> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf > Of Gary P. Grosso
> 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? Indeed, the icon shows "O"; I have no idea where the reference to "OT" originated. > 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? Yes, but as Antoine's message suggested, you need to understand what it does or doesn't imply. To get around terminology hurdles, I will refer to the "sfnt" file format. This is a file format for fonts that was first introduced when Apple and Microsoft developed TrueType fonts back around 1990. One of the features of the sfnt format is that it is extensible: it contains tables with various types of font-related data, and new tables can be added without affecting processes that know only about pre-existing tables. People have often used the term "TrueType" to refer to this extensible font file format, but this leads to confusion. "TrueType" fonts are fonts that use the sfnt format and that use TrueType outlines and hinting. OpenType differs from TrueType in two respects: 1) OpenType uses the extensibility of the sfnt format to define additional tables 2) OpenType allows for either TrueType outlines and hinting, or Postscript outlines and hinting Apart from the tables related to Postscript outlines, the OpenType spec defines six tables not found in the TrueType spec: one for a digital signature, and five related to advanced typographic capabilities. Strictly speaking, none of the six new tables are required by the OpenType spec. Therefore, any TrueType font could be considered an OpenType font. Of course, that's not particularly useful; generally people would like to talk about OpenType in contrast to TrueType. In terms of the icon that is displayed in the Windows font folder, it is the presence of the DSIG table that determines which fonts get the "O" icon rather than the "TT" icon. The distinction that most people are interested in, however, is whether there is support for advanced typographic capabilities. For instance, > Mostly how this comes up is we have customers ask if we support OpenType fonts... these people are probably interested in advanced typographic capabilities, not digital signatures. What they are asking, then, is whether your products support OpenType layout capabilities -- this is the advanced-typography functionality related to the other fives OpenType-specific tables. Three of these tables, in particular, are important: GSUB - glyph substitution data used to select alternate or presentation-form glyphs (e.g. ligatures, contextual forms) GPOS - glyph positioning data used to position combining marks and to kern glyphs GDEF - glyph definition data that is used to support substitution and positioning processes This is what you need to support in order to support scripts such as Arabic or Devanagari, or to support fine typography (e.g. true small caps, swashes, ligatures). Does that help? Peter Constable
