harfbuzz/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"
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#include "hb-ot-shape-complex-private.hh"
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/*
* 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
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* of 1:2 decompositions, marks reordered, and then recomposed if desired,
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* 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'
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* feature in the font is not adequate, use the precomposed character
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* which typically has better mark positioning.
*
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* - 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.
*
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* - 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);
}
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static bool
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decompose (hb_ot_shape_context_t *c,
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bool shortest,
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hb_codepoint_t ab)
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{
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hb_codepoint_t a, b, glyph;
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if (!hb_unicode_decompose (c->buffer->unicode, ab, &a, &b) ||
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(b && !hb_font_get_glyph (c->font, b, 0, &glyph)))
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return FALSE;
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bool has_a = hb_font_get_glyph (c->font, a, 0, &glyph);
if (shortest && has_a) {
/* Output a and b */
output_glyph (c, a);
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if (b)
output_glyph (c, b);
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return TRUE;
}
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if (decompose (c, shortest, a)) {
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if (b)
output_glyph (c, b);
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return TRUE;
}
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if (has_a) {
output_glyph (c, a);
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if (b)
output_glyph (c, b);
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return TRUE;
}
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return FALSE;
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}
static void
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decompose_current_glyph (hb_ot_shape_context_t *c,
bool shortest)
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{
if (decompose (c, shortest, c->buffer->info[c->buffer->idx].codepoint))
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c->buffer->skip_glyph ();
else
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c->buffer->next_glyph ();
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}
static void
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decompose_single_char_cluster (hb_ot_shape_context_t *c,
bool will_recompose)
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{
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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;
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}
decompose_current_glyph (c, will_recompose);
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}
static void
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decompose_multi_char_cluster (hb_ot_shape_context_t *c,
unsigned int end)
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{
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/* TODO Currently if there's a variation-selector we give-up, it's just too hard. */
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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;
}
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while (c->buffer->idx < end)
decompose_current_glyph (c, FALSE);
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}
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;
}
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void
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_hb_ot_shape_normalize (hb_ot_shape_context_t *c)
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{
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hb_buffer_t *buffer = c->buffer;
bool recompose = !hb_ot_shape_complex_prefer_decomposed (c->plan->shaper);
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bool has_multichar_clusters = FALSE;
unsigned int count;
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/* 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. */
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/* First round, decompose */
buffer->clear_output ();
count = buffer->len;
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for (buffer->idx = 0; buffer->idx < count;)
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{
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unsigned int end;
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for (end = buffer->idx + 1; end < count; end++)
if (buffer->info[buffer->idx].cluster != buffer->info[end].cluster)
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break;
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if (buffer->idx + 1 == end)
decompose_single_char_cluster (c, recompose);
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else {
decompose_multi_char_cluster (c, end);
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has_multichar_clusters = TRUE;
}
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}
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buffer->swap_buffers ();
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/* 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.
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* 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
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* that requests decomposed. If for Hangul we end up wanting composed, we
* can do that in the Hangul module.
*/
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if (!has_multichar_clusters)
return; /* Done! */
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/* 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;
}
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if (!recompose)
return;
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/* Third round, recompose */
/* As noted in the comment earlier, we don't try to combine
* ccc=0 chars with their previous Starter. */
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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);
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buffer->skip_glyph ();
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}
buffer->swap_buffers ();
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}