Liren Large Software Subsidy 15/15.iso/s/s076/2.img/TXT/EMBEDDIN.TXT

Text File | 1992-05-01 | 7.7 KB | 157 lines

  Technical Information for ISVs Implementing TrueType Font Embedding
           under Microsoft Windows 3.1 and Windows NT

Any application written for Microsoft Windows 3.1 or Windows NT can
store, or embed, the appropriately licensed TrueType fonts used in that
application's document. The document can then be transported to another
machine to be displayed or printed. Since TrueType fonts work on any
display and print to any printer under Windows, the user can be assured
of WYSIWYG between different platforms.  Font embedding consists of
two parts: the inclusion of the fonts in the document on the current
machine and the installation of the fonts on the target machine.
Specific information on the format of the APIs can be found in the
Windows 3.1 SDK.


Embedding the fonts
===================

Applications can use the GetFontData() function to save TrueType
scalable fonts with their documents. The application reads the
entire font file using this function with the DWORD table set to
zero. The application must check the font's license bit otmfstype
bits 1 and 2 to ensure that embedding is permitted.

To determine that a font can be embedded first call the
GetOutlineTextMetrics() function and check the otmfsType field,
bits 1 and 2. The values and their assigned meanings are:

Bit #
1    2    Meaning
-----------------------
0    0    Read-write and read-only embedding permitted
0    1    Only read-only embedding permitted
1    x    Embedding is not permitted

Embedding any fonts for which embedding is not permitted (that is,
if bit 1 = 1) or not following the guidelines below may violate
the font vendor's proprietary rights and/or the end-user's licensing
agreement.

After you determine which fonts can be embedded, you can read in
the complete font using the GetFontData() function (set the dwTable
and dwOffset arguments to 0L to ensure that you read the entire
font file, starting at the beginning of the font). The font data
stream is stored with the document that uses the font; use the
format that best suits your application.  We suggest that you build
a font directory in the document, noting which fonts are bundled
(you should use at least the otmpStyleName, otmpFamilyName,
otmTextMetrics.tmWeight, otmTextMetrics.tmItalic, and otmfsType
fields that the GetOutlineTextMetrics() function returns) and which
are read-write or read-only embedded fonts.

If the read-only embedding bit is set for a font (that is, if
otmfsType&6 is TRUE), you must apply a form of simple encryption to
the font data before storing it with the document. Although you can
do so any way that you prefer, XORing the font data with a specific
byte value that you choose and use consistently suffices (this
method is also fairly fast).  Since the actual embedding is
completely under the control of the application, ISVs who are
worried about file size can choose to do compression of the
included TrueType font.

When all fonts are bundled with the document, embedding is complete.


Installation of fonts
=====================

When an application encounters a document that contains embedded
fonts, it must separate and install them for Windows to use them.
Precisely how an application does this depends on how the fonts
were bundled, but in general the steps are as follows.

1. Resolve name conflicts before installing the fonts. For example,
   using each family name, call the EnumFontFamilies() function to
   see if any style names are duplicated; the application must avoid
   duplication. If duplicate fonts are installed, Windows typically,
   though not necessarily, selects the first font installed.

   The directory containing family name, style name, weight, italic
   flag, and fsType information suffices for the pupose of checking
   for duplicates.

2. For all fonts to be installed, access the bundled font and write
   all the data to a file, decoding any fonts that are read-only
   embedded. Read-write embedded fonts should use the TTF file
   extension. Read-only embedded fonts cannot use TTF and should
   avoid FOT and FON; these fonts should have an entirely different
   file extenstion, for example, TTR.

   You need not place the font files in any specific directory. We
   suggest, however, that you place read-write embedded fonts in a
   the Windows or appliction directory and that you place read-only
   embedded fonts in a temporary file directory.

3. Use the CreateScalableFontResource function to create font resource
   files for each TrueType font unbundled. Use the extension FOT for
   read-write embedded fonts, and ensure that the first parameter is 0.
   Use a different extension for read-only embedded fonts, for example,
   FOR; the first parameter must be 1. Use the AddFontResource()
   function to install each font resource file. Place the FOT and
   FOR files in the same directory as the font itself.

Because Windows resources are normally available to all Windows
processes, all fonts that are installed with the AddFontResource()
function are typically available to all other applications that are
active at the time. To prevent a read-only embedded font from being
used in other documents, Windows suppresses the enumeration and
availability of these fonts. As noted above, this is controlled by
parameter #1 of CreateScalableFontResource(). If this parameter is
set to 0, the font is considered "normal." If it is set to 1, the
font is considered "read-only embedded" and will not be enumerated
under any circumstances. Further, the font can only be selected if
the CLIP_EMBEDDED flag is or'd into the lfClipPrecision field of the
LOGFONT. This should prevent other active applications from making
use of your application's read-only embedded fonts.

Because users can use read-write embedded fonts on an ongoing basis,
offer them the option of installing read-write embedded fonts
permanently. To install a font permanently, concatenate the family
and style names into one string, and insert this string with the FOT
file name in the WIN.INI [Fonts] section. (See the documentation on
WIN.INI for details on the format of the [Fonts] section.)

You must never install read-only embedded fonts permanently. You
must remove them from the system and from the hard disk when the
document in which they are bundled is closed.

The fonts are now ready to be used with the document in which they
were bundled. If a document contains one or more read-only embedded
fonts, however, the user must not be permitted to edit the document.
The user can only view the document on the screen or print it. Before
any editing can occur, the application must strip away and delete
the read-only embedded fonts. To delete the fonts, the application must:

   1. Call the DeleteFontResource function for each font to be deleted.
   2. Delete the font resource file for each font.
   3. Delete each TrueType font file for each font.

Documents with read-only embedded fonts are themselves read-only and
print-only. The document cannot be edited until every read-only embedded
font has been removed. This option should be provided to the user.

When the document is closed, read-write embedded fonts can be installed
on the user's machine. The user can delete the fonts through Control
Panel, however, if the above installation process was followed.

If, for some reason, you are unable to delete one or more FOR files,
don't worry; all you waste is disk space. If, however, you are unable
to delete one or more TTR files, the application should make every
effort to delete these files later (for example, when the application
itself exits, when the application starts up again, or after an
elapsed period of time).