[vset VERSION 0.1]
[comment {-*- tcl -*- doctools manpage}]
[manpage_begin canvas::edit::polyline n [vset VERSION]]
[moddesc   {Variations on a canvas}]
[titledesc {Editing a polyline on a canvas}]
[require Tcl 8.5]
[require Tk 8.5]
[require canvas::edit::points [opt 0.1]]
[require canvas::edit::polyline [opt [vset VERSION]]]
[keywords canvas editing polyline]
[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.

[section {Class API}]

[list_begin definitions]
[comment {= = == === ===== ======== ============= =====================}]
[call [cmd ::canvas::edit] [method polyline] [arg objectName] [arg canvas] [arg options]...]

This, the class command, creates and configures a new instance of a
polyline editor, named [arg objectName]. The instance will be
connected to the specified [arg canvas] widget.

[para] The result of the command is the fully qualified name of the
instance command.

[para] The options accepted here, and their values, are explained in
the section [sectref Options].

[list_end]

[section {Instance API}]

Instances of the polyline editors provide the following API:

[list_begin definitions]
[comment {= = == === ===== ======== ============= =====================}]
[call [cmd objectName] [method destroy]]

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

[para] Note that this operation does not destroy the items the editor
managed on the attached canvas, nor the canvas itself.

[para] The result of the method is an empty string.

[comment {= = == === ===== ======== ============= =====================}]
[call [cmd objectName] [method 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.

[para] The result of the method is an empty string.

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

[comment {= = == === ===== ======== ============= =====================}]
[call [cmd objectName] [method disable]]

This method disables editing of the polyline on the canvas. A call
is ignored if the editor is already disabled.

[para] The result of the method is an empty string.

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


[comment {= = == === ===== ======== ============= =====================}]
[call [cmd objectName] [method active]]

This method queries the editor state.

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

[para] The methods to change the state are [method enable] and
[method disable].

[comment {= = == === ===== ======== ============= =====================}]
[call [cmd objectName] [method add] [arg x] [arg y]]

This method programmatically adds a vertex at the specified location to the line.

[para] The result of the method is an empty string.

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

[para] 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.

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

[comment {= = == === ===== ======== ============= =====================}]
[call [cmd objectName] [method clear]]

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

[para] The result of the method is an empty string.

[para] Note that this method goes through the same callbacks invoked
when the user interactively removes a vertex, i.e. [option -data-cmd].

[list_end]

[section Options]

The class command accepts the following options

[list_begin options]
[comment {= = == === ===== ======== ============= =====================}]
[comment {= = == === ===== ======== ============= =====================}]
[opt_def -tag [arg 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.

[para] This option can only be set at construction time.

[para] If not specified it defaults to [const POLYLINE]

[comment {= = == === ===== ======== ============= =====================}]
[comment {= = == === ===== ======== ============= =====================}]
[opt_def -create-cmd [arg command-prefix]]

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

[para] This option can only be set at construction time.

[para] 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.

[para] The signature of this command prefix is

[list_begin definitions]
[comment {= = == === ===== ======== ============= =====================}]
[call [cmd createCmd] [arg canvas] [arg x] [arg y]]

The result of the command prefix [emph 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.

[para] 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.

[list_end]


[comment {= = == === ===== ======== ============= =====================}]
[comment {= = == === ===== ======== ============= =====================}]
[opt_def -highlight-cmd [arg command-prefix]]

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

[para] This option can only be set at construction time.

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

[para] The two signatures of this command prefix are

[list_begin definitions]
[comment {= = == === ===== ======== ============= =====================}]
[call [cmd highlightCmd] [method on] [arg canvas] [arg item]]

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

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

[comment {= = == === ===== ======== ============= =====================}]
[call [cmd highlightCmd] [method off] [arg canvas] [arg state]]

[para] This method is invoked to unhighlight a vertex described by the
[arg state], which is the unchanged result of the [method on] method
of the command prefix. The result of this method is ignored.

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

[list_end]

[comment {= = == === ===== ======== ============= =====================}]
[comment {= = == === ===== ======== ============= =====================}]
[opt_def -data-cmd [arg 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.

[para] This option can only be set at construction time.

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

[para] The signature of this command prefix is

[list_begin definitions]
[comment {= = == === ===== ======== ============= =====================}]
[call [cmd dataCmd] [arg editorObj] [arg coordinates]]

This callback is invoked when the line was changed either interactively,
or programmatically.

See instance method [method add] for the latter.

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

[para] The result of this method is ignored.

[list_end][comment callback-signatures]
[list_end][comment options]
[manpage_end]
