ref: ed4d0710f14878b51ce1885e0f3221e2d6d97a5a
dir: /src/sfnt/ttkern.c/
/****************************************************************************
*
* ttkern.c
*
* Load the basic TrueType kerning table. This doesn't handle
* kerning data within the GPOS table at the moment.
*
* Copyright (C) 1996-2022 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 */