ref: 5cf01aa2b26727abd97ef202a3687cd7a43819c3
dir: /src/autofit/afhints.h/
/****************************************************************************
*
* afhints.h
*
* Auto-fitter hinting routines (specification).
*
* Copyright (C) 2003-2022 by
* David Turner, Robert Wilhelm, and Werner Lemberg.
*
* This file is part of the FreeType project, and may only be used,
* modified, and distributed under the terms of the FreeType project
* license, LICENSE.TXT. By continuing to use, modify, or distribute
* this file you indicate that you have read the license and
* understand and accept it fully.
*
*/
#ifndef AFHINTS_H_
#define AFHINTS_H_
#include "aftypes.h"
#define xxAF_SORT_SEGMENTS
FT_BEGIN_HEADER
/*
* The definition of outline glyph hints. These are shared by all
* writing system analysis routines (until now).
*/
typedef enum AF_Dimension_
{
AF_DIMENSION_HORZ = 0, /* x coordinates, */
/* i.e., vertical segments & edges */
AF_DIMENSION_VERT = 1, /* y coordinates, */
/* i.e., horizontal segments & edges */
AF_DIMENSION_MAX /* do not remove */
} AF_Dimension;
/* hint directions -- the values are computed so that two vectors are */
/* in opposite directions iff `dir1 + dir2 == 0' */
typedef enum AF_Direction_
{
AF_DIR_NONE = 4,
AF_DIR_RIGHT = 1,
AF_DIR_LEFT = -1,
AF_DIR_UP = 2,
AF_DIR_DOWN = -2
} AF_Direction;
/*
* The following explanations are mostly taken from the article
*
* Real-Time Grid Fitting of Typographic Outlines
*
* by David Turner and Werner Lemberg
*
* https://www.tug.org/TUGboat/Articles/tb24-3/lemberg.pdf
*
* with appropriate updates.
*
*
* Segments
*
* `af_{cjk,latin,...}_hints_compute_segments' are the functions to
* find segments in an outline.
*
* A segment is a series of at least two consecutive points that are
* approximately aligned along a coordinate axis. The analysis to do
* so is specific to a writing system.
*
*
* Edges
*
* `af_{cjk,latin,...}_hints_compute_edges' are the functions to find
* 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).
*
* As an example, the `latin' writing system first tries to grid-fit
* edges, then to align segments on the edges unless it detects that
* they form a serif.
*
*
* A H
* | |
* | |
* | |
* | |
* C | | F
* +------<-----+ +-----<------+
* | B G |
* | |
* | |
* +--------------->------------------+
* D E
*
*
* Stems
*
* Stems are detected by `af_{cjk,latin,...}_hint_edges'.
*
* 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'.
*
* In the above ASCII drawing, the horizontal segments are BC, DE, and
* FG; the vertical segments are AB, CD, EF, and GH.
*
* 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'.
*
* In the above ASCII drawing, the best candidate for both AB and CD is
* GH, while the best candidate for GH is AB. Similarly, the best
* candidate for EF and GH is AB, while the best candidate for AB is
* GH.
*
* The detection and handling of stems is dependent on the writing
* system.
*
*
* Serifs
*
* Serifs are detected by `af_{cjk,latin,...}_hint_edges'.
*
* In comparison to a stem, a serif (as handled by the auto-hinter
* module that takes care of the `latin' writing system) has
*
* best segment_1 = segment_2 && best segment_2 != segment_1
*
* where segment_1 corresponds to the serif segment (CD and EF in the
* above ASCII drawing).
*
* The best candidate is stored in field `serif' in structure
* `AF_Segment' (and `link' is set to NULL).
*
*
* 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 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) [currently, such points
* aren't handled specially in the auto-hinter]
*
* `af_glyph_hints_align_strong_points' is the function that 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 */
#define AF_FLAG_NONE 0
/* point type flags */
#define AF_FLAG_CONIC ( 1U << 0 )
#define AF_FLAG_CUBIC ( 1U << 1 )
#define AF_FLAG_CONTROL ( AF_FLAG_CONIC | AF_FLAG_CUBIC )
/* point touch flags */
#define AF_FLAG_TOUCH_X ( 1U << 2 )
#define AF_FLAG_TOUCH_Y ( 1U << 3 )
/* candidates for weak interpolation have this flag set */
#define AF_FLAG_WEAK_INTERPOLATION ( 1U << 4 )
/* the distance to the next point is very small */
#define AF_FLAG_NEAR ( 1U << 5 )
/* edge hint flags */
#define AF_EDGE_NORMAL 0
#define AF_EDGE_ROUND ( 1U << 0 )
#define AF_EDGE_SERIF ( 1U << 1 )
#define AF_EDGE_DONE ( 1U << 2 )
#define AF_EDGE_NEUTRAL ( 1U << 3 ) /* edge aligns to a neutral blue zone */
typedef struct AF_PointRec_* AF_Point;
typedef struct AF_SegmentRec_* AF_Segment;
typedef struct AF_EdgeRec_* AF_Edge;
typedef struct AF_PointRec_
{
FT_UShort flags; /* point flags used by hinter */
FT_Char in_dir; /* direction of inwards vector */
FT_Char out_dir; /* direction of outwards vector */
FT_Pos ox, oy; /* original, scaled position */
FT_Short fx, fy; /* original, unscaled position (in font units) */
FT_Pos x, y; /* current position */
FT_Pos u, v; /* current (x,y) or (y,x) depending on context */
AF_Point next; /* next point in contour */
AF_Point prev; /* previous point in contour */
#ifdef FT_DEBUG_AUTOFIT
/* track `before' and `after' edges for strong points */
AF_Edge before[2];
AF_Edge after[2];
#endif
} AF_PointRec;
typedef struct AF_SegmentRec_
{
FT_Byte flags; /* edge/segment flags for this segment */
FT_Char dir; /* segment direction */
FT_Short pos; /* position of segment */
FT_Short delta; /* deviation from segment position */
FT_Short min_coord; /* minimum coordinate of segment */
FT_Short max_coord; /* maximum coordinate of segment */
FT_Short height; /* the hinted segment height */
AF_Edge edge; /* the segment's parent edge */
AF_Segment edge_next; /* link to next segment in parent edge */
AF_Segment link; /* (stem) link segment */
AF_Segment serif; /* primary segment for serifs */
FT_Pos score; /* used during stem matching */
FT_Pos len; /* used during stem matching */
AF_Point first; /* first point in edge segment */
AF_Point last; /* last point in edge segment */
} AF_SegmentRec;
typedef struct AF_EdgeRec_
{
FT_Short fpos; /* original, unscaled position (in font units) */
FT_Pos opos; /* original, scaled position */
FT_Pos pos; /* current position */
FT_Byte flags; /* edge flags */
FT_Char dir; /* edge direction */
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; /* link edge */
AF_Edge serif; /* primary edge for serifs */
FT_Int score; /* used during stem matching */
AF_Segment first; /* first segment in edge */
AF_Segment last; /* last segment in edge */
} AF_EdgeRec;
#define AF_SEGMENTS_EMBEDDED 18 /* number of embedded segments */
#define AF_EDGES_EMBEDDED 12 /* number of embedded edges */
typedef struct AF_AxisHintsRec_
{
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; /* number of used edges */
FT_Int max_edges; /* number of allocated edges */
AF_Edge edges; /* edges array */
AF_Direction major_dir; /* either vertical or horizontal */
/* two arrays to avoid allocation penalty */
struct
{
AF_SegmentRec segments[AF_SEGMENTS_EMBEDDED];
AF_EdgeRec edges[AF_EDGES_EMBEDDED];
} embedded;
} AF_AxisHintsRec, *AF_AxisHints;
#define AF_POINTS_EMBEDDED 96 /* number of embedded points */
#define AF_CONTOURS_EMBEDDED 8 /* number of embedded contours */
typedef struct AF_GlyphHintsRec_
{
FT_Memory memory;
FT_Fixed x_scale;
FT_Pos x_delta;
FT_Fixed y_scale;
FT_Pos y_delta;
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; /* number of allocated contours */
FT_Int num_contours; /* number of used contours */
AF_Point* contours; /* contours array */
AF_AxisHintsRec axis[AF_DIMENSION_MAX];
FT_UInt32 scaler_flags; /* copy of scaler flags */
FT_UInt32 other_flags; /* free for style-specific */
/* implementations */
AF_StyleMetrics metrics;
/* Two arrays to avoid allocation penalty. */
/* The `embedded' structure must be the last element! */
struct
{
AF_Point contours[AF_CONTOURS_EMBEDDED];
AF_PointRec points[AF_POINTS_EMBEDDED];
} embedded;
} AF_GlyphHintsRec;
#define AF_HINTS_TEST_SCALER( h, f ) ( (h)->scaler_flags & (f) )
#define AF_HINTS_TEST_OTHER( h, f ) ( (h)->other_flags & (f) )
#ifdef FT_DEBUG_AUTOFIT
#define AF_HINTS_DO_HORIZONTAL( h ) \
( !_af_debug_disable_horz_hints && \
!AF_HINTS_TEST_SCALER( h, AF_SCALER_FLAG_NO_HORIZONTAL ) )
#define AF_HINTS_DO_VERTICAL( h ) \
( !_af_debug_disable_vert_hints && \
!AF_HINTS_TEST_SCALER( h, AF_SCALER_FLAG_NO_VERTICAL ) )
#define AF_HINTS_DO_BLUES( h ) ( !_af_debug_disable_blue_hints )
#else /* !FT_DEBUG_AUTOFIT */
#define AF_HINTS_DO_HORIZONTAL( h ) \
!AF_HINTS_TEST_SCALER( h, AF_SCALER_FLAG_NO_HORIZONTAL )
#define AF_HINTS_DO_VERTICAL( h ) \
!AF_HINTS_TEST_SCALER( h, AF_SCALER_FLAG_NO_VERTICAL )
#define AF_HINTS_DO_BLUES( h ) 1
#endif /* !FT_DEBUG_AUTOFIT */
#define AF_HINTS_DO_ADVANCE( h ) \
!AF_HINTS_TEST_SCALER( h, AF_SCALER_FLAG_NO_ADVANCE )
FT_LOCAL( AF_Direction )
af_direction_compute( FT_Pos dx,
FT_Pos dy );
FT_LOCAL( FT_Error )
af_axis_hints_new_segment( AF_AxisHints axis,
FT_Memory memory,
AF_Segment *asegment );
FT_LOCAL( FT_Error)
af_axis_hints_new_edge( AF_AxisHints axis,
FT_Int fpos,
AF_Direction dir,
FT_Bool top_to_bottom_hinting,
FT_Memory memory,
AF_Edge *edge );
FT_LOCAL( void )
af_glyph_hints_init( AF_GlyphHints hints,
FT_Memory memory );
FT_LOCAL( void )
af_glyph_hints_rescale( AF_GlyphHints hints,
AF_StyleMetrics metrics );
FT_LOCAL( FT_Error )
af_glyph_hints_reload( AF_GlyphHints hints,
FT_Outline* outline );
FT_LOCAL( void )
af_glyph_hints_save( AF_GlyphHints hints,
FT_Outline* outline );
FT_LOCAL( void )
af_glyph_hints_align_edge_points( AF_GlyphHints hints,
AF_Dimension dim );
FT_LOCAL( void )
af_glyph_hints_align_strong_points( AF_GlyphHints hints,
AF_Dimension dim );
FT_LOCAL( void )
af_glyph_hints_align_weak_points( AF_GlyphHints hints,
AF_Dimension dim );
FT_LOCAL( void )
af_glyph_hints_done( AF_GlyphHints hints );
/* */
#define AF_SEGMENT_LEN( seg ) ( (seg)->max_coord - (seg)->min_coord )
#define AF_SEGMENT_DIST( seg1, seg2 ) ( ( (seg1)->pos > (seg2)->pos ) \
? (seg1)->pos - (seg2)->pos \
: (seg2)->pos - (seg1)->pos )
FT_END_HEADER
#endif /* AFHINTS_H_ */
/* END */