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.TH "canvas::edit::quadrilateral" n 0\&.1 tklib "Variations on a canvas"
.BS
.SH NAME
canvas::edit::quadrilateral \- Editing a quadrilateral on a canvas
.SH SYNOPSIS
package require \fBTcl  8\&.5\fR
.sp
package require \fBTk  8\&.5\fR
.sp
package require \fBcanvas::edit::points  ?0\&.1?\fR
.sp
package require \fBcanvas::edit::quadrilateral  ?0\&.1?\fR
.sp
\fB::canvas::edit\fR \fBquadrilateral\fR \fIobjectName\fR \fIcanvas\fR \fIoptions\fR\&.\&.\&.
.sp
\fBobjectName\fR \fBdestroy\fR
.sp
\fBobjectName\fR \fBenable\fR
.sp
\fBobjectName\fR \fBdisable\fR
.sp
\fBobjectName\fR \fBactive\fR
.sp
\fBobjectName\fR \fBadd\fR \fIx\fR \fIy\fR
.sp
\fBobjectName\fR \fBclear\fR
.sp
\fBcreateCmd\fR \fIcanvas\fR \fIx\fR \fIy\fR
.sp
\fBhighlightCmd\fR \fBon\fR \fIcanvas\fR \fIitem\fR
.sp
\fBhighlightCmd\fR \fBoff\fR \fIcanvas\fR \fIstate\fR
.sp
\fBdataCmd\fR \fIeditorObj\fR \fIcoordinates\fR
.sp
.BE
.SH 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\&.
.SH "CLASS API"
.TP
\fB::canvas::edit\fR \fBquadrilateral\fR \fIobjectName\fR \fIcanvas\fR \fIoptions\fR\&.\&.\&.
This, the class command, creates and configures a new instance of a
quadrilateral editor, named \fIobjectName\fR\&. The instance will be
connected to the specified \fIcanvas\fR widget\&.
.sp
The result of the command is the fully qualified name of the
instance command\&.
.sp
The options accepted here, and their values, are explained in
the section \fBOptions\fR\&.
.PP
.SH "INSTANCE API"
Instances of the quadrilateral editors provide the following API:
.TP
\fBobjectName\fR \fBdestroy\fR
This method destroys the quadrilateral editor and releases all its
internal resources\&.
.sp
Note that this operation does not destroy the items the editor
managed on the attached canvas, nor the canvas itself\&.
.sp
The result of the method is an empty string\&.
.TP
\fBobjectName\fR \fBenable\fR
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\&.
.sp
The result of the method is an empty string\&.
.sp
The complementary method is \fBdisable\fR\&. The interogatory
method for the current state is \fBactive\fR\&.
.TP
\fBobjectName\fR \fBdisable\fR
This method disables editing of the quadrilateral on the canvas\&. A call
is ignored if the editor is already disabled\&.
.sp
The result of the method is an empty string\&.
.sp
The complementary method is \fBenable\fR\&. The interogatory
method for the current state is \fBactive\fR\&.
.TP
\fBobjectName\fR \fBactive\fR
This method queries the editor state\&.
.sp
The result of the method is a boolean value, \fBtrue\fR if
the editor is active, and \fBfalse\fR otherwise, i\&.e\&. disabled\&.
.sp
The methods to change the state are \fBenable\fR and
\fBdisable\fR\&.
.TP
\fBobjectName\fR \fBadd\fR \fIx\fR \fIy\fR
This method programmatically adds a vertex at the specified location
to the quadrilateral\&.
.sp
The result of the method is an empty string\&.
.sp
Note that this method goes through the whole set of callbacks
invoked when the user interactively creates a vertex, i\&.e\&.
\fB-create-cmd\fR, and, more importantly, \fB-data-cmd\fR\&.
.sp
This is the method through which to load the vertices of a
pre-existing quadrilateral into an editor instance\&.
.sp
Note that at most 4 vertices can be specified, and at least 4
must be specified for the quadrilateral to be complete\&.
.TP
\fBobjectName\fR \fBclear\fR
This method programmatically unset the quadrilateral in the editor\&.
.sp
The result of the method is an empty string\&.
.sp
Note that this method goes through the same callback invoked
when the user interactively removes a vertex, i\&.e\&. \fB-data-cmd\fR\&.
.PP
.SH OPTIONS
The class command accepts the following options
.TP
\fB-convex\fR \fIboolean\fR
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\&.
.sp
This option can only be set at construction time\&.
.sp
If not specified it defaults to \fBfalse\fR, i\&.e\&. acceptance
of any quadrilateral\&.
.TP
\fB-tag\fR \fIstring\fR
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\&.
.sp
This option can only be set at construction time\&.
.sp
If not specified it defaults to \fBQUADRILATERAL\fR
.TP
\fB-create-cmd\fR \fIcommand-prefix\fR
The value of this option is a command prefix the editor will invoke
when it has to create a new vertex\&.
.sp
This option can only be set at construction time\&.
.sp
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\&.
.sp
The signature of this command prefix is
.RS
.TP
\fBcreateCmd\fR \fIcanvas\fR \fIx\fR \fIy\fR
The result of the command prefix \fImust\fR 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\&.
.RE
.TP
\fB-highlight-cmd\fR \fIcommand-prefix\fR
The value of this option is a command prefix the editor will invoke
when it has to (un)highlight a vertex\&.
.sp
This option can only be set at construction time\&.
.sp
If not specified it defaults to a command which will re-color
the item to highlight in red (and restores the color for
unhighlighting)\&.
.sp
The two signatures of this command prefix are
.RS
.TP
\fBhighlightCmd\fR \fBon\fR \fIcanvas\fR \fIitem\fR
.sp
This method of the command prefix has to perform whatever is
needed to highlight the vertex the \fIitem\fR is a part of (remember
the note above about quadrilateral allowed to be constructed from multiple
canvas items)\&.
.sp
The result of the command can be anything and will be passed as
is as argument \fIstate\fR to the \fBoff\fR method\&.
.TP
\fBhighlightCmd\fR \fBoff\fR \fIcanvas\fR \fIstate\fR
.sp
This method is invoked to unhighlight a vertex described by the
\fIstate\fR, which is the unchanged result of the \fBon\fR method
of the command prefix\&. The result of this method is ignored\&.
.sp
Note any interaction between dragging and highlighting of
quadrilateral is handled within the editor, and that the callback bears no
responsibility for doing such\&.
.RE
.TP
\fB-data-cmd\fR \fIcommand-prefix\fR
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\&.
.sp
This option can only be set at construction time\&.
.sp
If not specified it defaults to an empty string and is ignored
by the editor, i\&.e\&. not invoked\&.
.sp
The signatures of this command prefix are
.RS
.TP
\fBdataCmd\fR \fIeditorObj\fR \fIcoordinates\fR
This callback is invoked when the quarilateral was changed either
interactively, or programmatically\&.
See instance method \fBadd\fR for the latter\&.
.sp
The \fIeditorObj\fR identifies the instance invoking the
callback, whereas \fIcoordinates\fR is a list of vertex locations,
with each location a pair of x- and y-coordinates\&.
.sp
The result of this method is ignored\&.
.RE
.PP
.SH KEYWORDS
canvas, concave, convex, editing, non-convex, quadrilateral