canvas::edit::points - Variations on a canvas

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# canvas::edit::points(n) 0.1 tklib "Variations on a canvas"

## 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 ?0.1?

- ::canvas::edit points 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 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 (regular, and highlighted). Note that instances do not store the edited points themselves, but delegate this to a configurable object.

## 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:

objectName destroy

  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.

objectName enable

  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.

objectName disable

  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.

objectName 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.

objectName add x y

  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.

objectName clear

  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

-tag string

  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

-create-cmd command-prefix

  The value of this option is a command prefix the editor will invoke when it has to create a new point.

  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

  createCmd canvas x y

    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.

-highlight-cmd command-prefix

  The value of this option is a command prefix the editor will invoke when it has to (un)highlight a point.

  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

  highlightCmd on canvas item

    This method of the command prefix has to perform whatever is needed to highlight the point the item is a part of (remember the note above about points 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.

  highlightCmd off canvas state

    This method is invoked to unhighlight a point 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 points is handled within the editor, and that the callback bears no responsibility for doing such.

-data-cmd command-prefix

  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

  dataCmd add editorObj id x y

    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.

  dataCmd remove editorObj id

    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.

  dataCmd move start editorObj id

    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.

  dataCmd move delta editorObj id x y dx dy

    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.

  dataCmd move done editorObj id

    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.

## 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.

## Keywords

canvas, editing, point cloud, points