method is an empty string.

              The complementary method is enable. The interogatory method for
              the current state is active.

       objectName active
              This method queries the editor state.

              The result of the method is a boolean value, true if the editor
              is active, and false otherwise, i.e. disabled.

              The methods to change the state are enable and disable.

       objectName add x y
              This method programmatically creates a point at the specified
              location.

              The result of the method is an empty string.

              Note that this method goes through the whole set of callbacks
              invoked when the user interactively creates a point, i.e.
              -create-cmd, and, more importantly, -data-cmd.

              This is the method through which to load pre-existing points
              into an editor instance.

       objectName clear
              This method programmatically removes all points from the editor.

              The result of the method is an empty string.

              Note that this method goes through the same callback invoked
              when the user interactively removes a point, i.e. -data-cmd.

OPTIONS
       The class command accepts the following options

       -tag string
              The value of this option is the name of the canvas tag with
              which to identify all items of all points managed by the editor.

              This option can only be set at construction time.

              If not specified it defaults to POINT

       -create-cmd command-prefix
              The value of this option is a command prefix the editor will
              invoke when it has to create a new point.

              This option can only be set at construction time.

              If not specified it defaults to a command which will create a
              black-bordered blue circle of radius 3 centered on the location
              of the new point.

              The signature of this command prefix is

              createCmd canvas x y
                     The result of the command prefix must be a list of the
                     canvas items it created to represent the marker. Note
                     here that the visual representation of a "point" may
                     consist of multiple canvas items in an arbitrary shape.

                     The returned list of items is allowed to be empty, and
                     such is taken as signal that the callback vetoed the
                     creation of the point.

       -highlight-cmd command-prefix
              The value of this option is a command prefix the editor will
              invoke when it has to (un)highlight a point.

              This option can only be set at construction time.

              If not specified it defaults to a command which will re-color
              the item to highlight in red (and restores the color for
              unhighlighting).

              The two signatures of this command prefix are

              highlightCmd on canvas item

                     This method of the command prefix has to perform whatever
                     is needed to highlight the point the item is a part of
                     (remember the note above about points allowed to be
                     constructed from multiple canvas items).

                     The result of the command can be anything and will be
                     passed as is as argument state to the off method.

              highlightCmd off canvas state

                     This method is invoked to unhighlight a point described
                     by the state, which is the unchanged result of the on
                     method of the command prefix. The result of this method
                     is ignored.

                     Note any interaction between dragging and highlighting of
                     points is handled within the editor, and that the
                     callback bears no responsibility for doing such.

       -data-cmd command-prefix
              The value of this option is a command prefix the editor will
              invoke when a point was edited in some way. This is how the
              editor delegates the actual storage of point information to an
              outside object.

              This option can only be set at construction time.

              If not specified it defaults to an empty string and is ignored
              by the editor, i.e. not invoked.

              The signatures of this command prefix are

              dataCmd add editorObj id x y
                     This callback is invoked when a new point was added to
                     the instance, either interactively, or programmatically.
                     See instance method add for the latter.

                     The id identifies the point within the editor and will be
                     used by the two other callbacks to specify which point to
                     modify.

                     The last two arguments x and y specify the location of
                     the new point in canvas coordinates.

                     The result of this method is ignored.

              dataCmd remove editorObj id
                     This callback is invoked when a point removed from the
                     editor instance.

                     The id identifies the removed point within the editor.

                     The result of this method is ignored.

              dataCmd move start editorObj id
                     This callback is invoked when the movement of a point in
                     the editor instance has started.

                     The id identifies the point within the editor about to be
                     moved.

                     The result of this method is ignored.

              dataCmd move delta editorObj id x y dx dy
                     This callback is invoked when the point moved in the
                     editor instance.

                     The id identifies the moved point within the editor, and
                     the remaining arguments x, y, dx, and dy provide the new
                     absolute location of the point, and full delta to the
                     original location.

                     At the time of the calls the system is not committed to
                     the move yet. Only after method move done was invoked and
                     has accepted or rejected the last position will the
                     editor update its internal data structures, either
                     committing to the new location, or rolling the move back
                     to the original one.

                     Given this the location data provided here should be
                     saved only in temporary storage until then.

                     The result of this method is ignored.

              dataCmd move done editorObj id
                     This callback is invoked when the movement of a point in
                     the editor instance is complete.

                     The id identifies the moved point within the editor.

                     The result of this method must be a boolean value. If the
                     method returns false the move is vetoed and rollbed back.

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, editing, point cloud, points



tklib                                 0.1              canvas::edit::points(n)
