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authormarha <marha@users.sourceforge.net>2011-09-12 11:27:51 +0200
committermarha <marha@users.sourceforge.net>2011-09-12 11:27:51 +0200
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@@ -1,659 +1,659 @@
-<?xml version="1.0" encoding="UTF-8" ?>
-<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
- "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" >
-<!-- lifted from troff+ms by doclifter -->
-<!-- previous version was in xorg-docs/specs/Xserver/fontlib.ms -->
-
- <article id='fontlib'>
-<!-- .ps 12 -->
-<!-- .EF 'Font Library Interface'\- % \-'July 27, 1991' -->
-<!-- .OF 'Font Library Interface'\- % \-'July 27, 1991' -->
-<!-- .EH '''' -->
-<!-- .OH '''' -->
-<!-- body begins here -->
- <articleinfo>
- <title>
- The X Font Library
- </title>
- <pubdate>July 27, 1991</pubdate>
- <authorgroup>
- <author>
- <firstname>Keith</firstname>
- <surname>Packard</surname>
- <affiliation>
- <orgname>MIT X Consortium</orgname>
- </affiliation>
- </author>
- <author>
- <firstname>David</firstname>
- <surname>Lemke</surname>
- <affiliation>
- <orgname>Network Computing Devices</orgname>
- </affiliation>
- </author>
- </authorgroup>
- <legalnotice>
- <para>
- Copyright 1993 <orgname>Network Computing Devices</orgname>
- </para>
- <para>
- Permission to use, copy, modify, distribute, and sell this
- software and its documentation for any purpose is hereby
- granted without fee, provided that the above copyright
- notice appear in all copies and that both that copyright
- notice and this permission notice appear in supporting
- documentation, and that the name of Network Computing
- Devices not be used in advertising or publicity pertaining
- to distribution of the software without specific, written
- prior permission. Network Computing Devices makes no
- representations about the suitability of this software for
- any purpose. It is provided &ldquo;as is&rdquo; without
- express or implied warranty.
- </para>
- <para>
- Copyright 1993, 1994 <orgname>X Consortium</orgname>
- </para>
- <para>
- Permission is hereby granted, free of charge, to any person
- obtaining a copy of this software and associated
- documentation files (the &ldquo;Software&rdquo;), to deal in the
- Software without restriction, including without limitation
- the rights to use, copy, modify, merge, publish, distribute,
- sublicense, and/or sell copies of the Software, and to
- permit persons to whom the Software is furnished to do so,
- subject to the following conditions:
- </para><para>
- The above copyright notice and this permission notice shall be
- included in all copies or substantial portions of the Software.
- </para><para>
- THE SOFTWARE IS PROVIDED &ldquo;AS IS&rdquo;, WITHOUT WARRANTY
- OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO
- THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
- PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE X
- CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
- OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
- SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
- </para><para>
- Except as contained in this notice, the name of the X
- Consortium shall not be used in advertising or otherwise to
- promote the sale, use or other dealings in this Software
- without prior written authorization from the X Consortium.
- </para>
- </legalnotice>
- </articleinfo>
-
- <warning>
- <para>
- This document has not been updated since X11R6, and is likely
- to be somewhat out of date for the current libXfont.
- </para>
- </warning>
-
- <para>
- This document describes the data structures and interfaces for
- using the X Font library. It is intended as a reference for
- programmers building X and Font servers. You may want to refer
- to the following documents:
- </para>
-
- <itemizedlist>
- <listitem>
- <para>
- <citetitle pubwork="article">Definition of the Porting Layer for
- the X v11 Sample Server</citetitle> for a discussion on how this
- library interacts with the X server
- </para>
- </listitem>
- <listitem>
- <para>
- <citetitle pubwork="article">Font Server Implementation
- Overview</citetitle> which discusses the design of the font
- server.
- </para>
- </listitem>
- <listitem>
- <para>
- <citetitle pubwork="article">Bitmap Distribution Format</citetitle>
- which covers the contents of the bitmap font files which this
- library reads; although the library is capable of reading other
- formats as well, including non-bitmap fonts.
- </para>
- </listitem>
- <listitem>
- <para>
- <citetitle pubwork="article">The X Font Service Protocol</citetitle>
- for a description of the constraints placed on the design by
- including support for this font service mechanism.
- </para>
- </listitem>
- </itemizedlist>
-
- <para>
- This document assumes the reader is familiar with the X server design,
- the X protocol as it relates to fonts and the C programming language.
- As with most MIT produced documentation, this relies heavily on the
- source code, so have a listing handy.
- </para>
-
- <sect1 id='requirements_for_the_font_library'>
- <title>
- Requirements for the Font library
- </title>
-
- <para>
- To avoid miles of duplicate code in the X server, the font server
- and the various font manipulation tools, the font library should
- provide interfaces appropriate for all of these tasks. In
- particular, the X server and font server should be able to both
- use the library to access disk based fonts, and to communicate
- with a font server. By providing a general library, we hoped to
- avoid duplicating code between the X server and font server.
- </para>
-
- <para>
- Another requirement is that the X server (or even a font server)
- be able to continue servicing requests from other clients while
- awaiting a response from the font server on behalf of one client.
- This is the strongest requirement placed on the font library, and
- has warped the design in curious ways. Because both the X server
- and font server are single threaded, the font library must not
- suspend internally, rather it returns an indication of suspension
- to the application which continues processing other things, until
- the font data is ready, at which time it restarts the suspended
- request.
- </para>
-
- <para>
- Because the code for reading and manipulating bitmap font data is
- used by the font applications <command>mkfontdir</command> and
- <command>bdftopcf</command>, the font library includes
- bitmap-font specific interfaces which those applications use,
- instead of the more general interfaces used by the X and font
- servers, which are unaware of the source of the font data.
- These routines will be refered to as the bitmap font access
- methods.
- </para>
-
- </sect1>
-
- <sect1 id='general_font_library_interface_details'>
- <title>
- General Font Library Interface details.
- </title>
-
- <para>
- To avoid collision between the #define name space for errors, the Font
- library defines a new set of return values:
- </para>
-
- <programlisting remap='.nf'>
-#define AllocError 80
-#define StillWorking 81
-#define FontNameAlias 82
-#define BadFontName 83
-#define Suspended 84
-#define Successful 85
-#define BadFontPath 86
-#define BadCharRange 87
-#define BadFontFormat 88
-#define FPEResetFailed 89
- </programlisting> <!-- .fi -->
-
- <para>
- Whenever a routine returns <errorname>Suspended</errorname>,
- the font library will notify the caller (via the ClientSignal
- interface described below) who should then reinvoke the same routine
- again with the same arguments.
- </para>
-
- </sect1>
-
- <sect1 id='font_path_elements'>
- <title>
- Font Path Elements
- </title>
-
- <para>
- At the center of the general font access methods used by X and
- <command>xfs</command> is the Font Path Element data structure.
- Like most structures in the X server, this contains a collection
- of data and some function pointers for manipulating this data:
- </para>
-
- <programlisting remap='.nf'>
-/* External view of font paths */
-typedef struct _FontPathElement {
- int name_length;
- char *name;
- int type;
- int refcount;
- pointer private;
-} FontPathElementRec, *FontPathElementPtr;
-
-typedef struct _FPEFunctions {
- int (*name_check) ( /* name */ );
- int (*init_fpe) ( /* fpe */ );
- int (*reset_fpe) ( /* fpe */ );
- int (*free_fpe) ( /* fpe */ );
- int (*open_font) ( /* client, fpe, flags,
- name, namelen, format,
- fid, ppfont, alias */ );
- int (*close_font) ( /* pfont */ );
- int (*list_fonts) ( /* client, fpe, pattern,
- patlen, maxnames, paths */ );
- int (*start_list_fonts_with_info) (
- /* client, fpe, name, namelen,
- maxnames, data */ );
- int (*list_next_font_with_info) (
- /* client, fpe, name, namelen,
- info, num, data */ );
- int (*wakeup_fpe) ( /* fpe, mask */ );
- int (*client_died) ( /* client, fpe */ );
-} FPEFunctionsRec, FPEFunctions;
- </programlisting> <!-- .fi -->
-
- <para>
- The function pointers are split out from the data structure to
- save memory; additionally, this avoids any complications when
- initializing the data structure as there would not be any way
- to discover the appropriate function to call (a chicken and
- egg problem).
- </para>
-
- <para>
- When a font path type is initialized, it passes the function
- pointers to the server which are then stored in an
- <structname>FPEFunctionsRec</structname>. Each function is
- described below in turn.
- </para>
-
- <sect2 id='name_check'>
- <title>
- (*name_check)
- </title>
-
- <para>
- Each new font path member is passed to this function; if
- the return value is <errorname>Successful</errorname>, then
- the FPE recognises the format of the string. This does not
- guarantee that the FPE will be able to successfully use this
- member. For example, the disk-based font directory file
- <filename>fonts.dir</filename> may be corrupted, this will
- not be detected until the font path is initialized. This
- routine never returns <errorname>Suspended</errorname>.
- </para>
- </sect2>
-
- <sect2 id='init_fpe'>
- <title>
- (*init_fpe)
- </title>
-
- <para>
- Initialize a new font path element. This function prepares
- a new font path element for other requests: the disk font
- routine reads the <filename>fonts.dir</filename> and
- <filename>fonts.alias</filename> files into the internal
- format, while the font server routine connects to the
- requested font server and prepares for using it. This
- routine returns <errorname>Successful</errorname> if
- everything went OK, otherwise the return value indicates the
- source of the problem. This routine never returns
- <errorname>Suspended</errorname>.
- </para>
- </sect2>
-
- <sect2 id='reset_fpe'>
- <title>
- (*reset_fpe)
- </title>
-
- <para>
- When the X font path is reset, and some of the new members
- are also in the old font path, this function is called to
- reinitialize those FPEs. This routine returns
- <errorname>Successful</errorname> if everything went OK. It
- returns <errorname>FPEResetFailed</errorname> if (for some
- reason) the reset failed, and the caller should remove the
- old FPE and simply create a new one in its place. This is
- used by the disk-based fonts routine as resetting the
- internal directory structures would be more complicated than
- simply having destroying the old and creating a new.
- </para>
- </sect2>
-
- <sect2 id='free_fpe'>
- <title>
- (*free_fpe)
- </title>
-
- <para>
- When the server is finished with an FPE, this function is
- called to dispose of any internal state. It should return
- <errorname>Successful</errorname>, unless something terrible
- happens.
- </para>
- </sect2>
-
- <sect2 id='open_font'>
- <title>
- (*open_font)
- </title>
-
- <para>
- This routine requests that a font be opened. The <parameter
- class='function'>client</parameter> argument is used by the
- font library only in connection with suspending/restarting
- the request. The <parameter class='function'>flags</parameter>
- argument specifies some behaviour for the library and can be
- any of:
- </para>
-
- <programlisting remap='.nf'>
-/* OpenFont flags */
-#define FontLoadInfo 0x0001
-#define FontLoadProps 0x0002
-#define FontLoadMetrics 0x0004
-#define FontLoadBitmaps 0x0008
-#define FontLoadAll 0x000f
-#define FontOpenSync 0x0010
- </programlisting> <!-- .fi -->
-
- <para>
- The various fields specify which portions of the font should
- be loaded at this time. When <constant>FontOpenSync</constant>
- is specified, this routine will not return until all of the
- requested portions are loaded. Otherwise, this routine may
- return <errorname>Suspended</errorname>. When the presented
- font name is actually an alias for some other font name,
- <errorname>FontNameAlias</errorname> is returned, and the
- actual font name is stored in the location pointed to by the
- <parameter class='function'>alias</parameter> argument as a
- null-terminated string.
- </para>
- </sect2>
-
- <sect2 id='close_font'>
- <title>
- (*close_font)
- </title>
-
- <para>
- When the server is finished with a font, this routine
- disposes of any internal state and frees the font data
- structure.
- </para>
- </sect2>
-
- <sect2 id='list_fonts'>
- <title>
- (*list_fonts)
- </title>
-
- <para>
- The <parameter class='function'>paths</parameter> argument is
- a data structure which will be filled with all of the font names
- from this directory which match the specified
- <parameter class='function'>pattern</parameter>. At
- most <parameter class='function'>maxnames</parameter> will be added.
- This routine may return <errorname>Suspended</errorname>.
- </para>
- </sect2>
-
- <sect2 id='start_list_fonts_with_info'>
- <title>
- (*start_list_fonts_with_info)
- </title>
-
- <para>
- This routine sets any internal state for a verbose listing of
- all fonts matching the specified pattern. This routine may
- return <errorname>Suspended</errorname>.
- </para>
- </sect2>
-
- <sect2 id='list_next_font_with_info'>
- <title>
- (*list_next_font_with_info)
- </title>
-
- <para>
- To avoid storing huge amounts of data, the interface for
- ListFontsWithInfo allows the server to get one reply at a time
- and forward that to the client. When the font name returned
- is actually an alias for some other font,
- <errorname>FontNameAlias</errorname> will be returned. The
- actual font name is return instead, and the font alias which
- matched the pattern is returned in the location pointed to by
- data as a null-terminated string. The caller can then get the
- information by recursively listing that font name with a
- maxnames of 1. When <errorname>Successful</errorname> is
- returned, the matching font name is returned, and a
- FontInfoPtr is stored in the location pointed to by
- <parameter class='function'>data</parameter>.
- <parameter class='function'>Data</parameter> must be initialized
- with a pointer to a FontInfoRec allocated by the caller. When the
- pointer pointed to by <parameter class='function'>data</parameter>
- is not left pointing at that storage, the caller mustn't free the
- associated property data. This routine may return
- <errorname>Suspended</errorname>.
- </para>
- </sect2>
-
- <sect2 id='wakeup_fpe'>
- <title>
- (*wakeup_fpe)
- </title>
-
- <para>
- Whenever an FPE function has returned
- <errorname>Suspended</errorname>, this routine is called
- whenever the application wakes up from waiting for input
- (from <citerefentry><refentrytitle>select</refentrytitle>
- <manvolnum>2</manvolnum></citerefentry>). This
- <parameter class='function'>mask</parameter> argument should be
- the value returned from <function>select(2)</function>.
- </para>
- </sect2>
-
- <sect2 id='client_died'>
- <title>
- (*client_died)
- </title>
-
- <para>
- When an FPE function has returned <errorname>Suspended</errorname>
- and the associated client is being destroyed, this function
- allows the font library to dispose of any state associated
- with that client.
- </para>
- </sect2>
- </sect1>
-
- <sect1 id='fonts'>
- <title>
- Fonts
- </title>
-
- <para>
- The data structure which actually contains the font information has
- changed significantly since previous releases; it now attempts to
- hide the actual storage format for the data from the application,
- providing accessor functions to get at the data. This allows a
- range of internal details for different font sources. The structure
- is split into two pieces, so that ListFontsWithInfo can share
- information from the font when it has been loaded. The
- <structname>FontInfo</structname> structure, then, contains only
- information germane to LFWI.
- </para>
-
- <programlisting remap='.nf'>
-typedef struct _FontInfo {
- unsigned short firstCol; /* range of glyphs for this font */
- unsigned short lastCol;
- unsigned short firstRow;
- unsigned short lastRow;
- unsigned short defaultCh; /* default character index */
- unsigned int noOverlap:1; /* no combination of glyphs overlap */
- unsigned int terminalFont:1; /* Character cell font */
- unsigned int constantMetrics:1; /* all metrics are the same */
- unsigned int constantWidth:1; /* all character widths are the same*/
- unsigned int inkInside:1; /* all ink inside character cell */
- unsigned int inkMetrics:1; /* font has ink metrics */
- unsigned int allExist:1; /* no missing chars in range */
- unsigned int drawDirection:2; /* left-to-right/right-to-left*/
- unsigned int cachable:1; /* font needn't be opened each time*/
- unsigned int anamorphic:1; /* font is strangely scaled */
- short maxOverlap; /* maximum overlap amount */
- short pad; /* unused */
- xCharInfo maxbounds; /* glyph metrics maximums */
- xCharInfo minbounds; /* glyph metrics minimums */
- xCharInfo ink_maxbounds; /* ink metrics maximums */
- xCharInfo ink_minbounds; /* ink metrics minimums */
- short fontAscent; /* font ascent amount */
- short fontDescent; /* font descent amount */
- int nprops; /* number of font properties */
- FontPropPtr props; /* font properties */
- char *isStringProp; /* boolean array */
-} FontInfoRec, *FontInfoPtr;
- </programlisting> <!-- .fi -->
-
- <para>
- The font structure, then, contains a font info record, the format of
- the bits in each bitmap and the functions which access the font
- records (which are stored in an opaque format hung off of
- <structfield>fontPrivate</structfield>).
- </para>
-
- <programlisting remap='.nf'>
-typedef struct _Font {
- int refcnt;
- FontInfoRec info;
- char bit; /* bit order: LSBFirst/MSBFirst */
- char byte; /* byte order: LSBFirst/MSBFirst */
- char glyph; /* glyph pad: 1, 2, 4 or 8 */
- char scan; /* glyph scan unit: 1, 2 or 4 */
- fsBitmapFormat format; /* FS-style format (packed) */
- int (*get_glyphs) ( /* font, count, chars, encoding, count, glyphs */ );
- int (*get_metrics) ( /* font, count, chars, encoding, count, glyphs */ );
- int (*get_bitmaps) ( /* client, font, flags, format,
- flags, nranges, ranges, data_sizep,
- num_glyphsp, offsetsp, glyph_datap,
- free_datap */ );
- int (*get_extents) ( /* client, font, flags, nranges,
- ranges, nextentsp, extentsp */);
- void (*unload_font) ( /* font */ );
- FontPathElementPtr fpe; /* FPE associated with this font */
- pointer svrPrivate; /* X/FS private data */
- pointer fontPrivate; /* private to font */
- pointer fpePrivate; /* private to FPE */
- int maxPrivate; /* devPrivates (see below) */
- pointer *devPrivates; /* ... */
-} FontRec, *FontPtr;
- </programlisting> <!-- .fi -->
-
- <para>
- Yes, there are several different private pointers in the
- <structfield>Font</structfield> structure; they were added
- haphazardly until the devPrivate pointers were added. Future
- releases may remove some (or all) of the specific pointers,
- leaving only the <structfield>devPrivates</structfield>mechanism.
- </para>
-
- <para>
- There are two similar interfaces implemented -
- <structfield>get_glyphs</structfield>/<structfield>get_metrics</structfield>
- and
- <structfield>get_bitmaps</structfield>/<structfield>get_extents</structfield>.
- Too little time caused the font-server specific interfaces to
- be placed in the font library (and portions duplicated in each
- renderer) instead of having them integrated into the font server
- itself. This may change. The X server uses only
- <structfield>get_glyphs</structfield>/<structfield>get_metrics</structfield>,
- and those will not change dramatically. Each of the routines
- is described below.
- </para>
-
- <sect2 id='get_glyphs'>
- <title>
- (*get_glyphs)
- </title>
-
- <para>
- This routine returns <structname>CharInfoPtrs</structname>
- for each of the requested characters in the font. If the
- character does not exist in the font, the default character
- will be returned, unless no default character exists in
- which case that character is skipped. Thus, the number of
- glyphs returned will not always be the same as the number of
- characters passed in.
- </para>
- </sect2>
-
- <sect2 id='get_metrics'>
- <title>
- (*get_metrics)
- </title>
-
- <para>
- This is similar to <structfield>(*get_glyphs)</structfield>
- except that pointers to <structname>xCharInfo</structname>
- structures are returned, and, if the font has ink metrics,
- those are returned instead of the bitmap metrics.
- </para>
- </sect2>
-
- <sect2 id='getbitmaps'>
- <title>
- (*get_bitmaps)
- </title>
-
- <para>
- This packs the glyph image data in the requested
- <parameter class='function'>format</parameter> and returns it. The
- <parameter class='function'>ranges</parameter>/<parameter class='function'>nranges</parameter>
- argument specify the set of glyphs from the font to pack together.
- </para>
- </sect2>
-
- <sect2 id='get_extents'>
- <title>
- (*get_extents)
- </title>
-
- <para>
- This returns the metrics for the specified font from the
- specified <parameter class='function'>ranges</parameter>.
- </para>
-
- </sect2>
-
- <sect2 id='unload_font'>
- <title>
- (*unload_font)
- </title>
-
- <para>
- This is called from the FPE routine
- <function>(*close_font)</function>, and so should not ever be
- called from the application.
- </para>
- </sect2>
-
- <sect2 id='maxprivate'>
- <title>
- maxPrivate
- </title>
-
- <para>
- When initializing a new font structure,
- <structfield>maxPrivate</structfield> should be set to -1 so
- that the <function>FontSetPrivate()</function> macro works
- properly with an index of 0. Initializing
- <structfield>maxPrivate</structfield> to 0 can cause
- problems if the server tries to set something at index 0.
- </para>
- </sect2>
- </sect1>
- </article>
+<?xml version="1.0" encoding="UTF-8" ?>
+<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+ "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" >
+<!-- lifted from troff+ms by doclifter -->
+<!-- previous version was in xorg-docs/specs/Xserver/fontlib.ms -->
+
+ <article id='fontlib'>
+<!-- .ps 12 -->
+<!-- .EF 'Font Library Interface'\- % \-'July 27, 1991' -->
+<!-- .OF 'Font Library Interface'\- % \-'July 27, 1991' -->
+<!-- .EH '''' -->
+<!-- .OH '''' -->
+<!-- body begins here -->
+ <articleinfo>
+ <title>
+ The X Font Library
+ </title>
+ <pubdate>July 27, 1991</pubdate>
+ <authorgroup>
+ <author>
+ <firstname>Keith</firstname>
+ <surname>Packard</surname>
+ <affiliation>
+ <orgname>MIT X Consortium</orgname>
+ </affiliation>
+ </author>
+ <author>
+ <firstname>David</firstname>
+ <surname>Lemke</surname>
+ <affiliation>
+ <orgname>Network Computing Devices</orgname>
+ </affiliation>
+ </author>
+ </authorgroup>
+ <legalnotice>
+ <para>
+ Copyright 1993 <orgname>Network Computing Devices</orgname>
+ </para>
+ <para>
+ Permission to use, copy, modify, distribute, and sell this
+ software and its documentation for any purpose is hereby
+ granted without fee, provided that the above copyright
+ notice appear in all copies and that both that copyright
+ notice and this permission notice appear in supporting
+ documentation, and that the name of Network Computing
+ Devices not be used in advertising or publicity pertaining
+ to distribution of the software without specific, written
+ prior permission. Network Computing Devices makes no
+ representations about the suitability of this software for
+ any purpose. It is provided &ldquo;as is&rdquo; without
+ express or implied warranty.
+ </para>
+ <para>
+ Copyright 1993, 1994 <orgname>X Consortium</orgname>
+ </para>
+ <para>
+ Permission is hereby granted, free of charge, to any person
+ obtaining a copy of this software and associated
+ documentation files (the &ldquo;Software&rdquo;), to deal in the
+ Software without restriction, including without limitation
+ the rights to use, copy, modify, merge, publish, distribute,
+ sublicense, and/or sell copies of the Software, and to
+ permit persons to whom the Software is furnished to do so,
+ subject to the following conditions:
+ </para><para>
+ The above copyright notice and this permission notice shall be
+ included in all copies or substantial portions of the Software.
+ </para><para>
+ THE SOFTWARE IS PROVIDED &ldquo;AS IS&rdquo;, WITHOUT WARRANTY
+ OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO
+ THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+ PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE X
+ CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+ OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ </para><para>
+ Except as contained in this notice, the name of the X
+ Consortium shall not be used in advertising or otherwise to
+ promote the sale, use or other dealings in this Software
+ without prior written authorization from the X Consortium.
+ </para>
+ </legalnotice>
+ </articleinfo>
+
+ <warning>
+ <para>
+ This document has not been updated since X11R6, and is likely
+ to be somewhat out of date for the current libXfont.
+ </para>
+ </warning>
+
+ <para>
+ This document describes the data structures and interfaces for
+ using the X Font library. It is intended as a reference for
+ programmers building X and Font servers. You may want to refer
+ to the following documents:
+ </para>
+
+ <itemizedlist>
+ <listitem>
+ <para>
+ <citetitle pubwork="article">Definition of the Porting Layer for
+ the X v11 Sample Server</citetitle> for a discussion on how this
+ library interacts with the X server
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <citetitle pubwork="article">Font Server Implementation
+ Overview</citetitle> which discusses the design of the font
+ server.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <citetitle pubwork="article">Bitmap Distribution Format</citetitle>
+ which covers the contents of the bitmap font files which this
+ library reads; although the library is capable of reading other
+ formats as well, including non-bitmap fonts.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <citetitle pubwork="article">The X Font Service Protocol</citetitle>
+ for a description of the constraints placed on the design by
+ including support for this font service mechanism.
+ </para>
+ </listitem>
+ </itemizedlist>
+
+ <para>
+ This document assumes the reader is familiar with the X server design,
+ the X protocol as it relates to fonts and the C programming language.
+ As with most MIT produced documentation, this relies heavily on the
+ source code, so have a listing handy.
+ </para>
+
+ <sect1 id='requirements_for_the_font_library'>
+ <title>
+ Requirements for the Font library
+ </title>
+
+ <para>
+ To avoid miles of duplicate code in the X server, the font server
+ and the various font manipulation tools, the font library should
+ provide interfaces appropriate for all of these tasks. In
+ particular, the X server and font server should be able to both
+ use the library to access disk based fonts, and to communicate
+ with a font server. By providing a general library, we hoped to
+ avoid duplicating code between the X server and font server.
+ </para>
+
+ <para>
+ Another requirement is that the X server (or even a font server)
+ be able to continue servicing requests from other clients while
+ awaiting a response from the font server on behalf of one client.
+ This is the strongest requirement placed on the font library, and
+ has warped the design in curious ways. Because both the X server
+ and font server are single threaded, the font library must not
+ suspend internally, rather it returns an indication of suspension
+ to the application which continues processing other things, until
+ the font data is ready, at which time it restarts the suspended
+ request.
+ </para>
+
+ <para>
+ Because the code for reading and manipulating bitmap font data is
+ used by the font applications <command>mkfontdir</command> and
+ <command>bdftopcf</command>, the font library includes
+ bitmap-font specific interfaces which those applications use,
+ instead of the more general interfaces used by the X and font
+ servers, which are unaware of the source of the font data.
+ These routines will be refered to as the bitmap font access
+ methods.
+ </para>
+
+ </sect1>
+
+ <sect1 id='general_font_library_interface_details'>
+ <title>
+ General Font Library Interface details.
+ </title>
+
+ <para>
+ To avoid collision between the #define name space for errors, the Font
+ library defines a new set of return values:
+ </para>
+
+ <programlisting remap='.nf'>
+#define AllocError 80
+#define StillWorking 81
+#define FontNameAlias 82
+#define BadFontName 83
+#define Suspended 84
+#define Successful 85
+#define BadFontPath 86
+#define BadCharRange 87
+#define BadFontFormat 88
+#define FPEResetFailed 89
+ </programlisting> <!-- .fi -->
+
+ <para>
+ Whenever a routine returns <errorname>Suspended</errorname>,
+ the font library will notify the caller (via the ClientSignal
+ interface described below) who should then reinvoke the same routine
+ again with the same arguments.
+ </para>
+
+ </sect1>
+
+ <sect1 id='font_path_elements'>
+ <title>
+ Font Path Elements
+ </title>
+
+ <para>
+ At the center of the general font access methods used by X and
+ <command>xfs</command> is the Font Path Element data structure.
+ Like most structures in the X server, this contains a collection
+ of data and some function pointers for manipulating this data:
+ </para>
+
+ <programlisting remap='.nf'>
+/* External view of font paths */
+typedef struct _FontPathElement {
+ int name_length;
+ char *name;
+ int type;
+ int refcount;
+ pointer private;
+} FontPathElementRec, *FontPathElementPtr;
+
+typedef struct _FPEFunctions {
+ int (*name_check) ( /* name */ );
+ int (*init_fpe) ( /* fpe */ );
+ int (*reset_fpe) ( /* fpe */ );
+ int (*free_fpe) ( /* fpe */ );
+ int (*open_font) ( /* client, fpe, flags,
+ name, namelen, format,
+ fid, ppfont, alias */ );
+ int (*close_font) ( /* pfont */ );
+ int (*list_fonts) ( /* client, fpe, pattern,
+ patlen, maxnames, paths */ );
+ int (*start_list_fonts_with_info) (
+ /* client, fpe, name, namelen,
+ maxnames, data */ );
+ int (*list_next_font_with_info) (
+ /* client, fpe, name, namelen,
+ info, num, data */ );
+ int (*wakeup_fpe) ( /* fpe, mask */ );
+ int (*client_died) ( /* client, fpe */ );
+} FPEFunctionsRec, FPEFunctions;
+ </programlisting> <!-- .fi -->
+
+ <para>
+ The function pointers are split out from the data structure to
+ save memory; additionally, this avoids any complications when
+ initializing the data structure as there would not be any way
+ to discover the appropriate function to call (a chicken and
+ egg problem).
+ </para>
+
+ <para>
+ When a font path type is initialized, it passes the function
+ pointers to the server which are then stored in an
+ <structname>FPEFunctionsRec</structname>. Each function is
+ described below in turn.
+ </para>
+
+ <sect2 id='name_check'>
+ <title>
+ (*name_check)
+ </title>
+
+ <para>
+ Each new font path member is passed to this function; if
+ the return value is <errorname>Successful</errorname>, then
+ the FPE recognises the format of the string. This does not
+ guarantee that the FPE will be able to successfully use this
+ member. For example, the disk-based font directory file
+ <filename>fonts.dir</filename> may be corrupted, this will
+ not be detected until the font path is initialized. This
+ routine never returns <errorname>Suspended</errorname>.
+ </para>
+ </sect2>
+
+ <sect2 id='init_fpe'>
+ <title>
+ (*init_fpe)
+ </title>
+
+ <para>
+ Initialize a new font path element. This function prepares
+ a new font path element for other requests: the disk font
+ routine reads the <filename>fonts.dir</filename> and
+ <filename>fonts.alias</filename> files into the internal
+ format, while the font server routine connects to the
+ requested font server and prepares for using it. This
+ routine returns <errorname>Successful</errorname> if
+ everything went OK, otherwise the return value indicates the
+ source of the problem. This routine never returns
+ <errorname>Suspended</errorname>.
+ </para>
+ </sect2>
+
+ <sect2 id='reset_fpe'>
+ <title>
+ (*reset_fpe)
+ </title>
+
+ <para>
+ When the X font path is reset, and some of the new members
+ are also in the old font path, this function is called to
+ reinitialize those FPEs. This routine returns
+ <errorname>Successful</errorname> if everything went OK. It
+ returns <errorname>FPEResetFailed</errorname> if (for some
+ reason) the reset failed, and the caller should remove the
+ old FPE and simply create a new one in its place. This is
+ used by the disk-based fonts routine as resetting the
+ internal directory structures would be more complicated than
+ simply having destroying the old and creating a new.
+ </para>
+ </sect2>
+
+ <sect2 id='free_fpe'>
+ <title>
+ (*free_fpe)
+ </title>
+
+ <para>
+ When the server is finished with an FPE, this function is
+ called to dispose of any internal state. It should return
+ <errorname>Successful</errorname>, unless something terrible
+ happens.
+ </para>
+ </sect2>
+
+ <sect2 id='open_font'>
+ <title>
+ (*open_font)
+ </title>
+
+ <para>
+ This routine requests that a font be opened. The <parameter
+ class='function'>client</parameter> argument is used by the
+ font library only in connection with suspending/restarting
+ the request. The <parameter class='function'>flags</parameter>
+ argument specifies some behaviour for the library and can be
+ any of:
+ </para>
+
+ <programlisting remap='.nf'>
+/* OpenFont flags */
+#define FontLoadInfo 0x0001
+#define FontLoadProps 0x0002
+#define FontLoadMetrics 0x0004
+#define FontLoadBitmaps 0x0008
+#define FontLoadAll 0x000f
+#define FontOpenSync 0x0010
+ </programlisting> <!-- .fi -->
+
+ <para>
+ The various fields specify which portions of the font should
+ be loaded at this time. When <constant>FontOpenSync</constant>
+ is specified, this routine will not return until all of the
+ requested portions are loaded. Otherwise, this routine may
+ return <errorname>Suspended</errorname>. When the presented
+ font name is actually an alias for some other font name,
+ <errorname>FontNameAlias</errorname> is returned, and the
+ actual font name is stored in the location pointed to by the
+ <parameter class='function'>alias</parameter> argument as a
+ null-terminated string.
+ </para>
+ </sect2>
+
+ <sect2 id='close_font'>
+ <title>
+ (*close_font)
+ </title>
+
+ <para>
+ When the server is finished with a font, this routine
+ disposes of any internal state and frees the font data
+ structure.
+ </para>
+ </sect2>
+
+ <sect2 id='list_fonts'>
+ <title>
+ (*list_fonts)
+ </title>
+
+ <para>
+ The <parameter class='function'>paths</parameter> argument is
+ a data structure which will be filled with all of the font names
+ from this directory which match the specified
+ <parameter class='function'>pattern</parameter>. At
+ most <parameter class='function'>maxnames</parameter> will be added.
+ This routine may return <errorname>Suspended</errorname>.
+ </para>
+ </sect2>
+
+ <sect2 id='start_list_fonts_with_info'>
+ <title>
+ (*start_list_fonts_with_info)
+ </title>
+
+ <para>
+ This routine sets any internal state for a verbose listing of
+ all fonts matching the specified pattern. This routine may
+ return <errorname>Suspended</errorname>.
+ </para>
+ </sect2>
+
+ <sect2 id='list_next_font_with_info'>
+ <title>
+ (*list_next_font_with_info)
+ </title>
+
+ <para>
+ To avoid storing huge amounts of data, the interface for
+ ListFontsWithInfo allows the server to get one reply at a time
+ and forward that to the client. When the font name returned
+ is actually an alias for some other font,
+ <errorname>FontNameAlias</errorname> will be returned. The
+ actual font name is return instead, and the font alias which
+ matched the pattern is returned in the location pointed to by
+ data as a null-terminated string. The caller can then get the
+ information by recursively listing that font name with a
+ maxnames of 1. When <errorname>Successful</errorname> is
+ returned, the matching font name is returned, and a
+ FontInfoPtr is stored in the location pointed to by
+ <parameter class='function'>data</parameter>.
+ <parameter class='function'>Data</parameter> must be initialized
+ with a pointer to a FontInfoRec allocated by the caller. When the
+ pointer pointed to by <parameter class='function'>data</parameter>
+ is not left pointing at that storage, the caller mustn't free the
+ associated property data. This routine may return
+ <errorname>Suspended</errorname>.
+ </para>
+ </sect2>
+
+ <sect2 id='wakeup_fpe'>
+ <title>
+ (*wakeup_fpe)
+ </title>
+
+ <para>
+ Whenever an FPE function has returned
+ <errorname>Suspended</errorname>, this routine is called
+ whenever the application wakes up from waiting for input
+ (from <citerefentry><refentrytitle>select</refentrytitle>
+ <manvolnum>2</manvolnum></citerefentry>). This
+ <parameter class='function'>mask</parameter> argument should be
+ the value returned from <function>select(2)</function>.
+ </para>
+ </sect2>
+
+ <sect2 id='client_died'>
+ <title>
+ (*client_died)
+ </title>
+
+ <para>
+ When an FPE function has returned <errorname>Suspended</errorname>
+ and the associated client is being destroyed, this function
+ allows the font library to dispose of any state associated
+ with that client.
+ </para>
+ </sect2>
+ </sect1>
+
+ <sect1 id='fonts'>
+ <title>
+ Fonts
+ </title>
+
+ <para>
+ The data structure which actually contains the font information has
+ changed significantly since previous releases; it now attempts to
+ hide the actual storage format for the data from the application,
+ providing accessor functions to get at the data. This allows a
+ range of internal details for different font sources. The structure
+ is split into two pieces, so that ListFontsWithInfo can share
+ information from the font when it has been loaded. The
+ <structname>FontInfo</structname> structure, then, contains only
+ information germane to LFWI.
+ </para>
+
+ <programlisting remap='.nf'>
+typedef struct _FontInfo {
+ unsigned short firstCol; /* range of glyphs for this font */
+ unsigned short lastCol;
+ unsigned short firstRow;
+ unsigned short lastRow;
+ unsigned short defaultCh; /* default character index */
+ unsigned int noOverlap:1; /* no combination of glyphs overlap */
+ unsigned int terminalFont:1; /* Character cell font */
+ unsigned int constantMetrics:1; /* all metrics are the same */
+ unsigned int constantWidth:1; /* all character widths are the same*/
+ unsigned int inkInside:1; /* all ink inside character cell */
+ unsigned int inkMetrics:1; /* font has ink metrics */
+ unsigned int allExist:1; /* no missing chars in range */
+ unsigned int drawDirection:2; /* left-to-right/right-to-left*/
+ unsigned int cachable:1; /* font needn't be opened each time*/
+ unsigned int anamorphic:1; /* font is strangely scaled */
+ short maxOverlap; /* maximum overlap amount */
+ short pad; /* unused */
+ xCharInfo maxbounds; /* glyph metrics maximums */
+ xCharInfo minbounds; /* glyph metrics minimums */
+ xCharInfo ink_maxbounds; /* ink metrics maximums */
+ xCharInfo ink_minbounds; /* ink metrics minimums */
+ short fontAscent; /* font ascent amount */
+ short fontDescent; /* font descent amount */
+ int nprops; /* number of font properties */
+ FontPropPtr props; /* font properties */
+ char *isStringProp; /* boolean array */
+} FontInfoRec, *FontInfoPtr;
+ </programlisting> <!-- .fi -->
+
+ <para>
+ The font structure, then, contains a font info record, the format of
+ the bits in each bitmap and the functions which access the font
+ records (which are stored in an opaque format hung off of
+ <structfield>fontPrivate</structfield>).
+ </para>
+
+ <programlisting remap='.nf'>
+typedef struct _Font {
+ int refcnt;
+ FontInfoRec info;
+ char bit; /* bit order: LSBFirst/MSBFirst */
+ char byte; /* byte order: LSBFirst/MSBFirst */
+ char glyph; /* glyph pad: 1, 2, 4 or 8 */
+ char scan; /* glyph scan unit: 1, 2 or 4 */
+ fsBitmapFormat format; /* FS-style format (packed) */
+ int (*get_glyphs) ( /* font, count, chars, encoding, count, glyphs */ );
+ int (*get_metrics) ( /* font, count, chars, encoding, count, glyphs */ );
+ int (*get_bitmaps) ( /* client, font, flags, format,
+ flags, nranges, ranges, data_sizep,
+ num_glyphsp, offsetsp, glyph_datap,
+ free_datap */ );
+ int (*get_extents) ( /* client, font, flags, nranges,
+ ranges, nextentsp, extentsp */);
+ void (*unload_font) ( /* font */ );
+ FontPathElementPtr fpe; /* FPE associated with this font */
+ pointer svrPrivate; /* X/FS private data */
+ pointer fontPrivate; /* private to font */
+ pointer fpePrivate; /* private to FPE */
+ int maxPrivate; /* devPrivates (see below) */
+ pointer *devPrivates; /* ... */
+} FontRec, *FontPtr;
+ </programlisting> <!-- .fi -->
+
+ <para>
+ Yes, there are several different private pointers in the
+ <structfield>Font</structfield> structure; they were added
+ haphazardly until the devPrivate pointers were added. Future
+ releases may remove some (or all) of the specific pointers,
+ leaving only the <structfield>devPrivates</structfield>mechanism.
+ </para>
+
+ <para>
+ There are two similar interfaces implemented -
+ <structfield>get_glyphs</structfield>/<structfield>get_metrics</structfield>
+ and
+ <structfield>get_bitmaps</structfield>/<structfield>get_extents</structfield>.
+ Too little time caused the font-server specific interfaces to
+ be placed in the font library (and portions duplicated in each
+ renderer) instead of having them integrated into the font server
+ itself. This may change. The X server uses only
+ <structfield>get_glyphs</structfield>/<structfield>get_metrics</structfield>,
+ and those will not change dramatically. Each of the routines
+ is described below.
+ </para>
+
+ <sect2 id='get_glyphs'>
+ <title>
+ (*get_glyphs)
+ </title>
+
+ <para>
+ This routine returns <structname>CharInfoPtrs</structname>
+ for each of the requested characters in the font. If the
+ character does not exist in the font, the default character
+ will be returned, unless no default character exists in
+ which case that character is skipped. Thus, the number of
+ glyphs returned will not always be the same as the number of
+ characters passed in.
+ </para>
+ </sect2>
+
+ <sect2 id='get_metrics'>
+ <title>
+ (*get_metrics)
+ </title>
+
+ <para>
+ This is similar to <structfield>(*get_glyphs)</structfield>
+ except that pointers to <structname>xCharInfo</structname>
+ structures are returned, and, if the font has ink metrics,
+ those are returned instead of the bitmap metrics.
+ </para>
+ </sect2>
+
+ <sect2 id='getbitmaps'>
+ <title>
+ (*get_bitmaps)
+ </title>
+
+ <para>
+ This packs the glyph image data in the requested
+ <parameter class='function'>format</parameter> and returns it. The
+ <parameter class='function'>ranges</parameter>/<parameter class='function'>nranges</parameter>
+ argument specify the set of glyphs from the font to pack together.
+ </para>
+ </sect2>
+
+ <sect2 id='get_extents'>
+ <title>
+ (*get_extents)
+ </title>
+
+ <para>
+ This returns the metrics for the specified font from the
+ specified <parameter class='function'>ranges</parameter>.
+ </para>
+
+ </sect2>
+
+ <sect2 id='unload_font'>
+ <title>
+ (*unload_font)
+ </title>
+
+ <para>
+ This is called from the FPE routine
+ <function>(*close_font)</function>, and so should not ever be
+ called from the application.
+ </para>
+ </sect2>
+
+ <sect2 id='maxprivate'>
+ <title>
+ maxPrivate
+ </title>
+
+ <para>
+ When initializing a new font structure,
+ <structfield>maxPrivate</structfield> should be set to -1 so
+ that the <function>FontSetPrivate()</function> macro works
+ properly with an index of 0. Initializing
+ <structfield>maxPrivate</structfield> to 0 can cause
+ problems if the server tries to set something at index 0.
+ </para>
+ </sect2>
+ </sect1>
+ </article>