canvas::edit::quadrilateral - Editing a quadrilateral on a canvas
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
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.
-
::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.
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.
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.
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.
canvas, concave, convex, editing, non-convex, quadrilateral