[autofit] Fix style assignments to glyphs.
* src/autofit/hbshim.c (af_get_coverage) [FT_CONFIG_OPTION_USE_HARFBUZZ]: Scan GPOS coverage of features also so that we can skip glyphs that have both GSUB and GPOS data.
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Werner Lemberg
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0950f3a50e
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@ -1,3 +1,11 @@
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2014-01-01 Werner Lemberg <wl@gnu.org>
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[autofit] Fix style assignments to glyphs.
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* src/autofit/hbshim.c (af_get_coverage)
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[FT_CONFIG_OPTION_USE_HARFBUZZ]: Scan GPOS coverage of features also
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so that we can skip glyphs that have both GSUB and GPOS data.
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2014-01-01 Werner Lemberg <wl@gnu.org>
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* src/autofit/hbshim.c: s/{lookups,glyphs}/gsub_{lookups,glyphs}/.
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@ -102,6 +102,8 @@
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hb_set_t* gsub_lookups; /* GSUB lookups for a given script */
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hb_set_t* gsub_glyphs; /* glyphs covered by GSUB lookups */
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hb_set_t* gpos_lookups; /* GPOS lookups for a given script */
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hb_set_t* gpos_glyphs; /* glyphs covered by GPOS lookups */
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hb_tag_t script;
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const hb_tag_t* coverage_tags;
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@ -123,6 +125,8 @@
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gsub_lookups = hb_set_create();
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gsub_glyphs = hb_set_create();
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gpos_lookups = hb_set_create();
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gpos_glyphs = hb_set_create();
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coverage_tags = coverages[style_class->coverage];
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script = scripts[style_class->script];
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@ -162,6 +166,12 @@
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NULL,
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coverage_tags,
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gsub_lookups );
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hb_ot_layout_collect_lookups( face,
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HB_OT_TAG_GPOS,
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script_tags,
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NULL,
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coverage_tags,
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gpos_lookups );
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FT_TRACE4(( "GSUB lookups (style `%s'):\n"
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" ",
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@ -178,6 +188,7 @@
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count++;
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#endif
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/* get output coverage of GSUB feature */
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hb_ot_layout_lookup_collect_glyphs( face,
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HB_OT_TAG_GSUB,
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idx,
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@ -191,9 +202,84 @@
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if ( !count )
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FT_TRACE4(( " (none)" ));
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FT_TRACE4(( "\n\n" ));
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#endif
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FT_TRACE4(( " glyphs (`*' means already assigned)" ));
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FT_TRACE4(( "GPOS lookups (style `%s'):\n"
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" ",
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af_style_names[style_class->style] ));
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#ifdef FT_DEBUG_LEVEL_TRACE
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count = 0;
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#endif
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for ( idx = -1; hb_set_next( gpos_lookups, &idx ); )
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{
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#ifdef FT_DEBUG_LEVEL_TRACE
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FT_TRACE4(( " %d", idx ));
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count++;
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#endif
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/* get input coverage of GPOS feature */
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hb_ot_layout_lookup_collect_glyphs( face,
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HB_OT_TAG_GPOS,
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idx,
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NULL,
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gpos_glyphs,
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NULL,
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NULL );
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}
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#ifdef FT_DEBUG_LEVEL_TRACE
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if ( !count )
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FT_TRACE4(( " (none)" ));
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FT_TRACE4(( "\n\n" ));
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#endif
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/*
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* Various OpenType features might use the same glyphs at different
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* vertical positions; for example, superscript and subscript glyphs
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* could be the same. However, FreeType's auto-hinting is completely
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* agnostic of OpenType features after the feature analysis has been
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* completed: FreeType then simply receives a glyph index and returns a
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* hinted and usually rendered glyph.
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*
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* Consider the superscript feature of font `pala.ttf': Some of the
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* glyphs are `real', this is, they have a zero vertical offset, but
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* most of them are small caps glyphs shifted up to the superscript
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* position (this is, the `sups' feature is present in both the GSUB and
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* GPOS tables). The code for blue zones computation actually uses a
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* feature's y offset so that the `real' glyphs get correct hints. But
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* later on it is impossible to decide whether a glyph index belongs to,
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* say, the small caps or superscript feature.
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*
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* For this reason, we don't assign a style to a glyph if the current
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* feature covers the glyph in both the GSUB and the GPOS tables. This
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* is quite a broad condition, assuming that
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*
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* (a) glyphs that get used in multiple features are present in a
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* feature without vertical shift,
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*
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* and
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*
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* (b) a feature's GPOS data really moves the glyph vertically.
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*
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* Not fulfilling condition (a) makes a font larger; it would also
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* reduce the number of glyphs that could be addressed directly without
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* using OpenType features, so this assumption is rather strong.
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*
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* Condition (b) is much weaker, and there might be glyphs which get
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* missed. However, the OpenType features we are going to handle are
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* primarily located in GSUB, and HarfBuzz doesn't provide an API to
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* directly get the necessary information from the GPOS table. A
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* possible solution might be to directly parse the GPOS table to find
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* out whether a glyph gets shifted vertically, but this is something I
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* would like to avoid if not really necessary.
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*
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*/
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hb_set_subtract( gsub_glyphs, gpos_glyphs );
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#ifdef FT_DEBUG_LEVEL_TRACE
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FT_TRACE4(( " glyphs without GPOS data (`*' means already assigned)" ));
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count = 0;
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#endif
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@ -225,6 +311,8 @@
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hb_set_destroy( gsub_lookups );
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hb_set_destroy( gsub_glyphs );
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hb_set_destroy( gpos_lookups );
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hb_set_destroy( gpos_glyphs );
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return FT_Err_Ok;
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}
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