Re: Dotted Circle plus Combining Mark as Text

From: Philippe Verdy <>
Date: Mon, 21 Oct 2013 00:45:19 +0200

2013/10/20 Asmus Freytag <>

> Incidentally, the dotted circle shown in the Unicode Code charts is *not*
> 25CC, and if I were to implement a "show dotted circle" feature in a
> program I would not use 25CC for this - that character has a standard glyph
> of rather unsuitable metrics for the purpose, never mind that many people
> have co-opted it.

In fact the OpenType specs suggests assigning a glyph for the dotted
circle so that renderers can use a glyph with the correct metrics for
combining marks that are mapped in the font. The font may also assign
distinct glyphs for some pairs with that base character, if the font
supports multiple scripts.

Many OpenType fonts are built like that so that the combining marks in
isolation will not show on top of an unknown glyph with incorrect metrics,
or worse over a zero-width space where they will collide with everything
else on both sides.

OpenType fonts however do not determine themselves is sequence is
ill-formed : it is the renderer that parse these contexts and which then
infer when to insert the base placeholder (it gets the glyph to insert by
looking in the same font for the U+25CC mapping, otherwise it will use
random or default or builtin font to get the dotted circle glyph, but it
won't be able to correctly position that glyph and the combining mark from
the font).
Received on Sun Oct 20 2013 - 17:48:11 CDT

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