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

Table Of Contents


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


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.


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

Instance API

Instances of the point cloud editors provide the following API:


The class command accepts the following options

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. Please also report any ideas for enhancements you may have for either package and/or documentation.


canvas, editing, point cloud, points