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kc3-lang/freetype/src/sfnt/ttkern.c
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Author :
Werner Lemberg
Date : 2025-07-04 19:52:53
Hash : b04db387
Message : [sfnt] Rewrite GPOS kerning support. (2/2) The previous code had a fundamental flaw: it didn't validate the necessary parts of the 'GPOS' table before accessing it, causing crashes with malformed data (since `TT_CONFIG_OPTION_GPOS_KERNING` is off by default, standard fuzzers don't catch these problems). Additionally, it did a lot of parsing while accessing kerning data, making it rather slow. The new implementation fixes this. After validation, offsets to the 'GPOS' lookup subtables used in the 'kern' feature that correspond to 'simple' kerning (i.e., similar to 'kern' table kerning) are stored in `TT_Face`; this greatly simplifies and accelerates access to the kerning data. Testing with font `SF-Pro.ttf` version '1.00', the validation time for the 'GPOS' table increases the start-up time of `FT_New_Face` by less than 1%, while calls to `FT_Get_Kerning` become about 3.5 times faster. * include/freetype/internal (gpos_kerning_available): Replace with... (gpos_lookups_kerning, num_gpos_lookups_kerning): ... these new fields. Update callers. * src/ttgpos.c [TT_CONFIG_OPTION_GPOS_KERNING]: A new implementation.
- src/sfnt/ttkern.c
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/**************************************************************************** * * ttkern.c * * Routines to parse and access the 'kern' table for kerning (body). * * Copyright (C) 1996-2024 by * David Turner, Robert Wilhelm, and Werner Lemberg. * * This file is part of the FreeType project, and may only be used, * modified, and distributed under the terms of the FreeType project * license, LICENSE.TXT. By continuing to use, modify, or distribute * this file you indicate that you have read the license and * understand and accept it fully. * */ #include <freetype/internal/ftdebug.h> #include <freetype/internal/ftstream.h> #include <freetype/tttags.h> #include "ttkern.h" #include "sferrors.h" /************************************************************************** * * The macro FT_COMPONENT is used in trace mode. It is an implicit * parameter of the FT_TRACE() and FT_ERROR() macros, used to print/log * messages during execution. */ #undef FT_COMPONENT #define FT_COMPONENT ttkern #undef TT_KERN_INDEX #define TT_KERN_INDEX( g1, g2 ) ( ( (FT_ULong)(g1) << 16 ) | (g2) ) FT_LOCAL_DEF( FT_Error ) tt_face_load_kern( TT_Face face, FT_Stream stream ) { FT_Error error; FT_ULong table_size; FT_Byte* p; FT_Byte* p_limit; FT_UInt nn, num_tables; FT_UInt32 avail = 0, ordered = 0; /* the kern table is optional; exit silently if it is missing */ error = face->goto_table( face, TTAG_kern, stream, &table_size ); if ( error ) goto Exit; if ( table_size < 4 ) /* the case of a malformed table */ { FT_ERROR(( "tt_face_load_kern:" " kerning table is too small - ignored\n" )); error = FT_THROW( Table_Missing ); goto Exit; } if ( FT_FRAME_EXTRACT( table_size, face->kern_table ) ) { FT_ERROR(( "tt_face_load_kern:" " could not extract kerning table\n" )); goto Exit; } face->kern_table_size = table_size; p = face->kern_table; p_limit = p + table_size; p += 2; /* skip version */ num_tables = FT_NEXT_USHORT( p ); if ( num_tables > 32 ) /* we only support up to 32 sub-tables */ num_tables = 32; for ( nn = 0; nn < num_tables; nn++ ) { FT_UInt num_pairs, length, coverage, format; FT_Byte* p_next; FT_UInt32 mask = (FT_UInt32)1UL << nn; if ( p + 6 > p_limit ) break; p_next = p; p += 2; /* skip version */ length = FT_NEXT_USHORT( p ); coverage = FT_NEXT_USHORT( p ); if ( length <= 6 + 8 ) break; p_next += length; if ( p_next > p_limit ) /* handle broken table */ p_next = p_limit; format = coverage >> 8; /* we currently only support format 0 kerning tables */ if ( format != 0 ) goto NextTable; /* only use horizontal kerning tables */ if ( ( coverage & 3U ) != 0x0001 || p + 8 > p_next ) goto NextTable; num_pairs = FT_NEXT_USHORT( p ); p += 6; if ( ( p_next - p ) < 6 * (int)num_pairs ) /* handle broken count */ num_pairs = (FT_UInt)( ( p_next - p ) / 6 ); avail |= mask; /* * Now check whether the pairs in this table are ordered. * We then can use binary search. */ if ( num_pairs > 0 ) { FT_ULong count; FT_ULong old_pair; old_pair = FT_NEXT_ULONG( p ); p += 2; for ( count = num_pairs - 1; count > 0; count-- ) { FT_UInt32 cur_pair; cur_pair = FT_NEXT_ULONG( p ); if ( cur_pair < old_pair ) break; p += 2; old_pair = cur_pair; } if ( count == 0 ) ordered |= mask; } NextTable: p = p_next; } face->num_kern_tables = nn; face->kern_avail_bits = avail; face->kern_order_bits = ordered; Exit: return error; } FT_LOCAL_DEF( void ) tt_face_done_kern( TT_Face face ) { FT_Stream stream = face->root.stream; FT_FRAME_RELEASE( face->kern_table ); face->kern_table_size = 0; face->num_kern_tables = 0; face->kern_avail_bits = 0; face->kern_order_bits = 0; } FT_LOCAL_DEF( FT_Int ) tt_face_get_kerning( TT_Face face, FT_UInt left_glyph, FT_UInt right_glyph ) { FT_Int result = 0; FT_UInt count, mask; FT_Byte* p; FT_Byte* p_limit; if ( !face->kern_table ) return result; p = face->kern_table; p_limit = p + face->kern_table_size; p += 4; mask = 0x0001; for ( count = face->num_kern_tables; count > 0 && p + 6 <= p_limit; count--, mask <<= 1 ) { FT_Byte* base = p; FT_Byte* next; FT_UInt version = FT_NEXT_USHORT( p ); FT_UInt length = FT_NEXT_USHORT( p ); FT_UInt coverage = FT_NEXT_USHORT( p ); FT_UInt num_pairs; FT_Int value = 0; FT_UNUSED( version ); next = base + length; if ( next > p_limit ) /* handle broken table */ next = p_limit; if ( ( face->kern_avail_bits & mask ) == 0 ) goto NextTable; FT_ASSERT( p + 8 <= next ); /* tested in tt_face_load_kern */ num_pairs = FT_NEXT_USHORT( p ); p += 6; if ( ( next - p ) < 6 * (int)num_pairs ) /* handle broken count */ num_pairs = (FT_UInt)( ( next - p ) / 6 ); switch ( coverage >> 8 ) { case 0: { FT_ULong key0 = TT_KERN_INDEX( left_glyph, right_glyph ); if ( face->kern_order_bits & mask ) /* binary search */ { FT_UInt min = 0; FT_UInt max = num_pairs; while ( min < max ) { FT_UInt mid = ( min + max ) >> 1; FT_Byte* q = p + 6 * mid; FT_ULong key; key = FT_NEXT_ULONG( q ); if ( key == key0 ) { value = FT_PEEK_SHORT( q ); goto Found; } if ( key < key0 ) min = mid + 1; else max = mid; } } else /* linear search */ { FT_UInt count2; for ( count2 = num_pairs; count2 > 0; count2-- ) { FT_ULong key = FT_NEXT_ULONG( p ); if ( key == key0 ) { value = FT_PEEK_SHORT( p ); goto Found; } p += 2; } } } break; /* * We don't support format 2 because we haven't seen a single font * using it in real life... */ default: ; } goto NextTable; Found: if ( coverage & 8 ) /* override or add */ result = value; else result += value; NextTable: p = next; } return result; } #undef TT_KERN_INDEX /* END */