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canvas::edit::circle(3tk) Variations on a canvas canvas::edit::circle(3tk) 





NAME


canvas::edit::circle - Editing a circle 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::circle ?0.1?


::canvas::edit circle objectName
    canvas options...


objectName destroy


objectName enable


objectName disable


objectName active


objectName set minx miny maxx
    maxy


objectName clear


activeCmd editorObj id


createCmd canvas x y


dataCmd editorObj coordinates










DESCRIPTION


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.






INTERACTION


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.






CLASS API



  
::canvas::edit circle objectName canvas
    options...

  
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.

  








INSTANCE API


Instances of the circle editors provide the following API:



  

  
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.

  

  

  
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.

  

  

  
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.

  

  

  
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.

  

  

  
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.

  

  

  
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.

  








OPTIONS


The class command accepts the following options



  

  
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

  







  

  

    
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.

  







  

  
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.

  

  

  
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.

  

  

  
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.

  

  

  
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

  







  

  
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.

  







  

  
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

  







  

  
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.

  







  

  
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.

  

  

  
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.

  

  

  
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.

  

  

  
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.

  

  

  
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

  








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, circle, editing







  

    0.1
    tklib