canvas::edit::points - Editing a cloud of points on a canvas
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:
Clicking anywhere with button 1 adds a new point.
Clicking on a point with button 2 removes that point.
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.
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.
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.
The class command accepts the following options
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.