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[autofit] New algorithm for preventing hinting of tilde glyphs.

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The old algorithm removed segments from edges to make the auto-hinter ignore
a tilde.  However, the implementation had two flaws.

- Edge array elements were moved around without reordering them afterwards.
- The linking between edges and segments wasn't correctly updated for moved
  edges, which could cause endless loops.

Correcting both problems are non-trivial; additionally, a fix would make
the auto-hinter slower.

For these reasons, a new, simpler approach is taken: A new flag allows
points to be tagged as being ignored, and if such a point is enountered, it
doesn't get added to a segment.

Fixes issue #1333.

* src/autofit/afhints.h (AF_FLAG_IGNORE): New macro.

* src/autofit/aflatin.c (af_latin_hints_compute_segments, af_touch_contour):
  Use it.
  (af_remove_segments_containing_point, af_remove_top_points_from_edges,
  af_remove_bottom_points_from_edges): Removed.
  (af_latin_stretch_top_tilde): Call `af_touch_top_contours` and
  `af_touch_bottom_contours` unconditionally.
  (af_latin_hints_apply): Updated.
This commit is contained in:
Werner Lemberg
2025-05-12 08:28:55 +02:00
parent 89e3e98e47
commit fd66a29d10
2 changed files with 20 additions and 166 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
src/autofit/afhints.h
View File

@@ -222,6 +222,9 @@ FT_BEGIN_HEADER
/* the distance to the next point is very small */
#define AF_FLAG_NEAR ( 1U << 5 )
/* prevent the auto-hinter from adding such a point to a segment */
#define AF_FLAG_IGNORE ( 1U << 6 )
/* edge hint flags */
#define AF_EDGE_NORMAL 0

183
src/autofit/aflatin.c
View File

@@ -1638,7 +1638,8 @@
FT_Pos prev_max_on_coord = max_on_coord;
if ( FT_ABS( last->out_dir ) == major_dir &&
if ( !( point->flags & AF_FLAG_IGNORE ) &&
FT_ABS( last->out_dir ) == major_dir &&
FT_ABS( point->out_dir ) == major_dir )
{
/* we are already on an edge, try to locate its start */
@@ -1697,13 +1698,17 @@
max_on_coord = v;
}
if ( point->out_dir != segment_dir || point == last )
if ( point->flags & AF_FLAG_IGNORE ||
point->out_dir != segment_dir ||
point == last )
{
/* check whether the new segment's start point is identical to */
/* the previous segment's end point; for example, this might */
/* happen for spikes */
if ( !prev_segment || segment->first != prev_segment->last )
if ( point->flags & AF_FLAG_IGNORE ||
!prev_segment ||
segment->first != prev_segment->last )
{
/* points are different: we are just leaving an edge, thus */
/* record a new segment */
@@ -1863,7 +1868,8 @@
/* if we are not on an edge, check whether the major direction */
/* coincides with the current point's `out' direction, or */
/* whether we have a single-point contour */
if ( !on_edge &&
if ( !( point->flags & AF_FLAG_IGNORE ) &&
!on_edge &&
( FT_ABS( point->out_dir ) == major_dir ||
point == point->prev ) )
{
@@ -3023,144 +3029,6 @@
}
static void
af_remove_segments_containing_point( AF_GlyphHints hints,
AF_Point point )
{
AF_AxisHints axis = &hints->axis[AF_DIMENSION_VERT];
AF_Segment segments = axis->segments;
FT_UInt i;
for ( i = 0; i < axis->num_segments; i++ )
{
AF_Segment seg = &segments[i];
AF_Point p = seg->first;
FT_Bool remove = 0;
while ( 1 )
{
if ( p == point )
{
remove = 1;
break;
}
if ( p == seg->last )
break;
p = p->next;
}
if ( remove )
{
/* First, check the first and last segment of the edge. */
AF_Edge edge = seg->edge;
if ( !edge )
continue;
if ( edge->first == seg && edge->last == seg )
{
/* The edge only consists of the segment to be removed. */
/* Remove the edge. */
*edge = axis->edges[--axis->num_edges];
}
else
{
if ( edge->first == seg )
edge->first = seg->edge_next;
if ( edge->last == seg )
{
edge->last = edge->first;
while ( edge->last && edge->last->edge_next != seg )
edge->last = edge->last->edge_next;
}
}
/* Now, delete the segment. */
*seg = axis->segments[--axis->num_segments];
i--; /* We have to check the new segment at this position. */
}
}
}
/* Remove all segments containing points on `limit_contour` */
/* and all higher contours. */
static void
af_remove_top_points_from_edges( AF_GlyphHints hints,
FT_Int limit_contour )
{
FT_Pos limit = hints->contour_y_minima[limit_contour];
FT_Int contour;
for ( contour = 0; contour < hints->num_contours; contour++ )
{
FT_Pos min_y = hints->contour_y_minima[contour];
FT_Pos max_y = hints->contour_y_maxima[contour];
if ( min_y < max_y &&
min_y >= limit )
{
AF_Point first_point = hints->contours[contour];
AF_Point p = first_point;
do
{
p = p->next;
af_remove_segments_containing_point( hints, p );
} while ( p != first_point );
}
}
}
static void
af_remove_bottom_points_from_edges( AF_GlyphHints hints,
FT_Int limit_contour )
{
FT_Pos limit = hints->contour_y_maxima[limit_contour];
FT_Int contour;
for ( contour = 0; contour < hints->num_contours; contour++ )
{
FT_Pos min_y = hints->contour_y_minima[contour];
FT_Pos max_y = hints->contour_y_maxima[contour];
if ( min_y < max_y &&
max_y <= limit )
{
AF_Point first_point = hints->contours[contour];
AF_Point p = first_point;
do
{
p = p->next;
af_remove_segments_containing_point( hints, p );
} while ( p != first_point );
}
}
}
/* While aligning edges to blue zones, make the auto-hinter */
/* ignore the ones that are higher than `pos`. */
static void
@@ -3285,6 +3153,8 @@
do
{
p = p->next;
p->flags |= AF_FLAG_IGNORE;
if ( !( p->flags & AF_FLAG_CONTROL ) )
p->flags |= AF_FLAG_TOUCH_Y;
@@ -3424,15 +3294,10 @@
FT_TRACE4(( "af_latin_stretch_top_tilde: min measurement %ld\n",
min_measurement ));
/* To preserve the stretched shape we suppress any */
/* auto-hinting if the tilde height is less than 4 pixels; */
/* we do this for all contours equal or above the vertical */
/* minimum of `tilde_contour`. */
/* */
/* The second part is to remove the affected points from */
/* edges, done in `af_latin_hints_apply`. */
if ( height < 64 * 4 )
af_touch_top_contours( hints, tilde_contour );
/* To preserve the stretched shape we prevent that the tilde */
/* gets auto-hinted; we do this for all contours equal or */
/* above the vertical minimum of `tilde_contour`. */
af_touch_top_contours( hints, tilde_contour );
/* XXX This is an important element of the algorithm; */
/* we need a description. */
@@ -3529,8 +3394,7 @@
FT_TRACE4(( "af_latin_stretch_bottom_tilde: min measurement %ld\n",
min_measurement ));
if ( height < 64 * 4 )
af_touch_bottom_contours( hints, tilde_contour );
af_touch_bottom_contours( hints, tilde_contour );
target_height = min_measurement + 64;
if ( height >= target_height )
@@ -5024,19 +4888,6 @@
small_top_blue, small_bottom_blue );
}
/* Second part of making everything of a top tilde and above (or */
/* a bottom tilde and below) be ignored by the auto-hinter. */
if ( is_top_tilde || is_below_top_tilde )
af_remove_top_points_from_edges( hints,
is_top_tilde
? top_tilde_contour
: below_top_tilde_contour );
if ( is_bottom_tilde || is_above_bottom_tilde )
af_remove_bottom_points_from_edges( hints,
is_bottom_tilde
? bottom_tilde_contour
: above_bottom_tilde_contour );
if ( error )
goto Exit;