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New base function `FT_Matrix_Check' (#54019).

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* src/base/ftcalc.c (FT_Matrix_Check): New base function to properly
reject degenerate font matrices.

* include/freetype/internal/ftcalc.h: Updated.

* src/cff/cffparse.c (cff_parse_font_matrix), src/cid/cidload.c
(cid_parse_font_matrix), src/type1/t1load.c (t1_parse_font_matrix),
src/type42/t42parse.c (t42_parse_font_matrix): Use
`FT_Matrix_Check'.
This commit is contained in:
Werner Lemberg 2018-06-24 06:22:48 +02:00
parent d7393e22ee
commit cc3333902b
7 changed files with 141 additions and 18 deletions
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14
ChangeLog
View File

@ -1,3 +1,17 @@
2018-06-24 Werner Lemberg <wl@gnu.org>
New base function `FT_Matrix_Check' (#54019).
* src/base/ftcalc.c (FT_Matrix_Check): New base function to properly
reject degenerate font matrices.
* include/freetype/internal/ftcalc.h: Updated.
* src/cff/cffparse.c (cff_parse_font_matrix), src/cid/cidload.c
(cid_parse_font_matrix), src/type1/t1load.c (t1_parse_font_matrix),
src/type42/t42parse.c (t42_parse_font_matrix): Use
`FT_Matrix_Check'.
2018-06-23 Werner Lemberg <wl@gnu.org>
Fix typo.

15
include/freetype/internal/ftcalc.h
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@ -292,6 +292,21 @@ FT_BEGIN_HEADER
FT_Long scaling );
/*
* Check a matrix. If the transformation would lead to extreme shear or
* extreme scaling, for example, return 0. If everything is OK, return 1.
*
* Based on geometric considerations we use the following inequality to
* identify a degenerate matrix.
*
* 50 * abs(xx*yy - xy*yx) < xx^2 + xy^2 + yx^2 + yy^2
*
* Value 50 is heuristic.
*/
FT_BASE( FT_Bool )
FT_Matrix_Check( const FT_Matrix* matrix );
/*
* A variant of FT_Vector_Transform. See comments for
* FT_Matrix_Multiply_Scaled.

66
src/base/ftcalc.c
View File

@ -745,6 +745,72 @@
}
/* documentation is in ftcalc.h */
FT_BASE_DEF( FT_Bool )
FT_Matrix_Check( const FT_Matrix* matrix )
{
FT_Matrix m;
FT_Fixed val[4];
FT_Fixed nonzero_minval, maxval;
FT_Fixed temp1, temp2;
FT_UInt i;
if ( !matrix )
return 0;
val[0] = FT_ABS( matrix->xx );
val[1] = FT_ABS( matrix->xy );
val[2] = FT_ABS( matrix->yx );
val[3] = FT_ABS( matrix->yy );
/*
* To avoid overflow, we ensure that each value is not larger than
*
* int(sqrt(2^31 / 4)) = 23170 ;
*
* we also check that no value becomes zero if we have to scale.
*/
maxval = 0;
nonzero_minval = FT_LONG_MAX;
for ( i = 0; i < 4; i++ )
{
if ( val[i] > maxval )
maxval = val[i];
if ( val[i] && val[i] < nonzero_minval )
nonzero_minval = val[i];
}
if ( maxval > 23170 )
{
FT_Fixed scale = FT_DivFix( maxval, 23170 );
if ( !FT_DivFix( nonzero_minval, scale ) )
return 0; /* value range too large */
m.xx = FT_DivFix( matrix->xx, scale );
m.xy = FT_DivFix( matrix->xy, scale );
m.yx = FT_DivFix( matrix->yx, scale );
m.yy = FT_DivFix( matrix->yy, scale );
}
else
m = *matrix;
temp1 = FT_ABS( m.xx * m.yy - m.xy * m.yx );
temp2 = m.xx * m.xx + m.xy * m.xy + m.yx * m.yx + m.yy * m.yy;
if ( temp1 == 0 ||
temp2 / temp1 > 50 )
return 0;
return 1;
}
/* documentation is in ftcalc.h */
FT_BASE_DEF( void )

43
src/cff/cffparse.c
View File

@ -604,7 +604,6 @@
FT_Vector* offset = &dict->font_offset;
FT_ULong* upm = &dict->units_per_em;
FT_Byte** data = parser->stack;
FT_Error error = FT_ERR( Stack_Underflow );
if ( parser->top >= parser->stack + 6 )
@ -616,8 +615,6 @@
int i;
error = FT_Err_Ok;
dict->has_font_matrix = TRUE;
/* We expect a well-formed font matrix, this is, the matrix elements */
@ -646,22 +643,11 @@
( max_scaling - min_scaling ) < 0 ||
( max_scaling - min_scaling ) > 9 )
{
/* Return default matrix in case of unlikely values. */
FT_TRACE1(( "cff_parse_font_matrix:"
" strange scaling values (minimum %d, maximum %d),\n"
" "
" using default matrix\n", min_scaling, max_scaling ));
matrix->xx = 0x10000L;
matrix->yx = 0;
matrix->xy = 0;
matrix->yy = 0x10000L;
offset->x = 0;
offset->y = 0;
*upm = 1;
goto Exit;
goto Unlikely;
}
for ( i = 0; i < 6; i++ )
@ -708,10 +694,31 @@
(double)matrix->yy / *upm / 65536,
(double)offset->x / *upm / 65536,
(double)offset->y / *upm / 65536 ));
}
Exit:
return error;
if ( !FT_Matrix_Check( matrix ) )
{
FT_TRACE1(( "cff_parse_font_matrix:"
" degenerate values, using default matrix\n" ));
goto Unlikely;
}
return FT_Err_Ok;
}
else
return FT_THROW( Stack_Underflow );
Unlikely:
/* Return default matrix in case of unlikely values. */
matrix->xx = 0x10000L;
matrix->yx = 0;
matrix->xy = 0;
matrix->yy = 0x10000L;
offset->x = 0;
offset->y = 0;
*upm = 1;
return FT_Err_Ok;
}

7
src/cid/cidload.c
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@ -200,6 +200,13 @@
matrix->xy = temp[2];
matrix->yy = temp[3];
if ( !FT_Matrix_Check( matrix ) )
{
FT_ERROR(( "t1_parse_font_matrix: invalid font matrix\n" ));
parser->root.error = FT_THROW( Invalid_File_Format );
return FT_THROW( Invalid_File_Format );
}
/* note that the font offsets are expressed in integer font units */
offset->x = temp[4] >> 16;
offset->y = temp[5] >> 16;

7
src/type1/t1load.c
View File

@ -1286,6 +1286,13 @@
matrix->xy = temp[2];
matrix->yy = temp[3];
if ( !FT_Matrix_Check( matrix ) )
{
FT_ERROR(( "t1_parse_font_matrix: invalid font matrix\n" ));
parser->root.error = FT_THROW( Invalid_File_Format );
return;
}
/* note that the offsets must be expressed in integer font units */
offset->x = temp[4] >> 16;
offset->y = temp[5] >> 16;

7
src/type42/t42parse.c
View File

@ -284,6 +284,13 @@
matrix->xy = temp[2];
matrix->yy = temp[3];
if ( !FT_Matrix_Check( matrix ) )
{
FT_ERROR(( "t42_parse_font_matrix: invalid font matrix\n" ));
parser->root.error = FT_THROW( Invalid_File_Format );
return;
}
/* note that the offsets must be expressed in integer font units */
offset->x = temp[4] >> 16;
offset->y = temp[5] >> 16;