The Tor Browser: gfx/harfbuzz/src/hb-ot-shape-normalize.cc@925c144e1f1f (annotated)

gfx/harfbuzz/src/hb-ot-shape-normalize.cc@925c144e1f1f (annotated)

gfx/harfbuzz/src/hb-ot-shape-normalize.cc

Fri, 16 Jan 2015 18:13:44 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Fri, 16 Jan 2015 18:13:44 +0100
branch: TOR_BUG_9701
changeset 14: 925c144e1f1f
permissions: -rw-r--r--

Integrate suggestion from review to improve consistency with existing code.

 /*
  * Copyright © 2011,2012  Google, Inc.
  *
  *  This is part of HarfBuzz, a text shaping library.
  *
  * Permission is hereby granted, without written agreement and without
  * license or royalty fees, to use, copy, modify, and distribute this
  * software and its documentation for any purpose, provided that the
  * above copyright notice and the following two paragraphs appear in
  * all copies of this software.
  *
  * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
  * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
  * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
  * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
  * DAMAGE.
  *
  * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
  * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
  * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
  * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
  * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
  *
  * Google Author(s): Behdad Esfahbod
  */
 #include "hb-ot-shape-normalize-private.hh"
 #include "hb-ot-shape-complex-private.hh"
 #include "hb-ot-shape-private.hh"
 /*
  * HIGHLEVEL DESIGN:
  *
  * This file exports one main function: _hb_ot_shape_normalize().
  *
  * This function closely reflects the Unicode Normalization Algorithm,
  * yet it's different.
  *
  * Each shaper specifies whether it prefers decomposed (NFD) or composed (NFC).
  * The logic however tries to use whatever the font can support.
  *
  * In general what happens is that: each grapheme is decomposed in a chain
  * of 1:2 decompositions, marks reordered, and then recomposed if desired,
  * so far it's like Unicode Normalization.  However, the decomposition and
  * recomposition only happens if the font supports the resulting characters.
  *
  * The goals are:
  *
  *   - Try to render all canonically equivalent strings similarly.  To really
  *     achieve this we have to always do the full decomposition and then
  *     selectively recompose from there.  It's kinda too expensive though, so
  *     we skip some cases.  For example, if composed is desired, we simply
  *     don't touch 1-character clusters that are supported by the font, even
  *     though their NFC may be different.
  *
  *   - When a font has a precomposed character for a sequence but the 'ccmp'
  *     feature in the font is not adequate, use the precomposed character
  *     which typically has better mark positioning.
  *
  *   - When a font does not support a combining mark, but supports it precomposed
  *     with previous base, use that.  This needs the itemizer to have this
  *     knowledge too.  We need to provide assistance to the itemizer.
  *
  *   - When a font does not support a character but supports its decomposition,
  *     well, use the decomposition (preferring the canonical decomposition, but
  *     falling back to the compatibility decomposition if necessary).  The
  *     compatibility decomposition is really nice to have, for characters like
  *     ellipsis, or various-sized space characters.
  *
  *   - The complex shapers can customize the compose and decompose functions to
  *     offload some of their requirements to the normalizer.  For example, the
  *     Indic shaper may want to disallow recomposing of two matras.
  *
  *   - We try compatibility decomposition if decomposing through canonical
  *     decomposition alone failed to find a sequence that the font supports.
  *     We don't try compatibility decomposition recursively during the canonical
  *     decomposition phase.  This has minimal impact.  There are only a handful
  *     of Greek letter that have canonical decompositions that include characters
  *     with compatibility decomposition.  Those can be found using this command:
  *
  *     egrep  "`echo -n ';('; grep ';<' UnicodeData.txt | cut -d';' -f1 | tr '\n' '|'; echo ') '`" UnicodeData.txt
  */
 static bool
 decompose_unicode (const hb_ot_shape_normalize_context_t *c,
 		   hb_codepoint_t  ab,
 		   hb_codepoint_t *a,
 		   hb_codepoint_t *b)
 {
   return c->unicode->decompose (ab, a, b);
 }
 static bool
 compose_unicode (const hb_ot_shape_normalize_context_t *c,
 		 hb_codepoint_t  a,
 		 hb_codepoint_t  b,
 		 hb_codepoint_t *ab)
 {
   return c->unicode->compose (a, b, ab);
 }
 static inline void
 set_glyph (hb_glyph_info_t &info, hb_font_t *font)
 {
   font->get_glyph (info.codepoint, 0, &info.glyph_index());
 }
 static inline void
 output_char (hb_buffer_t *buffer, hb_codepoint_t unichar, hb_codepoint_t glyph)
 {
   buffer->cur().glyph_index() = glyph;
   buffer->output_glyph (unichar);
   _hb_glyph_info_set_unicode_props (&buffer->prev(), buffer->unicode);
 }
 static inline void
 next_char (hb_buffer_t *buffer, hb_codepoint_t glyph)
 {
   buffer->cur().glyph_index() = glyph;
   buffer->next_glyph ();
 }
 static inline void
 skip_char (hb_buffer_t *buffer)
 {
   buffer->skip_glyph ();
 }
 /* Returns 0 if didn't decompose, number of resulting characters otherwise. */
 static inline unsigned int
 decompose (const hb_ot_shape_normalize_context_t *c, bool shortest, hb_codepoint_t ab)
 {
   hb_codepoint_t a, b, a_glyph, b_glyph;
   hb_buffer_t * const buffer = c->buffer;
   hb_font_t * const font = c->font;
   if (!c->decompose (c, ab, &a, &b) ||
       (b && !font->get_glyph (b, 0, &b_glyph)))
     return 0;
   bool has_a = font->get_glyph (a, 0, &a_glyph);
   if (shortest && has_a) {
     /* Output a and b */
     output_char (buffer, a, a_glyph);
     if (likely (b)) {
       output_char (buffer, b, b_glyph);
       return 2;
     }
     return 1;
   }
   unsigned int ret;
   if ((ret = decompose (c, shortest, a))) {
     if (b) {
       output_char (buffer, b, b_glyph);
       return ret + 1;
     }
     return ret;
   }
   if (has_a) {
     output_char (buffer, a, a_glyph);
     if (likely (b)) {
       output_char (buffer, b, b_glyph);
       return 2;
     }
     return 1;
   }
   return 0;
 }
 /* Returns 0 if didn't decompose, number of resulting characters otherwise. */
 static inline unsigned int
 decompose_compatibility (const hb_ot_shape_normalize_context_t *c, hb_codepoint_t u)
 {
   unsigned int len, i;
   hb_codepoint_t decomposed[HB_UNICODE_MAX_DECOMPOSITION_LEN];
   hb_codepoint_t glyphs[HB_UNICODE_MAX_DECOMPOSITION_LEN];
   len = c->buffer->unicode->decompose_compatibility (u, decomposed);
   if (!len)
     return 0;
   for (i = 0; i < len; i++)
     if (!c->font->get_glyph (decomposed[i], 0, &glyphs[i]))
       return 0;
   for (i = 0; i < len; i++)
     output_char (c->buffer, decomposed[i], glyphs[i]);
   return len;
 }
 static inline void
 decompose_current_character (const hb_ot_shape_normalize_context_t *c, bool shortest)
 {
   hb_buffer_t * const buffer = c->buffer;
   hb_codepoint_t glyph;
   /* Kind of a cute waterfall here... */
   if (shortest && c->font->get_glyph (buffer->cur().codepoint, 0, &glyph))
     next_char (buffer, glyph);
   else if (decompose (c, shortest, buffer->cur().codepoint))
     skip_char (buffer);
   else if (!shortest && c->font->get_glyph (buffer->cur().codepoint, 0, &glyph))
     next_char (buffer, glyph);
   else if (decompose_compatibility (c, buffer->cur().codepoint))
     skip_char (buffer);
   else
     next_char (buffer, glyph); /* glyph is initialized in earlier branches. */
 }
 static inline void
 handle_variation_selector_cluster (const hb_ot_shape_normalize_context_t *c, unsigned int end, bool short_circuit)
 {
   /* TODO Currently if there's a variation-selector we give-up, it's just too hard. */
   hb_buffer_t * const buffer = c->buffer;
   hb_font_t * const font = c->font;
   for (; buffer->idx < end - 1;) {
     if (unlikely (buffer->unicode->is_variation_selector (buffer->cur(+1).codepoint))) {
       /* The next two lines are some ugly lines... But work. */
       if (font->get_glyph (buffer->cur().codepoint, buffer->cur(+1).codepoint, &buffer->cur().glyph_index()))
       {
 	buffer->replace_glyphs (2, 1, &buffer->cur().codepoint);
       }
       else
       {
         /* Just pass on the two characters separately, let GSUB do its magic. */
 	set_glyph (buffer->cur(), font);
 	buffer->next_glyph ();
 	set_glyph (buffer->cur(), font);
 	buffer->next_glyph ();
       }
       /* Skip any further variation selectors. */
       while (buffer->idx < end && unlikely (buffer->unicode->is_variation_selector (buffer->cur().codepoint)))
       {
 	set_glyph (buffer->cur(), font);
 	buffer->next_glyph ();
       }
     } else {
       set_glyph (buffer->cur(), font);
       buffer->next_glyph ();
     }
   }
   if (likely (buffer->idx < end)) {
     set_glyph (buffer->cur(), font);
     buffer->next_glyph ();
   }
 }
 static inline void
 decompose_multi_char_cluster (const hb_ot_shape_normalize_context_t *c, unsigned int end, bool short_circuit)
 {
   hb_buffer_t * const buffer = c->buffer;
   for (unsigned int i = buffer->idx; i < end; i++)
     if (unlikely (buffer->unicode->is_variation_selector (buffer->info[i].codepoint))) {
       handle_variation_selector_cluster (c, end, short_circuit);
       return;
     }
   while (buffer->idx < end)
     decompose_current_character (c, short_circuit);
 }
 static inline void
 decompose_cluster (const hb_ot_shape_normalize_context_t *c, unsigned int end, bool might_short_circuit, bool always_short_circuit)
 {
   if (likely (c->buffer->idx + 1 == end))
     decompose_current_character (c, might_short_circuit);
   else
     decompose_multi_char_cluster (c, end, always_short_circuit);
 }
 static int
 compare_combining_class (const hb_glyph_info_t *pa, const hb_glyph_info_t *pb)
 {
   unsigned int a = _hb_glyph_info_get_modified_combining_class (pa);
   unsigned int b = _hb_glyph_info_get_modified_combining_class (pb);
   return a < b ? -1 : a == b ? 0 : +1;
 }
 void
 _hb_ot_shape_normalize (const hb_ot_shape_plan_t *plan,
 			hb_buffer_t *buffer,
 			hb_font_t *font)
 {
   hb_ot_shape_normalization_mode_t mode = plan->shaper->normalization_preference;
   const hb_ot_shape_normalize_context_t c = {
     plan,
     buffer,
     font,
     buffer->unicode,
     plan->shaper->decompose ? plan->shaper->decompose : decompose_unicode,
     plan->shaper->compose   ? plan->shaper->compose   : compose_unicode
   };
   bool always_short_circuit = mode == HB_OT_SHAPE_NORMALIZATION_MODE_NONE;
   bool might_short_circuit = always_short_circuit ||
 			     (mode != HB_OT_SHAPE_NORMALIZATION_MODE_DECOMPOSED &&
 			      mode != HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_DIACRITICS_NO_SHORT_CIRCUIT);
   unsigned int count;
   /* We do a fairly straightforward yet custom normalization process in three
    * separate rounds: decompose, reorder, recompose (if desired).  Currently
    * this makes two buffer swaps.  We can make it faster by moving the last
    * two rounds into the inner loop for the first round, but it's more readable
    * this way. */
   /* First round, decompose */
   buffer->clear_output ();
   count = buffer->len;
   for (buffer->idx = 0; buffer->idx < count;)
   {
     unsigned int end;
     for (end = buffer->idx + 1; end < count; end++)
       if (buffer->cur().cluster != buffer->info[end].cluster)
         break;
     decompose_cluster (&c, end, might_short_circuit, always_short_circuit);
   }
   buffer->swap_buffers ();
   /* Second round, reorder (inplace) */
   count = buffer->len;
   for (unsigned int i = 0; i < count; i++)
   {
     if (_hb_glyph_info_get_modified_combining_class (&buffer->info[i]) == 0)
       continue;
     unsigned int end;
     for (end = i + 1; end < count; end++)
       if (_hb_glyph_info_get_modified_combining_class (&buffer->info[end]) == 0)
         break;
     /* We are going to do a bubble-sort.  Only do this if the
      * sequence is short.  Doing it on long sequences can result
      * in an O(n^2) DoS. */
     if (end - i > 10) {
       i = end;
       continue;
     }
     hb_bubble_sort (buffer->info + i, end - i, compare_combining_class);
     i = end;
   }
   if (mode == HB_OT_SHAPE_NORMALIZATION_MODE_NONE ||
       mode == HB_OT_SHAPE_NORMALIZATION_MODE_DECOMPOSED)
     return;
   /* Third round, recompose */
   /* As noted in the comment earlier, we don't try to combine
    * ccc=0 chars with their previous Starter. */
   buffer->clear_output ();
   count = buffer->len;
   unsigned int starter = 0;
   buffer->next_glyph ();
   while (buffer->idx < count)
   {
     hb_codepoint_t composed, glyph;
     if (/* We don't try to compose a non-mark character with it's preceding starter.
 	 * This is both an optimization to avoid trying to compose every two neighboring
 	 * glyphs in most scripts AND a desired feature for Hangul.  Apparently Hangul
 	 * fonts are not designed to mix-and-match pre-composed syllables and Jamo. */
 	HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&buffer->cur())) &&
 	/* If there's anything between the starter and this char, they should have CCC
 	 * smaller than this character's. */
 	(starter == buffer->out_len - 1 ||
 	 _hb_glyph_info_get_modified_combining_class (&buffer->prev()) < _hb_glyph_info_get_modified_combining_class (&buffer->cur())) &&
 	/* And compose. */
 	c.compose (&c,
 		   buffer->out_info[starter].codepoint,
 		   buffer->cur().codepoint,
 		   &composed) &&
 	/* And the font has glyph for the composite. */
 	font->get_glyph (composed, 0, &glyph))
     {
       /* Composes. */
       buffer->next_glyph (); /* Copy to out-buffer. */
       if (unlikely (buffer->in_error))
         return;
       buffer->merge_out_clusters (starter, buffer->out_len);
       buffer->out_len--; /* Remove the second composable. */
       /* Modify starter and carry on. */
       buffer->out_info[starter].codepoint = composed;
       buffer->out_info[starter].glyph_index() = glyph;
       _hb_glyph_info_set_unicode_props (&buffer->out_info[starter], buffer->unicode);
       continue;
     }
     /* Blocked, or doesn't compose. */
     buffer->next_glyph ();
     if (_hb_glyph_info_get_modified_combining_class (&buffer->prev()) == 0)
       starter = buffer->out_len - 1;
   }
   buffer->swap_buffers ();
 }

The Tor Browser / annotate

gfx/harfbuzz/src/hb-ot-shape-normalize.cc@925c144e1f1f (annotated)

gfx/harfbuzz/src/hb-ot-shape-normalize.cc