DOKK / manpages / debian 10 / tklib / canvas::edit::quadrilateral.3tk.en
canvas::edit::quadrilateral(3tk) Variations on a canvas canvas::edit::quadrilateral(3tk) 







canvas::edit::quadrilateral - Editing a quadrilateral on a
  canvas








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












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.









  
::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.

  










Instances of the quadrilateral editors provide the following
  API:



  

  
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.

  

  

  
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.

  

  

  
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.

  

  

  
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 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.

  

  

  
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.

  










The class command accepts the following options



  

  
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.

  

  

  
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

  

  

  
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

  







  

  
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.







  

  
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

  







  

  

    
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.

  

  

  

    
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.

  







  

  
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

  







  

  
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.

  












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.








canvas, concave, convex, editing, non-convex, quadrilateral







  

    0.1
    canvas