/*
* 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_buffer_assert_unicode_vars (buffer);
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 ();
}