Commit c5bda503b9b15bdd042e2c9696f2b1975f49d98c
2011-02-16T21:59:44
[autofit] Add a lot of comments and do some minor formatting.
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diff --git a/src/autofit/afhints.c b/src/autofit/afhints.c
index c349709..9859370 100644
--- a/src/autofit/afhints.c
+++ b/src/autofit/afhints.c
@@ -4,7 +4,7 @@
/* */
/* Auto-fitter hinting routines (body). */
/* */
-/* Copyright 2003, 2004, 2005, 2006, 2007, 2009, 2010 by */
+/* Copyright 2003-2007, 2009-2011 by */
/* David Turner, Robert Wilhelm, and Werner Lemberg. */
/* */
/* This file is part of the FreeType project, and may only be used, */
@@ -21,6 +21,8 @@
#include FT_INTERNAL_CALC_H
+ /* Get new segment for given axis. */
+
FT_LOCAL_DEF( FT_Error )
af_axis_hints_new_segment( AF_AxisHints axis,
FT_Memory memory,
@@ -61,6 +63,8 @@
}
+ /* Get new edge for given axis, direction, and position. */
+
FT_LOCAL( FT_Error )
af_axis_hints_new_edge( AF_AxisHints axis,
FT_Int fpos,
@@ -169,20 +173,20 @@
printf( "Table of points:\n" );
- printf( " [ index | xorg | yorg | xscale | yscale "
- "| xfit | yfit | flags ]\n" );
+ printf( " [ index | xorg | yorg | xscale | yscale"
+ " | xfit | yfit | flags ]\n" );
for ( point = points; point < limit; point++ )
{
- printf( " [ %5d | %5d | %5d | %-5.2f | %-5.2f "
- "| %-5.2f | %-5.2f | %c%c%c%c%c%c ]\n",
+ printf( " [ %5d | %5d | %5d | %-5.2f | %-5.2f"
+ " | %-5.2f | %-5.2f | %c%c%c%c%c%c ]\n",
point - points,
point->fx,
point->fy,
- point->ox/64.0,
- point->oy/64.0,
- point->x/64.0,
- point->y/64.0,
+ point->ox / 64.0,
+ point->oy / 64.0,
+ point->x / 64.0,
+ point->y / 64.0,
( point->flags & AF_FLAG_WEAK_INTERPOLATION ) ? 'w' : ' ',
( point->flags & AF_FLAG_INFLECTION ) ? 'i' : ' ',
( point->flags & AF_FLAG_EXTREMA_X ) ? '<' : ' ',
@@ -222,7 +226,8 @@
}
- /* A function to dump the array of linked segments. */
+ /* Dump the array of linked segments. */
+
void
af_glyph_hints_dump_segments( AF_GlyphHints hints )
{
@@ -260,6 +265,8 @@
}
+ /* Dump the array of linked edges. */
+
void
af_glyph_hints_dump_edges( AF_GlyphHints hints )
{
@@ -276,7 +283,7 @@
/*
* note: AF_DIMENSION_HORZ corresponds to _vertical_ edges
- * since they have constant a X coordinate.
+ * since they have a constant X coordinate.
*/
printf ( "Table of %s edges:\n",
dimension == AF_DIMENSION_HORZ ? "vertical" : "horizontal" );
@@ -329,7 +336,8 @@
#endif /* !AF_DEBUG */
- /* compute the direction value of a given vector */
+ /* Compute the direction value of a given vector. */
+
FT_LOCAL_DEF( AF_Direction )
af_direction_compute( FT_Pos dx,
FT_Pos dy )
@@ -369,6 +377,8 @@
}
}
+ /* return no direction if arm lengths differ too much */
+ /* (value 14 is heuristic) */
ss *= 14;
if ( FT_ABS( ll ) <= FT_ABS( ss ) )
dir = AF_DIR_NONE;
@@ -397,7 +407,7 @@
/*
* note that we don't need to free the segment and edge
- * buffers, since they are really within the hints->points array
+ * buffers since they are really within the hints->points array
*/
for ( dim = 0; dim < AF_DIMENSION_MAX; dim++ )
{
@@ -408,8 +418,8 @@
axis->max_segments = 0;
FT_FREE( axis->segments );
- axis->num_edges = 0;
- axis->max_edges = 0;
+ axis->num_edges = 0;
+ axis->max_edges = 0;
FT_FREE( axis->edges );
}
@@ -426,6 +436,8 @@
}
+ /* Reset metrics. */
+
FT_LOCAL_DEF( void )
af_glyph_hints_rescale( AF_GlyphHints hints,
AF_ScriptMetrics metrics )
@@ -435,6 +447,9 @@
}
+ /* Recompute all AF_Point in AF_GlyphHints from the definitions */
+ /* in a source outline. */
+
FT_LOCAL_DEF( FT_Error )
af_glyph_hints_reload( AF_GlyphHints hints,
FT_Outline* outline )
@@ -457,12 +472,12 @@
hints->axis[1].num_segments = 0;
hints->axis[1].num_edges = 0;
- /* first of all, reallocate the contours array when necessary */
+ /* first of all, reallocate the contours array if necessary */
new_max = (FT_UInt)outline->n_contours;
old_max = hints->max_contours;
if ( new_max > old_max )
{
- new_max = ( new_max + 3 ) & ~3;
+ new_max = ( new_max + 3 ) & ~3; /* round up to a multiple of 4 */
if ( FT_RENEW_ARRAY( hints->contours, old_max, new_max ) )
goto Exit;
@@ -479,7 +494,7 @@
old_max = hints->max_points;
if ( new_max > old_max )
{
- new_max = ( new_max + 2 + 7 ) & ~7;
+ new_max = ( new_max + 2 + 7 ) & ~7; /* round up to a multiple of 8 */
if ( FT_RENEW_ARRAY( hints->points, old_max, new_max ) )
goto Exit;
@@ -545,7 +560,7 @@
point->flags = AF_FLAG_CUBIC;
break;
default:
- point->flags = 0;
+ point->flags = AF_FLAG_NONE;
}
point->prev = prev;
@@ -563,7 +578,7 @@
}
}
- /* set-up the contours array */
+ /* set up the contours array */
{
AF_Point* contour = hints->contours;
AF_Point* contour_limit = contour + hints->num_contours;
@@ -611,6 +626,8 @@
in_dir = af_direction_compute( out_x, out_y );
point->out_dir = (FT_Char)in_dir;
+ /* check for weak points */
+
if ( point->flags & ( AF_FLAG_CONIC | AF_FLAG_CUBIC ) )
{
Is_Weak_Point:
@@ -639,6 +656,8 @@
}
+ /* Store the hinted outline in an FT_Outline structure. */
+
FT_LOCAL_DEF( void )
af_glyph_hints_save( AF_GlyphHints hints,
FT_Outline* outline )
@@ -671,6 +690,9 @@
****************************************************************/
+ /* Align all points of an edge to the same coordinate value, */
+ /* either horizontally or vertically. */
+
FT_LOCAL_DEF( void )
af_glyph_hints_align_edge_points( AF_GlyphHints hints,
AF_Dimension dim )
@@ -704,7 +726,6 @@
break;
point = point->next;
-
}
}
}
@@ -744,8 +765,8 @@
****************************************************************/
- /* hint the strong points -- this is equivalent to the TrueType `IP' */
- /* hinting instruction */
+ /* Hint the strong points -- this is equivalent to the TrueType `IP' */
+ /* hinting instruction. */
FT_LOCAL_DEF( void )
af_glyph_hints_align_strong_points( AF_GlyphHints hints,
@@ -827,11 +848,12 @@
max = edge_limit - edges;
#if 1
- /* for small edge counts, a linear search is better */
+ /* for a small number of edges, a linear search is better */
if ( max <= 8 )
{
FT_PtrDist nn;
+
for ( nn = 0; nn < max; nn++ )
if ( edges[nn].fpos >= u )
break;
@@ -863,6 +885,7 @@
}
}
+ /* point is not on an edge */
{
AF_Edge before = edges + min - 1;
AF_Edge after = edges + min + 0;
@@ -898,6 +921,10 @@
****************************************************************/
+ /* Shift the original coordinates of all points between `p1' and */
+ /* `p2' to get hinted coordinates, using the same difference as */
+ /* given by `ref'. */
+
static void
af_iup_shift( AF_Point p1,
AF_Point p2,
@@ -906,6 +933,7 @@
AF_Point p;
FT_Pos delta = ref->u - ref->v;
+
if ( delta == 0 )
return;
@@ -917,6 +945,13 @@
}
+ /* Interpolate the original coordinates of all points between `p1' and */
+ /* `p2' to get hinted coordinates, using `ref1' and `ref2' as the */
+ /* reference points. The `u' and `v' members are the current and */
+ /* original coordinate values, respectively. */
+ /* */
+ /* Details can be found in the TrueType bytecode specification. */
+
static void
af_iup_interp( AF_Point p1,
AF_Point p2,
@@ -985,6 +1020,9 @@
}
+ /* Hint the weak points -- this is equivalent to the TrueType `IUP' */
+ /* hinting instruction. */
+
FT_LOCAL_DEF( void )
af_glyph_hints_align_weak_points( AF_GlyphHints hints,
AF_Dimension dim )
@@ -1050,17 +1088,18 @@
for (;;)
{
- FT_ASSERT( point <= end_point &&
+ FT_ASSERT( point <= end_point &&
( point->flags & touch_flag ) != 0 );
- /* skip any touched neighbhours */
- while ( point < end_point && ( point[1].flags & touch_flag ) != 0 )
+ /* skip any touched neighbours */
+ while ( point < end_point &&
+ ( point[1].flags & touch_flag ) != 0 )
point++;
last_touched = point;
/* find the next touched point, if any */
- point ++;
+ point++;
for (;;)
{
if ( point > end_point )
@@ -1080,9 +1119,8 @@
EndContour:
/* special case: only one point was touched */
if ( last_touched == first_touched )
- {
af_iup_shift( first_point, end_point, first_touched );
- }
+
else /* interpolate the last part */
{
if ( last_touched < end_point )
diff --git a/src/autofit/afhints.h b/src/autofit/afhints.h
index 10e673b..d63b979 100644
--- a/src/autofit/afhints.h
+++ b/src/autofit/afhints.h
@@ -4,7 +4,7 @@
/* */
/* Auto-fitter hinting routines (specification). */
/* */
-/* Copyright 2003, 2004, 2005, 2006, 2007, 2008, 2010 by */
+/* Copyright 2003-2008, 2010-2011 by */
/* David Turner, Robert Wilhelm, and Werner Lemberg. */
/* */
/* This file is part of the FreeType project, and may only be used, */
@@ -25,10 +25,10 @@
FT_BEGIN_HEADER
- /*
- * The definition of outline glyph hints. These are shared by all
- * script analysis routines (until now).
- */
+ /*
+ * The definition of outline glyph hints. These are shared by all
+ * script analysis routines (until now).
+ */
typedef enum AF_Dimension_
{
@@ -55,6 +55,128 @@ FT_BEGIN_HEADER
} AF_Direction;
+ /*
+ * The following explanations are mostly taken from the article
+ *
+ * Real-Time Grid Fitting of Typographic Outlines
+ *
+ * by David Turner and Werner Lemberg
+ *
+ * http://www.tug.org/TUGboat/Articles/tb24-3/lemberg.pdf
+ *
+ *
+ * Segments
+ *
+ * `af_{cjk,latin,...}_hints_compute_segments' are the functions to
+ * find segments in an outline. A segment is a series of consecutive
+ * points that are approximately aligned along a coordinate axis. The
+ * analysis to do so is specific to a script.
+ *
+ * A segment must have at least two points, except in the case of
+ * `fake' segments that are generated to hint metrics appropriately,
+ * and which consist of a single point.
+ *
+ *
+ * Edges
+ *
+ * As soon as segments are defined, the auto-hinter groups them into
+ * edges. An edge corresponds to a single position on the main
+ * dimension that collects one or more segments (allowing for a small
+ * threshold).
+ *
+ * The auto-hinter first tries to grid fit edges, then to align
+ * segments on the edges unless it detects that they form a serif.
+ *
+ * `af_{cjk,latin,...}_hints_compute_edges' are the functions to find
+ * edges; they are specific to a script.
+ *
+ *
+ * Stems
+ *
+ * Segments need to be `linked' to other ones in order to detect stems.
+ * A stem is made of two segments that face each other in opposite
+ * directions and that are sufficiently close to each other. Using
+ * vocabulary from the TrueType specification, stem segments form a
+ * `black distance'.
+ *
+ * Each segment has at most one `best' candidate to form a black
+ * distance, or no candidate at all. Notice that two distinct segments
+ * can have the same candidate, which frequently means a serif.
+ *
+ * A stem is recognized by the following condition:
+ *
+ * best segment_1 = segment_2 && best segment_2 = segment_1
+ *
+ * The best candidate is stored in field `link' in structure
+ * `AF_Segment'.
+ *
+ * Stems are detected by `af_{cjk,latin,...}_hint_edges'.
+ *
+ *
+ * Serifs
+ *
+ * On the opposite, a serif has
+ *
+ * best segment_1 = segment_2 && best segment_2 != segment_1
+ *
+ * where segment_1 corresponds to the serif segment.
+ *
+ * The best candidate is stored in field `serif' in structure
+ * `AF_Segment' (and `link' is set to NULL).
+ *
+ * Serifs are detected by `af_{cjk,latin,...}_hint_edges'.
+ *
+ *
+ * Touched points
+ *
+ * A point is called `touched' if it has been processed somehow by the
+ * auto-hinter. It basically means that it shouldn't be moved again
+ * (or moved only under certain constraints to preserve the already
+ * applied processing).
+ *
+ *
+ * Flat and round segments
+ *
+ * Segments are `round' or `flat', depending on the series of points
+ * that define them. A segment is round if the next and previous point
+ * of an extremum (which can be either a single point or sequence of
+ * points) are both conic or cubic control points. Otherwise, a
+ * segment with an extremum is flat.
+ *
+ *
+ * Strong Points
+ *
+ * Experience has shown that points which are not part of an edge need
+ * to be interpolated linearly between their two closest edges, even if
+ * these are not part of the contour of those particular points.
+ * Typical candidates for this are
+ *
+ * - angle points (i.e., points where the `in' and `out' direction
+ * differ greatly)
+ *
+ * - inflection points (i.e., where the `in' and `out' angles are the
+ * same, but the curvature changes sign)
+ *
+ * `af_glyph_hints_align_strong_points' is the function which takes
+ * care of such situations; it is equivalent to the TrueType `IP'
+ * hinting instruction.
+ *
+ *
+ * Weak Points
+ *
+ * Other points in the outline must be interpolated using the
+ * coordinates of their previous and next unfitted contour neighbours.
+ * These are called `weak points' and are touched by the function
+ * `af_glyph_hints_align_weak_points', equivalent to the TrueType `IUP'
+ * hinting instruction. Typical candidates are control points and
+ * points on the contour without a major direction.
+ *
+ * The major effect is to reduce possible distortion caused by
+ * alignment of edges and strong points, thus weak points are processed
+ * after strong points.
+ */
+
+
/* point hint flags */
typedef enum AF_Flags_
{
@@ -155,32 +277,31 @@ FT_BEGIN_HEADER
FT_Fixed scale; /* used to speed up interpolation between edges */
AF_Width blue_edge; /* non-NULL if this is a blue edge */
- AF_Edge link;
- AF_Edge serif;
- FT_Short num_linked;
+ AF_Edge link; /* link edge */
+ AF_Edge serif; /* primary edge for serifs */
+ FT_Short num_linked; /* number of linked edges */
+ FT_Int score; /* used during stem matching */
- FT_Int score;
-
- AF_Segment first;
- AF_Segment last;
+ AF_Segment first; /* first segment in edge */
+ AF_Segment last; /* last segment in edge */
} AF_EdgeRec;
typedef struct AF_AxisHintsRec_
{
- FT_Int num_segments;
- FT_Int max_segments;
- AF_Segment segments;
+ FT_Int num_segments; /* number of used segments */
+ FT_Int max_segments; /* number of allocated segments */
+ AF_Segment segments; /* segments array */
#ifdef AF_SORT_SEGMENTS
FT_Int mid_segments;
#endif
- FT_Int num_edges;
- FT_Int max_edges;
- AF_Edge edges;
+ FT_Int num_edges; /* number of used edges */
+ FT_Int max_edges; /* number of allocated edges */
+ AF_Edge edges; /* edges array */
- AF_Direction major_dir;
+ AF_Direction major_dir; /* either vertical or horizontal */
} AF_AxisHintsRec, *AF_AxisHints;
@@ -197,13 +318,13 @@ FT_BEGIN_HEADER
FT_Pos edge_distance_threshold;
- FT_Int max_points;
- FT_Int num_points;
- AF_Point points;
+ FT_Int max_points; /* number of allocated points */
+ FT_Int num_points; /* number of used points */
+ AF_Point points; /* points array */
- FT_Int max_contours;
- FT_Int num_contours;
- AF_Point* contours;
+ FT_Int max_contours; /* number of allocated contours */
+ FT_Int num_contours; /* number of used contours */
+ AF_Point* contours; /* contours array */
AF_AxisHintsRec axis[AF_DIMENSION_MAX];
@@ -214,7 +335,7 @@ FT_BEGIN_HEADER
FT_Pos xmin_delta; /* used for warping */
FT_Pos xmax_delta;
-
+
} AF_GlyphHintsRec;
@@ -274,12 +395,6 @@ FT_BEGIN_HEADER
af_glyph_hints_init( AF_GlyphHints hints,
FT_Memory memory );
-
-
- /*
- * recompute all AF_Point in a AF_GlyphHints from the definitions
- * in a source outline
- */
FT_LOCAL( void )
af_glyph_hints_rescale( AF_GlyphHints hints,
AF_ScriptMetrics metrics );