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





NAME


canvas::edit::points - Editing a cloud of points on a canvas






SYNOPSIS


package require Tcl 8.5


package require Tk 8.5


package require canvas::edit::points ?0.3?


::canvas::edit points objectName
    canvas options...


objectName destroy


objectName enable


objectName disable


objectName active


objectName add x y


objectName clear


activeCmd editorObj id


createCmd canvas x y


dataCmd add editorObj id x
    y


dataCmd remove editorObj id


dataCmd move start editorObj id


dataCmd move delta editorObj id
    x y dx dy


dataCmd move done editorObj id










DESCRIPTION


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






INTERACTION


The default bindings enable the creation, removal and dragging of
    point (markers) using the mouse buttons 1, 2, and 3. Specifically:



  
[1]

  
Clicking anywhere with button 1 adds a new point.

  
[2]

  
Clicking on a point with button 2 removes that point.

  
[3]

  
Clicking on a point with button 3 starts a drag operation ending with the
      release of the button.




The option -drag-point can be used to change the button
    used to initiate drag operations. Note that the option value may not only
    contain the button number, but also modifier prefix separated from the
    button by a dash "-". The recognized modifiers are
    Control, Shift, and Alt.


The option -add-remove-point can be used to change the
    button used to add/remove points. This works because removal is an item
    binding, while adding is canvas global. The option recognizes the same
    syntax for button as -drag-point.


In the standard configuration the canvas item representing a point
    is a circle configured using the appearance options -color,
    -hilit-color, and -radius. Their defaults are Skyblue2,
    red, and 3, repsectively.


The option -kind can be used to slightly customize the
    canvas item to any kind accepting the item options -width,
    -outline, -fill, and -activefill.


For more extensive customization its is necessary to configure a
    creation callback using option -create-cmd. The callback takes the
    canvas and x. y coordinates as arguments, in this order, and is expected to
    return a list of the canvas items representing the point.


Note the plural. With the callback it is possible to visualize a
    point using a group of items.


Further note that when the callback return an empty list no point
    is created. In other words, the callback can also be used to perform checks
    if a point at the given location is desirable, or not. This can be combined
    with the default creation behaviour as the option can be queried, and its
    default value is the callback for the default behaviour.


Keeping with the callback for a bit, the option -active-cmd
    sets a callback invoked whenever the mouse is over one of the created
    points, i.e. active. This can be used to drive derived displays. For example
    highlighting the point's entry in a table or other widget.


The last option of importance is -tag. Its value is the
    name of the canvas tag used to mark all the items owned, i.e. created and
    managed by an. The default is POINT.


When attaching multiple instances of this behaviour to the same
    canvas each instance has to be configured with a unique tag, to prevent them
    from interfering with each other.






CLASS API



  
::canvas::edit points objectName canvas
    options...

  
This, the class command, creates and configures a new instance of a point
      cloud 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 point cloud editors provide the following
  API:



  

  
This method destroys the point cloud editor and releases all its internal
      resources.
    
Note that this operation does not destroy the items of the
        point markers 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 point cloud 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 point cloud 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 creates a point at the specified location.
    
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 point, i.e.
        -create-cmd, and, more importantly, -data-cmd.

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

  

  

  
This method programmatically removes all points from 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 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 a point 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 point within the editor.

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

    
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 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 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 "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 point.

  







  

  
The value of this option is a command prefix the editor will invoke when a
      point was edited in some way. This is how the editor delegates the actual
      storage of point 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 a new point was added to the instance,
      either interactively, or programmatically. See instance method add
      for the latter.
    
The id identifies the point within the editor and will
        be used by the two other callbacks to specify which point to modify.

    
The last two arguments x and y specify the
        location of the new point in canvas coordinates.

    
The result of this method is ignored.

  

  

  
This callback is invoked when a point removed from the editor instance.
    
The id identifies the removed point within the
      editor.

    
The result of this method is ignored.

  

  

  
This callback is invoked when the movement of a point in the editor
      instance has started.
    
The id identifies the point within the editor about to
        be moved.

    
The result of this method is ignored.

  

  

  
This callback is invoked when the point moved in the editor instance.
    
The id identifies the moved point within the editor,
        and the remaining arguments x, y, dx, and dy
        provide the new absolute location of the point, and full delta to the
        original location.

    
At the time of the calls the system is not committed to
        the move yet. Only after method move done was invoked and has
        accepted or rejected the last position will the editor update its
        internal data structures, either committing to the new location, or
        rolling the move back to the original one.

    
Given this the location data provided here should be saved
        only in temporary storage until then.

    
The result of this method is ignored.

  

  

  
This callback is invoked when the movement of a point in the editor
      instance is complete.
    
The id identifies the moved point within the
      editor.

    
The result of this method must be a boolean value. If the
        method returns false the move is vetoed and rollbed back.

  







  

  
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 points managed by the editor.
    
This option can only be set at construction time.

    
If not specified it defaults to POINT

  








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, editing, point cloud, points







  

    0.3
    tklib