canvas::edit::circle - Editing a circle on a canvas

       This document, and the package it describes, will undoubtedly contain bugs and  other  problems.   Please
       report  such  in the category canvas of the TklibTrackers [http://core.tcl.tk/tklib/reportlist].  Please
       also report any ideas for enhancements you may have for either package and/or documentation.

::canvas::editcircleobjectNamecanvasoptions...
              This, the class command, creates  and  configures  a  new  instance  of  a  circle  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.

       This  package  provides  a  class  whose  instances handle editing a circle on a canvas. Instances can be
       configured with regard to the visual appearance of the markers denoting the  circle's  principal  points.
       Note  that  instances  do  not  store  the  edited circle themselves, but delegate this to a configurable
       object.

       Instances of the circle editors provide the following API:

       objectNamedestroy
              This method destroys the circle 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.

       objectNameenable
              This  method  activates  editing  of  the circle 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.

       objectNamedisable
              This method disables editing of the circle 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.

       objectNameactive
              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.

       objectNamesetminxminymaxxmaxy
              This method programmatically set the circle from the  border  coordinates.   This  writes  over  a
              previous (possibly partial) circle.

              The result of the method is an empty string.

              Note  that  this  method goes through the whole set of callbacks invoked when the principal points
              are created, i.e. -create-cmd, and, more importantly, -data-cmd.

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

       objectNameclear
              This method programmatically removes the circle from the editor, making the way free for  creating
              a new one.

              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 principal point, i.e. -data-cmd.

       The circle editor internally uses an instance of  package  canvas::edit::points,  and  inherits  all  the
       options  and  behaviours for it. The color options are additionally applied to the circle element of this
       editor

       Beyond that it provides an option, -circle-config, to customize the circle item used to render the circle
       through its principal points. Note that it cannot overide the inherited color options.

       During interaction instances execute a state machine where the user creates two points,  at  which  point
       the  system  completes  the  circle and reports it. At that point the system prevents adding more points.
       Dragging the points is still possible, enabling resizing and moving  the  circle.  Deleting  any  of  the
       principal  points deletes the entire circle, at which point the system is again ready for the creation of
       a new circle from two points.

       canvas, circle, editing

tklib                                                  0.1                             canvas::edit::circle(3tk)

       canvas::edit::circle - Editing a circle on a canvas

       The class command accepts the following options

       -active-cmdcommand-prefix
              The value of this option is a command prefix the editor will  invoke  when  the  mouse  enters  or
              leaves the circle or one of the principal points managed by the instance.

              If not specified it defaults to an empty command which does nothing.

              The signature of this command prefix is

              activeCmdeditorObjid

                     The id identifies the entered object.

                     An empty id indicates that the last entered object was left.

                     The value circle indicates that the circle's outline was entered.

                     Any other value is a code for one of the circle's principal points, i.e. center, and edge.

                     The result of this method is ignored.

       -add-remove-pointeventspec
              The  value  of  this  option is an event specification (without bracketing angles) declaring which
              event will trigger adding and removing a point.

              This option can only be set at construction time.

              The default setup uses  different  events  for  adding  and  removing  points,  ButtonPress-1  and
              ButtonPress-2 respectively.

              When  using  this  option  the  same event is used for both operations. This is no problem because
              adding is bound as canvas-global event while removal is bound to the relevant canvas items.

       -circle-configlist
              The value of this option is a list of options and their values  to  be  applied  to  the  internal
              circle item whenever it is regenerated after changes.  Note that these options cannot override the
              principal coloring of the circle as applied by the main options -color and -hilit-color.

              If not specified it defaults to the empty list.

       -colorcolorspec
              The  value  of this option is the fill color for the default item created when adding a point, and
              no -create-cmd is specified.

              The default value is SkyBlue2.

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

              While  this  option can be set after construction, it is recommended to use this feature only as a
              means of inserting custom processing to be done at creation time which  remembers  and  calls  the
              previous value of the option.

              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

              createCmdcanvasxy
                     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 "principal 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 principal point.

       -data-cmdcommand-prefix
              The  value of this option is a command prefix the editor will invoke when the circle was edited in
              some way (created, modified, deleted). This is how the editor delegates the actual storage of  the
              circle 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

              dataCmdeditorObjcoordinates
                     This   callback   is   invoked  when  the  circle  was  changed  either  interactively,  or
                     programmatically.  See instance method set for the latter.

                     The editorObj identifies the instance invoking the callback, whereas coordinates is a  list
                     of  4 elements, containing the min x, and y, and the max x and y coordinates of the circle,
                     in this order.

                     The result of this method is ignored.

       -drag-pointeventspec
              The value of this option is an event specification (without  bracketing  angles)  declaring  which
              event will trigger a drag action on points.

              This option can only be set at construction time.

              The default specification is ButtonPress-3.

       -hilit-colorcolorspec
              The  value of this option is the highlight color for the default item created when adding a point,
              and no -highlight-cmd is specified.

              The default value is red.

       -kindname
              The value of this option is the canvas item type for the default item created when adding a point,
              and no -create-cmd is specified.  Only item types specified through a bounding box are suitable.

              The default value is oval.

       -radiusint
              The value of this option is the radius for the default item created when adding a  point,  and  no
              -create-cmd is specified.

              The default value is 3.

       -tagstring
              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 CIRCLE

       package require Tcl8.5

       package require Tk8.5

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

       package require canvas::edit::circle?0.1?::canvas::editcircleobjectNamecanvasoptions...

       objectNamedestroyobjectNameenableobjectNamedisableobjectNameactiveobjectNamesetminxminymaxxmaxyobjectNameclearactiveCmdeditorObjidcreateCmdcanvasxydataCmdeditorObjcoordinates

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