








	    Font server implementation overview

			 Dave Lemke
	      Network Computing Devices, Inc.
     Copyright (C) 1991 Network Computing Devices, Inc.


1.  Introduction

     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 os and
difs (device independent font server) layers familiar.



			+-----------------+
		  +-----|      difs	  |------+
		  |	+-----------------+	 |
		  |				 |
		+----+			+------------+
		| os |			| renderers  |
		+----+			+------------+


Definitions

o  Renderer.  Code that knows how to take font data in its
   raw format and convert it to the font server's format.

o  Font Path Element (FPE).  An instance of a renderer,
   associated with a specific font source, (ie a directory
   of PCF bitmaps).

     The difs 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 swap-
ping.

     The os 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.

     The renderer 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 out-
line data), computing a fonts properties and header informa-
tion.










			     -2-


2.  Startup

     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).

     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.

     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
``understand'' 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 FPE has a set
of functions to support opening a font and accessing its
data.

     Font information is accessed via method functions in
the Font.  When a font is first loaded, the header informa-
tion and properties are loaded/computed.  The font also ini-
tializes 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.

3.  Per client processing

     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.

     After initialization, new clients can attach to the
font server and have their requests processed.	For each
request that is searching for a font (OpenBitmapFont) or
listing font names (ListFonts, ListFontsWithXInfo), the pat-
tern is given to each FPE.

     OpenBitmapFont will take the supplied name and pass it
to each FPE.  The FPE will return one of three things:









			     -3-


Success, and the font object; BadFont, because it doesn't
know the font; or BadFont and an alias name, when it has an
alias for the font.  If Success is returned, the server goes
on to create an ID (or find an existing one) and return a
reply.	If BadFont is returned, it goes on to the next FPE.
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 FPE and starts again, using the alias as
the new font name.  This allows aliases to work across dif-
ferent FPEs, without any ordering restrictions.

     When each FPE 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 BadFont and any alias.  If it
finds the font, it checks the authorization and license sta-
tus 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.)

     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.


4.  Client shutdown

     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.


5.  Server reset and cleanup

     A server may be reset to flush the caches, re-read the
configuration file, and a new list of FPEs to be built, via
an OS-specific outside action.	In UNIX, this will be han-
dled via signals; in VMS it could be handled via an async
trap or event flag.


6.  Server offloading

     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









			     -4-


memory, assigning an alternate server on a different host
may be a good choice.  The server will make this decision
based on configuration options.


7.  Font server data structures


     The Client handles per-client information and inter-
     preter status.


     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;



     The Font contains basic font information, including
     header information and properties.


     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;













			     -5-


     The ClientFont is a wrapper on top of Font, handling
     client specific font information.


     typedef struct _clientfont {
	   FontPtr     font;
	   int	 clientindex;
     }	   ClientFontRec, *ClientFontRec;



     The AuthContext contains authorization information.



     typedef	 struct _authcontext	 {
	   char  *authname;
	   char  *authdata;
	   FSID  acid;
     }	   AuthContextRec *AuthContextPtr;




8.  Font Path Element functions

     These functions are associated with each renderer, and
handle all aspects of font access.  Font data access is con-
trolled 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 difs layer needs to
access a font, it uses these functions.



     typedef unsigned long   Mask;

     typedef unsigned char   *pointer;

     typedef struct _FontPathElement {
	 int	     name_length;
	 char	    *name;
	 int	     type;
	 int	     refcount;
	 pointer     private;
     }		 FontPathElementRec, *FontPathElementPtr;



     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









			     -6-


handled by the difs 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.




     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)()
		 )




This is called by the renderer when it is initialized at the
beginning of time, and sets up an FPEFunctions entry for the
renderer.

The FPEFunctions have the following parameters:



     Bool  name_check(char *name);













			     -7-


If name is something the renderer recognizes as a valid font
source name, it return True, otherwise False.  ie, if name
is a directory name, or is prefixed by the renderer's pre-
fix, and the directory contains font data the renderer can
interpret, it would return True.



     int   init_fpe(FontPathElementPtr fpe);



Does any initialization work for the renderer.	The name in
fpe will be one whose prefix matches the list returned when
the renderer was initialized.



     int   reset_fpe(FontPathElementPtr fpe);



Tells fpe to reset any internal state about what fonts it
has available.	This will typically be called because the
font server's FPE search list has been changed.  The fpe
should reset any cached state of available fonts (ie, re-
read thisfonts.dir)when



     int   free_fpe(FontPathElementPtr fpe);



Frees any renderer-specific data and closes any files or
sockets.



     int   open_font(pointer client, FontPathElementPtr fpe, Mask flags,
		 char *fontname, int namelength,
		 fsBitmapFormat format_hint, fsBitmapFormatMask format_mask,
		 XID fontid, FontPtr *ppfont, char **alias);



Opens the font.  The bits marked by theformat_maskin for-
mat_hint are used where applicable.  The resulting FontPtr
is returned in ppfont.	The client is optional state infor-
mation for use with blocking renderers.  If the fontname
 resolves to an alias, it is returned in alias with a Font-
NameAlias error.  This tells the calling code to start
searching again, using alias as the font name.	The renderer
is expected to fill in any information specified by the









			     -8-


flags.

     Possible flags values are:


     #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 */



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 restricted_access flag.



     int   close_font(FontPtr pfont);



Frees up all the data associated with the font.



     int   list_fonts(pointer client, FontPathElementPtr fpe,
		 char *pattern, int pattern_length, int maxnames,
		 FontNamesPtr *paths);



Returns in paths up to maxnames font names the fpe recog-
nizes as matching the given pattern.



     int   start_list_fonts_with_info(pointer client,
		 FontPathElementPtr fpe, char *pattern, int pattern_length,
		 int maxnames, pointer fpe_data);



Initiates a ListFontsWithXInfo.  Typically, a disk-based
renderer will do the equivalent of ListFonts to gather all
the font names matching the pattern.  A font server renderer
will send the request.	fpe_data provides a handle for any
FPE-private data that needs to be passed in later via
list_next_font_with_info(), eg, the list of font names for a
disk-based renderer.









			     -9-


     int   list_next_font_with_info(pointer client, FontPathElementPtr fpe,
		 char **name, int *namelen, FontInfoPtr &pinfo,
		 int &num_fonts, pointer fpe_data);



Returns the next font's information.  The renderer should
keep any state it requires in the fpe_data field.  num_fonts
contains the number of replies remaining.

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 sec-
ond is used to gather the results.  For a disk-based ren-
derer, a list of font names matching the pattern is first
built up when start_list_fonts_with_info() is called, and
the results are gathered with each call to
list_next_font_with_info.  In a font server renderer, the
first function sends the ListFontsWithXInfo request, and the
second processes the replies.



     int   wakeup_fpe(FontPathElementPtr fpe, unsigned long *mask)



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.



     int   client_died(pointer client, FontPathElementPtr fpe)



This function is called when a client dies in the middle of
a blocked request, allowing the renderer to clean up.


9.  Font specific functions

These functions are contained in each Font.  For many ren-
derers, every font will use the same functions, but some
renderers may wish to use different interfaces for different
fonts.















			    -10-


     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 client,
		 FontPtr pfont, Mask flags, int num_ranges, fsRange *ranges,
		 int *num_extents, fsCharInfo **extents);



Possible flags:



     LoadAll	       /* ignore the ranges and get everything */
     FinishRange /* magic for range completion as specified by protocol */



Builds up the requested array of extents.  The extent data
(which the renderer allocates) is returned, as well as the
number of extents.  closure contains any blocking state
information.



     int   get_bitmaps(pointer client,
		 FontPtr pfont, fsBitmapFormat format, Mask flags,
		 int num_ranges, fsRange *ranges,
		 unsigned long *size, unsigned long *num_glyphs,
		 unsigned long **offsets, pointer *glyph_data);



Possible flags:













			    -11-


     LoadAll
     FinishRange /* magic for range completion as specified by protocol */



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 closure contains any
blocking state information.  This function will build up the
bitmap data in the format specified by format so that the
interpreter can return it without any additional modifica-
tion.  This should minimize data massaging, since outline
renderers will hopefully be able to produce the bitmaps in
the proper format.



     void  unload_font(FontPtr pfont)



The render will free any allocated data.  Note that the FPE
function close_font() will also be called, and should handle
any FPE data allocated for the font.



     int   get_glyphs()
     int   get_metrics()



These two functions are used by the X server for loading
glyphs and metrics.  They expect the results in a consider-
ably different form.  The get_bitmaps() and get_extents()
routines both allow for better cache control by the ren-
derer.


10.  Font directories and aliases

     Existing bitmap renderers already have their own con-
cept of font organization.  In the X sample server, the
files fonts.dir and fonts.alias are used to list the known
fonts.	fonts.dir maps file names to font names, while
fonts.alias maps font names to other font names.

     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.













			    -12-


11.  Handling scalable fonts

     For those renderers that support scalable fonts, sev-
eral issues must be addressed:

o  Name Parsing.  An XLFD name must be parsed to determine
   the requested resolutions and/or sizes.

o  Property scaling.  Many of the standard font properties
   have values that depend on scaling (eg, RESOLUTION_X.
   POINT_SIZE)

o  Default values.  If resolution information is wildcarded,
   the proper default resolution should be supplied.

Name Parsing

     The font name pattern supplied to OpenBitmapFont or
ListFonts may require some parsing to be recognized as a
scalable font known to the renderer.  The PIXEL_SIZE,
POINT_SIZE, RESOLUTION_X, RESOLUTION_Y and AVERAGE_WIDTH 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.

Property scaling

     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 ``mas-
ter'' outline to keep track of the property names, and sup-
ply new values for each instance of the font.  If the prop-
erty names are stored as Atoms, memory usage is kept to a
minimum.

Using defaults

     Using default values as substitutions for missing val-
ues was covered above.	These defaults will also be useful
in handling ListFonts requests.  Returning a scalable font
with an instance using the default values will provide the
most user-friendly environment.


12.  Access control

     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.










			    -13-


     Limiting the number of users is as much a server load-
ing issue as a security issue.	The limitation will be typi-
cally be set via configuration options or OS limitations.
To change it, use:



     void  AccessSetConnectionLimit(int limit)



A limit of 0 will set it to a compiled constant based on OS
resources (eg, number of file descriptors).

     Client-host based access control can be used to supple-
ment licensing, and support font server load balancing by
restricting access.  As with licensing, this is OS-specific
code.  To manipulate these functions, use:



     typedef struct _host_address {
	   int	 type;
	   pointer     address;
	   struct _host_address *next;
     } HostAddress;

     typedef HostAddress     *HostList;

     int   AddHost(HostList list, HostAddress *address)
     int   RemoveHost(HostList list, HostAddress *address)
     Bool  ValidHost(HostList list, HostAddress *address)



AddHost() adds a host to the list.  RemoveHost() removes it,
and ValidHost() checks to see if its on the list.  In all
functions, the address has will ignore any value in the next
field.

     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 type and address fields could
include:


















			    -14-


     #define	 HOST_AF_INET	   1
     struct in_addr    *address;

     #define	 HOST_AF_DECnet    2
     struct	 dn_addr     *address;



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.


13.  Licensing

     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.

Host Address licensing

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:



     void  GetHostAddress(HostAddress *address);



A renderer can also use the host access functions to keep a
list of the licensed hosts, and ValidHost() to check a
client.

Simultaneous use license

     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.


14.  DIFS contents

     This contains the protocol dispatcher, interpreter and
reply encoding routines.

     The interpreter is table driven off the request code.
The dispatcher gets a request from the os layer from Wait-
ForSomething(), and uses the request code to determine which
function to call.  eg, a CloseFont request would call









			    -15-


ProcCloseFont().

     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.

     If any replies are generated, the reply data is gath-
ered into the bytestream format, and sent via os write func-
tions to the client.

     If the byte order of the client and server differ, the
above is modified by having the dispatcher call an interme-
diate function which re-orders the request to the proper
byte order.  Replies go through similar swapping.

Client blocking

     To minimize delay caused by font server request,
clients can be blocked while they wait for data to be pro-
duced.	This is primarily intended for FPEs 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 pro-
cesses).



     Bool  ClientSleep(ClientPtr client, Bool (*function)(), pointer closure)



Puts a client to 'sleep'.  This means the client will no
longer be considered while the server is dispatching
requests.  function will be called when the client is sig-
naled, with the client and closure as its arguments.


Bool  ClientSignal(ClientPtr client)



This should be called when the client is ready to do more
work.  At this point, the function given to ClientSleep()
will be called.


void ClientWakeup(ClientPtr client)



Puts the client back to its normal state processing
requests.










			    -16-


Bool ClientIsAsleep(ClientPtr client)



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 properply cleaned up.

Sample Usage

     For handling a font server renderer request for Open-
BitmapFont the renderer will send the request to the remote
font server, and the call ClientSleep().  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 wakeup_fpe()
function is called.  At this point the font server renderer
will read and process the reply.  ClientSignal() will be
called, and the closure function will be called.  It will
request the data from the renderer, completing the request,
and call ClientWakeup() to return the client to normal sta-
tus.


     This layer also contains the resource database, which
associates fonts with IDs, extension interface functions and
the server initialization and reset control.

15.  OS contents

     This layer contains OS specific routines for configura-
tion, command line parsing, client/server communications,
and various OS-dependent utilities such as memory management
and error handling.

     ReadRequestFromClient() returns a full request to the
dispatcher.  WaitForSomething() is where the server spends
its idle time, waiting for any action from a client or pro-
cessing any work left from a blocked client.

     When a client attempts to connect, the server will call



     int   CheckClientAuthorization(ClientPtr client, AuthPtr client_auth,
		 int *accept, int *index, int *size, char **authdata)



to see if the server is set to allow the client to connect.
It may use licensing or configuration information to deter-
mine if the client can connect.











			    -17-


     When then connection is established, the server will
use the



     typedef struct _alt_server {
	 char	     subset;
	 char	     namelen;
	 char	    *name;
     }		 AlternateServerRec, *AlternateServerPtr;

     int ListAlternateServers(AlternateServerPtr *servers)



to return any alternate server information it may have.

When the client limit is reached, the font server may
attempt to copy itself, by calling



     int CloneMyself()



This function will (if the configuartion 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.

Catalogue manipulation

     Catalogues are configuration dependent, and hence sent
by OS-dependent methods.  In order for the difs layer to get
them, it uses



     int   ListCatalogues(char *pattern, int pattern_length,
		 int maxnames, char **catalogues, int *len)



which returns the list of all catalogues it supports which
match the pattern.  This function will be used by the cata-
logue manipulation requests, as well as by renderers when
they give their ListFonts results.














			    -18-


int ValidateCatalogues(int number, char *catalogues)



Can be used to validate a list of catalogues, returning True
if the list is acceptable.


16.  Utility functions

Client data functions

     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 FPE functions
because the data may be complex and/or uninteresting to all
renderers.



     AuthContextPtr    GetClientAuthorization()



Returns the authorization data for the current client.



     fsResolution      *GetClientResolutions(int  *num_resolutions)



Returns the list of resolutions that the current client has
set.



Caching functions

     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.


















			    -19-


     typedef void (*CacheFree)();
     typedef unsigned long   CacheID;
     typedef unsigned long   Cache;


     Cache CacheInit(int renderer_id)



Initializes a cache object for the renderer.  the returned
ID should be passed to CacheStoreMemory() when adding an
object to the cache.



     void CacheStats(Cache cid, unsigned long *num_entries,
	   unsigned long *max_storage, unsigned long *current_storage,
	   unsigned long *num_lookups, unsigned long *hit_ratio)



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.



     CacheID	 CacheStoreMemory(Cache cacheid, pointer data, unsigned long size,
		       CacheFree free_func)



The renderer hands the cache some chunk of contiguous mem-
ory, which the cache timestamps and stores.  When it needs
to remove them, it calls the free_func, which must take
responsibility for properly freeing the data.  size is pri-
marily 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.



     pointer CacheFetchMemory(CacheID cid, Bool update)



Returns the memory attached to the id.	If update is set,
the timestamp is updated.  (some accesses may wish to be
'silent', which allows some control over the freeing









			    -20-


scheduling.)  If the cid is invalid, NULL is returned.



     int   CacheFreeMemory(CacheID cid, Bool notify)



Allows the cache to flush the data.  If notify is set, the
CacheFree function passed in when the data was cached will
also be called.



     void  MemoryFreed(CacheID cid, pointer data, int reason)



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.  reason may be one of:



     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 */



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 bypass-
ing the cache, or re-inserting it.)  Note that the cache
will consider the data gone, so it must be re-inserted to
keep it alive.



     void  CacheSimpleFree(CacheID cid, pointer data, int reason)



Just calls free() on the data.	Simple CacheFree defined
here to prevent it being redefined in each renderer.

     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.











			    -21-


     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.

     Cache statistics may want to be available for adminis-
trators.  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.

     Cached data could also be compressed, if the memory/CPU
tradeoffs make it worthwhile.

     ISSUE:  Is a time-based freeing schedule sufficient?
Should priorities or size also be taken into account?  [ No.
Anything that the renderer thinks should have a higher pri-
ority should probably not be placed into the cache. ]



Byte swapping

Functions for swapping a 4-byte quantity, a 2-byte quantity
and inverting a byte.



     void  BitOrderInvert(pointer buffer, unsigned long num_bytes)
     void  TwoByteSwap(pointer buffer, unsigned long num_shorts)
     void  FourByteSwap(pointer buffer, unsigned long num_longs)



Bitmap padding

Functions taking a desired extents and a bitmap that will
return the bitmap properly padded.


int   RepadBitmap(pointer src, pointer dst, fsFormat src_format,
	     fsFormat dst_format, int width, int height)



Takes a bitmap in src_format and converts it to one in
dst_format.

Atoms

     Existing bitmap-based renderers use atoms to store
strings for property information.  Rather than duplicate









			    -22-


this code in each renderer, it lives in the util directory.

     Atoms will be especially useful for property informa-
tion, 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 atoms will will
exist until the server is reset, they may want to be used
sparingly for property values to avoid extraneous string
data.



     typedef unsigned long   Atom;

     Atom  MakeAtom(char *string, unsigned int length, Bool create)



Returns the atom associated with string.  If create is true,
a new atom will be created.



     char  *NameForAtom(Atom atom)



Returns the string associated with atom.


17.  Server request details

     This section describes in-depth the action of each pro-
tocol 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.

17.1.  Connection

     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 CheckClientAuthorization().  If
it passes this test, and the server has sufficient to
resources to talk to it, the server sends accepts the con-
nection 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 ListAl-
ternateServers().)

17.2.  ListExtension

     Returns the list of extensions the server knows about.
Any extensions will be initialized when the server is first









			    -23-


started.

17.3.  QueryExtension

     Returns the information about the requested extension,
which was set when the extension was initialized.

17.4.  ListCatalogues

     Returns the catalogues the server recognizes (the
results of ListCatalogues().)

17.5.  SetCatalogues

     Sets the requesting client's catalogues after verifying
them with the supported catalogues.

17.6.  GetCatalogues

     Returns the requesting client's catalogues.

17.7.  CreateAC

     Creates a new authorization context and fills it in.
The list of authorization protocols is then checked by the
server with CheckClientAuthorization().  If any are
accepted, the AC is placed in the resource database and Suc-
cess is returned with the name of the accepted protocol.  If
more than one is accepted, Continue is returned with each of
the accepted protocols, until the last one which has status
Success Otherwise Denied is returned.

17.8.  FreeAC

     Looks up the AC in the resource database, and frees it
if it finds it.  Otherwise an Access error is returned.

17.9.  SetAuthorization

     Looks up the AC in the resource database, and set the
client's AuthContextPtr to its value if it is found.  Other-
wise it sends an Access error.

17.10.	SetResolution

     Sets the requesting client's resolution list to the
supplied list.

17.11.	GetResolution

     Returns the requesting client's list of resolutions.












			    -24-


17.12.	ListFonts

     Iterates over each open FPE, calling the FPE's
list_fonts() 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 FontNamesPtr 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 cata-
logue.

17.13.	ListFontsWithXInfo

     Iterates over each FPE, calling its
start_list_fonts_with_info() function to prime the FPE's
renderer.  It then calls the FPE's
list_next_font_with_info(), 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.

17.14.	OpenBitmapFont

     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 open_font function with the supplied
pattern.  This will return one of the following values:

o  an Access error, which means the renderer has the font
   but the client does not have access to it because of some
   form of licensing restriction

o  a Font error and a NULL alias parameter, which will cause
   the next FPE to be tried

o  a Font error but a non-NULL alias, which will cause the
   search to start over with the first FPE using alias as
   the new font pattern

o  Success, in which case a valid font has been found.

     If the end of the FPE list is reached without having
found the font, an error is returned to the client.  If an
Access error was encountered, it is returned, otherwise a
Font error is returned.  If a valid font is found, its ref-
erence 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.











			    -25-


     The renderer will fill in the font's header and prop-
erty 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 format hint.

     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 modi-
fied.  Client's with private font catalogues will require
private name caches.

17.15.	QueryXInfo

     The fontid is looked up in the resource database, and
the font's header and property info is returned.

17.16.	QueryXExtents8 QueryXExtents16

     The fontid 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 get_extents() 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.

17.17.	QueryXBitmaps8 QueryXBitmaps16

     The fontid 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 get_bitmaps() function is called, and the renderer
will build up the requested bitmaps, using the specified
format, and returns the bitmaps, the number of glyphs and
the offsets.  The offsets are properly swapped and the off-
sets and bitmaps are sent to the clients.

17.18.	CloseFont

     The font's reference count is decremented.  If this was
the last reference, the font's unload_font() function is
called to free the renderer's data, and the font's FPE
close_font() function is called to free up any FPE specific
data.


18.  Configuration

     The configuration mechanism is a simple keyword-value
pair, separated by an '='.

Configuration types:










			    -26-


      cardinal	     non-negative number

      boolean	     "[Yy]es", "[Yy]" "on", "1", "[Nn]o", "[Nn]", "off", "0"

      resolution     cardinal,cardinal

      list of foo    1 or more of foo, separated by commas


Here is an incomplete list of the supported keywords:

#	       in the first column, a comment character

catalogue (list of string)
	       Ordered list of font path element names.

alternate-servers (list of string)
	       List of alternate servers for this FS.

client-limit (cardinal)
	       Number of clients this FS will support before refusing
	       service.

clone-self (boolean)
	       Whether this FS should attempt to clone itself or
	       use delegates when it reachs the client-limit.

default-point-size (cardinal)
	       The default pointsize (in decipoints) for fonts that
	       don't specify.

default-resolutions (list of resolutions)
	       Resolutions the server supports by default.
	       This information may be used as a hint for pre-rendering.

error-file (string)
	       Filename of the error file.  All warnings and errors
	       will be logged here.

port (cardinal)
	       The TCP port on which the server will listen for connections.

use-syslog (boolean)
	       Whether syslog(3) is to be used for errors.

     Each renderer may also want private configuration
     options.  The names should be prefixed by the renderer
     name, ie pcf-, atm-.

Examples:

# allow a ~a megabyte of memory to be reserved for cache
data
cache-size = 1000000









			    -27-


catalogue =
pcf:/usr/lib/X11/fonts/misc,speedo:/usr/lib/fonts/speedo


























































