ttochap1.htm

TrueType字库标准文档

<LI>Using <I>design coordinates</I> the client determines device-independent line breaks. Design coordinates are high-resolution and device-independent.
<LI>Using information in the JSTF table, the client justifies the lines, if the user has specified such&nbsp;alignment.
<LI>The operating system rasterizes the line of glyphs and renders the glyphs in <I>device coordinates</I> that correspond to the resolution of the output&nbsp;device.
</OL>
<P>
Throughout this process the text-processing client keeps track of the association between the character codes for the original text and the glyph indices of the final, rendered text. In addition, the client may save language and script information within the text stream to clearly associate character codes with typographical behavior.
<P>
<BR>
<B>TrueType Open fonts in Windows&nbsp;95</B><BR>
The core system fonts in the Middle East and Far East versions of Windows 95 are TrueType Open fonts. These fonts demonstrate aspects of TrueType Open's versatility.
<P>
<BR>
<I>Middle East Windows 95</I><BR>
Middle East Windows 95 uses several Arabic TrueType Open fonts: fixed regular weight, proportional regular weight, fixed bold, and proportional bold. These fonts take advantage of many glyph substitution features available in TrueType Open, namely simple substitution (one-to-one contextual), ligature substitution (many-to-one), and mark set substitutions. In Middle East Windows 95, the operating system itself handles glyph substitution, using data in the GSUB table of each&nbsp;font.
<P>
<BR>
<I>Far East Windows 95</I><BR>
Far East Windows 95 also uses several TrueType Open fonts: fixed serif, proportional serif, fixed sans serif, and proportional sans serif. The Japanese fonts take advantage of a subset of TrueType Open features, including vertical glyph substitution and baseline positioning. As with Middle East Windows 95, the operating system in Far East Windows 95 will handle glyph substitution, using data in the GSUB table in each font. However, the text-processing client will need to handle baseline positioning, using data in the BASE table in each&nbsp;font.
<P>
<BR>
<H2><A NAME="MM">How Multiple Master OpenType Fonts Use TrueType Open Tables</A></H2>

<p>Metric data for multiple master fonts is represented
by Type 2 font programs that may be interpreted at a specific instance resulting
in a metric value being pushed onto the Type 2 interpreter stack. In
instance in the design space of a multiple master font may be specified
by a User Design Vector, an array of per-axis user design coordinates.

<p>Rather than store metric font programs in TTO tables
they are stored in a new MMFX table and are referenced using new metric id
formats defined in TTO.

<p>Applications reading TTO tables will read the metric
id value and pass it through the system to the PostScript scaler which
will interpret the relevant metric charstring specified by the metric id and
return the result. (The TrueType scaler utilizes a similar mechanism when handling
control points but in that case it returns, possibly hinted, points from the
glyf table at a given point size.)

<p>Three TTO tables are extended to support new formats
that allow metric ids to be specified in place of metric values. These extensions
are as follows:

<p>The GPOS.ValueRecord is extended by the addition of four more optional fields:<BR>&nbsp;

<TABLE BGCOLOR="#F0F0F0"  WIDTH="50%" BORDER=0 CELLPADDING=3>
<THEAD>
<TR>
<TH BGCOLOR="#C0C0C0">Type</TH><TH BGCOLOR="#C0C0C0">Name</TH><TH BGCOLOR="#C0C0C0">Description</TH></TR>
</THEAD><TBODY>
<TR>
<TD>uint16</TD><TD>XIdPlacement</TD><TD NOWRAP=NOWRAP>Horizontal placement metric id</TD></TR>
<TR>
<TD>uint16</TD><TD>YIdPlacement</TD><TD NOWRAP=NOWRAP>Vertical placement metric id</TD></TR>
<TR>
<TD>uint16</TD><TD>XIdAdvance</TD><TD NOWRAP=NOWRAP>Horizontal advance metric id</TD></TR>
<TR>
<TD>uint16</TD><TD>YIdAdvance</TD><TD NOWRAP=NOWRAP>Vertical advance metric id
</TD></TR>
</TABLE>&nbsp;&nbsp;<P>

<p>The GPOS.ValueFormat bit enumeration is extended
by the addition of four more bits:<BR>&nbsp;

<TABLE BGCOLOR="#F0F0F0"  WIDTH="50%" BORDER=0 CELLPADDING=3>
<THEAD>
<TR>
<TH BGCOLOR="#C0C0C0">Mask</TH><TH BGCOLOR="#C0C0C0">Name</TH><TH BGCOLOR="#C0C0C0">Description</TH></TR>
<TBODY>
<TR>
<TD>0x0100</TD><TD>XIdPlacement</TD><TD NOWRAP=NOWRAP>Includes horizontal placement id</TD></TR>
<TR>
<TD>0x0200</TD><TD>YIdPlacement</TD><TD NOWRAP=NOWRAP>Includes vertical placement id</TD></TR>
<TR>
<TD>0x0400</TD><TD>XIdAdvance</TD><TD NOWRAP=NOWRAP>Includes horizontal advance id</TD></TR>
<TR>
<TD>0x0800</TD><TD>YIdAdvance</TD><TD NOWRAP=NOWRAP>Includes vertical advance id</TD></TR>
<TR>
<TD>0xF000</TD><TD>Reserved</TD><TD NOWRAP=NOWRAP>For future use</TD></TR>
</TABLE>&nbsp;&nbsp;<P>

The GPOS.AnchorRecord is extended by the addition
of a new format:<BR>&nbsp;

<TABLE BGCOLOR="#F0F0F0"  WIDTH="50%" BORDER=0 CELLPADDING=3>
<THEAD>
<TR>
<TH BGCOLOR="#C0C0C0">Type</TH><TH BGCOLOR="#C0C0C0">Name</TH><TH BGCOLOR="#C0C0C0">Description</TH></TR>
</THEAD><TBODY>
<TR>
<TD>uint16</TD><TD>AnchorFormat</TD><TD NOWRAP=NOWRAP>Format identifier--format=4</TD></TR>
<TR>
<TD>uint16</TD><TD>XIdAnchor</TD><TD NOWRAP=NOWRAP>Horizontal metric id</TD></TR>
<TR>
<TD>uint16</TD><TD>YIdAnchor</TD><TD NOWRAP=NOWRAP>Vertical metric id</TD></TR>
</TABLE>&nbsp;&nbsp;<P>

The BASE.BaseCoord is extended by the addition of
a new format:<BR>&nbsp;

<TABLE BGCOLOR="#F0F0F0"  WIDTH="50%" BORDER=0 CELLPADDING=3>
<THEAD>
<TR>
<TH BGCOLOR="#C0C0C0">Type</TH><TH BGCOLOR="#C0C0C0">Name</TH><TH BGCOLOR="#C0C0C0">Description</TH></TR>
</THEAD><TBODY>
<TR>
<TD>uint16</TD><TD>BaseCoordFormat</TD><TD NOWRAP=NOWRAP>Format identifier--format=4</TD></TR>
<TR>
<TD>uint16</TD><TD>IdBaseCoord</TD><TD NOWRAP=NOWRAP>Metric id</TD></TR></TABLE>&nbsp;&nbsp;<P>

The GDEF.CaretValue is extended by the addition of
a new format:<BR>&nbsp;

<TABLE BGCOLOR="#F0F0F0"  WIDTH="50%" BORDER=0 CELLPADDING=3>
<THEAD>
<TR>
<TH BGCOLOR="#C0C0C0">Type</TH><TH BGCOLOR="#C0C0C0">Name</TH><TH BGCOLOR="#C0C0C0">Description
<TBODY></TD></TR>
<TR>
<TD>uint16</TD><TD>CaretValueFormat</TD><TD NOWRAP=NOWRAP>Format identifier--format=4</TD></TR>
<TR>
<TD>uint16</TD><TD>IdCaretValue</TD><TD NOWRAP=NOWRAP>Metric id</TD></TR>
</TABLE>

&nbsp;<br>&nbsp;<br>
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Microsoft Typography Web Site <A HREF="/truetype/otspec/CPYRIGHT.htm">&copy; 1996 Microsoft Corporation</A>
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Last updated 05 September 1996
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