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[truetype] Increase precision of font variation (#54371).

Browse Source 
This patch make FreeType use font units in 26.6 format internally
instead of integers.

* src/truetype/ttgxvar.c (FT_fixedToFdot6): New macro.
(TT_Vary_Apply_Glyph_Deltas): Add argument to output unrounded font
coordinates.
* src/truetype/ttgxvar.h: Updated.

* src/truetype/ttgload.c (TT_Process_Simple_Glyph): Use
`extra_points2' array to temporarily hold unrounded point
coordinates; use them to compute scaled coordinates and linear
advance width and height.
(load_truetype_code): Adjust similarly.
cmakelists-updates
Werner Lemberg 6 years ago
parent a113e5df0c
commit 1178227b39
5 changed files with 89 additions and 24 deletions
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  1. 18
      ChangeLog
  2. 7
      include/freetype/freetype.h
  3. 62
      src/truetype/ttgload.c
  4. 25
      src/truetype/ttgxvar.c
  5. 1
      src/truetype/ttgxvar.h

18
ChangeLog
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@ -1,3 +1,21 @@
2019-05-09 Werner Lemberg <wl@gnu.org>
[truetype] Increase precision of font variation (#54371).
This patch make FreeType use font units in 26.6 format internally
instead of integers.
* src/truetype/ttgxvar.c (FT_fixedToFdot6): New macro.
(TT_Vary_Apply_Glyph_Deltas): Add argument to output unrounded font
coordinates.
* src/truetype/ttgxvar.h: Updated.
* src/truetype/ttgload.c (TT_Process_Simple_Glyph): Use
`extra_points2' array to temporarily hold unrounded point
coordinates; use them to compute scaled coordinates and linear
advance width and height.
(load_truetype_code): Adjust similarly.
2019-05-09 Werner Lemberg <wl@gnu.org>
* src/truetype/ttgload.c (TT_Process_Simple_Glyph): Minor.

7
include/freetype/freetype.h
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@ -1766,6 +1766,13 @@ FT_BEGIN_HEADER
* transformed, distorted, emboldened, etc. However, it must not be
* freed.
*
* [Since 2.10.1] If @FT_LOAD_NO_SCALE is set, outline coordinates of
* OpenType variation fonts for a selected instance are internally
* handled as 26.6 fractional font units but returned as (rounded)
* integers, as expected. To get unrounded font units, don't use
* @FT_LOAD_NO_SCALE but load the glyph with @FT_LOAD_NO_HINTING and
* scale it, using the font's `units_per_EM` value as the ppem.
*
* num_subglyphs ::
* The number of subglyphs in a composite glyph. This field is only
* valid for the composite glyph format that should normally only be

62
src/truetype/ttgload.c
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@ -925,6 +925,7 @@
FT_GlyphLoader gloader = loader->gloader;
FT_Error error = FT_Err_Ok;
FT_Outline* outline;
FT_Vector* unrounded;
FT_Int n_points;
@ -950,20 +951,26 @@
if ( FT_IS_NAMED_INSTANCE( FT_FACE( loader->face ) ) ||
FT_IS_VARIATION( FT_FACE( loader->face ) ) )
{
/* Deltas apply to the unscaled data. */
/* Deltas apply to the unscaled data. */
/* We temporarily use `extra_points2' to hold unrounded values. */
unrounded = gloader->current.extra_points2;
error = TT_Vary_Apply_Glyph_Deltas( loader->face,
loader->glyph_index,
outline,
unrounded,
(FT_UInt)n_points );
/* recalculate linear horizontal and vertical advances */
/* if we don't have HVAR and VVAR, respectively */
/* XXX: change all FreeType modules to store `linear' and `vadvance' */
/* in 26.6 format before the `base' module scales them to 16.16 */
if ( !( loader->face->variation_support & TT_FACE_FLAG_VAR_HADVANCE ) )
loader->linear = outline->points[n_points - 3].x -
outline->points[n_points - 4].x;
loader->linear = FT_PIX_ROUND( unrounded[n_points - 3].x -
unrounded[n_points - 4].x ) / 64;
if ( !( loader->face->variation_support & TT_FACE_FLAG_VAR_VADVANCE ) )
loader->vadvance = outline->points[n_points - 1].x -
outline->points[n_points - 2].x;
loader->vadvance = FT_PIX_ROUND( unrounded[n_points - 1].x -
unrounded[n_points - 2].x ) / 64;
if ( error )
return error;
@ -1013,10 +1020,17 @@
/* compensate for any scaling by de/emboldening; */
/* the amount was determined via experimentation */
if ( x_scale_factor != 1000 && ppem > 11 )
{
FT_Vector* orig_points = outline->points;
outline->points = unrounded;
FT_Outline_EmboldenXY( outline,
FT_MulFix( 1280 * ppem,
1000 - x_scale_factor ),
0 );
outline->points = orig_points;
}
do_scale = TRUE;
}
}
@ -1037,10 +1051,10 @@
if ( do_scale )
{
for ( ; vec < limit; vec++ )
for ( ; vec < limit; vec++, unrounded++ )
{
vec->x = FT_MulFix( vec->x, x_scale );
vec->y = FT_MulFix( vec->y, y_scale );
vec->x = FT_MulDiv( unrounded->x, x_scale, 0x10000L * 64 );
vec->y = FT_MulDiv( unrounded->y, y_scale, 0x10000L * 64 );
}
}
@ -1678,6 +1692,9 @@
short contours[4] = { 0, 1, 2, 3 };
FT_Outline outline;
/* unrounded values */
FT_Vector unrounded[4];
points[0].x = loader->pp1.x;
points[0].y = loader->pp1.y;
@ -1699,6 +1716,7 @@
error = TT_Vary_Apply_Glyph_Deltas( loader->face,
glyph_index,
&outline,
unrounded,
(FT_UInt)outline.n_points );
if ( error )
goto Exit;
@ -1716,9 +1734,11 @@
/* recalculate linear horizontal and vertical advances */
/* if we don't have HVAR and VVAR, respectively */
if ( !( loader->face->variation_support & TT_FACE_FLAG_VAR_HADVANCE ) )
loader->linear = loader->pp2.x - loader->pp1.x;
loader->linear = FT_PIX_ROUND( unrounded[1].x -
unrounded[0].x ) / 64;
if ( !( loader->face->variation_support & TT_FACE_FLAG_VAR_VADVANCE ) )
loader->vadvance = loader->pp4.x - loader->pp3.x;
loader->vadvance = FT_PIX_ROUND( unrounded[3].x -
unrounded[2].x ) / 64;
}
#endif /* TT_CONFIG_OPTION_GX_VAR_SUPPORT */
@ -1858,9 +1878,10 @@
FT_SubGlyph subglyph;
FT_Outline outline;
FT_Vector* points = NULL;
char* tags = NULL;
short* contours = NULL;
FT_Vector* points = NULL;
char* tags = NULL;
short* contours = NULL;
FT_Vector* unrounded = NULL;
limit = (short)gloader->current.num_subglyphs;
@ -1874,9 +1895,10 @@
outline.tags = NULL;
outline.contours = NULL;
if ( FT_NEW_ARRAY( points, outline.n_points ) ||
FT_NEW_ARRAY( tags, outline.n_points ) ||
FT_NEW_ARRAY( contours, outline.n_points ) )
if ( FT_NEW_ARRAY( points, outline.n_points ) ||
FT_NEW_ARRAY( tags, outline.n_points ) ||
FT_NEW_ARRAY( contours, outline.n_points ) ||
FT_NEW_ARRAY( unrounded, outline.n_points ) )
goto Exit1;
subglyph = gloader->current.subglyphs;
@ -1925,6 +1947,7 @@
face,
glyph_index,
&outline,
unrounded,
(FT_UInt)outline.n_points ) ) )
goto Exit1;
@ -1952,14 +1975,17 @@
/* recalculate linear horizontal and vertical advances */
/* if we don't have HVAR and VVAR, respectively */
if ( !( face->variation_support & TT_FACE_FLAG_VAR_HADVANCE ) )
loader->linear = loader->pp2.x - loader->pp1.x;
loader->linear = FT_PIX_ROUND( unrounded[1].x -
unrounded[0].x ) / 64;
if ( !( face->variation_support & TT_FACE_FLAG_VAR_VADVANCE ) )
loader->vadvance = loader->pp4.x - loader->pp3.x;
loader->vadvance = FT_PIX_ROUND( unrounded[3].x -
unrounded[2].x ) / 64;
Exit1:
FT_FREE( outline.points );
FT_FREE( outline.tags );
FT_FREE( outline.contours );
FT_FREE( unrounded );
if ( error )
goto Exit;

25
src/truetype/ttgxvar.c
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@ -68,12 +68,14 @@
/* some macros we need */
#define FT_fdot14ToFixed( x ) \
( (FT_Fixed)( (FT_ULong)(x) << 2 ) )
#define FT_intToFixed( i ) \
( (FT_Fixed)( (FT_ULong)(i) << 16 ) )
#define FT_fixedToInt( x ) \
( (FT_Short)( ( (FT_UInt32)(x) + 0x8000U ) >> 16 ) )
#define FT_fdot14ToFixed( x ) \
( (FT_Fixed)( (FT_ULong)(x) << 2 ) )
#define FT_intToFixed( i ) \
( (FT_Fixed)( (FT_ULong)(i) << 16 ) )
#define FT_fixedToInt( x ) \
( (FT_Short)( ( (FT_UInt32)(x) + 0x8000U ) >> 16 ) )
#define FT_fixedToFdot6( x ) \
( (FT_Pos)( ( (FT_UInt32)(x) + 0x20 ) >> 10 ) )
/**************************************************************************
@ -3674,6 +3676,11 @@
* outline ::
* The outline to change.
*
* @Output:
* unrounded ::
* An array with `n_points' elements that is filled with unrounded
* point coordinates (in 26.6 format).
*
* @Return:
* FreeType error code. 0 means success.
*/
@ -3681,6 +3688,7 @@
TT_Vary_Apply_Glyph_Deltas( TT_Face face,
FT_UInt glyph_index,
FT_Outline* outline,
FT_Vector* unrounded,
FT_UInt n_points )
{
FT_Error error;
@ -4068,6 +4076,11 @@
for ( i = 0; i < n_points; i++ )
{
unrounded[i].x = INT_TO_F26DOT6( outline->points[i].x ) +
FT_fixedToFdot6( point_deltas_x[i] );
unrounded[i].y = INT_TO_F26DOT6( outline->points[i].y ) +
FT_fixedToFdot6( point_deltas_y[i] );
outline->points[i].x += FT_fixedToInt( point_deltas_x[i] );
outline->points[i].y += FT_fixedToInt( point_deltas_y[i] );
}

1
src/truetype/ttgxvar.h
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@ -416,6 +416,7 @@ FT_BEGIN_HEADER
TT_Vary_Apply_Glyph_Deltas( TT_Face face,
FT_UInt glyph_index,
FT_Outline* outline,
FT_Vector* unrounded,
FT_UInt n_points );
FT_LOCAL( FT_Error )

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