/**************************************************************************** * * afhints.h * * Auto-fitter hinting routines (specification). * * Copyright (C) 2003-2023 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" FT_BEGIN_HEADER /* * The definition of outline glyph hints. These are shared by all * writing system analysis routines (until now). */ AF_Dimension; /* hint directions -- the values are computed so that two vectors are */ /* in opposite directions iff `dir1 + dir2 == 0' */ 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 … /* point type flags */ #define AF_FLAG_CONIC … #define AF_FLAG_CUBIC … #define AF_FLAG_CONTROL … /* point touch flags */ #define AF_FLAG_TOUCH_X … #define AF_FLAG_TOUCH_Y … /* candidates for weak interpolation have this flag set */ #define AF_FLAG_WEAK_INTERPOLATION … /* the distance to the next point is very small */ #define AF_FLAG_NEAR … /* edge hint flags */ #define AF_EDGE_NORMAL … #define AF_EDGE_ROUND … #define AF_EDGE_SERIF … #define AF_EDGE_DONE … #define AF_EDGE_NEUTRAL … AF_Point; AF_Segment; AF_Edge; AF_PointRec; AF_SegmentRec; AF_EdgeRec; #define AF_SEGMENTS_EMBEDDED … #define AF_EDGES_EMBEDDED … AF_AxisHints; #define AF_POINTS_EMBEDDED … #define AF_CONTOURS_EMBEDDED … AF_GlyphHintsRec; #define AF_HINTS_TEST_SCALER( h, f ) … #define AF_HINTS_TEST_OTHER( h, f ) … #ifdef FT_DEBUG_AUTOFIT #define AF_HINTS_DO_HORIZONTAL … #define AF_HINTS_DO_VERTICAL … #define AF_HINTS_DO_BLUES … #else /* !FT_DEBUG_AUTOFIT */ #define AF_HINTS_DO_HORIZONTAL( h ) … #define AF_HINTS_DO_VERTICAL( h ) … #define AF_HINTS_DO_BLUES( h ) … #endif /* !FT_DEBUG_AUTOFIT */ #define AF_HINTS_DO_ADVANCE( h ) … 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 ) … #define AF_SEGMENT_DIST( seg1, seg2 ) … FT_END_HEADER #endif /* AFHINTS_H_ */ /* END */