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update to xfs 1.1.0.
2009-10-10 04:12:48 -06:00
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<!-- lifted from troff+ms by doclifter -->
<!-- previous version was in xorg-docs/specs/xfs/design.ms -->
<!-- encoding notes:
- for lack of a better match, the systemitem tag is used for
protocol request names
-->
<article id='designms'>
<articleinfo>
<title>Font server implementation overview</title>
<author>
<firstname>Dave</firstname>
<surname>Lemke</surname>
<affiliation>
<orgname>Network Computing Devices, Inc.</orgname>
</affiliation>
</author>
<copyright>
<year>1991</year>
<holder>Network Computing Devices, Inc.</holder>
</copyright>
</articleinfo>
<sect1 id='introduction'>
<title>Introduction</title>
<para>The font server uses the same client/server model as X.
The basic structure is that of the X Consortium X11R5 X server,
and those who know that code should find the
<firstterm remap='I'>os</firstterm> and
<firstterm remap='I'>difs</firstterm> (device independent font
server) layers familiar.</para>
<literallayout class='monospaced'>
&boxdr;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxdl;
&boxdr;&boxh;&boxh;&boxh;&boxh;&boxh;&boxvl; difs &boxvr;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxdl;
&boxv; &boxur;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxul; &boxv;
&boxv; &boxv;
&boxdr;&boxh;&boxhu;&boxh;&boxh;&boxdl; &boxdr;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxhu;&boxh;&boxh;&boxh;&boxdl;
&boxv; os &boxv; &boxv; renderers &boxv;
&boxur;&boxh;&boxh;&boxh;&boxh;&boxul; &boxur;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxh;&boxul;
</literallayout>
<sect2 id='definitions'>
<title>Definitions</title>
<glosslist>
<glossentry>
<glossterm>
<firstterm>Renderer</firstterm>
<indexterm><primary>renderer</primary></indexterm>
</glossterm>
<glossdef><para>Code that knows how to take font data in
its raw format and convert it to the font server's
format.</para></glossdef>
</glossentry>
<glossentry>
<glossterm>
<firstterm>Font Path Element (<acronym>FPE</acronym>)</firstterm>
<indexterm><primary>Font Path Element</primary></indexterm>
<indexterm><primary><acronym>FPE</acronym></primary><see>Font Path Element</see></indexterm>
</glossterm>
<glossdef><para>An instance of a renderer, associated with a specific
font source, (ie a directory of PCF bitmaps).</para></glossdef>
</glossentry>
</glosslist>
<para><indexterm><primary>difs layer</primary></indexterm>
The <firstterm>difs</firstterm> layer interprets the
requests, and handles the renderer independent work. This
includes error checking of requests, and the top level
font database. It also contains various utility
functionality such as caching and byte swapping.</para>
<para><indexterm><primary>os layer</primary></indexterm>
The <firstterm>os</firstterm> layer sets up the
communications channel, reads requests and sends the raw
data of replies and events. It also handles font server
configuration issues, controlled by command line
arguments and a configuration file.</para>
<para><indexterm><primary>renderer layer</primary></indexterm>
The <firstterm>renderer</firstterm> layer contains all
font-specific code, and is responsible for rendering a font
(which may mean just reading a bitmap from disk, or may
include scaling of outline data), computing a fonts
properties and header information.</para>
</sect2>
</sect1>
<sect1 id='startup'>
<title>Startup</title>
<para>At startup, the font server handles any command line
arguments, initializes any OS-specific data, and then sets up
the communications. Various internal databases are then
initialized (extensions, the font catalogue, etc).</para>
<para><indexterm><primary>configuration file</primary></indexterm>
The config file, an ordered list of font sources, cache
size hints, default resolutions, and security information, is
then read in. Each of these source names could be a directory
name, the name of another font server, or some other string
that a particular renderer can recognize.</para>
<para>The default font catalogue is then built up by taking
each of the font source names and comparing it with the
names a renderer recognizes. The one that matches this name
will become attached to this source. A renderer will
&ldquo;understand&rdquo; a name if it can parse the data in
that directory, or recognize that it is a valid font server
address, or recognizes a special string. Thus a collection
of valid font path elements is built up. Each
<emphasis remap='B'>FPE</emphasis> has a set of functions to
support opening a font and accessing its data.</para>
<para>Font information is accessed via method functions in the
<indexterm><primary><structname>Font</structname></primary></indexterm>
<structname>Font</structname>. When a font is first
loaded, the header information and properties are
loaded/computed. The font also initializes its function
pointers to do the proper work. When specific metrics or
bitmaps are required, they are access via the font's
functions. A disk-based bitmap font will probably want to
load all data when first accessed. A scaled font or FS font
may want to do more selective caching. In both cases, the
renderer can use the utility functions to keep track of this
data. Changing values of bitmap formats could result in the
font having multiple copies of data in different formats,
which the renderer may use the utility functions to
manage.</para>
</sect1>
<sect1 id='per_client_processing'>
<title>Per client processing</title>
<para>Each entity attaching to the server is a client. Each
client has its own authorization and resolution information,
and its own view of the font database. A font open to one
client may not be open to another, though the font server
may have it loaded.</para>
<para>After initialization, new clients can attach to the font
server and have their requests processed. For each request that
is searching for a font (<systemitem>OpenBitmapFont</systemitem>) or
listing font names (<systemitem>ListFonts</systemitem>,
<systemitem>ListFontsWithXInfo</systemitem>), the pattern
is given to each <emphasis remap='B'>FPE</emphasis>.</para>
<para><indexterm><primary><systemitem>OpenBitmapFont</systemitem></primary></indexterm>
<systemitem>OpenBitmapFont</systemitem> will take the supplied
name and pass it to each <emphasis remap='B'>FPE</emphasis>.
The <emphasis remap='B'>FPE</emphasis> will return one of
three things: <errorname>Success</errorname>, and the font
object; <errorname>BadFont</errorname>, because it doesn't
know the font; or <errorname>BadFont</errorname> and an
alias name, when it has an alias for the font. If
<errorname>Success</errorname> is returned, the server goes
on to create an ID (or find an existing one) and return a
reply. If <errorname>BadFont</errorname> is returned, it
goes on to the next <emphasis remap='B'>FPE</emphasis>. If
it reaches the end without finding a font, an error is
returned to the client. If an alias is returned, the search
resets to the first <emphasis remap='B'>FPE</emphasis> and
starts again, using the alias as the new font name. This
allows aliases to work across different
<emphasis remap='B'>FPEs</emphasis>, without any ordering
restrictions.</para>
<para>When each <emphasis remap='B'>FPE</emphasis> receives a font
name to open, it searches for the font's existence. If it
can't find, or can only find an alias, it returns
<errorname>BadFont</errorname> and any alias. If it finds
the font, it checks the authorization and license status of
the font to that of the client. If it passes, it then
creates a new font object, and reads and/or computes at
least the font's header information and properties. (It may
also want to produce the bitmaps and extents, but that
choice is left to the renderer.)</para>
<para>When a font's information is accessed, the interpreter
routine looks up the font ID to find the font object, and
then uses the font's access functions to get the data. These
functions will return the data in the format expected by the
client.</para>
</sect1>
<sect1 id='client_shutdown'>
<title>Client shutdown</title>
<para>When a client disconnects, all its references to any
fonts it still has opened are removed. If no other clients
reference these fonts, they may be freed, though the server may
choose to cache them.</para>
</sect1>
<sect1 id='server_reset_and_cleanup'>
<title>Server reset and cleanup</title>
<para>A server may be reset to flush the caches, re-read the
configuration file, and a new list of
<emphasis remap='B'>FPEs</emphasis> to be built, via an
OS-specific outside action. In UNIX, this will be handled via
signals; in VMS it could be handled via an async trap or event
flag.</para>
</sect1>
<sect1 id='server_offloading'>
<title>Server offloading</title>
<para>In order to deal with numerous clients without major
performance degradation, the server must be able to clone
itself, or provide the client with a substitute server via the
alternate server mechanism. Since both strategies have their
uses, both will be supported. For a server that has plenty of
host memory or CPU, but insufficient sockets, cloning may be a
good choice. For a host with limited memory, assigning an
alternate server on a different host may be a good choice. The
server will make this decision based on configuration options.</para>
</sect1>
<sect1 id='font_server_data_structures'>
<title>Font server data structures</title>
<para>The
<indexterm><primary><structname>Client</structname></primary></indexterm>
<firstterm id='struct_client'><structname>Client</structname></firstterm>
handles per-client information and interpreter status.
<synopsis>
typedef struct _Client {
int index;
pointer osPrivate;
int noClientException;
int (**requestVector) ();
pointer requestBuffer;
int clientGone;
int sequence;
Bool swapped;
long last_request_time;
void (*pSwapReplyFunc) ();
AuthContextPtr auth;
char *catalogues;
int num_catalogues;
Mask eventmask;
fsResolution *resolutions;
int num_resolutions;
} ClientRec, *ClientPtr;
</synopsis></para>
<para>The
<indexterm><primary><structname>Font</structname></primary></indexterm>
<firstterm id='struct_font'><structname>Font</structname></firstterm>
contains basic font information, including header information and
properties.
<synopsis>
typedef struct _font {
int refcount;
fsHeader header;
fsBitmapFormat format;
int (*get_glyphs)();
int (*get_metrics)();
int (*get_extents)();
int (*get_bitmaps)();
int (*unload_font)();
FontPathElementPtr fpe;
int *client_ids;
Bool restricted_font;
} FontRec *FontPtr;
</synopsis></para>
<para>The
<indexterm><primary><structname>ClientFont</structname></primary></indexterm>
<firstterm id='struct_clientfont'><structname>ClientFont</structname></firstterm>
is a wrapper on top of <structname>Font</structname>,
handling client specific font information.
<synopsis>
typedef struct _clientfont {
FontPtr font;
int clientindex;
} ClientFontRec, *ClientFontRec;
</synopsis></para>
<para>The
<indexterm><primary><structname>AuthContext</structname></primary></indexterm>
<firstterm id='struct_authcontext'><structname>AuthContext</structname></firstterm>
contains authorization information.
<synopsis>
typedef struct _authcontext {
char *authname;
char *authdata;
FSID acid;
} AuthContextRec *AuthContextPtr;
</synopsis></para>
</sect1>
<sect1 id='font_path_element_functions'>
<title>Font Path Element functions</title>
<indexterm id='fpe_functions' class='startofrange'>
<primary>Font Path Element</primary></indexterm>
<para>These functions are associated with each renderer, and
handle all aspects of font access. Font data access is
controlled via another set of functions described later. These
functions are intended to support the R5 X server as well as
the font server. As a result, some design decisions were made
to support both models. When the
<emphasis remap='I'>difs</emphasis> layer needs to access a
font, it uses these functions.</para>
<synopsis>
typedef unsigned long Mask;
typedef unsigned char *pointer;
typedef struct _FontPathElement {
int name_length;
char *name;
int type;
int refcount;
pointer private;
} FontPathElementRec, *FontPathElementPtr;
</synopsis>
<para>The FPE's reference count is incremented when it is added
to the current list of FPEs and when it opens a font. It is
decremented when it is no longer in the current list and when
it closes a font. All reference changes are handled by the
<emphasis remap='I'>difs</emphasis> layer. The count is required
to support font catalogue changes that may occur while the
fontserver has fonts open, and keeps FPEs from being
lost.</para>
<synopsis>
typedef struct FontNames {
int nnames;
int size;
int *length;
char **names;
} FontNamesRec, *FontNamesPtr;
typedef struct {
Bool (*name_check)();
int (*init_fpe)();
int (*reset_fpe)();
int (*free_fpe)();
int (*open_font)();
int (*close_font)();
int (*list_fonts)();
int (*start_list_fonts_with_info)();
int (*list_next_font_with_info)();
int (*wakeup_fpe)();
int (*client_died);
FontNamesPtr renderer_names;
} FPEFunctions;
int init_fpe_type(Bool (name_func)(),
int (init_func)(), int (free_func)(), int (reset_func),
int (open_func)(), int (close_func)(),
int (list_func)(),
int (start_lfwi_func)(), int (next_lfwi_func)(),
int (wakeup_func)(),
int (client_died_func)()
)
</synopsis>
<para>This is called by the renderer when it is initialized at
the beginning of time, and sets up an FPEFunctions entry for
the renderer.</para>
<para>The
<emphasis remap='B'>FPEFunctions</emphasis> have the following
parameters:</para>
<para>
<synopsis>
Bool name_check(char *<parameter>name</parameter>);
</synopsis>
If <parameter class="function">name</parameter> is something the
renderer recognizes as a valid font source name, it returns
<constant>True</constant>, otherwise <constant>False</constant>.
ie, if <parameter class="function">name</parameter>
is a directory name, or is prefixed by the renderer's prefix,
and the directory contains font data the renderer can interpret,
it would return <constant>True</constant>.
</para>
<para>
<synopsis>
int init_fpe(FontPathElementPtr <parameter>fpe</parameter>);
</synopsis>
Does any initialization work for the renderer. The name in
<parameter class="function">fpe</parameter> will be one whose prefix
matches the list returned when the renderer was initialized.
</para>
<para>
<synopsis>
int reset_fpe(FontPathElementPtr <parameter>fpe</parameter>);
</synopsis>
Tells <parameter class="function">fpe</parameter> to reset any
internal state about what fonts it has available. This will typically be
called because the font server's <emphasis remap='B'>FPE</emphasis>
search list has been changed. The
<parameter class="function">fpe</parameter> should reset any cached state
of available fonts (ie, re-read <filename>fonts.dir</filename>)
</para>
<para>
<synopsis>
int free_fpe(FontPathElementPtr <parameter>fpe</parameter>);
</synopsis>
Frees any renderer-specific data and closes any files or sockets.
</para>
<para>
<synopsis>
int open_font(pointer <parameter>client</parameter>, FontPathElementPtr <parameter>fpe</parameter>, Mask <parameter>flags</parameter>,
char *<parameter>fontname</parameter>, int <parameter>namelength</parameter>,
fsBitmapFormat <parameter>format_hint</parameter>, fsBitmapFormatMask <parameter>format_mask</parameter>,
XID <parameter>fontid</parameter>, FontPtr *<parameter>ppfont</parameter>, char **<parameter>alias</parameter>);
</synopsis>
Opens the font. The bits marked by
<parameter class="function">format_mask</parameter> and
<parameter class="function">format_hint</parameter>
are used where applicable. The resulting FontPtr is returned in
<parameter class="function">ppfont</parameter>. The
<parameter class="function">client</parameter> is optional state
information for use with blocking renderers. If the
<parameter class="function">fontname</parameter> resolves to an
alias, it is returned in <parameter class="function">alias</parameter>
with a <errorcode>FontNameAlias</errorcode> error. This tells
the calling code to start searching again, using
<parameter class="function">alias</parameter> as the font name. The
renderer is expected to fill in any information specified by the
<parameter class="function">flags</parameter>.
</para>
<para>Possible <parameter class="function">flags</parameter> values are:
<synopsis>
#define FontLoadInfo 0x0001 /* font header info */
#define FontLoadProps 0x0002 /* font properties */
#define FontLoadMetrics 0x0004 /* font extents */
#define FontLoadBitmaps 0x0008 /* glyph bitmaps */
#define FontLoadAll 0x000f
#define FontOpenSync 0x0010 /* force synchronous loading */
</synopsis>
</para>
<para>Once a font has been opened, the server may place it and
the pattern it matched into a name cache, to avoid lengthy
searching if the font is reopened. If the renderer does not wish
the font to be in this cache (for licensing reasons), it should
set the font's <emphasis remap='I'>restricted_access</emphasis>
flag.
</para>
<para>
<synopsis>
int close_font(FontPtr <parameter>pfont</parameter>);
</synopsis>
Frees up all the data associated with the font.
</para>
<para>
<synopsis>
int list_fonts(pointer <parameter>client</parameter>, FontPathElementPtr <parameter>fpe</parameter>,
char *<parameter>pattern</parameter>, int <parameter>pattern_length</parameter>, int <parameter>maxnames</parameter>,
FontNamesPtr *<parameter>paths</parameter>);
</synopsis>
Returns in <parameter class="function">paths</parameter> up to
<parameter class="function">maxnames</parameter> font names the fpe
recognizes as matching the given pattern.
</para>
<para>
<synopsis>
int start_list_fonts_with_info(pointer <parameter>client</parameter>,
FontPathElementPtr <parameter>fpe</parameter>, char *<parameter>pattern</parameter>, int <parameter>pattern_length</parameter>,
int <parameter>maxnames</parameter>, pointer <parameter>fpe_data</parameter>);
</synopsis>
Initiates a <systemitem>ListFontsWithXInfo</systemitem>.
Typically, a disk-based renderer will do the equivalent of
<systemitem>ListFonts</systemitem> to gather all the font names
matching the pattern. A font server renderer will send the
request. <parameter class="function">fpe_data</parameter>
provides a handle for any FPE-private data that needs to be
passed in later via
<function>list_next_font_with_info()</function>, eg, the list of
font names for a disk-based renderer.
</para>
<para>
<synopsis>
int list_next_font_with_info(pointer <parameter>client</parameter>, FontPathElementPtr <parameter>fpe</parameter>,
char **<parameter>name</parameter>, int *<parameter>namelen</parameter>, FontInfoPtr *<parameter>pinfo</parameter>,
int *<parameter>num_fonts</parameter>, pointer <parameter>fpe_data</parameter>);
</synopsis>
Returns the next font's information. The renderer should keep any state
it requires in the <parameter class="function">fpe_data</parameter>
field. <parameter class="function">num_fonts</parameter> contains the
number of replies remaining.
</para>
<para>These two routines are split for because of the way both
disk-based renderers and font server renderers handle this
request. The first function initiates the action, the second is
used to gather the results. For a disk-based renderer, a list of
font names matching the pattern is first built up when
<function>start_list_fonts_with_info()</function>is called, and
the results are gathered with each call to
<function>list_next_font_with_info()</function>. In a font
server renderer, the first function sends the
<systemitem>ListFontsWithXInfo</systemitem> request, and the
second processes the replies.
</para>
<para>
<synopsis>
int wakeup_fpe(FontPathElementPtr <parameter>fpe</parameter>, unsigned long *<parameter>mask</parameter>)
</synopsis>
Optional function which can be used for blocking
renderers. Typical usage is for a font server renderer, where it
is called when a reply is received, allowing the data to be read
and the client to be signaled and unblocked.
</para>
<para>
<synopsis>
int client_died(pointer <parameter>client</parameter>, FontPathElementPtr <parameter>fpe</parameter>)
</synopsis>
This function is called when a client dies in the middle of a
blocked request, allowing the renderer to clean up.
</para>
<indexterm startref='fpe_functions' class='endofrange' />
</sect1>
<sect1 id='font_specific_functions'>
<title>Font specific functions</title>
<indexterm id='font_functions' class='startofrange'>
<primary><structname>Font</structname></primary></indexterm>
<para>These functions are contained in each
<structname>Font</structname>. For many renderers, every
font will use the same functions, but some renderers may wish
to use different interfaces for different fonts.</para>
<synopsis>
typedef struct {
INT16 left B16,
right B16;
INT16 width B16;
INT16 ascent B16,
descent B16;
CARD16 attributes B16;
} fsCharInfo;
typedef struct {
CARD8 low,
high;
} fsChar2b;
typedef struct {
fsChar2b min_char,
max_char;
} fsRange;
int get_extents(pointer <parameter>client</parameter>,
FontPtr <parameter>pfont</parameter>, Mask <parameter>flags</parameter>, int <parameter>num_ranges</parameter>, fsRange *<parameter>ranges</parameter>,
int *<parameter>num_extents</parameter>, fsCharInfo **<parameter>extents</parameter>);
</synopsis>
<para>Possible flags:</para>
<synopsis>
LoadAll /* ignore the ranges and get everything */
FinishRange /* magic for range completion as specified by protocol */
</synopsis>
<para>Builds up the requested array of extents. The extent data
(which the renderer allocates) is returned, as well as the
number of extents.
<emphasis remap='I'>closure</emphasis> contains any blocking
state information.</para>
<synopsis>
int get_bitmaps(pointer <parameter>client</parameter>,
FontPtr <parameter>pfont</parameter>, fsBitmapFormat <parameter>format</parameter>, Mask <parameter>flags</parameter>,
int <parameter>num_ranges</parameter>, fsRange *<parameter>ranges</parameter>,
unsigned long *<parameter>size</parameter>, unsigned long *<parameter>num_glyphs</parameter>,
unsigned long **<parameter>offsets</parameter>, pointer *<parameter>glyph_data</parameter>);
</synopsis>
<para>Possible flags:</para>
<synopsis>
LoadAll
FinishRange /* magic for range completion as specified by protocol */
</synopsis>
<para>Builds up the requested array of bitmaps. The glyph and
offset data (which the renderer allocates) is returned, as well
as the number of glyphs. The
<emphasis remap='I'>closure</emphasis> contains any blocking
state information. This function will build up the bitmap data
in the format specified by
<parameter class="function">format</parameter> so that the interpreter
can return it without any additional modification. This should
minimize data massaging, since outline renderers will hopefully
be able to produce the bitmaps in the proper format.</para>
<synopsis>
void unload_font(FontPtr <parameter>pfont</parameter>)
</synopsis>
<para>The render will free any allocated data. Note that the
<emphasis remap='B'>FPE</emphasis> function
<function>close_font()</function> will also be called, and
should handle any
<emphasis remap='B'>FPE</emphasis> data allocated for the
font.</para>
<synopsis>
int get_glyphs()
int get_metrics()
</synopsis>
<para>These two functions are used by the X server for loading
glyphs and metrics. They expect the results in a considerably
different form. The
<function>get_bitmaps()</function> and
<function>get_extents()</function> routines both allow for
better cache control by the renderer.</para>
<indexterm startref='font_functions' class='endofrange' />
</sect1>
<sect1 id='font_directories_and_aliases'>
<title>Font directories and aliases</title>
<para>Existing bitmap renderers already have their own concept
of font organization. In the X sample server, the files
<filename>fonts.dir</filename> and <filename>fonts.alias</filename>
are used to list the known fonts. <filename>fonts.dir</filename>
maps file names to font names, while <filename>fonts.alias</filename>
maps font names to other font names.
</para>
<para>These concepts will also be needed by other forms of
fonts which the sample X server does not currently use, but the
font server will, like Bitstream outlines.</para>
</sect1>
<sect1 id='handling_scalable_fonts'>
<title>Handling scalable fonts</title>
<para>For those renderers that support scalable fonts, several
issues must be addressed:</para>
<variablelist spacing='compact'>
<varlistentry>
<term><link linkend='name_parsing'>Name Parsing</link>.</term>
<listitem>
<para>An <acronym>XLFD</acronym> name must be parsed to
determine the requested resolutions and/or sizes.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><link linkend='property_scaling'>Property scaling</link>.</term>
<listitem>
<para>Many of the standard font
properties have values that depend on scaling (eg,
<property>RESOLUTION_X</property>,
<property>POINT_SIZE</property>). </para>
</listitem>
</varlistentry>
<varlistentry>
<term><link linkend='default_values'>Default values</link>.</term>
<listitem>
<para>If resolution information is
wildcarded, the proper default resolution should be
supplied.</para>
</listitem>
</varlistentry>
</variablelist>
<sect2 id='name_parsing'>
<title>Name Parsing</title>
<para>The font name pattern supplied to
<systemitem>OpenBitmapFont</systemitem> or
<systemitem>ListFonts</systemitem> may require some
parsing to be recognized as a scalable font known to the
renderer. The
<property>PIXEL_SIZE</property>,
<property>POINT_SIZE</property>,
<property>RESOLUTION_X</property>,
<property>RESOLUTION_Y</property>, and
<property>AVERAGE_WIDTH</property> all need to
determined from the font name pattern. The master font
must then be found, and scaled appropriately. Any
unspecified values that cannot be determined should be
replaced by the proper defaults. For size fields, this is
whatever the configuration specifies. For resolution
fields, these should be taken from the client's
resolution list, if set, or from the server's
configuration.</para>
</sect2>
<sect2 id='property_scaling'>
<title>Property scaling</title>
<para>Part of scaling a font is scaling its properties.
Many scalable fonts will have a very large number of
scalable properties. One way to deal with these is for
the &ldquo;master&rdquo; outline to keep track of the
property names, and supply new values for each instance
of the font. If the property names are stored as Atoms,
memory usage is kept to a minimum.</para>
</sect2>
<sect2 id='default_values'>
<title>Using defaults</title>
<para>Using default values as substitutions for missing
values was covered above. These defaults will also be
useful in handling <systemitem>ListFonts</systemitem> requests.
Returning a scalable font with an instance using the
default values will provide the most user-friendly
environment.</para>
</sect2>
</sect1>
<sect1 id='access_control'>
<title>Access control</title>
<para>The font server will also support large grain security.
It will have both a limit of the number of users, and on the
hosts which it will support.</para>
<para>Limiting the number of users is as much a server loading
issue as a security issue. The limitation will be typically be
set via configuration options or OS limitations. To change it,
use:</para>
<synopsis>
void AccessSetConnectionLimit(int <parameter>limit</parameter>)
</synopsis>
<para>A
<parameter class="function">limit</parameter> of 0 will set it to a
compiled constant based on OS resources (eg, number of file
descriptors).</para>
<para>Client-host based access control can be used to
supplement licensing, and support font server load balancing by
restricting access. As with licensing, this is OS-specific
code. To manipulate these functions, use:
<synopsis>
typedef struct _host_address {
int type;
pointer address;
struct _host_address *next;
} HostAddress;
typedef HostAddress *HostList;
int AddHost(HostList <parameter>list</parameter>, HostAddress *<parameter>address</parameter>)
int RemoveHost(HostList <parameter>list</parameter>, HostAddress *<parameter>address</parameter>)
Bool ValidHost(HostList <parameter>list</parameter>, HostAddress *<parameter>address</parameter>)
</synopsis>
<function>AddHost()</function> adds a host to the
<parameter class="function">list</parameter>.
<function>RemoveHost()</function> removes it, and
<function>ValidHost()</function> checks to see if its on the
<parameter class="function">list</parameter>. In all functions,
the <parameter class="function">address</parameter> will ignore
any value in the <structfield>next</structfield> field.
</para>
<para>Network addresses are used here to avoid issues with host
name aliases. The caller fills in the desired type, and an
address of that form is returned. This is highly OS-specific,
but values for the <structfield>type</structfield> and
<structfield>address</structfield> fields could include:
<synopsis>
#define HOST_AF_INET 1
struct in_addr *address;
#define HOST_AF_DECnet 2
struct dn_addr *address;
</synopsis>
</para>
<para>The server will use a global host list, but having the
list as an argument will allow licensing schemes to have their
own host lists.</para>
</sect1>
<sect1 id='licensing'>
<title>Licensing</title>
<para>Licensing is a tricky issue, which each renderer will
support in a different way. The sample font server will attempt
to provide some guidelines, and present a possible
implementation of some simple licensing schemes.</para>
<sect2>
<title>Host Address licensing</title>
<para>This is simplistic licensing based on the client's host.
With this form of licensing, a font may be accessible to some
host but not others. To get the current client's host, the
following is used:
<synopsis>
void GetHostAddress(HostAddress *<parameter>address</parameter>);
</synopsis>
A renderer can also use the host access functions to keep
a list of the licensed hosts, and <function>ValidHost()</function>
to check a client.</para>
</sect2>
<sect2>
<title>Simultaneous use license</title>
<para>This licensing allows for a limited number of copies of
the font to be open at once. Since this should be a simple
per-font counter, no support should be required outside of the
renderer.</para>
</sect2>
</sect1>
<sect1 id='difs_contents'>
<title>DIFS contents</title>
<indexterm id='difs_functions' class='startofrange'>
<primary>difs layer</primary></indexterm>
<para>This contains the protocol dispatcher, interpreter and
reply encoding routines.</para>
<para>The interpreter is table driven off the request code. The
dispatcher gets a request from the os layer from
<function>WaitForSomething()</function>, and uses the
request code to determine which function to call. eg, a
<systemitem>CloseFont</systemitem> request would call
<function>ProcCloseFont()</function>.</para>
<para>Each request's routine handles any applicable error
checking, and then does as much work as it can. For font
related requests, this means converting the request to the
proper arguments for the renderers.</para>
<para>If any replies are generated, the reply data is gathered
into the bytestream format, and sent via
<emphasis remap='I'>os</emphasis> write functions to the
client.</para>
<para>If the byte order of the client and server differ, the
above is modified by having the dispatcher call an intermediate
function which re-orders the request to the proper byte order.
Replies go through similar swapping.</para>
<sect2>
<title>Client blocking</title>
<para>To minimize delay caused by font server request, clients
can be blocked while they wait for data to be produced. This is
primarily intended for
<emphasis remap='B'>FPEs</emphasis> using a remote font server,
but can be used anywhere where the font server can pause to
handle other client requests while data needed to satisfy
another is produced (possibly via multiple processes).</para>
<para>
<synopsis>
Bool ClientSleep(ClientPtr <parameter>client</parameter>, Bool (*<parameter>function</parameter>)(), pointer <parameter>closure</parameter>)
</synopsis>
Puts a client to 'sleep'. This means the client will no
longer be considered while the server is dispatching requests.
<parameter class="function">function</parameter> will be called
when the client is signaled, with the
<parameter class="function">client</parameter> and
<parameter class="function">closure</parameter> as its arguments.
</para>
<para>
<synopsis>
Bool ClientSignal(ClientPtr <parameter>client</parameter>)
</synopsis>
This should be called when the client is ready to do more
work. At this point, the function given to
<function>ClientSleep()</function> will be called.
</para>
<para>
<synopsis>
void ClientWakeup(ClientPtr <parameter>client</parameter>)
</synopsis>
Puts the client back to its normal state processing requests.
</para>
<para>
<synopsis>
Bool ClientIsAsleep(ClientPtr <parameter>client</parameter>)
</synopsis>
Can be used to check if a client is asleep. This is
useful for handling client termination, so that any requests
the client is waiting upon can be properly cleaned up.
</para>
</sect2>
<sect2>
<title>Sample Usage</title>
<para>For handling a font server renderer request for
<function>OpenBitmapFont</function> the renderer will
send the request to the remote font server, and the call
<function>ClientSleep()</function>. The font server
will then continue processing requests from other clients,
while the one making the request is blocked. When the reply
returns, the renderer will notice when its
<function>wakeup_fpe()</function> function is called. At this
point the font server renderer will read and process the reply,
<function>ClientSignal()</function> will be called,
and the <parameter>closure</parameter> function will be called.
It will request the data from the renderer, completing the
request, and call
<function>ClientWakeup()</function> to return the
client to normal status.</para>
<para>This layer also contains the resource database, which
associates fonts with IDs, extension interface functions and
the server initialization and reset control.</para>
<indexterm startref='difs_functions' class='endofrange' />
</sect2>
</sect1>
<sect1 id='os_contents'>
<title>OS contents</title>
<indexterm id='os_functions' class='startofrange'>
<primary>os layer</primary></indexterm>
<para>This layer contains OS specific routines for
configuration, command line parsing, client/server
communications, and various OS-dependent utilities such as
memory management and error handling.</para>
<para><function>ReadRequestFromClient()</function>
returns a full request to the dispatcher.
<function>WaitForSomething()</function> is where the
server spends its idle time, waiting for any action from a
client or processing any work left from a blocked
client.</para>
<para>When a client attempts to connect, the server will
call
<synopsis>
int CheckClientAuthorization(ClientPtr <parameter>client</parameter>, AuthPtr <parameter>client_auth</parameter>,
int *<parameter>accept</parameter>, int *<parameter>index</parameter>, int *<parameter>size</parameter>, char **<parameter>authdata</parameter>)
</synopsis>
to see if the server is set to allow the client to connect. It
may use licensing or configuration information to determine if
the client can connect.
</para>
<para>When then connection is established, the server will use the
<synopsis>
typedef struct _alt_server {
char subset;
char namelen;
char *name;
} AlternateServerRec, *AlternateServerPtr;
int ListAlternateServers(AlternateServerPtr *<parameter>servers</parameter>)
</synopsis>
to return any alternate server information it may have.
</para>
<para>When the client limit is reached, the font server may
attempt to copy itself, by calling
<synopsis>
int CloneMyself()
</synopsis>
This function will (if the configuration options allow)
start a new font server process. This is done in such a way
that no pending connections should be lost, and that the
original server will accept no new connections. Once the
original server has no more clients, it will exit.</para>
<sect2>
<title>Catalogue manipulation</title>
<para>Catalogues are configuration dependent, and hence sent by
OS-dependent methods. In order for the
<emphasis remap='I'>difs</emphasis> layer to get them, it
uses
<synopsis>
int ListCatalogues(char *<parameter>pattern</parameter>, int <parameter>pattern_length</parameter>,
int <parameter>maxnames</parameter>, char **<parameter>catalogues</parameter>, int *<parameter>len</parameter>)
</synopsis>
which returns the list of all catalogues it supports which match
the pattern. This function will be used by the catalogue
manipulation requests, as well as by renderers when they give
their <systemitem>ListFonts</systemitem> results.
</para>
<para>
<synopsis>
int ValidateCatalogues(int <parameter>number</parameter>, char *<parameter>catalogues</parameter>)
</synopsis>
Can be used to validate a list of catalogues, returning
<constant>True</constant> if the list is acceptable.</para>
<indexterm startref='os_functions' class='endofrange' />
</sect2>
</sect1>
<sect1 id='utility_functions'>
<title>Utility functions</title>
<sect2>
<title>Client data functions</title>
<para>These provide access to the current client's resolution
and authorization data. This form of interface is supplied
rather than passing it to all renderers in the <emphasis
remap='B'>FPE</emphasis> functions because the data may be
complex and/or uninteresting to all renderers.</para>
<para><synopsis>
AuthContextPtr GetClientAuthorization()
</synopsis>
<indexterm><primary><structname>AuthContext</structname></primary></indexterm>
Returns the authorization data for the current client.</para>
<para><synopsis>
fsResolution *GetClientResolutions(int *<parameter>num_resolutions</parameter>)
</synopsis>
Returns the list of resolutions that the current client has set.</para>
</sect2>
<sect2>
<title>Caching functions</title>
<para>These are functions that simplify caching of renderer
data. These are for use by renderers that take significant
resources to produce data. The data must be re-creatable -- the
cache is not meant for general storage. The data may also be
moved by the cache, so it should only be accessed by
CacheID.</para>
<para><synopsis>
typedef void (*CacheFree)();
typedef unsigned long CacheID;
typedef unsigned long Cache;
Cache CacheInit(int <parameter>renderer_id</parameter>)
</synopsis>
Initializes a cache object for the renderer. the returned
ID should be passed to <function>CacheStoreMemory()</function>
when adding an object to the cache.</para>
<para><synopsis>
void CacheStats(Cache <parameter>cid</parameter>, unsigned long *<parameter>num_entries</parameter>,
unsigned long *<parameter>max_storage</parameter>, unsigned long *<parameter>current_storage</parameter>,
unsigned long *<parameter>num_lookups</parameter>, unsigned long *<parameter>hit_ratio</parameter>)
</synopsis>
Returns statistics on the cache. Useful if the renderer
wants some hints about whether to place an object in the cache.
If the cache is nearly full, and the priority low, it may want
to take different action.</para>
<para><synopsis>
CacheID CacheStoreMemory(Cache <parameter>cacheid</parameter>, pointer <parameter>data</parameter>, unsigned long <parameter>size</parameter>,
CacheFree <parameter>free_func</parameter>)
</synopsis>
The renderer hands the cache some chunk of contiguous
memory, which the cache timestamps and stores. When it needs to
remove them, it calls the
<parameter class="function">free_func</parameter>, which must
take responsibility for properly freeing the data.
<parameter class="function">size</parameter> is primarily a hint
to the cache, so that cache limits can be properly calculated. A
return value of zero means the store failed, probably because
the given size was over the cache limit. If the given data is
too large for the current cache, it will attempt to free old
data to make room. The returned ID is a unique value that refers
both to the object and the cache in which it was placed.</para>
<para><synopsis>
pointer CacheFetchMemory(CacheID <parameter>cid</parameter>, Bool <parameter>update</parameter>)
</synopsis>
Returns the memory attached to the id. If
<parameter class="function">update</parameter> is set, the
timestamp is updated. (Some accesses may wish to be 'silent',
which allows some control over the freeing scheduling.) If the
cid is invalid, <constant>NULL</constant> is returned.</para>
<para><synopsis>
pointer CacheFetchMemory(CacheID <parameter>cid</parameter>, Bool <parameter>update</parameter>)
</synopsis>
Allows the cache to flush the data. If
<emphasis remap='I'>notify</emphasis> is set, the CacheFree
function passed in when the data was cached will also be
called.</para>
<para><synopsis>
void MemoryFreed(CacheID <parameter>cid</parameter>, pointer <parameter>data</parameter>, int <parameter>reason</parameter>)
</synopsis>
Callback function from the cache to the renderer notifying
it that its data has been flushed. This function then has the
responsibility to free that data.
<parameter class="function">reason</parameter> may be one of:
<synopsis>
CacheReset /* all cache freed because of server reset */
CacheEntryFreed /* explicit request via free_memory() */
CacheEntryOld /* cache hit limit, and memory being freed because its old */
</synopsis>
and is supplied so that the renderer may choose how to
deal with the free request. (It will probably be ignored by
most, but some may want to keep the memory around by bypassing
the cache, or re-inserting it.) Note that the cache will
consider the data gone, so it <emphasis remap='B'>must</emphasis>
be re-inserted to keep it alive.</para>
<para><synopsis>
void CacheSimpleFree(CacheID <parameter>cid</parameter>, pointer <parameter>data</parameter>, int <parameter>reason</parameter>)
</synopsis>
Just calls <function>free()</function> on the data. Simple
CacheFree defined here to prevent it being redefined in each
renderer.</para>
<para>Typical usage of the cache is for the renderer to store a
CacheID rather than a pointer to the cacheable data. The
renderer is responsible for both allocating and freeing the
data, as well as keeping track of just what it is. When the
renderer needs the cached data, it will request it from the
cache. If it fails, it must rebuild it.</para>
<para>A possible configuration parameter is the size of the
cache. when the cache is filled (with the calculation based on
the given size), it sweeps the cache and frees old data. The
amount of memory actually freed may wish to be tunable: some
systems may want to keep the cache as full as possible, others
may want to free some percentage such that sweeps occur less
frequently.</para>
<para>Cache statistics may want to be available for
administrators. They could be dumped to a file when a signal is
received. (SNMP seems like a perfect match, but apparently the
technology isn't there yet.)</para>
<para>Cached data could also be compressed, if the memory/CPU
tradeoffs make it worthwhile.</para>
<note><title>ISSUE: Is a time-based freeing schedule sufficient?</title>
<para>Should priorities or size also be taken into account? [ No.
Anything that the renderer thinks should have a higher priority
should probably not be placed into the cache. ]</para></note>
</sect2>
<sect2>
<title>Byte swapping</title>
<para>Functions for swapping a 4-byte quantity, a 2-byte
quantity and inverting a byte.</para>
<synopsis>
void BitOrderInvert(pointer <parameter>buffer</parameter>, unsigned long <parameter>num_bytes</parameter>)
void TwoByteSwap(pointer <parameter>buffer</parameter>, unsigned long <parameter>num_shorts</parameter>)
void FourByteSwap(pointer <parameter>buffer</parameter>, unsigned long <parameter>num_longs</parameter>)
</synopsis>
</sect2>
<sect2>
<title>Bitmap padding</title>
<para>Functions taking a desired extents and a bitmap that will
return the bitmap properly padded.</para>
<para><synopsis>
int RepadBitmap(pointer <parameter>src</parameter>, pointer <parameter>dst</parameter>, fsFormat <parameter>src_format</parameter>,
fsFormat <parameter>dst_format</parameter>, int <parameter>width</parameter>, int <parameter>height</parameter>)
</synopsis>
Takes a bitmap in <parameter class="function">src_format</parameter>
and converts it to one in
<parameter class="function">dst_format</parameter>.</para>
</sect2>
<sect2>
<title>Atoms</title>
<para>Existing bitmap-based renderers use atoms to store strings
for property information. Rather than duplicate this code in
each renderer, it lives in the
<filename class="directory">util</filename> directory.</para>
<para>Atoms will be especially useful for property information,
to prevent many copies of the same strings from being saved.
Using atoms for comparison when modifying properties after
scaling is also more efficient. Since
<emphasis remap='I'>atoms</emphasis> will will exist until the
server is reset, they may want to be used sparingly for property
values to avoid extraneous string data.</para>
<para><synopsis>
typedef unsigned long Atom;
Atom MakeAtom(char *<parameter>string</parameter>, unsigned int <parameter>length</parameter>, Bool <parameter>create</parameter>)
</synopsis>
Returns the atom associated with
<parameter class='function'>string</parameter>. If
<parameter>create</parameter> is true, a new atom will be
created.
</para>
<para><synopsis>
char *NameForAtom(Atom atom)
</synopsis>
Returns the string associated with
<parameter class="function">atom</parameter>.
</para>
</sect2>
</sect1>
<sect1 id='server_request_details'>
<title>Server request details</title>
<para>This section describes in-depth the action of each
protocol request. In all cases, the request is first error
checked for simple length or value errors, with the server
immediately returning an error if one is encountered.</para>
<sect2 id='connection'>
<title>Connection</title>
<para>When a new client attempts to connect, the server first
checks its initial authorization information to see if the
server is willing to talk to it. This will be handled in some
OS-specific form using <function>CheckClientAuthorization()</function>.
If it passes this test, and the server has sufficient to
resources to talk to it, the server sends accepts the
connection and returns its connection block. If the
connection fails, the server returns the proper status and a
list of any alternate servers it may know of (gathered from
<function>
ListAlternateServers().)</function></para>
</sect2>
<sect2 id='listextension'>
<title>ListExtension</title>
<para>Returns the list of extensions the server knows about.
Any extensions will be initialized when the server is first
started.</para>
</sect2>
<sect2 id='queryextension'>
<title>QueryExtension</title>
<para>Returns the information about the requested extension,
which was set when the extension was initialized.</para>
</sect2>
<sect2 id='listcatalogues'>
<title>ListCatalogues</title>
<para>Returns the catalogues the server recognizes (the
results of <function>ListCatalogues()</function>.)</para>
</sect2>
<sect2 id='setcatalogues'>
<title>SetCatalogues</title>
<para>Sets the requesting client's catalogues after verifying
them with the supported catalogues.</para>
</sect2>
<sect2 id='getcatalogues'>
<title>GetCatalogues</title>
<para>Returns the requesting client's catalogues.</para>
</sect2>
<sect2 id='createac'>
<title>CreateAC</title>
<para>Creates a new authorization context and fills it in.
The list of authorization protocols is then checked by the
server with
<function>CheckClientAuthorization()</function>. If
any are accepted, the
<emphasis remap='B'>AC</emphasis> is placed in the resource
database and <constant>Success</constant> is returned with the
name of the accepted protocol. If more than one is accepted,
<constant>Continue</constant> is returned with each
of the accepted protocols, until the last one which has
status <constant>Success</constant>. Otherwise
<constant>Denied</constant> is returned.</para>
</sect2>
<sect2 id='freeac'>
<title>FreeAC</title>
<para>Looks up the
<emphasis remap='B'>AC</emphasis> in the resource database,
and frees it if it finds it. Otherwise an
<errorname>Access</errorname> error is returned.</para>
</sect2>
<sect2 id='setauthorization'>
<title>SetAuthorization</title>
<indexterm><primary><structname>AuthContext</structname></primary></indexterm>
<para>Looks up the
<emphasis remap='B'>AC</emphasis> in the resource database,
and set the client's AuthContextPtr to its value if it is
found. Otherwise it sends an
<errorname>Access</errorname> error.</para>
</sect2>
<sect2 id='setresolution'>
<title>SetResolution</title>
<para>Sets the requesting client's resolution list to the
supplied list.</para>
</sect2>
<sect2 id='getresolution'>
<title>GetResolution</title>
<para>Returns the requesting client's list of resolutions.</para>
</sect2>
<sect2 id='listfonts'>
<title>ListFonts</title>
<para>Iterates over each open FPE, calling the FPE's
<function>list_fonts()</function>routine passing it the
pattern. When all FPE's have been processed, the list that
has been built up is returned. Note that the same
<structname>FontNamesPtr</structname> is sent to each
FPE in turn, so that one list is built up. An FPE may
restrict the fonts it returns based on the client's
catalogue.</para>
</sect2>
<sect2 id='listfontswithxinfo'>
<title>ListFontsWithXInfo</title>
<para>Iterates over each FPE, calling its
<function>start_list_fonts_with_info()</function>function to
prime the FPE's renderer. It then calls the FPE's
<function>list_next_font_with_info()</function>, sending each font's
data to the client until no more fonts remain. When all FPEs
have been processed, the final reply with a zero-length name
is then sent to mark the end of the replies. An FPE may
restrict the fonts it returns based on the client's
catalogue. Note: an issue exists with font aliases which may
require this to change, since an FPE may contain an alias
pointing to another FPE, and cannot therefore return the
font's info.</para>
</sect2>
<sect2 id='openbitmapfont'>
<title>OpenBitmapFont</title>
<para>The pattern is first searched for in the font server's
name cache. If it doesn't find it, the server iterates over
each FPE, calling its
<function>open_font</function> function with the
supplied pattern. This will return one of the following
values:</para>
<itemizedlist remap='IP'>
<listitem>
<para>an <errorname>Access</errorname> error, which means
the renderer has the font but the client does not have
access to it because of some form of licensing
restriction</para>
</listitem>
<listitem>
<para>a <errorname>Font</errorname> error and a NULL
<emphasis remap='I'>alias</emphasis> parameter, which
will cause the next FPE to be tried</para>
</listitem>
<listitem>
<para>a <errorname>Font</errorname> error but a non-NULL
<emphasis remap='I'>alias</emphasis>, which will cause
the search to start over with the first FPE using
<emphasis remap='I'>alias</emphasis> as the new font
pattern</para>
</listitem>
<listitem>
<para><errorname>Success</errorname>,
in which case a valid font has been found.</para>
</listitem>
</itemizedlist>
<para>If the end of the FPE list is reached without having found
the font, an error is returned to the client. If an
<errorname>Access</errorname> error was encountered, it is
returned, otherwise a <errorname>Font</errorname> error is
returned. If a valid font is found, its reference count will
be incremented and it will be checked to see if the client has
already opened it before. If so, the previous ID will be
returned. Otherwise the font will be placed in the resource
database.</para>
<para>The renderer will fill in the font's header and property
information, and may also choose to load or create the font's
metrics or glyphs. If the glyphs are built, they will use any
supplied <emphasis remap='I'>format hint</emphasis>.</para>
<para>Whenever a new font is successfuly opened, the font and
its name pattern will be placed in a name cache. This cache
exists to minimize the amount of work spent searching for a
font. It will be flushed when the font catalogue is
modified. Client's with private font catalogues will require
private name caches.</para>
</sect2>
<sect2 id='queryxinfo'>
<title>QueryXInfo</title>
<para>The
<emphasis remap='I'>fontid</emphasis> is looked up in the
resource database, and the font's header and property info is
returned.</para>
</sect2>
<sect2 id='queryxextents8_queryxextents16'>
<title>QueryXExtents8 QueryXExtents16</title>
<para>The
<emphasis remap='I'>fontid</emphasis> is looked up in the
resource database. The supplied list of characters
(interpreted according to request type) is then translated
into a list of ranges. The font's
<function>get_extents()</function>function is then called. It
builds the requested list of extents, and returns them along
with the number of extents. The results are properly swapped
and sent to the client.</para>
</sect2>
<sect2 id='queryxbitmaps8_queryxbitmaps16'>
<title>QueryXBitmaps8 QueryXBitmaps16</title>
<para>The
<emphasis remap='I'>fontid</emphasis> is looked up in the
resource database. The supplied list of characters
(interpreted according to request type) is then translated
into a list of ranges. The font's
<function>get_bitmaps()</function>function is called, and the
renderer will build up the requested bitmaps, using the
specified
<emphasis remap='I'>format</emphasis>, and returns the
bitmaps, the number of glyphs and the offsets. The offsets
are properly swapped and the offsets and bitmaps are sent to
the clients.</para>
</sect2>
<sect2 id='closefont'>
<title>CloseFont</title>
<para>The font's reference count is decremented. If this was
the last reference, the font's
<function>unload_font()</function>function is called to free
the renderer's data, and the font's FPE
<function>close_font()</function>function is called to free
up any FPE specific data.</para>
</sect2>
</sect1>
<sect1 id='configuration'>
<title>Configuration</title>
<indexterm><primary>configuration file</primary></indexterm>
<para>The configuration mechanism is a simple keyword-value
pair, separated by an '<literal>=</literal>'.</para>
<variablelist>
<title>Configuration types:</title>
<varlistentry>
<term><type>cardinal</type></term>
<listitem><para>non-negative number</para></listitem>
</varlistentry>
<varlistentry>
<term><type>boolean</type></term>
<listitem><para>"[Yy]es", "[Yy]" "on", "1", "[Nn]o", "[Nn]", "off", "0"</para></listitem>
</varlistentry>
<varlistentry>
<term><type>resolution</type></term>
<listitem><para><type>cardinal</type><literal>,</literal><type>cardinal</type></para></listitem>
</varlistentry>
<varlistentry>
<term><type>list of foo</type></term>
<listitem><para>1 or more of foo, separated by commas</para></listitem>
</varlistentry>
</variablelist>
<variablelist>
<title>Here is an incomplete list of the supported keywords:</title>
<varlistentry>
<term><literal>#</literal></term>
<listitem><para>in the first column, a comment character</para></listitem>
</varlistentry>
<!--
<varlistentry>
<term><literal>cache-size</literal> <type>(cardinal)</type></term>
<listitem><para>Size in bytes of the FS cache.r</para></listitem>
</varlistentry>
-->
<varlistentry>
<term><literal>catalogue</literal> <type>(list of string)</type></term>
<listitem><para>Ordered list of font path element names.</para></listitem>
</varlistentry>
<varlistentry>
<term><literal>alternate-servers</literal> <type>(list of string)</type></term>
<listitem><para>List of alternate servers for this FS.</para></listitem>
</varlistentry>
<varlistentry>
<term><literal>client-limit</literal> <type>(cardinal)</type></term>
<listitem><para>Number of clients this FS will support before refusing
service.</para></listitem>
</varlistentry>
<varlistentry>
<term><literal>clone-self</literal> <type>(boolean)</type></term>
<listitem><para>Whether this FS should attempt to clone itself or
use delegates when it reachs the client-limit.</para></listitem>
</varlistentry>
<varlistentry>
<term><literal>default-point-size</literal> <type>(cardinal)</type></term>
<listitem><para>The default pointsize (in decipoints) for fonts that
don't specify.</para></listitem>
</varlistentry>
<varlistentry>
<term><literal>default-resolutions</literal> <type>(list of resolutions)</type></term>
<listitem><para>Resolutions the server supports by default.
This information may be used as a hint for pre-rendering.</para></listitem>
</varlistentry>
<varlistentry>
<term><literal>error-file</literal> <type>(string)</type></term>
<listitem><para>Filename of the error file. All warnings and errors
will be logged here. This information may be used as a hint
for pre-rendering.</para></listitem>
</varlistentry>
<varlistentry>
<term><literal>port</literal> <type>(cardinal)</type></term>
<listitem><para>
The TCP port on which the server will listen for connections.
</para></listitem>
</varlistentry>
<varlistentry>
<term><literal>use-syslog</literal> <type>(boolean)</type></term>
<listitem><para>
Whether syslog(3) is to be used for errors.
</para></listitem>
</varlistentry>
<!--
<varlistentry>
<term><literal>trusted-clients</literal> <type>(list of string)</type></term>
<listitem><para>
Those clients the fontserver will talk to. Others
will be refused for the initial connection. An empty
list means the server will talk to any client.
</para></listitem>
</varlistentry>
-->
</variablelist>
<para>Each renderer may also want private configuration
options. The names should be prefixed by the renderer name, ie
<literal>pcf-</literal>, <literal>atm-</literal>.</para>
<example>
<title>Sample Configuration Entries:</title>
<programlisting>
# allow a ~a megabyte of memory to be reserved for cache data
cache-size = 1000000
catalogue = pcf:/usr/lib/X11/fonts/misc,speedo:/usr/lib/fonts/speedo
</programlisting>
</example>
</sect1>
<index/>
</article>
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