Provided by: tklib_0.8~20230222-1_all bug

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

_________________________________________________________________________________________________

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