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[autofit] Fix vertical adjustment of (mainly) double diacritics.

Browse source 
The series of commits that introduced this adjustment support had some
flaws.

- If there were two diacritics on top of a base glyph, and the upper
  diacritic was a tilde, the vertical centering correction was incorrectly
  applied to the lower, non-tilde glyph instead of the tilde.

- The maximum value allowed to shift a glyph was too strict (and also not
  handling rounding issues), causing some diacritics and combinations of
  diacritics to be not shifted at all.

* src/autofit/aflatin.c
  (af_glyph_hints_apply_vertical_separation_adjustments): Correctly handle
  vertical centering correction.
This commit is contained in:
Werner Lemberg 2025-05-13 14:44:20 +02:00
parent 4c9f14f422
commit d3fbbed91f
2 changed files with 140 additions and 65 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

4
src/autofit/afadjust.h
View file

@ -70,12 +70,12 @@ FT_BEGIN_HEADER
/* The contour below the topmost contour is a tilde. Enlarge it */
/* vertically so that it stays legible at small sizes, not degenerating */
/* to a horizontal line. */
/* to a horizontal line. To be used with `AF_ADJUST_UP2` only. */
#define AF_ADJUST_TILDE_TOP2 0x40
/* The contour above the bottommost contour is a tilde. Enlarge it */
/* vertically so that it stays legible at small sizes, not degenerating */
/* to a horizontal line. */
/* to a horizontal line. To be used with `AF_ADJUST_DOWN2` only. */
#define AF_ADJUST_TILDE_BOTTOM2 0x80
/* Make the auto-hinter ignore any diacritic (either a separate contour */

201
src/autofit/aflatin.c
View file

@ -3624,24 +3624,30 @@
if ( ( adjust_top && hints->num_contours >= 2 ) ||
( adjust_below_top && hints->num_contours >= 3 ) )
{
FT_Int high_contour = 0;
FT_Int high_contour;
FT_Pos high_min_y;
FT_Pos high_max_y;
FT_Pos high_height;
FT_Int tilde_contour;
FT_Pos tilde_min_y;
FT_Pos tilde_max_y;
FT_Pos tilde_height;
FT_Int contour;
FT_Bool horizontal_overlap;
FT_Pos min_distance = 64;
FT_Pos min_distance = 64;
FT_Pos adjustment_amount;
FT_Pos calculated_amount;
FT_Pos centering_adjustment = 0;
FT_Pos pos;
FT_Bool is_tilde = FALSE;
FT_Bool is_top_tilde =
!!( db_entry->flags & AF_ADJUST_TILDE_TOP );
FT_Bool is_below_top_tilde =
!!( db_entry->flags & AF_ADJUST_TILDE_TOP2 );
FT_Bool grid_aligned_after_adjustment;
FT_Pos height;
if ( db_entry )
is_tilde = db_entry->flags & AF_ADJUST_TILDE_TOP;
FT_TRACE4(( "af_glyph_hints_apply_vertical_separation_adjustments:\n"
" Applying vertical adjustment: %s\n",
@ -3663,15 +3669,16 @@
return;
}
high_min_y = hints->contour_y_minima[high_contour];
high_max_y = hints->contour_y_maxima[high_contour];
high_min_y = hints->contour_y_minima[high_contour];
high_max_y = hints->contour_y_maxima[high_contour];
high_height = high_max_y - high_min_y;
if ( high_max_y - high_min_y > accent_height_limit )
if ( high_height > accent_height_limit )
{
FT_TRACE4(( " High contour height (%.2f) exceeds accent height"
" limit (%.2f).\n"
" Skipping adjustment.\n",
(double)( high_max_y - high_min_y ) / 64,
(double)high_height / 64,
(double)accent_height_limit / 64 ));
return;
}
@ -3705,39 +3712,61 @@
adjustment_amount = 64 - min_distance;
/* The vertical separation adjustment potentially undoes a tilde */
/* center alignment. If the vertical adjustment would grid-align */
/* a tilde less than 3 pixels in height, add an offset to the */
/* vertical adjustment to re-center it. */
grid_aligned_after_adjustment =
( ( high_min_y + adjustment_amount ) % 64 == 0 );
height = high_max_y - high_min_y;
if ( is_tilde && grid_aligned_after_adjustment && height < 3 * 64 )
if ( is_top_tilde || is_below_top_tilde )
{
FT_Pos centering_adjustment =
( FT_PIX_ROUND( height ) - height ) / 2;
tilde_contour = adjust_top
? high_contour
: ( is_below_top_tilde
? high_contour
: af_find_highest_contour( hints ) );
tilde_min_y = hints->contour_y_minima[tilde_contour];
tilde_max_y = hints->contour_y_maxima[tilde_contour];
tilde_height = tilde_max_y - tilde_min_y;
adjustment_amount += centering_adjustment;
FT_TRACE4(( " Additional centering: %ld\n",
centering_adjustment ));
/* The vertical separation adjustment potentially undoes a */
/* tilde center alignment. If it would grid-align a tilde */
/* less than 3 pixels in height, shift additionally to */
/* re-center the tilde. */
pos = high_min_y + adjustment_amount;
if ( adjust_below_top && is_top_tilde )
pos += high_height;
if ( pos % 64 == 0 && tilde_height < 3 * 64 )
{
centering_adjustment = ( FT_PIX_ROUND( tilde_height ) -
tilde_height ) / 2;
FT_TRACE4(( " Additional tilde centering adjustment: %ld\n",
centering_adjustment ));
}
}
FT_TRACE4(( " Calculated adjustment amount: %ld%s\n",
adjustment_amount,
( adjustment_amount < 0 || adjustment_amount > 64 )
? " (out of range [0;64], not adjusting)" : "" ));
if ( ( adjust_top && is_top_tilde ) ||
( adjust_below_top && is_below_top_tilde ) )
calculated_amount = adjustment_amount + centering_adjustment;
else
calculated_amount = adjustment_amount;
if ( adjustment_amount > 0 && adjustment_amount <= 64 )
/* allow a delta of 2/64px to handle rounding differences */
FT_TRACE4(( " Calculated adjustment amount: %ld%s\n",
calculated_amount,
( calculated_amount < -2 ||
( adjustment_amount > 66 && calculated_amount > 66 ) )
? " (out of range [-2;66], not adjusting)" : "" ));
if ( calculated_amount != 0 &&
calculated_amount >= -2 &&
( calculated_amount <= 66 || adjustment_amount <= 66 ) )
{
/* Value 8 is heuristic. */
FT_Pos height_delta = ( high_max_y - high_min_y ) / 8;
FT_Pos height_delta = high_height / 8;
FT_Pos min_y_limit = high_min_y - height_delta;
FT_TRACE4(( " Pushing high contour %ld units up\n",
adjustment_amount ));
calculated_amount ));
/* While we use only a single contour (the 'high' one) for */
/* computing `adjustment_amount`, we apply it to all contours */
@ -3746,30 +3775,46 @@
/* the Czech ring accent or the second acute accent in the */
/* Hungarian double acute accent. */
af_move_contours_up( hints, min_y_limit, adjustment_amount );
if ( adjust_below_top && is_top_tilde )
{
FT_TRACE4(( " Pushing top tilde %ld units up\n",
centering_adjustment ));
af_move_contours_up( hints,
min_y_limit + high_height,
centering_adjustment );
}
}
}
if ( ( adjust_bottom && hints->num_contours >= 2 ) ||
( adjust_above_bottom && hints->num_contours >= 3 ) )
{
FT_Int low_contour = 0;
FT_Int low_contour;
FT_Pos low_min_y;
FT_Pos low_max_y;
FT_Pos low_height;
FT_Int tilde_contour;
FT_Pos tilde_min_y;
FT_Pos tilde_max_y;
FT_Pos tilde_height;
FT_Int contour;
FT_Bool horizontal_overlap;
FT_Pos min_distance = 64;
FT_Pos min_distance = 64;
FT_Pos adjustment_amount;
FT_Pos calculated_amount;
FT_Pos centering_adjustment = 0;
FT_Pos pos;
FT_Bool is_tilde = FALSE;
FT_Bool is_bottom_tilde =
!!( db_entry->flags & AF_ADJUST_TILDE_BOTTOM );
FT_Bool is_above_bottom_tilde =
!!( db_entry->flags & AF_ADJUST_TILDE_BOTTOM2 );
FT_Bool grid_aligned_after_adjustment;
FT_Pos height;
if ( db_entry )
is_tilde = db_entry->flags & AF_ADJUST_TILDE_BOTTOM;
FT_TRACE4(( "af_glyph_hints_apply_vertical_separation_adjustments:\n"
" Applying vertical adjustment: %s\n",
@ -3789,15 +3834,16 @@
return;
}
low_min_y = hints->contour_y_minima[low_contour];
low_max_y = hints->contour_y_maxima[low_contour];
low_min_y = hints->contour_y_minima[low_contour];
low_max_y = hints->contour_y_maxima[low_contour];
low_height = low_max_y - low_min_y;
if ( low_max_y - low_min_y > accent_height_limit )
if ( low_height > accent_height_limit )
{
FT_TRACE4(( " Low contour height (%.2f) exceeds accent height"
" limit (%.2f).\n"
" Skipping adjustment.\n",
(double)( low_max_y - low_min_y ) / 64,
(double)low_height / 64,
(double)accent_height_limit / 64 ));
return;
}
@ -3824,37 +3870,66 @@
adjustment_amount = 64 - min_distance;
grid_aligned_after_adjustment =
( ( low_max_y - adjustment_amount ) % 64 == 0 );
height = low_max_y - low_min_y;
if ( is_tilde && grid_aligned_after_adjustment && height < 3 * 64 )
if ( is_bottom_tilde || is_above_bottom_tilde )
{
FT_Pos centering_adjustment =
( FT_PIX_ROUND( height ) - height ) / 2;
tilde_contour = adjust_bottom
? low_contour
: ( is_above_bottom_tilde
? low_contour
: af_find_lowest_contour( hints ) );
tilde_min_y = hints->contour_y_minima[tilde_contour];
tilde_max_y = hints->contour_y_maxima[tilde_contour];
tilde_height = tilde_max_y - tilde_min_y;
adjustment_amount += centering_adjustment;
FT_TRACE4(( " Additional centering: %ld\n",
centering_adjustment ));
pos = low_max_y - adjustment_amount;
if ( adjust_above_bottom && is_bottom_tilde )
pos -= low_height;
if ( pos % 64 == 0 && tilde_height < 3 * 64 )
{
centering_adjustment = ( FT_PIX_ROUND( tilde_height ) -
tilde_height ) / 2;
FT_TRACE4(( " Additional tilde centering adjustment: %ld\n",
centering_adjustment ));
}
}
if ( ( adjust_bottom && is_bottom_tilde ) ||
( adjust_above_bottom && is_above_bottom_tilde ) )
calculated_amount = adjustment_amount + centering_adjustment;
else
calculated_amount = adjustment_amount;
FT_TRACE4(( " Calculated adjustment amount: %ld%s\n",
adjustment_amount,
( adjustment_amount < 0 || adjustment_amount > 64 )
? " (out of range [0;64], not adjusting)" : "" ));
calculated_amount,
( calculated_amount < -2 ||
( adjustment_amount > 66 && calculated_amount > 66 ) )
? " (out of range [-2;66], not adjusting)" : "" ));
if ( adjustment_amount > 0 && adjustment_amount <= 64 )
if ( calculated_amount != 0 &&
calculated_amount >= -2 &&
( calculated_amount <= 66 || adjustment_amount <= 66 ) )
{
FT_Pos height_delta = ( low_max_y - low_min_y ) / 8;
FT_Pos height_delta = low_height / 8;
FT_Pos max_y_limit = low_max_y + height_delta;
FT_TRACE4(( " Pushing low contour %ld units down\n",
adjustment_amount ));
calculated_amount ));
af_move_contours_down( hints, max_y_limit, adjustment_amount );
if ( adjust_above_bottom && is_bottom_tilde )
{
FT_TRACE4(( " Pushing bottom tilde %ld units down\n",
centering_adjustment ));
af_move_contours_down( hints,
max_y_limit - low_height,
centering_adjustment );
}
}
}