L2/02-080
February 11, 2002
Proposed new property "Invisible"
It is useful for any Unicode rendering system (e.g., Apple's) to know whether a particular Unicode character normally has a visual representation; if not, the rendering system can bypass certain steps, such as attempting to find a font which contains a glyph that can represent the character. This can be formalized as "does not normally have a visual representation or affect advance."
Unicode currently includes the character property "Default_Ignorable_Code_Point". However, this property does not exactly correspond to the above definition. Apple requests that the UTC consider the addition of a new property, "Invisible", which indicates that while the character may affect layout, it does not normally have a visual representation: neither a glyph nor an advance.
Deborah Goldsmith
Manager, Fonts & Language Kits
Apple Computer, Inc.
goldsmith@apple.com
Begin forwarded message:
> From: Mark Davis <mark@macchiato.com>
> Date: Fri Feb 08, 2002 04:16:26 PM US/Pacific
> To: Kenneth Whistler <kenw@sybase.com>, Deborah Goldsmith
> <goldsmit@apple.com>
> Cc: unicore@unicode.org
> Subject: Re: Invisibility (was: Re: Agenda items from Apple)
> Reply-To: Mark Davis <mark@macchiato.com>
>
>> Taking the Hangul filler characters into account, I'd say that
>> Deborah has a reasonable case for "Invisible" not being an easily
>> derived property from what is already defined.
>
>> Yes, "no visible glyph" and "does not affect advance" is what we had in
>> mind. Colloquially, "you don't need to worry about drawing this."
>>
>> Should we put this back on the agenda?
>
> I think it should be a subject on the agenda. In particular, some or
> all of Ken's list are candidates for changes to DICP: characters that
> if you don't support you should not draw, so we should consider that
> before we lock down the list in Unicode 3.2.
>
> Note: we have to be careful about the statement that "you don't need
> to worry about drawing this". That could be interpreted as saying that
> you could remove them from the text before drawing and still always
> get the same result. There are very vew such characters (that was my
> (a)). For example, RLM has no glyph and no advance, but if you deleted
> it it can certainly change the rendering of the text.
>
> Mark
>
> ----- Original Message -----
> From: "Deborah Goldsmith" <goldsmit@apple.com>
> To: "Kenneth Whistler" <kenw@sybase.com>
> Cc: <mark@macchiato.com>; <unicore@unicode.org>
> Sent: Friday, February 08, 2002 15:24
> Subject: Re: Invisibility (was: Re: Agenda items from Apple)
>
>> On Friday, February 8, 2002, at 03:16 PM, Kenneth Whistler wrote:
>>
>>> Taking the Hangul filler characters into account, I'd say that
>>> Deborah has a reasonable case for "Invisible" not being an easily
>>> derived property from what is already defined.
>>>
>> Yes, "no visible glyph" and "does not affect advance" is what we had in
>> mind. Colloquially, "you don't need to worry about drawing this."
>>
>> Should we put this back on the agenda?
[Please see L2/02-081 for more comments by Ken Whistler and Mark Davis]