Re: Dotted Circle plus Combining Mark as Text

From: Asmus Freytag <>
Date: Sun, 20 Oct 2013 16:01:52 -0700

On 10/20/2013 3:45 PM, Philippe Verdy wrote:
> 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.

If that is so, the it is an unfortunate problem with the OpenType
It is not in agreement with the way U+25CC was encoded.

> 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.

Which is a limitation of the technology not based on conformance
requirements by the Unicode Standard.
> 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 - 18:03:42 CDT

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