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



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NAME
       canvas::edit::polyline - Editing a polyline on a canvas

SYNOPSIS
       package require Tcl  8.5

       package require Tk  8.5

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

       package require canvas::edit::polyline  ?0.1?

       ::canvas::edit polyline 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 editorObj coordinates

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DESCRIPTION
       This package provides a class whose instances handle editing a single
       poly-line on a canvas. Instances can be configured with regard to the
       visual appearance (regular, and highlighted) of the markers denoting
       the line's vertices. Note that instances do not store the edited
       polyline themselves, but delegate this to a configurable object.

CLASS API
       ::canvas::edit polyline objectName canvas options...
              This, the class command, creates and configures a new instance
              of a polyline 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 polyline editors provide the following API:

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

              Note that this operation does not destroy the items 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 polyline 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 polyline 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 adds a vertex at the specified
              location to the line.

              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 vertex, i.e.
              -create-cmd, and, more importantly, -data-cmd.

              One important difference however. The new vertex is always added
              at the end of the line, whereas interactive creation uses
              heuristics to splice it into the line at a suitable location.

              This is the method through which to load the vertices of a pre-
              existing line into an editor instance.

       objectName clear
              This method programmatically removes all vertices from the
              editor, essentially removing the whole line.

              The result of the method is an empty string.

              Note that this method goes through the same callbacks invoked
              when the user interactively removes a vertex, 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 vertices managed by the
              editor.

              This option can only be set at construction time.

              If not specified it defaults to POLYLINE

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

              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 "vertex" 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 vertex.

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

              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 vertex 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 vertex 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
                     vertices 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 the line was edited in some way (vertex added,
              removed, moved). This is how the editor delegates the actual
              storage of the line 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 signature of this command prefix is

              dataCmd editorObj coordinates
                     This callback is invoked when the line was changed either
                     interactively, or programmatically.  See instance method
                     add for the latter.

                     The editorObj identifies the instance invoking the
                     callback, whereas coordinates is a list of vertex
                     locations, with each location a pair of x- and y-
                     coordinates.

                     The result of this method is ignored.

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, polyline



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