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[buffer] Add docs for the new cluster level

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Behdad Esfahbod 2025-03-10 01:02:11 -06:00
parent 9305aae476
commit 1531be8a1d
2 changed files with 20 additions and 1 deletions
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3
docs/harfbuzz-sections.txt
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@ -114,6 +114,9 @@ hb_glyph_position_t
hb_buffer_content_type_t
hb_buffer_flags_t
hb_buffer_cluster_level_t
HB_BUFFER_CLUSTER_LEVEL_IS_CHARACTERS
HB_BUFFER_CLUSTER_LEVEL_IS_GRAPHEMES
HB_BUFFER_CLUSTER_LEVEL_IS_MONOTONE
hb_segment_properties_t
hb_buffer_serialize_format_t
hb_buffer_serialize_flags_t

18
src/hb-buffer.h
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@ -422,6 +422,7 @@ hb_buffer_get_flags (const hb_buffer_t *buffer);
* @HB_BUFFER_CLUSTER_LEVEL_CHARACTERS: Don't group cluster values.
* @HB_BUFFER_CLUSTER_LEVEL_DEFAULT: Default cluster level,
* equal to @HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES.
* @HB_BUFFER_CLUSTER_LEVEL_GRAPHEMES: Only group clusters, but don't enfore monotone order.
*
* Data type for holding HarfBuzz's clustering behavior options. The cluster level
* dictates one aspect of how HarfBuzz will treat non-base characters
@ -429,11 +430,26 @@ hb_buffer_get_flags (const hb_buffer_t *buffer);
*
* In @HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES, non-base
* characters are merged into the cluster of the base character that precedes them.
* There is also cluster merging evertim the clusters will otherwise become non-monotone.
*
* In @HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS, non-base characters are initially
* assigned their own cluster values, which are not merged into preceding base
* clusters. This allows HarfBuzz to perform additional operations like reorder
* sequences of adjacent marks.
* sequences of adjacent marks. The output is still monotone, but the cluster
* values are more granular.
*
* In @HB_BUFFER_CLUSTER_LEVEL_CHARACTERS, non-base characters are assigned their
* own cluster values, which are not merged into preceding base clusters. Moreover,
* the cluster values are not merged into monotone order. This is the most granular
* cluster level, and it is useful for clients that need to know the exact cluster
* values of each character, but is harder to use for clients, since clusters
* might appear in any order.
*
* In @HB_BUFFER_CLUSTER_LEVEL_GRAPHEMES, non-base characters are merged into the
* cluster of the base character that precedes them. This is similar to the Unicode
* Grapheme Cluster algorithm, but it is not exactly the same. The output is
* not forced to be monotone. This is useful for clients that want to use HarfBuzz
* as a cheap implementation of the Unicode Grapheme Cluster algorithm.
*
* @HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES is the default, because it maintains
* backward compatibility with older versions of HarfBuzz. New client programs that