TIP 300: Examine Glyph Substitution in the 'font actual' Command

Author:         Kevin B. Kenny <[email protected]>
State:          Final
Type:           Project
Vote:           Done
Created:        25-Nov-2006
Tcl-Version:    8.5
Keywords:	Tk
Tk-Ticket:	1602955


This TIP proposes enhancing the font actual command to allow determining the actual font to be used when rendering a specific character.


Tk, when rendering strings in a widget, often needs to augment the characters in the requested font with characters borrowed from other fonts. As of the date of this TIP, there is no way for a program to introspect this mechanism. This ability has been requested by several user interface designers, because the interfaces are often more attractive if the substitute fonts are used directly, or simply to determine what font was chosen.

Proposed Change

This TIP proposes modifying the font actual command to have the syntax:

font actual font ?-displayof window? ?option? ?--? ?char?

The font, -displayof and option arguments are unchanged from the current [font actual] command.

The -- option marks the end of options. It is needed if option is not supplied and char may be a hyphen, to distinguish _char' from a misspelt option.

The char option must be a single character.

The result of the command, if the char option is supplied, is the actual font used to render the given character, rather than the base font.

Reference Implementation

A reference implementation for the proposed feature, including documentation and test suite updates, is at SourceForge as Tk Patch #1602955.


This document has been placed in the public domain.