TIP:            236
Title:          Absolute Positioning of Canvas Items
Version:        $Revision: 1.10 $
Author:         Neil McKay <mckay@eecs.umich.edu>
State:          Final
Type:           Project
Vote:           Done
Created:        25-Dec-2004
Post-History:   
Keywords:       Tk,anchor,place
Tcl-Version:    8.6

~ Abstract

This TIP proposes adding a canvas widget command to set the absolute position
of canvas items.

~Rationale

There are many situations where it is desirable to move a group of canvas
items to a given position. Currently, this is done by getting the items' first
coordinate, calculating the offset required to move the items to the desired
position, and using the canvas '''move''' command to translate the items to
where we want them. This is tedious and inefficient.

~The 'moveto' Canvas Command

This TIP proposes adding a subcommand called '''moveto''' to the canvas widget
command. It is analogous to the canvas '''move''' command, except that it
accepts an absolute position instead of a relative displacement. For instance,
the command

|	.c moveto stuff 100 200

will displace all items tagged with ''stuff'' so that the first coordinate of
the first (bottom-most) tagged item lies at the point (100,200).

The result of the command will be the empty string.

~~Formal Syntax

 > ''canvas'' '''moveto''' ''tagOrId'' ''x'' ''y''

Argument description:

 canvas: The canvas instance's command.

 tagOrId: A specifier that selects one or more items. If no items are
 selected, the command does nothing.

 x, y: The absolute coordinates of the target location. If either coordinate
 is given as an empty string, then that coordinate will remain unchanged.

~Patches

A patch (against tcl8.5a3) that implements the '''moveto''' canvas subcommand
is available [http://www.eecs.umich.edu/~mckay/canvmoveto.patch.gz].

~Copyright

This document is in the public domain.