xref: /xsrc/external/mit/xfs/dist/doc/xfs-design.xml

<?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>