Update harfbuzz-ng to 1a5a91dc0d8bf4b72a2f22dc6300b06ad7000b79.

third_party/harfbuzz-ng/src/hb-ot-shape-normalize.cc

Index: third_party/harfbuzz-ng/src/hb-ot-shape-normalize.cc
diff --git a/third_party/harfbuzz-ng/src/hb-ot-shape-normalize.cc b/third_party/harfbuzz-ng/src/hb-ot-shape-normalize.cc
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+/*
+ * Copyright © 2011  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-private.hh"
+#include "hb-ot-shape-complex-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.  The shaper an either prefer decomposed (NFD) or
+ * composed (NFC).
+ *
+ * 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.  This needs the itemizer to have this knowledge too.
+ *     We need ot provide assistance to the itemizer.
+ *
+ *   - When a font does not support a character but supports its decomposition,
+ *     well, use the decomposition.
+ *
+ *   - The Indic shaper requests decomposed output.  This will handle splitting
+ *     matra for the Indic shaper.
+ */
+
+static void
+output_glyph (hb_ot_shape_context_t *c,
+	      hb_codepoint_t glyph)
+{
+  hb_buffer_t *buffer = c->buffer;
+
+  buffer->output_glyph (glyph);
+  hb_glyph_info_set_unicode_props (&buffer->out_info[buffer->out_len - 1], buffer->unicode);
+}
+
+static bool
+decompose (hb_ot_shape_context_t *c,
+	   bool shortest,
+	   hb_codepoint_t ab)
+{
+  hb_codepoint_t a, b, glyph;
+
+  if (!hb_unicode_decompose (c->buffer->unicode, ab, &a, &b) ||
+      (b && !hb_font_get_glyph (c->font, b, 0, &glyph)))
+    return FALSE;
+
+  bool has_a = hb_font_get_glyph (c->font, a, 0, &glyph);
+  if (shortest && has_a) {
+    /* Output a and b */
+    output_glyph (c, a);
+    if (b)
+      output_glyph (c, b);
+    return TRUE;
+  }
+
+  if (decompose (c, shortest, a)) {
+    if (b)
+      output_glyph (c, b);
+    return TRUE;
+  }
+
+  if (has_a) {
+    output_glyph (c, a);
+    if (b)
+      output_glyph (c, b);
+    return TRUE;
+  }
+
+  return FALSE;
+}
+
+static void
+decompose_current_glyph (hb_ot_shape_context_t *c,
+			 bool shortest)
+{
+  if (decompose (c, shortest, c->buffer->info[c->buffer->idx].codepoint))
+    c->buffer->skip_glyph ();
+  else
+    c->buffer->next_glyph ();
+}
+
+static void
+decompose_single_char_cluster (hb_ot_shape_context_t *c,
+			       bool will_recompose)
+{
+  hb_codepoint_t glyph;
+
+  /* If recomposing and font supports this, we're good to go */
+  if (will_recompose && hb_font_get_glyph (c->font, c->buffer->info[c->buffer->idx].codepoint, 0, &glyph)) {
+    c->buffer->next_glyph ();
+    return;
+  }
+
+  decompose_current_glyph (c, will_recompose);
+}
+
+static void
+decompose_multi_char_cluster (hb_ot_shape_context_t *c,
+			      unsigned int end)
+{
+  /* TODO Currently if there's a variation-selector we give-up, it's just too hard. */
+  for (unsigned int i = c->buffer->idx; i < end; i++)
+    if (unlikely (is_variation_selector (c->buffer->info[i].codepoint))) {
+      while (c->buffer->idx < end)
+	c->buffer->next_glyph ();
+      return;
+    }
+
+  while (c->buffer->idx < end)
+    decompose_current_glyph (c, FALSE);
+}
+
+static int
+compare_combining_class (const hb_glyph_info_t *pa, const hb_glyph_info_t *pb)
+{
+  unsigned int a = pa->combining_class();
+  unsigned int b = pb->combining_class();
+
+  return a < b ? -1 : a == b ? 0 : +1;
+}
+
+void
+_hb_ot_shape_normalize (hb_ot_shape_context_t *c)
+{
+  hb_buffer_t *buffer = c->buffer;
+  bool recompose = !hb_ot_shape_complex_prefer_decomposed (c->plan->shaper);
+  bool has_multichar_clusters = FALSE;
+  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->info[buffer->idx].cluster != buffer->info[end].cluster)
+        break;
+
+    if (buffer->idx + 1 == end)
+      decompose_single_char_cluster (c, recompose);
+    else {
+      decompose_multi_char_cluster (c, end);
+      has_multichar_clusters = TRUE;
+    }
+  }
+  buffer->swap_buffers ();
+
+
+  /* Technically speaking, two characters with ccc=0 may combine.  But all
+   * those cases are in languages that the indic module handles (which expects
+   * decomposed), or in Hangul jamo, which again, we want decomposed anyway.
+   * So we don't bother combining across cluster boundaries.  This is a huge
+   * performance saver if the compose() callback is slow.
+   *
+   * TODO: Am I right about Hangul?  If I am, we should add a Hangul module
+   * that requests decomposed.  If for Hangul we end up wanting composed, we
+   * can do that in the Hangul module.
+   */
+
+  if (!has_multichar_clusters)
+    return; /* Done! */
+
+
+  /* Second round, reorder (inplace) */
+
+  count = buffer->len;
+  for (unsigned int i = 0; i < count; i++)
+  {
+    if (buffer->info[i].combining_class() == 0)
+      continue;
+
+    unsigned int end;
+    for (end = i + 1; end < count; end++)
+      if (buffer->info[end].combining_class() == 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 (!recompose)
+    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)
+  {
+    if (buffer->info[buffer->idx].combining_class() == 0) {
+      starter = buffer->out_len;
+      buffer->next_glyph ();
+      continue;
+    }
+
+    hb_codepoint_t composed, glyph;
+    if ((buffer->out_info[buffer->out_len - 1].combining_class() >=
+	 buffer->info[buffer->idx].combining_class()) ||
+	!hb_unicode_compose (c->buffer->unicode,
+			     buffer->out_info[starter].codepoint,
+			     buffer->info[buffer->idx].codepoint,
+			     &composed) ||
+	!hb_font_get_glyph (c->font, composed, 0, &glyph))
+    {
+      /* Blocked, or doesn't compose. */
+      buffer->next_glyph ();
+      continue;
+    }
+
+    /* Composes. Modify starter and carry on. */
+    buffer->out_info[starter].codepoint = composed;
+    hb_glyph_info_set_unicode_props (&buffer->out_info[starter], buffer->unicode);
+
+    buffer->skip_glyph ();
+  }
+  buffer->swap_buffers ();
+
+}
+