TIP #119 Version 1.2: Angled Text on a Canvas

This is not necessarily the current version of this TIP.

Abstract

The current text object on a canvas does not support the creation of text strings at an arbitrary angle. For some applications this is limitation is sufficiently serious to disqualify Tk from use. This TIP removes this restriction.

Rationale

Using a Tk canvas to display e.g. an engineering drawing from a CAD application is limited - such applications will output angled text and there is simply no way of displaying such text on a canvas.

Another consideration is the competition. Both Qt and Java canvas objects support angled text on their canvas object - most new users would I believe be surprised to discover that this functionality is not supported.

Due to the internal architecture of Tk a side effect of this work would be to enable buttons (and possibly other widgets) to have their text written at an angle as well. This TIP does not expose that functionality.

Implementation

At the command level there would be an extra attribute, -angle, added to the canvas's text object:

<canvas> create text <x> <y> -text <str> ?-angle <angle>? ...

where the angle is specified in degrees. Manipulation of the angle would be done in the usual way through the itemconfigure and itemcget subcommands:

<canvas> itemconfigure <tag> -angle <angle>

Note that PostScript naturally supports rotation of text.

Reference Implementation

I have done an initial assessment of the amount of work required and have amended Tk 8.4.1 with the above syntax for the X version (on Linux). This initial work was fairly straightforward but the internal housekeeping work maintaining and interacting with an angled box will be more substantial. The patch is located at http://homepage.ntlworld.com/whiteowl/tk841_at_patch.gz The X version can be done with the xvertex.5.0 extension which is included in the above patch. I don't know how it would be done on non-X systems.

Copyright

This document has been placed in the public domain.

This is not necessarily the current version of this TIP.