canvas::edit::quadrilateral(Variations on a canvcanvas::edit::quadrilateral(n)



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NAME
       canvas::edit::quadrilateral - Editing a quadrilateral 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::quadrilateral  ?0.1?

       ::canvas::edit quadrilateral 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 the editing of a
       quadrilateral on a canvas. Instances can be configured with regard to
       the visual appearance (regular, and highlighted) of vertex markers.
       Note that instances do not store the edited quadrilateral themselves,
       but delegate this to a configurable object.

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

       objectName destroy
              This method destroys the quadrilateral 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 quadrilateral 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 quadrilateral 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 quadrilateral.

              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.

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

              Note that at most 4 vertices can be specified, and at least 4
              must be specified for the quadrilateral to be complete.

       objectName clear
              This method programmatically unset the quadrilateral in 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 vertex, i.e. -data-cmd.

OPTIONS
       The class command accepts the following options

       -convex boolean
              The value of this option is a boolean flag. When the flag is set
              the editor will accept only convex quadrilaterals and reject all
              operations which would result in a violation of convexity.

              This option can only be set at construction time.

              If not specified it defaults to false, i.e. acceptance of any
              quadrilateral.

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

              This option can only be set at construction time.

              If not specified it defaults to QUADRILATERAL

       -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.

       -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 quadrilateral 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
                     quadrilateral 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 quadrilateral was edited in some way. This is
              how the editor delegates the actual storage of quadrilateral
              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 editorObj coordinates
                     This callback is invoked when the quarilateral 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, concave, convex, editing, non-convex, quadrilateral



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