10  Enhanced Virtual Font Handling

Virtual font handling changes in the following respects:

• Nested virtual fonts are now recognized. Earlier releases would not recognize nested virtual fonts; only the first level of virtual character mapping would have an effect. This was not necessarily a limitation, since nested virtual font schemes can always be ``flattened'' into an equivalent single level, and single-level virtual fonts can be rendered much faster than nested ones. However, since certain packages (like L<sup>A</sup>T<sub>E</sub>X times) supply nested virtual fonts, and converting them to un-nested equivalents is difficult, direct support for nested virtual fonts is desirable.
• Actual font naming convention: Earlier releases used a non-standard convention that a virtual font, such as arial.vf, could map to a font of the same name (in this case, arial); it was implicit that the mapped-to font (arial) was the actual TrueType font and not a recursive reference to the virtual font arial.vf itself. This implicit convention is incompatible with support for nested virtual fonts, so the following convention now applies: A virtual font may map to a font name which includes a parenthesized suffix, and this will force the previewer to treat that mapped-to font as an actual font of the same name, less the suffix. For example, if the virtual font arial.vf contains a mapped-to font reference of the form: (MAPFONT D 0 (FONTNAME arial (Actual))(COMMENT Arial TrueType in Windows)) then the font name ``arial (Actual)'' refers to the actual font named ``arial''; the previewer will not attempt to find a nested virtual font of that name. In the old scheme no longer supported, arial.vf would have contained an apparently self-referencing mapped-to font of the form: (MAPFONT D 0 (FONTNAME arial)(COMMENT Arial TrueType in Windows))

  If you continue to use old virtual fonts with this obsolete convention, they will result in a warning message that arial.vf contains a circular self-reference; however the virtual font will still work correctly because the previewer will interrupt such circularity by converting the reference to an actual font reference.

  Recursive, self-referential virtual fonts, while not necessarily erroneous (see Knuth's example), are still not supported.

  In accord with this convention, the File Export Metrics function now names references to Windows fonts with ``(Actual)'' suffixed to the name. If you are creating virtual fonts by hand, you can use more specific suffixes as reminders of the actual font source, such as ``(ATM)'' for Adobe Type Manager. The previewer makes no use of the suffix; it is merely looking for the leading parenthesis as an actual-font indicator.

  Here is the precise rule used by the Previewer to detect names of actual fonts: If the font name referenced in a virtual font contains a left-parenthesis, the Previewer interprets the referenced font as an actual font with a name consisting of the referenced name truncated at the left-parenthesis. Thus the suffix ``(Actual)'' is not strictly required for you to indicate an actual font; any suffix with a left parenthesis will work, even a left parenthesis alone. Since TrueType and ATM font names do not use parentheses, this convention is orthogonally compatible with any system font names.

• New virtual fonts: DC fonts. A new set of virtual fonts provides access to the DC fonts using the Unicode rendering in the 32-bit previewer and the new naming convention for actual fonts. This provides correct rendering across all national versions of Windows 95 and Windows NT.
• New virtual fonts: times package. The L^AT_EX times package replaces the Computer Modern text fonts with the fonts Times (for Roman text), Helvetica (for sans serif text), and Courier (for typewriter text). These are implemented in the original package by three levels of nested virtual fonts, with the actual fonts being PostScript fonts rendered by the DVI-PostScript translator dvips. In TRUET_EX, we simply replace the lowest level of these virtual fonts with new virtual fonts resolving to the TrueType fonts Times New Roman, Arial, and Courier, with appropriate character code remapping. We assume that the multi-lingual extended character sets are available in these TrueType fonts, which is the default in Windows NT and available in Windows 95 when the Windows 95 ``multilanguage extensions'' (see the Windows 95 help for details) are installed. If the multilanguage extensions are not installed in Windows 95, or if you are running under Windows 3.1, many accented non-English characters will not render when using times. Note also that the multiple levels of virtual font nesting will noticeably slow preview rendering of documents using these fonts.
• New virtual fonts: MathTime package. The L<sup>A</sup>T<sub>E</sub>X mathtime package replaces the Computer Modern math fonts with the MathTime fonts, which are Type 1 fonts stylistically compatible with the Times text font. The MathTime fonts require Adobe Type Manager (ATM) version 3.01 running on Windows 95 (ATM is not available for Windows NT as of this writing). A set of virtual fonts for TRUET<sub>E</sub>X maps the character sets properly so that the L<sup>A</sup>T<sub>E</sub>X output will render properly with the ATM font encodings. While the virtual fonts are freely available with TRUET<sub>E</sub>X, the MathTime Type 1 font files and Adobe Type Manager are proprietary products available from other vendors.
• New encoding tables: Several new encoding tables are now included in the dialogs for the File Export Metrics function; these tables represent various Unicode encodings and the PSNFSS ``8r'' encoding.