diff options
Diffstat (limited to 'src/autofit/afhints.h')
| -rw-r--r-- | src/autofit/afhints.h | 217 |
1 files changed, 176 insertions, 41 deletions
diff --git a/src/autofit/afhints.h b/src/autofit/afhints.h index 10e673b..1c52e0d 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 +55,151 @@ 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. + * + * + * A H + * | | + * | | + * | | + * | | + * C | | F + * +------<-----+ +-----<------+ + * | B G | + * | | + * | | + * +--------------->------------------+ + * D E + * + * + * 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'. + * + * 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'. + * + * Stems are detected by `af_{cjk,latin,...}_hint_edges'. + * + * 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. + * + * + * 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 (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). + * + * 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_ { @@ -137,9 +282,8 @@ FT_BEGIN_HEADER 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_Point* contour; /* ptr to first point of segment's contour */ + AF_Point first; /* first point in edge segment */ + AF_Point last; /* last point in edge segment */ } AF_SegmentRec; @@ -155,32 +299,31 @@ 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; - - FT_Int score; + 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 */ - 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; @@ -195,15 +338,13 @@ FT_BEGIN_HEADER FT_Fixed y_scale; FT_Pos y_delta; - FT_Pos edge_distance_threshold; + FT_Int max_points; /* number of allocated points */ + FT_Int num_points; /* number of used points */ + AF_Point points; /* points array */ - FT_Int max_points; - FT_Int num_points; - AF_Point points; - - 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 +355,7 @@ FT_BEGIN_HEADER FT_Pos xmin_delta; /* used for warping */ FT_Pos xmax_delta; - + } AF_GlyphHintsRec; @@ -222,7 +363,7 @@ FT_BEGIN_HEADER #define AF_HINTS_TEST_OTHER( h, f ) ( (h)->other_flags & (f) ) -#ifdef AF_DEBUG +#ifdef FT_DEBUG_AUTOFIT #define AF_HINTS_DO_HORIZONTAL( h ) \ ( !_af_debug_disable_horz_hints && \ @@ -237,7 +378,7 @@ FT_BEGIN_HEADER #define AF_HINTS_DO_BLUES( h ) ( !_af_debug_disable_blue_hints ) -#else /* !AF_DEBUG */ +#else /* !FT_DEBUG_AUTOFIT */ #define AF_HINTS_DO_HORIZONTAL( h ) \ !AF_HINTS_TEST_SCALER( h, AF_SCALER_FLAG_NO_HORIZONTAL ) @@ -250,7 +391,7 @@ FT_BEGIN_HEADER #define AF_HINTS_DO_BLUES( h ) 1 -#endif /* !AF_DEBUG */ +#endif /* !FT_DEBUG_AUTOFIT */ FT_LOCAL( AF_Direction ) @@ -274,12 +415,6 @@ 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 ); @@ -304,7 +439,7 @@ FT_BEGIN_HEADER af_glyph_hints_align_weak_points( AF_GlyphHints hints, AF_Dimension dim ); -#ifdef AF_USE_WARPER +#ifdef AF_CONFIG_OPTION_USE_WARPER FT_LOCAL( void ) af_glyph_hints_scale_dim( AF_GlyphHints hints, AF_Dimension dim, |