Provided by: tklib_0.8~20230222-1_all 
NAME
canvas::edit::quadrilateral - Editing a quadrilateral on a canvas
SYNOPSIS
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
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DESCRIPTION
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.
CLASS API
::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.
INSTANCE API
Instances of the quadrilateral editors provide the following API:
objectName destroy
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.
objectName enable
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.
objectName disable
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.
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 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.
objectName clear
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.
OPTIONS
The class command accepts the following options
-convex boolean
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.
-tag string
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
-create-cmd command-prefix
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
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 "vertex" may consist of multiple canvas items in an arbitrary shape.
-highlight-cmd command-prefix
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
highlightCmd on canvas item
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.
highlightCmd off canvas state
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.
-data-cmd command-prefix
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
dataCmd editorObj coordinates
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.
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, concave, convex, editing, non-convex, quadrilateral