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-.\" Copyright 1993 Network Computing Devices
-.\"
-.\" Permission to use, copy, modify, distribute, and sell this software and
-.\" its documentation for any purpose is hereby granted without fee, provided
-.\" that the above copyright notice appear in all copies and that both that
-.\" copyright notice and this permission notice appear in supporting
-.\" documentation, and that the name of Network Computing Devices
-.\" not be used in advertising or
-.\" publicity pertaining to distribution of the software without specific,
-.\" written prior permission. Network Computing Devices makes
-.\" no representations about the
-.\" suitability of this software for any purpose. It is provided "as is"
-.\" without express or implied warranty.
-.\"
-.\" Copyright 1993, 1994 X Consortium
-.\"
-.\" Permission is hereby granted, free of charge, to any person obtaining
-.\" a copy of this software and associated documentation files (the
-.\" ``Software''), to deal in the Software without restriction, including
-.\" without limitation the rights to use, copy, modify, merge, publish,
-.\" distribute, sublicense, and/or sell copies of the Software, and to
-.\" permit persons to whom the Software is furnished to do so, subject to
-.\" the following conditions:
-.\"
-.\" The above copyright notice and this permission notice shall be
-.\" included in all copies or substantial portions of the Software.
-.\"
-.\" THE SOFTWARE IS PROVIDED ``AS IS'', WITHOUT WARRANTY OF ANY KIND,
-.\" EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
-.\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
-.\" IN NO EVENT SHALL THE X CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR
-.\" OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
-.\" ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
-.\" OTHER DEALINGS IN THE SOFTWARE.
-.\"
-.\" Except as contained in this notice, the name of the X Consortium shall
-.\" not be used in advertising or otherwise to promote the sale, use or
-.\" other dealings in this Software without prior written authorization
-.\" from the X Consortium.
-.ps 12
-.nr PS 12
-.de Cs
-.IP
-.nf
-.ft C
-..
-.de Ce
-.ft P
-.fi
-..
-.\" $Xorg: fontlib.ms,v 1.3 2000/08/17 19:42:42 cpqbld Exp $
-.EF 'Font Library Interface'- % -'July 27, 1991'
-.OF 'Font Library Interface'- % -'July 27, 1991'
-.EH ''''
-.OH ''''
-.TL
-The X Font Library
-.AU
-Keith Packard
-.AI
-MIT X Consortium
-.AU
-David Lemke
-.AI
-Network Computing Devices
-.LP
-This document describes the data structures and interfaces for using the X
-Font library. It is intended as a reference for programmers building X
-and Font servers. You may want to refer to the following documents:
-.IP \(bu 5
-"Definition of the Porting Layer for the X v11 Sample Server" for a
-discussion on how this library interacts with the X server
-.IP \(bu 5
-"Font Server Implementation Overview" which discusses the design of the font
-server.
-.IP \(bu 5
-"Bitmap Distribution Format" which covers the contents of the bitmap font
-files which this library reads; although the library is capable of reading
-other formats as well, including non-bitmap fonts.
-.IP \(bu 5
-"The X Font Service Protocol" for a description of the constraints placed on
-the design by including support for this font service mechanism.
-.LP
-This document assumes the reader is familiar with the X server design, the
-X protocol as it relates to fonts and the C programming language. As with
-most MIT produced documentation, this relies heavily on the source code, so
-have a listing handy.
-.NH 1
-Requirements for the Font library
-.LP
-To avoid miles of duplicate code in the X server, the font server and the
-various font manipulation tools, the font library should provide interfaces
-appropriate for all of these tasks. In particular, the X server and font
-server should be able to both use the library to access disk based fonts,
-and to communicate with a font server. By providing a general library, we
-hoped to avoid duplicating code between the X server and font server.
-.LP
-Another requirement is that the X server (or even a font server) be able to
-continue servicing requests from other clients while awaiting a response
-from the font server on behalf of one client. This is the strongest
-requirement placed on the font library, and has warped the design in curious
-ways. Because both the X server and font server are single threaded, the
-font library must not suspend internally, rather it returns an indication of
-suspension to the application which continues processing other things, until
-the font data is ready, at which time it restarts the suspended request.
-.LP
-Because the code for reading and manipulating bitmap font data is used by
-the font applications "mkfontdir" and "bdftopcf", the font library includes
-bitmap-font specific interfaces which those applications use, instead of the
-more general interfaces used by the X and font servers, which are unaware of
-the source of the font data. These routines will be refered to as the
-bitmap font access methods.
-.NH 1
-General Font Library Interface details.
-.LP
-To avoid collision between the #define name space for errors, the Font
-library defines a new set of return values:
-.Cs
-#define AllocError 80
-#define StillWorking 81
-#define FontNameAlias 82
-#define BadFontName 83
-#define Suspended 84
-#define Successful 85
-#define BadFontPath 86
-#define BadCharRange 87
-#define BadFontFormat 88
-#define FPEResetFailed 89
-.Ce
-.LP
-Whenever a routine returns \fBSuspended\fP, the font library will notify the
-caller (via the ClientSignal interface described below) who should then
-reinvoke the same routine again with the same arguments.
-.NH 1
-Font Path Elements
-.LP
-At the center of the general font access methods used by X and fs is the
-Font Path Element data structure. Like most structures in the X server,
-this contains a collection of data and some function pointers for
-manipulating this data:
-.Cs
-/* External view of font paths */
-typedef struct _FontPathElement {
- int name_length;
- char *name;
- int type;
- int refcount;
- pointer private;
-} FontPathElementRec, *FontPathElementPtr;
-
-typedef struct _FPEFunctions {
- int (*name_check) ( /* name */ );
- int (*init_fpe) ( /* fpe */ );
- int (*reset_fpe) ( /* fpe */ );
- int (*free_fpe) ( /* fpe */ );
- int (*open_font) ( /* client, fpe, flags,
- name, namelen, format,
- fid, ppfont, alias */ );
- int (*close_font) ( /* pfont */ );
- int (*list_fonts) ( /* client, fpe, pattern,
- patlen, maxnames, paths */ );
- int (*start_list_fonts_with_info) (
- /* client, fpe, name, namelen,
- maxnames, data */ );
- int (*list_next_font_with_info) (
- /* client, fpe, name, namelen,
- info, num, data */ );
- int (*wakeup_fpe) ( /* fpe, mask */ );
- int (*client_died) ( /* client, fpe */ );
-} FPEFunctionsRec, FPEFunctions;
-.Ce
-.LP
-The function pointers are split out from the data structure to save memory;
-additionally, this avoids any complications when initializing the data
-structure as there would not be any way to discover the appropriate function
-to call (a chicken and egg problem).
-.LP
-When a font path type is initialized, it passes the function pointers to the
-server which are then stored in an FPEFunctionsRec. Each function is
-described below in turn.
-.NH 2
-(*name_check)
-.LP
-Each new font path member is passed to this function; if the return value
-is Successful, then the FPE recognises the format of the string. This does
-not guarantee that the FPE will be able to successfully use this member.
-For example, the disk-based font directory file "fonts.dir" may be
-corrupted, this will not be detected until the font path is initialized.
-This routine never returns \fBSuspended\fP.
-.NH 2
-(*init_fpe)
-.LP
-Initialize a new font path element. This function prepares a new font path
-element for other requests: the disk font routine reads the "fonts.dir" and
-"fonts.alias" files into the internal format, while the font server routine
-connects to the requested font server and prepares for using it. This
-routine returns Successful if everything went OK, otherwise the return value
-indicates the source of the problem. This routine never returns \fBSuspended\fP.
-.NH 2
-(*reset_fpe)
-.LP
-When the X font path is reset, and some of the new members are also in the
-old font path, this function is called to reinitialize those FPEs. This
-routine returns Successful if everything went OK. It returns FPEResetFailed
-if (for some reason) the reset failed, and the caller should remove the old
-FPE and simply create a new one in its place. This is used by the
-disk-based fonts routine as resetting the internal directory structures
-would be more complicated than simply having destroying the old and creating
-a new.
-.NH 2
-(*free_fpe)
-.LP
-When the server is finished with an FPE, this function is called to dispose
-of any internal state. It should return Successful, unless something
-terrible happens.
-.NH 2
-(*open_font)
-.LP
-This routine requests that a font be opened. The client argument is used
-by the font library only in connection with suspending/restarting the
-request. The flags argument specifies some behaviour for the library and can
-be any of:
-.Cs
-/* OpenFont flags */
-#define FontLoadInfo 0x0001
-#define FontLoadProps 0x0002
-#define FontLoadMetrics 0x0004
-#define FontLoadBitmaps 0x0008
-#define FontLoadAll 0x000f
-#define FontOpenSync 0x0010
-.Ce
-.LP
-The various fields specify which portions of the font should be loaded at
-this time. When FontOpenSync is specified, this routine will not return
-until all of the requested portions are loaded. Otherwise, this routine may
-return \fBSuspended\fP. When the presented font name is actually an alias
-for some other font name, FontName Alias is returned, and the actual font
-name is stored in the location pointed to by the \fIalias\fP argument as a
-null-terminated string.
-.NH 2
-(*close_font)
-.LP
-When the server is finished with a font, this routine disposes of any
-internal state and frees the font data structure.
-.NH 2
-(*list_fonts)
-.LP
-The \fIpaths\fP argument is a data structure which will be filled with all
-of the font names from this directory which match the specified pattern. At
-most \fImaxnames\fP will be added. This routine may return \fBSuspended\fP.
-.NH 2
-(*start_list_fonts_with_info)
-.LP
-This routine sets any internal state for a verbose listing of all fonts
-matching the specified pattern. This routine may return \fBSuspended\fP.
-.NH 2
-(*list_next_font_with_info)
-.LP
-To avoid storing huge amounts of data, the interface for ListFontsWithInfo
-allows the server to get one reply at a time and forward that to the
-client. When the font name returned is actually an alias for some other
-font, \fBFontNameAlias\fP will be returned. The actual font name is return
-instead, and the font alias which matched the pattern is returned in the
-location pointed to by data as a null-terminated string. The caller can
-then get the information by recursively listing that font name with a
-maxnames of 1. When \fBSuccessful\fP is returned, the matching font name is
-returned, and a FontInfoPtr is stored in the location pointed to by
-\fIdata\fP. \fIData\fP must be initialized with a pointer to a FontInfoRec
-allocated by the caller. When the pointer pointed to by \fIdata\fP is not
-left pointing at that storage, the caller mustn't free the associated
-property data. This routine may return \fBSuspended\fP.
-.NH 2
-(*wakeup_fpe)
-.LP
-Whenever an FPE function has returned Suspended, this routine is called
-whenever the application wakes up from waiting for input (from select(2)).
-This mask argument should be the value returned from select(2).
-.NH 2
-(*client_died)
-.LP
-When an FPE function has returned \fBSuspended\fP and the associated client
-is being destroyed, this function allows the font library to dispose of any
-state associated with that client.
-.NH 1
-Fonts
-.LP
-The data structure which actually contains the font information has changed
-significantly since previous releases; it now attempts to hide the actual
-storage format for the data from the application, providing accessor
-functions to get at the data. This allows a range of internal details for
-different font sources. The structure is split into two pieces, so that
-ListFontsWithInfo can share information from the font when it has been
-loaded. The FontInfo structure, then, contains only information germane to
-LFWI.
-.Cs
-typedef struct _FontInfo {
- unsigned short firstCol; /* range of glyphs for this font */
- unsigned short lastCol;
- unsigned short firstRow;
- unsigned short lastRow;
- unsigned short defaultCh; /* default character index */
- unsigned int noOverlap:1; /* no combination of glyphs overlap */
- unsigned int terminalFont:1; /* Character cell font */
- unsigned int constantMetrics:1; /* all metrics are the same */
- unsigned int constantWidth:1; /* all character widths are the same*/
- unsigned int inkInside:1; /* all ink inside character cell */
- unsigned int inkMetrics:1; /* font has ink metrics */
- unsigned int allExist:1; /* no missing chars in range */
- unsigned int drawDirection:2; /* left-to-right/right-to-left*/
- unsigned int cachable:1; /* font needn't be opened each time*/
- unsigned int anamorphic:1; /* font is strangely scaled */
- short maxOverlap; /* maximum overlap amount */
- short pad; /* unused */
- xCharInfo maxbounds; /* glyph metrics maximums */
- xCharInfo minbounds; /* glyph metrics minimums */
- xCharInfo ink_maxbounds; /* ink metrics maximums */
- xCharInfo ink_minbounds; /* ink metrics minimums */
- short fontAscent; /* font ascent amount */
- short fontDescent; /* font descent amount */
- int nprops; /* number of font properties */
- FontPropPtr props; /* font properties */
- char *isStringProp; /* boolean array */
-} FontInfoRec, *FontInfoPtr;
-.Ce
-.LP
-The font structure, then, contains a font info record, the format of the
-bits in each bitmap and the functions which access the font records (which
-are stored in an opaque format hung off of fontPrivate).
-.Cs
-typedef struct _Font {
- int refcnt;
- FontInfoRec info;
- char bit; /* bit order: LSBFirst/MSBFirst */
- char byte; /* byte order: LSBFirst/MSBFirst */
- char glyph; /* glyph pad: 1, 2, 4 or 8 */
- char scan; /* glyph scan unit: 1, 2 or 4 */
- fsBitmapFormat format; /* FS-style format (packed) */
- int (*get_glyphs) ( /* font, count, chars, encoding, count, glyphs */ );
- int (*get_metrics) ( /* font, count, chars, encoding, count, glyphs */ );
- int (*get_bitmaps) (/* client, font, flags, format,
- flags, nranges, ranges, data_sizep,
- num_glyphsp, offsetsp, glyph_datap,
- free_datap */ );
- int (*get_extents) (/* client, font, flags, nranges,
- ranges, nextentsp, extentsp */);
- void (*unload_font) ( /* font */ );
- FontPathElementPtr fpe; /* FPE associated with this font */
- pointer svrPrivate; /* X/FS private data */
- pointer fontPrivate; /* private to font */
- pointer fpePrivate; /* private to FPE */
- int maxPrivate; /* devPrivates (see below) */
- pointer *devPrivates; /* ... */
-} FontRec, *FontPtr;
-.Ce
-.LP
-Yes, there are several different private pointers in the Font structure; they
-were added haphazardly until the devPrivate pointers were added. Future
-releases may remove some (or all) of the specific pointers, leaving only the
-devPrivates mechanism.
-.LP
-There are two similar interfaces implemented - get_glyphs/get_metrics and
-get_bitmaps/get_extents. Too little time caused the font-server specific
-interfaces to be placed in the font library (and portions duplicated in each
-renderer) instead of having them integrated into the font server itself.
-This may change. The X server uses only get_glyphs/get_metrics, and those
-will not change dramatically. Each of the routines is described below
-.NH 2
-(*get_glyphs)
-.LP
-This routine returns CharInfoPtrs for each of the requested characters in
-the font. If the character does not exist in the font, the default
-character will be returned, unless no default character exists in which case
-that character is skipped. Thus, the number of glyphs returned will not
-always be the same as the number of characters passed in.
-.NH 2
-(*get_metrics)
-.LP
-This is similar to (*get_glyphs) except that pointers to xCharInfo
-structures are returned, and, if the font has ink metrics, those are
-returned instead of the bitmap metrics.
-.NH 2
-(*get-bitmaps)
-.LP
-This packs the glyph image data in the requested format and returns it. The
-ranges/nranges argument specify the set of glyphs from the font to pack
-together.
-.NH 2
-(*get_extents)
-.LP
-This returns the metrics for the specified font from the specified ranges.
-.LP
-.NH 2
-(*unload_font)
-.LP
-This is called from the FPE routine (*close_font), and so should not ever be
-called from the application.
-.NH 2
-maxPrivate
-.LP
-When initializing a new font structure, maxPrivate should be set to -1
-so that the FontSetPrivate() macro works properly with an index of 0.
-Initializing maxPrivate to 0 can cause problems if the server tries to set
-something at index 0.