[Git][freetype/freetype][master] Add support for kerning from 'GPOS' tables.

[Werner Lemberg (@wl)]

Werner Lemberg pushed to branch master at FreeType / FreeType

Commits:

• 8f286c86
  by David Saltzman at 2024-01-27T10:55:04+01:00

  Add support for kerning from 'GPOS' tables.
  
  This commit adds support for kerning from 'GPOS' tables, while maintaining
  support for basic 'kern' tables.  `FT_HAS_KERNING` will be true for a font
  with either available and `FT_Get_Kerning` will still use the basic 'kern'
  table data if avilable, otherwise check the GPOS 'kern' feature.
  
  This feature is disabled by default; it can be enabled with the
  `TT_CONFIG_OPTION_GPOS_KERNING` flag.
  
  Only basic kerning (pair positioning with just an x advance) is supported
  from the GPOS layout features; support for that was added to make the
  existing `FT_Get_Kerning` API more consistently functional.  FreeType does
  not intend to extend itself to further GPOS functionality though; a
  higher-level library like HarfBuzz can be used instead for that.
  
  * include/freetype/config/ftoption.h, include/devel/ftoption.h
  (TT_CONFIG_OPTION_GPOS_KERNING): New configuration option.
  
  * include/freetype/internal/fttrace.h: Add `ttgpos` trace handler.
  
  * include/freetype/internal/sfnt.h (SFNT_Interface): Add `load_gpos` and
  `get_gpos_kerning` fields.
  (FT_DEFINE_SFNT_INTERFACE): Updated.
  
  * include/freetype/internal/tttypes.h: Include `fttypes.h`.
  (TT_FaceRec) [TT_CONFIG_OPTION_GPOS_KERNING]: Add `gpos_table` and
  `gpos_kerning_available` fields.
  
  * src/sfnt/ttgpos.c, src/sfnt/ttgpos.h: New files.
  
  * src/sfnt/sfdriver.c [TT_CONFIG_OPTION_GPOS_KERNING]: Include `ttgpos.h`.
  (sfnt_interface): Updated.
  
  * src/sfnt/sfnt.c: Include `ttgpos.c`.
  
  * src/sfnt/sfobjs.c [TT_CONFIG_OPTION_GPOS_KERNING]: Include `ttgpos.h`.
  (sfnt_load_face) [TT_CONFIG_OPTION_GPOS_KERNING]: Load and free GPOS kerning
  data; check GPOS kerning availability.
  
  * src/truetype/ttdriver.c (tt_get_kerning): Use GPOS kerning if there's no
  'kern' table.
  

13 changed files:

• devel/ftoption.h
• docs/CHANGES
• include/freetype/config/ftoption.h
• include/freetype/freetype.h
• include/freetype/internal/fttrace.h
• include/freetype/internal/sfnt.h
• include/freetype/internal/tttypes.h
• src/sfnt/sfdriver.c
• src/sfnt/sfnt.c
• src/sfnt/sfobjs.c
• + src/sfnt/ttgpos.c
• + src/sfnt/ttgpos.h
• src/truetype/ttdriver.c

Changes:

devel/ftoption.h

---

...	...	@@ -757,6 +757,22 @@ FT_BEGIN_HEADER
757	757	#endif
758	758
759	759
	760	+ /**************************************************************************
	761	+ *
	762	+ * Option `TT_CONFIG_OPTION_GPOS_KERNING` enables a basic GPOS kerning
	763	+ * implementation (for TrueType fonts only). With this defined, FreeType
	764	+ * is able to get kerning pair data from the GPOS 'kern' feature as well as
	765	+ * legacy 'kern' tables; without this defined, FreeType will only be able
	766	+ * to use legacy 'kern' tables.
	767	+ *
	768	+ * Note that FreeType does not support more advanced GPOS layout features;
	769	+ * even the 'kern' feature implemented here doesn't handle more
	770	+ * sophisticated kerning variants. Use a higher-level library like
	771	+ * HarfBuzz instead for that.
	772	+ */
	773	+#define TT_CONFIG_OPTION_GPOS_KERNING
	774	+
	775	+
760	776	/*************************************************************************/
761	777	/*************************************************************************/
762	778	/**** ****/

docs/CHANGES

---

...	...	@@ -11,6 +11,16 @@ CHANGES BETWEEN 2.13.2 and 2.13.3 (202Y-Mmm-DD)
11	11	large performance improvement. The rendering speed has increased
12	12	and even doubled for very complex glyphs.
13	13
	14	+ - If the new configuration option `TT_CONFIG_OPTION_GPOS_KERNING` is
	15	+ defined, `FT_Get_Kerning` understands rudimentary GPOS kerning
	16	+ (for TrueType fonts only). This is not enabled by default since
	17	+ its usage is very limited, mainly for legacy applications that
	18	+ have to support TrueType fonts automatically converted from 'kern'
	19	+ tables to GPOS kerning. If you need proper (GPOS) kerning support
	20	+ please use a higher-level library like HarfBuzz.
	21	+
	22	+ Code contributed by David Saltzman <davidbsaltzman@gmail.com>.
	23	+
14	24
15	25	======================================================================
16	26

include/freetype/config/ftoption.h

---

...	...	@@ -757,6 +757,22 @@ FT_BEGIN_HEADER
757	757	#endif
758	758
759	759
	760	+ /**************************************************************************
	761	+ *
	762	+ * Option `TT_CONFIG_OPTION_GPOS_KERNING` enables a basic GPOS kerning
	763	+ * implementation (for TrueType fonts only). With this defined, FreeType
	764	+ * is able to get kerning pair data from the GPOS 'kern' feature as well as
	765	+ * legacy 'kern' tables; without this defined, FreeType will only be able
	766	+ * to use legacy 'kern' tables.
	767	+ *
	768	+ * Note that FreeType does not support more advanced GPOS layout features;
	769	+ * even the 'kern' feature implemented here doesn't handle more
	770	+ * sophisticated kerning variants. Use a higher-level library like
	771	+ * HarfBuzz instead for that.
	772	+ */
	773	+/* #define TT_CONFIG_OPTION_GPOS_KERNING */
	774	+
	775	+
760	776	/*************************************************************************/
761	777	/*************************************************************************/
762	778	/**** ****/

include/freetype/freetype.h

---

...	...	@@ -1322,9 +1322,13 @@ FT_BEGIN_HEADER
1322	1322	* FT_FACE_FLAG_KERNING ::
1323	1323	* The face contains kerning information. If set, the kerning distance
1324	1324	* can be retrieved using the function @FT_Get_Kerning. Otherwise the
1325		- * function always returns the vector (0,0). Note that FreeType
1326		- * doesn't handle kerning data from the SFNT 'GPOS' table (as present
1327		- * in many OpenType fonts).
	1325	+ * function always returns the vector (0,0).
	1326	+ *
	1327	+ * Note that for TrueType fonts only, FreeType supports both the 'kern'
	1328	+ * table and the basic, pair-wise kerning feature from the 'GPOS' table
	1329	+ * (with `TT_CONFIG_OPTION_GPOS_KERNING` enabled), though FreeType does
	1330	+ * not support the more advanced GPOS layout features; use a library
	1331	+ * like HarfBuzz for those instead.
1328	1332	*
1329	1333	* FT_FACE_FLAG_FAST_GLYPHS ::
1330	1334	* THIS FLAG IS DEPRECATED. DO NOT USE OR TEST IT.
...	...	@@ -4058,9 +4062,26 @@ FT_BEGIN_HEADER
4058	4062	* out of the scope of this API function -- they can be implemented
4059	4063	* through format-specific interfaces.
4060	4064	*
4061		- * Kerning for OpenType fonts implemented in a 'GPOS' table is not
4062		- * supported; use @FT_HAS_KERNING to find out whether a font has data
4063		- * that can be extracted with `FT_Get_Kerning`.
	4065	+ * Note that, for TrueType fonts only, this can extract data from both
	4066	+ * the 'kern' table and the basic, pair-wise kerning feature from the
	4067	+ * GPOS table (with `TT_CONFIG_OPTION_GPOS_KERNING` enabled), though
	4068	+ * FreeType does not support the more advanced GPOS layout features; use
	4069	+ * a library like HarfBuzz for those instead. If a font has both a
	4070	+ * 'kern' table and kern features of a GPOS table, the 'kern' table will
	4071	+ * be used.
	4072	+ *
	4073	+ * Also note for right-to-left scripts, the functionality may differ for
	4074	+ * fonts with GPOS tables vs. 'kern' tables. For GPOS, right-to-left
	4075	+ * fonts typically use both a placement offset and an advance for pair
	4076	+ * positioning, which this API does not support, so it would output
	4077	+ * kerning values of zero; though if the right-to-left font used only
	4078	+ * advances in GPOS pair positioning, then this API could output kerning
	4079	+ * values for it, but it would use `left_glyph` to mean the first glyph
	4080	+ * for that case. Whereas 'kern' tables are always advance-only and
	4081	+ * always store the left glyph first.
	4082	+ *
	4083	+ * Use @FT_HAS_KERNING to find out whether a font has data that can be
	4084	+ * extracted with `FT_Get_Kerning`.
4064	4085	*/
4065	4086	FT_EXPORT( FT_Error )
4066	4087	FT_Get_Kerning( FT_Face face,

include/freetype/internal/fttrace.h

---

...	...	@@ -64,6 +64,7 @@ FT_TRACE_DEF( ttbdf ) /* TrueType embedded BDF (ttbdf.c) */
64	64	FT_TRACE_DEF( ttcmap ) /* charmap handler (ttcmap.c) */
65	65	FT_TRACE_DEF( ttcolr ) /* glyph layer table (ttcolr.c) */
66	66	FT_TRACE_DEF( ttcpal ) /* color palette table (ttcpal.c) */
	67	+FT_TRACE_DEF( ttgpos ) /* GPOS handler (ttgpos.c) */
67	68	FT_TRACE_DEF( ttsvg ) /* OpenType SVG table (ttsvg.c) */
68	69	FT_TRACE_DEF( ttkern ) /* kerning handler (ttkern.c) */
69	70	FT_TRACE_DEF( ttload ) /* basic TrueType tables (ttload.c) */

include/freetype/internal/sfnt.h

---

...	...	@@ -924,6 +924,7 @@ FT_BEGIN_HEADER
924	924	/* this field was called `load_kerning' up to version 2.1.10 */
925	925	TT_Load_Table_Func load_kern;
926	926
	927	+ TT_Load_Table_Func load_gpos;
927	928	TT_Load_Table_Func load_gasp;
928	929	TT_Load_Table_Func load_pclt;
929	930
...	...	@@ -944,6 +945,8 @@ FT_BEGIN_HEADER
944	945
945	946	/* new elements introduced after version 2.1.10 */
946	947
	948	+ TT_Face_GetKerningFunc get_gpos_kerning;
	949	+
947	950	/* load the font directory, i.e., the offset table and */
948	951	/* the table directory */
949	952	TT_Load_Table_Func load_font_dir;
...	...	@@ -1002,6 +1005,7 @@ FT_BEGIN_HEADER
1002	1005	load_name_, \
1003	1006	free_name_, \
1004	1007	load_kern_, \
	1008	+ load_gpos_, \
1005	1009	load_gasp_, \
1006	1010	load_pclt_, \
1007	1011	load_bhed_, \
...	...	@@ -1009,6 +1013,7 @@ FT_BEGIN_HEADER
1009	1013	get_psname_, \
1010	1014	free_psnames_, \
1011	1015	get_kerning_, \
	1016	+ get_gpos_kerning_, \
1012	1017	load_font_dir_, \
1013	1018	load_hmtx_, \
1014	1019	load_eblc_, \
...	...	@@ -1050,6 +1055,7 @@ FT_BEGIN_HEADER
1050	1055	load_name_, \
1051	1056	free_name_, \
1052	1057	load_kern_, \
	1058	+ load_gpos_, \
1053	1059	load_gasp_, \
1054	1060	load_pclt_, \
1055	1061	load_bhed_, \
...	...	@@ -1057,6 +1063,7 @@ FT_BEGIN_HEADER
1057	1063	get_psname_, \
1058	1064	free_psnames_, \
1059	1065	get_kerning_, \
	1066	+ get_gpos_kerning_, \
1060	1067	load_font_dir_, \
1061	1068	load_hmtx_, \
1062	1069	load_eblc_, \

include/freetype/internal/tttypes.h

---

...	...	@@ -24,6 +24,7 @@
24	24	#include <freetype/tttables.h>
25	25	#include <freetype/internal/ftobjs.h>
26	26	#include <freetype/ftcolor.h>
	27	+#include "freetype/fttypes.h"
27	28
28	29	#ifdef TT_CONFIG_OPTION_GX_VAR_SUPPORT
29	30	#include <freetype/ftmm.h>
...	...	@@ -1581,6 +1582,11 @@ FT_BEGIN_HEADER
1581	1582	FT_UInt32 kern_avail_bits;
1582	1583	FT_UInt32 kern_order_bits;
1583	1584
	1585	+#ifdef TT_CONFIG_OPTION_GPOS_KERNING
	1586	+ FT_Byte* gpos_table;
	1587	+ FT_Bool gpos_kerning_available;
	1588	+#endif
	1589	+
1584	1590	#ifdef TT_CONFIG_OPTION_BDF
1585	1591	TT_BDFRec bdf;
1586	1592	#endif /* TT_CONFIG_OPTION_BDF */

src/sfnt/sfdriver.c

---

...	...	@@ -49,6 +49,10 @@
49	49	#include <freetype/internal/services/svbdf.h>
50	50	#endif
51	51
	52	+#ifdef TT_CONFIG_OPTION_GPOS_KERNING
	53	+#include "ttgpos.h"
	54	+#endif
	55	+
52	56	#include "ttcmap.h"
53	57	#include "ttkern.h"
54	58	#include "ttmtx.h"
...	...	@@ -1249,6 +1253,12 @@
1249	1253	#define PUT_PS_NAMES( a ) a
1250	1254	#else
1251	1255	#define PUT_PS_NAMES( a ) NULL
	1256	+#endif
	1257	+
	1258	+#ifdef TT_CONFIG_OPTION_GPOS_KERNING
	1259	+#define PUT_GPOS_KERNING( a ) a
	1260	+#else
	1261	+#define PUT_GPOS_KERNING( a ) NULL
1252	1262	#endif
1253	1263
1254	1264	FT_DEFINE_SFNT_INTERFACE(
...	...	@@ -1274,6 +1284,8 @@
1274	1284	tt_face_free_name, /* TT_Free_Table_Func free_name */
1275	1285
1276	1286	tt_face_load_kern, /* TT_Load_Table_Func load_kern */
	1287	+ PUT_GPOS_KERNING( tt_face_load_gpos ),
	1288	+ /* TT_Load_Table_Func load_gpos */
1277	1289	tt_face_load_gasp, /* TT_Load_Table_Func load_gasp */
1278	1290	tt_face_load_pclt, /* TT_Load_Table_Func load_init */
1279	1291
...	...	@@ -1292,6 +1304,9 @@
1292	1304	/* since version 2.1.8 */
1293	1305	tt_face_get_kerning, /* TT_Face_GetKerningFunc get_kerning */
1294	1306
	1307	+ PUT_GPOS_KERNING( tt_face_get_gpos_kerning ),
	1308	+ /* TT_Face_GetKerningFunc get_gpos_kerning */
	1309	+
1295	1310	/* since version 2.2 */
1296	1311	tt_face_load_font_dir, /* TT_Load_Table_Func load_font_dir */
1297	1312	tt_face_load_hmtx, /* TT_Load_Metrics_Func load_hmtx */

src/sfnt/sfnt.c

---

...	...	@@ -29,6 +29,7 @@
29	29	#include "ttcpal.c"
30	30	#include "ttsvg.c"
31	31
	32	+#include "ttgpos.c"
32	33	#include "ttkern.c"
33	34	#include "ttload.c"
34	35	#include "ttmtx.c"

src/sfnt/sfobjs.c

---

...	...	@@ -40,6 +40,10 @@
40	40	#include "ttbdf.h"
41	41	#endif
42	42
	43	+#ifdef TT_CONFIG_OPTION_GPOS_KERNING
	44	+#include "ttgpos.h"
	45	+#endif
	46	+
43	47
44	48	/**************************************************************************
45	49	*
...	...	@@ -1026,6 +1030,10 @@
1026	1030	LOAD_( gasp );
1027	1031	LOAD_( kern );
1028	1032
	1033	+#ifdef TT_CONFIG_OPTION_GPOS_KERNING
	1034	+ LOAD_( gpos );
	1035	+#endif
	1036	+
1029	1037	face->root.num_glyphs = face->max_profile.numGlyphs;
1030	1038
1031	1039	/* Bit 8 of the `fsSelection' field in the `OS/2' table denotes */
...	...	@@ -1119,7 +1127,11 @@
1119	1127	flags |= FT_FACE_FLAG_VERTICAL;
1120	1128
1121	1129	/* kerning available ? */
1122		- if ( TT_FACE_HAS_KERNING( face ) )
	1130	+ if ( TT_FACE_HAS_KERNING( face )
	1131	+#ifdef TT_CONFIG_OPTION_GPOS_KERNING
	1132	+ || face->gpos_kerning_available
	1133	+#endif
	1134	+ )
1123	1135	flags |= FT_FACE_FLAG_KERNING;
1124	1136
1125	1137	#ifdef TT_CONFIG_OPTION_GX_VAR_SUPPORT
...	...	@@ -1470,6 +1482,11 @@
1470	1482	/* freeing the kerning table */
1471	1483	tt_face_done_kern( face );
1472	1484
	1485	+#ifdef TT_CONFIG_OPTION_GPOS_KERNING
	1486	+ /* freeing the GPOS table */
	1487	+ tt_face_done_gpos( face );
	1488	+#endif
	1489	+
1473	1490	/* freeing the collection table */
1474	1491	FT_FREE( face->ttc_header.offsets );
1475	1492	face->ttc_header.count = 0;

src/sfnt/ttgpos.c

---

	1	+/****************************************************************************
	2	+ *
	3	+ * ttgpos.c
	4	+ *
	5	+ * Load the TrueType GPOS table. The only GPOS layout feature this
	6	+ * currently supports is kerning, from x advances in the pair adjustment
	7	+ * layout feature.
	8	+ *
	9	+ * Parts of the implementation were adapted from:
	10	+ * https://github.com/nothings/stb/blob/master/stb_truetype.h
	11	+ *
	12	+ * GPOS spec reference available at:
	13	+ * https://learn.microsoft.com/en-us/typography/opentype/spec/gpos
	14	+ *
	15	+ * Copyright (C) 2024 by
	16	+ * David Saltzman
	17	+ *
	18	+ * This file is part of the FreeType project, and may only be used,
	19	+ * modified, and distributed under the terms of the FreeType project
	20	+ * license, LICENSE.TXT. By continuing to use, modify, or distribute
	21	+ * this file you indicate that you have read the license and
	22	+ * understand and accept it fully.
	23	+ */
	24	+
	25	+#include <freetype/internal/ftdebug.h>
	26	+#include <freetype/internal/ftstream.h>
	27	+#include <freetype/tttags.h>
	28	+#include "freetype/fttypes.h"
	29	+#include "freetype/internal/ftobjs.h"
	30	+#include "ttgpos.h"
	31	+
	32	+
	33	+#ifdef TT_CONFIG_OPTION_GPOS_KERNING
	34	+
	35	+ /**************************************************************************
	36	+ *
	37	+ * The macro FT_COMPONENT is used in trace mode. It is an implicit
	38	+ * parameter of the FT_TRACE() and FT_ERROR() macros, used to print/log
	39	+ * messages during execution.
	40	+ */
	41	+#undef FT_COMPONENT
	42	+#define FT_COMPONENT ttgpos
	43	+
	44	+
	45	+ typedef enum coverage_table_format_type_
	46	+ {
	47	+ COVERAGE_TABLE_FORMAT_LIST = 1,
	48	+ COVERAGE_TABLE_FORMAT_RANGE = 2
	49	+
	50	+ } coverage_table_format_type;
	51	+
	52	+ typedef enum class_def_table_format_type_
	53	+ {
	54	+ CLASS_DEF_TABLE_FORMAT_ARRAY = 1,
	55	+ CLASS_DEF_TABLE_FORMAT_RANGE_GROUPS = 2
	56	+
	57	+ } class_def_table_format_type;
	58	+
	59	+ typedef enum gpos_lookup_type_
	60	+ {
	61	+ GPOS_LOOKUP_TYPE_SINGLE_ADJUSTMENT = 1,
	62	+ GPOS_LOOKUP_TYPE_PAIR_ADJUSTMENT = 2,
	63	+ GPOS_LOOKUP_TYPE_CURSIVE_ATTACHMENT = 3,
	64	+ GPOS_LOOKUP_TYPE_MARK_TO_BASE_ATTACHMENT = 4,
	65	+ GPOS_LOOKUP_TYPE_MARK_TO_LIGATURE_ATTACHMENT = 5,
	66	+ GPOS_LOOKUP_TYPE_MARK_TO_MARK_ATTACHMENT = 6,
	67	+ GPOS_LOOKUP_TYPE_CONTEXT_POSITIONING = 7,
	68	+ GPOS_LOOKUP_TYPE_CHAINED_CONTEXT_POSITIONING = 8,
	69	+ GPOS_LOOKUP_TYPE_EXTENSION_POSITIONING = 9
	70	+
	71	+ } gpos_lookup_type;
	72	+
	73	+ typedef enum gpos_pair_adjustment_format_
	74	+ {
	75	+ GPOS_PAIR_ADJUSTMENT_FORMAT_GLYPH_PAIR = 1,
	76	+ GPOS_PAIR_ADJUSTMENT_FORMAT_CLASS_PAIR = 2
	77	+
	78	+ } gpos_pair_adjustment_format;
	79	+
	80	+ typedef enum gpos_value_format_bitmask_
	81	+ {
	82	+ GPOS_VALUE_FORMAT_NONE = 0x0000,
	83	+ GPOS_VALUE_FORMAT_X_PLACEMENT = 0x0001,
	84	+ GPOS_VALUE_FORMAT_Y_PLACEMENT = 0x0002,
	85	+ GPOS_VALUE_FORMAT_X_ADVANCE = 0x0004,
	86	+ GPOS_VALUE_FORMAT_Y_ADVANCE = 0x0008,
	87	+ GPOS_VALUE_FORMAT_X_PLACEMENT_DEVICE = 0x0010,
	88	+ GPOS_VALUE_FORMAT_Y_PLACEMENT_DEVICE = 0x0020,
	89	+ GPOS_VALUE_FORMAT_X_ADVANCE_DEVICE = 0x0040,
	90	+ GPOS_VALUE_FORMAT_Y_ADVANCE_DEVICE = 0x0080
	91	+
	92	+ } gpos_value_format_bitmask;
	93	+
	94	+
	95	+ typedef struct TT_GPOS_Subtable_Iterator_Context_
	96	+ {
	97	+ /* Iteration state. */
	98	+ FT_Byte* current_lookup_table;
	99	+ gpos_lookup_type current_lookup_type;
	100	+ FT_UShort subtable_count;
	101	+ FT_Byte* subtable_offsets;
	102	+ FT_UInt subtable_idx;
	103	+
	104	+ /* Element for the current iteration. */
	105	+ FT_Byte* subtable;
	106	+ gpos_lookup_type subtable_type;
	107	+
	108	+ } TT_GPOS_Subtable_Iterator_Context;
	109	+
	110	+
	111	+ /* Initialize a subtable iterator for a given lookup list index. */
	112	+ static void
	113	+ tt_gpos_subtable_iterator_init(
	114	+ TT_GPOS_Subtable_Iterator_Context* context,
	115	+ FT_Byte* gpos_table,
	116	+ FT_ULong lookup_list_idx )
	117	+ {
	118	+ FT_Byte* lookup_list = gpos_table + FT_PEEK_USHORT( gpos_table + 8 );
	119	+ FT_UInt16 lookup_count = FT_PEEK_USHORT( lookup_list );
	120	+
	121	+
	122	+ if ( lookup_list_idx < lookup_count )
	123	+ {
	124	+ context->current_lookup_table =
	125	+ lookup_list + FT_PEEK_USHORT( lookup_list + 2 + 2 * lookup_list_idx );
	126	+ context->current_lookup_type =
	127	+ (gpos_lookup_type)FT_PEEK_USHORT( context->current_lookup_table );
	128	+ context->subtable_count =
	129	+ FT_PEEK_USHORT( context->current_lookup_table + 4 );
	130	+ context->subtable_offsets = context->current_lookup_table + 6;
	131	+ }
	132	+ else
	133	+ {
	134	+ context->current_lookup_table = NULL;
	135	+ context->current_lookup_type = 0;
	136	+ context->subtable_count = 0;
	137	+ context->subtable_offsets = NULL;
	138	+ }
	139	+
	140	+ context->subtable_idx = 0;
	141	+ context->subtable = NULL;
	142	+ context->subtable_type = 0;
	143	+ }
	144	+
	145	+
	146	+ /* Get the next subtable. Return whether there was a next one. */
	147	+ static FT_Bool
	148	+ tt_gpos_subtable_iterator_next(
	149	+ TT_GPOS_Subtable_Iterator_Context* context )
	150	+ {
	151	+ if ( context->subtable_idx < context->subtable_count )
	152	+ {
	153	+ FT_UShort subtable_offset =
	154	+ FT_PEEK_USHORT( context->subtable_offsets +
	155	+ 2 * context->subtable_idx );
	156	+
	157	+
	158	+ context->subtable = context->current_lookup_table + subtable_offset;
	159	+
	160	+ if ( context->current_lookup_type ==
	161	+ GPOS_LOOKUP_TYPE_EXTENSION_POSITIONING )
	162	+ {
	163	+ /* Update type and subtable based on extension positioning header. */
	164	+ context->subtable_type =
	165	+ (gpos_lookup_type)FT_PEEK_USHORT( context->subtable + 2 );
	166	+ context->subtable += FT_PEEK_ULONG( context->subtable + 4 );
	167	+ }
	168	+ else
	169	+ context->subtable_type = context->current_lookup_type;
	170	+
	171	+ context->subtable_idx++;
	172	+ return TRUE;
	173	+ }
	174	+
	175	+ return FALSE;
	176	+ }
	177	+
	178	+
	179	+ static FT_Int
	180	+ tt_gpos_get_coverage_index( FT_Byte *coverage_table,
	181	+ FT_UInt glyph )
	182	+ {
	183	+ coverage_table_format_type coverage_format =
	184	+ (coverage_table_format_type)FT_PEEK_USHORT( coverage_table );
	185	+
	186	+
	187	+ switch ( coverage_format )
	188	+ {
	189	+ case COVERAGE_TABLE_FORMAT_LIST:
	190	+ {
	191	+ FT_UShort glyph_count = FT_PEEK_USHORT( coverage_table + 2 );
	192	+
	193	+ FT_Int l = 0;
	194	+ FT_Int r = glyph_count - 1;
	195	+ FT_Int m;
	196	+
	197	+ FT_Int straw;
	198	+ FT_Int needle = glyph;
	199	+
	200	+
	201	+ /* Binary search. */
	202	+ while ( l <= r )
	203	+ {
	204	+ FT_Byte *glyph_array = coverage_table + 4;
	205	+ FT_UShort glyph_id;
	206	+
	207	+
	208	+ m = ( l + r ) >> 1;
	209	+ glyph_id = FT_PEEK_USHORT( glyph_array + 2 * m );
	210	+ straw = glyph_id;
	211	+
	212	+ if ( needle < straw )
	213	+ r = m - 1;
	214	+ else if ( needle > straw )
	215	+ l = m + 1;
	216	+ else
	217	+ return m;
	218	+ }
	219	+ break;
	220	+ }
	221	+
	222	+ case COVERAGE_TABLE_FORMAT_RANGE:
	223	+ {
	224	+ FT_UShort range_count = FT_PEEK_USHORT( coverage_table + 2 );
	225	+ FT_Byte *range_array = coverage_table + 4;
	226	+
	227	+ FT_Int l = 0;
	228	+ FT_Int r = range_count - 1;
	229	+ FT_Int m;
	230	+
	231	+ FT_Int straw_start;
	232	+ FT_Int straw_end;
	233	+ FT_Int needle = glyph;
	234	+
	235	+
	236	+ /* Binary search. */
	237	+ while ( l <= r )
	238	+ {
	239	+ FT_Byte *range_record;
	240	+
	241	+
	242	+ m = ( l + r ) >> 1;
	243	+ range_record = range_array + 6 * m;
	244	+ straw_start = FT_PEEK_USHORT( range_record );
	245	+ straw_end = FT_PEEK_USHORT( range_record + 2 );
	246	+
	247	+ if ( needle < straw_start )
	248	+ r = m - 1;
	249	+ else if ( needle > straw_end )
	250	+ l = m + 1;
	251	+ else
	252	+ {
	253	+ FT_UShort start_coverage_index =
	254	+ FT_PEEK_USHORT( range_record + 4 );
	255	+
	256	+
	257	+ return start_coverage_index + glyph - straw_start;
	258	+ }
	259	+ }
	260	+ break;
	261	+ }
	262	+
	263	+ default:
	264	+ return -1; /* unsupported */
	265	+ }
	266	+
	267	+ return -1;
	268	+ }
	269	+
	270	+
	271	+ static FT_Int
	272	+ tt_gpos_get_glyph_class( FT_Byte *class_def_table,
	273	+ FT_UInt glyph )
	274	+ {
	275	+ class_def_table_format_type class_def_format =
	276	+ (class_def_table_format_type)FT_PEEK_USHORT( class_def_table );
	277	+
	278	+
	279	+ switch ( class_def_format )
	280	+ {
	281	+ case CLASS_DEF_TABLE_FORMAT_ARRAY:
	282	+ {
	283	+ FT_UShort start_glyph_id = FT_PEEK_USHORT( class_def_table + 2 );
	284	+ FT_UShort glyph_count = FT_PEEK_USHORT( class_def_table + 4 );
	285	+ FT_Byte *class_value_array = class_def_table + 6;
	286	+
	287	+
	288	+ if ( glyph >= start_glyph_id &&
	289	+ glyph < start_glyph_id + glyph_count )
	290	+ return (FT_Int)FT_PEEK_USHORT( class_value_array +
	291	+ 2 * ( glyph - start_glyph_id ) );
	292	+ break;
	293	+ }
	294	+
	295	+ case CLASS_DEF_TABLE_FORMAT_RANGE_GROUPS:
	296	+ {
	297	+ FT_UShort class_range_count = FT_PEEK_USHORT( class_def_table + 2 );
	298	+ FT_Byte *class_range_records = class_def_table + 4;
	299	+
	300	+ FT_Int l = 0;
	301	+ FT_Int r = class_range_count - 1;
	302	+ FT_Int m;
	303	+
	304	+ FT_Int straw_start;
	305	+ FT_Int straw_end;
	306	+ FT_Int needle = glyph;
	307	+
	308	+
	309	+ while ( l <= r )
	310	+ {
	311	+ FT_Byte *class_range_record;
	312	+
	313	+
	314	+ m = ( l + r ) >> 1;
	315	+ class_range_record = class_range_records + 6 * m;
	316	+ straw_start = FT_PEEK_USHORT( class_range_record );
	317	+ straw_end = FT_PEEK_USHORT( class_range_record + 2 );
	318	+
	319	+ if ( needle < straw_start )
	320	+ r = m - 1;
	321	+ else if ( needle > straw_end )
	322	+ l = m + 1;
	323	+ else
	324	+ return (FT_Int)FT_PEEK_USHORT( class_range_record + 4 );
	325	+ }
	326	+ break;
	327	+ }
	328	+
	329	+ default:
	330	+ return -1; /* Unsupported definition type, return an error. */
	331	+ }
	332	+
	333	+ /* "All glyphs not assigned to a class fall into class 0." */
	334	+ /* (OpenType spec) */
	335	+ return 0;
	336	+ }
	337	+
	338	+
	339	+ FT_LOCAL_DEF( FT_Error )
	340	+ tt_face_load_gpos( TT_Face face,
	341	+ FT_Stream stream )
	342	+ {
	343	+ FT_Error error;
	344	+ FT_ULong table_size;
	345	+
	346	+
	347	+ /* The GPOS table is optional; exit silently if it is missing. */
	348	+ error = face->goto_table( face, TTAG_GPOS, stream, &table_size );
	349	+ if ( error )
	350	+ goto Exit;
	351	+
	352	+ if ( table_size < 4 ) /* the case of a malformed table */
	353	+ {
	354	+ FT_ERROR(( "tt_face_load_gpos:"
	355	+ " GPOS table is too small - ignored\n" ));
	356	+ error = FT_THROW( Table_Missing );
	357	+ goto Exit;
	358	+ }
	359	+
	360	+ if ( FT_FRAME_EXTRACT( table_size, face->gpos_table ) )
	361	+ {
	362	+ FT_ERROR(( "tt_face_load_gpos:"
	363	+ " could not extract GPOS table\n" ));
	364	+ goto Exit;
	365	+ }
	366	+
	367	+ face->gpos_kerning_available = FALSE;
	368	+
	369	+ if ( face->gpos_table )
	370	+ {
	371	+ FT_Byte* feature_list = face->gpos_table +
	372	+ FT_PEEK_USHORT( face->gpos_table + 6 );
	373	+ FT_UInt16 feature_count = FT_PEEK_USHORT( feature_list );
	374	+ FT_Byte* feature_records = feature_list + 2;
	375	+
	376	+ FT_UInt idx;
	377	+
	378	+
	379	+ for ( idx = 0; idx < feature_count; idx++, feature_records += 6 )
	380	+ {
	381	+ FT_ULong feature_tag = FT_PEEK_ULONG( feature_records );
	382	+
	383	+
	384	+ if ( feature_tag == TTAG_kern )
	385	+ {
	386	+ face->gpos_kerning_available = TRUE;
	387	+ break;
	388	+ }
	389	+ }
	390	+ }
	391	+
	392	+ Exit:
	393	+ return error;
	394	+ }
	395	+
	396	+
	397	+ FT_LOCAL_DEF( void )
	398	+ tt_face_done_gpos( TT_Face face )
	399	+ {
	400	+ FT_Stream stream = face->root.stream;
	401	+
	402	+
	403	+ FT_FRAME_RELEASE( face->gpos_table );
	404	+ }
	405	+
	406	+
	407	+ FT_LOCAL_DEF( FT_Int )
	408	+ tt_face_get_gpos_kerning( TT_Face face,
	409	+ FT_UInt left_glyph,
	410	+ FT_UInt right_glyph )
	411	+ {
	412	+ FT_Byte* feature_list;
	413	+ FT_UInt16 feature_count;
	414	+ FT_Byte* feature_records;
	415	+ FT_UInt feature_idx;
	416	+
	417	+
	418	+ if ( !face->gpos_kerning_available )
	419	+ return 0;
	420	+
	421	+ feature_list = face->gpos_table +
	422	+ FT_PEEK_USHORT( face->gpos_table + 6 );
	423	+ feature_count = FT_PEEK_USHORT( feature_list );
	424	+ feature_records = feature_list + 2;
	425	+
	426	+ for ( feature_idx = 0;
	427	+ feature_idx < feature_count;
	428	+ feature_idx++, feature_records += 6 )
	429	+ {
	430	+ FT_ULong feature_tag = FT_PEEK_ULONG( feature_records );
	431	+ FT_Byte* feature_table;
	432	+ FT_UInt16 lookup_idx_count;
	433	+ FT_UInt16 lookup_idx;
	434	+
	435	+
	436	+ if ( feature_tag != TTAG_kern )
	437	+ continue;
	438	+
	439	+ feature_table = feature_list + FT_PEEK_USHORT( feature_records + 4 );
	440	+ lookup_idx_count = FT_PEEK_USHORT( feature_table + 2 );
	441	+
	442	+ for ( lookup_idx = 0; lookup_idx < lookup_idx_count; lookup_idx++ )
	443	+ {
	444	+ FT_UInt16 lookup_list_idx =
	445	+ FT_PEEK_USHORT( feature_table + 4 + 2 * lookup_idx );
	446	+ TT_GPOS_Subtable_Iterator_Context subtable_iter;
	447	+
	448	+
	449	+ tt_gpos_subtable_iterator_init( &subtable_iter,
	450	+ face->gpos_table,
	451	+ lookup_list_idx );
	452	+
	453	+ while ( tt_gpos_subtable_iterator_next( &subtable_iter ) )
	454	+ {
	455	+ FT_Byte* subtable;
	456	+
	457	+ gpos_value_format_bitmask value_format_1;
	458	+ gpos_value_format_bitmask value_format_2;
	459	+ gpos_pair_adjustment_format format;
	460	+
	461	+ FT_UShort coverage_offset;
	462	+ FT_Int coverage_index;
	463	+
	464	+
	465	+ if ( subtable_iter.subtable_type !=
	466	+ GPOS_LOOKUP_TYPE_PAIR_ADJUSTMENT )
	467	+ continue;
	468	+
	469	+ subtable = subtable_iter.subtable;
	470	+
	471	+ value_format_1 =
	472	+ (gpos_value_format_bitmask)FT_PEEK_USHORT( subtable + 4 );
	473	+ value_format_2 =
	474	+ (gpos_value_format_bitmask)FT_PEEK_USHORT( subtable + 6 );
	475	+
	476	+ if ( !( value_format_1 == GPOS_VALUE_FORMAT_X_ADVANCE &&
	477	+ value_format_2 == GPOS_VALUE_FORMAT_NONE ) )
	478	+ continue;
	479	+
	480	+ format = (gpos_pair_adjustment_format)FT_PEEK_USHORT( subtable );
	481	+
	482	+ coverage_offset = FT_PEEK_USHORT( subtable + 2 );
	483	+ coverage_index =
	484	+ tt_gpos_get_coverage_index( subtable + coverage_offset,
	485	+ left_glyph );
	486	+
	487	+ if ( coverage_index == -1 )
	488	+ continue;
	489	+
	490	+ switch ( format )
	491	+ {
	492	+ case GPOS_PAIR_ADJUSTMENT_FORMAT_GLYPH_PAIR:
	493	+ {
	494	+ FT_Int l, r, m;
	495	+ FT_Int straw, needle;
	496	+
	497	+ FT_Int value_record_pair_size_in_bytes = 2;
	498	+
	499	+ FT_UShort pair_set_count = FT_PEEK_USHORT( subtable + 8 );
	500	+ FT_UShort pair_pos_offset;
	501	+
	502	+ FT_Byte* pair_value_table;
	503	+ FT_UShort pair_value_count;
	504	+ FT_Byte* pair_value_array;
	505	+
	506	+
	507	+ if ( coverage_index >= pair_set_count )
	508	+ return 0;
	509	+
	510	+ pair_pos_offset =
	511	+ FT_PEEK_USHORT( subtable + 10 + 2 * coverage_index );
	512	+
	513	+ pair_value_table = subtable + pair_pos_offset;
	514	+ pair_value_count = FT_PEEK_USHORT( pair_value_table );
	515	+ pair_value_array = pair_value_table + 2;
	516	+
	517	+ needle = right_glyph;
	518	+ r = pair_value_count - 1;
	519	+ l = 0;
	520	+
	521	+ /* Binary search. */
	522	+ while ( l <= r )
	523	+ {
	524	+ FT_UShort second_glyph;
	525	+ FT_Byte* pair_value;
	526	+
	527	+
	528	+ m = ( l + r ) >> 1;
	529	+ pair_value = pair_value_array +
	530	+ ( 2 + value_record_pair_size_in_bytes ) * m;
	531	+ second_glyph = FT_PEEK_USHORT( pair_value );
	532	+ straw = second_glyph;
	533	+
	534	+ if ( needle < straw )
	535	+ r = m - 1;
	536	+ else if ( needle > straw )
	537	+ l = m + 1;
	538	+ else
	539	+ {
	540	+ FT_Short x_advance = FT_PEEK_SHORT( pair_value + 2 );
	541	+
	542	+
	543	+ return x_advance;
	544	+ }
	545	+ }
	546	+ break;
	547	+ }
	548	+
	549	+ case GPOS_PAIR_ADJUSTMENT_FORMAT_CLASS_PAIR:
	550	+ {
	551	+ FT_UShort class_def1_offset = FT_PEEK_USHORT( subtable + 8 );
	552	+ FT_UShort class_def2_offset = FT_PEEK_USHORT( subtable + 10 );
	553	+
	554	+ FT_Int left_glyph_class =
	555	+ tt_gpos_get_glyph_class( subtable + class_def1_offset,
	556	+ left_glyph );
	557	+ FT_Int right_glyph_class =
	558	+ tt_gpos_get_glyph_class( subtable + class_def2_offset,
	559	+ right_glyph );
	560	+
	561	+ FT_UShort class1_count = FT_PEEK_USHORT( subtable + 12 );
	562	+ FT_UShort class2_count = FT_PEEK_USHORT( subtable + 14 );
	563	+
	564	+ FT_Byte *class1_records, *class2_records;
	565	+ FT_Short x_advance;
	566	+
	567	+
	568	+ if ( left_glyph_class < 0 ||
	569	+ left_glyph_class >= class1_count )
	570	+ return 0; /* malformed */
	571	+ if ( right_glyph_class < 0 ||
	572	+ right_glyph_class >= class2_count )
	573	+ return 0; /* malformed */
	574	+
	575	+ if ( right_glyph_class == 0 )
	576	+ continue; /* right glyph not found in this table */
	577	+
	578	+ class1_records = subtable + 16;
	579	+ class2_records =
	580	+ class1_records + 2 * ( left_glyph_class * class2_count );
	581	+
	582	+ x_advance =
	583	+ FT_PEEK_SHORT( class2_records + 2 * right_glyph_class );
	584	+
	585	+ return x_advance;
	586	+ }
	587	+
	588	+ default:
	589	+ return 0;
	590	+ }
	591	+ }
	592	+ }
	593	+ }
	594	+
	595	+ return 0;
	596	+ }
	597	+
	598	+#else /* !TT_CONFIG_OPTION_GPOS_KERNING */
	599	+
	600	+ /* ANSI C doesn't like empty source files */
	601	+ typedef int tt_gpos_dummy_;
	602	+
	603	+#endif /* !TT_CONFIG_OPTION_GPOS_KERNING */
	604	+
	605	+
	606	+/* END */

src/sfnt/ttgpos.h

---

	1	+/****************************************************************************
	2	+ *
	3	+ * ttgpos.c
	4	+ *
	5	+ * Load the TrueType GPOS table. The only GPOS layout feature this
	6	+ * currently supports is kerning, from x advances in the pair adjustment
	7	+ * layout feature.
	8	+ *
	9	+ * Copyright (C) 2024 by
	10	+ * David Saltzman
	11	+ *
	12	+ * This file is part of the FreeType project, and may only be used,
	13	+ * modified, and distributed under the terms of the FreeType project
	14	+ * license, LICENSE.TXT. By continuing to use, modify, or distribute
	15	+ * this file you indicate that you have read the license and
	16	+ * understand and accept it fully.
	17	+ */
	18	+
	19	+
	20	+#ifndef TTGPOS_H_
	21	+#define TTGPOS_H_
	22	+
	23	+
	24	+#include <freetype/internal/ftstream.h>
	25	+#include <freetype/internal/tttypes.h>
	26	+
	27	+
	28	+FT_BEGIN_HEADER
	29	+
	30	+
	31	+#ifdef TT_CONFIG_OPTION_GPOS_KERNING
	32	+
	33	+ FT_LOCAL( FT_Error )
	34	+ tt_face_load_gpos( TT_Face face,
	35	+ FT_Stream stream );
	36	+
	37	+ FT_LOCAL( void )
	38	+ tt_face_done_gpos( TT_Face face );
	39	+
	40	+ FT_LOCAL( FT_Int )
	41	+ tt_face_get_gpos_kerning( TT_Face face,
	42	+ FT_UInt left_glyph,
	43	+ FT_UInt right_glyph );
	44	+
	45	+#endif /* TT_CONFIG_OPTION_GPOS_KERNING */
	46	+
	47	+
	48	+FT_END_HEADER
	49	+
	50	+#endif /* TTGPOS_H_ */
	51	+
	52	+
	53	+/* END */

src/truetype/ttdriver.c

---

...	...	@@ -217,7 +217,20 @@
217	217	kerning->y = 0;
218	218
219	219	if ( sfnt )
220		- kerning->x = sfnt->get_kerning( ttface, left_glyph, right_glyph );
	220	+ {
	221	+ /* Use 'kern' table if available since that can be faster; otherwise */
	222	+ /* use GPOS kerning pairs if available. */
	223	+ if ( ttface->kern_avail_bits != 0 )
	224	+ kerning->x = sfnt->get_kerning( ttface,
	225	+ left_glyph,
	226	+ right_glyph );
	227	+#ifdef TT_CONFIG_OPTION_GPOS_KERNING
	228	+ else if ( ttface->gpos_kerning_available )
	229	+ kerning->x = sfnt->get_gpos_kerning( ttface,
	230	+ left_glyph,
	231	+ right_glyph );
	232	+#endif
	233	+ }
221	234
222	235	return 0;
223	236	}

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