Gary P. Grosso wrote:
Hi Antoine, others,
Questions about OpenType vs TrueType come up often in my work, so perhaps the list will suffer a couple of questions in that regard.
First, I see an "O" icon, not an "OT" icon in Windows' "Fonts folder" for some fonts and a "TT" icon for others. Nothing looks like "OT" to me, so are we talking about the same thing?
Hi Gary
The "O" icon simply indicates the font has been digitally signed. Though the digital signature field is defined in the OpenType specification
the presence of a digital signature in a font does not necessarily indicate that the font has any other OpenType features. Many OpenType fonts with advanced features have not been digitally signed and consequently do not display the "O" icon in Windows.
Next, if I double-click on one of the "fonts" (files), I get a window which shows a sample of the font, at the top of which is the font name, followed by either "(OpenType)" or "(TrueType)". Can I believe what that says as indicative of whether this is truly OpenType or TrueType?
OpenType is a superset of TrueType - so all Windows fonts which conform to the TrueType specification could also be called OpenType. If it says
OpenType in the sample window it doesn't mean very much.
If you want to be able to find out more useful information about Windows fonts use Microsoft's Font Properties Extension: <http://www.microsoft.com/typography/TrueTypeProperty21.mspx>
If the Font Properties Extension is installed you can then R-click on a font file in Windows Explorer and bring up a "Properties" dialog - in this dialog there is a "Features" panel which will tell you whether or not there are any OpenType GSUB and GPOS tables in the font.
Mostly how this comes up is we have customers ask if we support OpenType fonts, to which I reply with some variation of "it depends". I usually say the OpenType spec is complex, but we handle all the commonly-used fonts we know of, and follow it by saying that they can look in their Fonts folder (at the icon) to see some examples of OpenType fonts. So that is the background for my questions.
When people ask whether your application supports OpenType fonts, what I expect they mean is "Does your application make use of the GSUB And
GPOS lookups in OpenType fonts?". Supporting OT GSUB and GPOS lookups is *necessary* for proper display of Unicode data for complex scripts (Arabic, Devanagari, Bengali, Tamil, Tibetan, Khmer, Sinhala etc.)in Windows (and many Linux) applications.
If your application supports TrueType but does not support the OpenType lookups you will still see some glyphs using the OpenType font but these will probably not be the correct ones as your application won't be showing the correct contextual forms necessary for languages written in these scripts.
Large "Pan-Unicode" fonts like "Arial Unicode MS" usually do not contain
proper OpenType tables and ligatures for *all* the scripts the font covers. For example "Arial Unicode MS" and "Code 2000" contain glyphs for Tibetan script but they *do not* contain the OpenType GSUB and GPOS lookups necessary to display Tibetan correctly.
If a Windows application needs to properly display Unicode text for languages such as Hindi, Tamil, Bengali, Nepali, Sinhala, Arabic, Urdu and so on then it probably needs to support OpenType GSUB and GPOS lookups.
For Latin script, OpenType lookups are mainly used to place combining diacritics properly and for advanced typographic features such as true small saps, Swashes, automatic ligatures, old-style figures and do on.
If you have more questions about OpenType, then the OpenType mailing list <[EMAIL PROTECTED]> may be a more appropriate forum to ask those questions.
Regards
Chris
== Christopher Fynn
