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hb-buffer: HarfBuzz Manual

Buffers serve a dual role in HarfBuzz; before shaping, they hold the input characters that are passed to hb_shape(), and after shaping they hold the output glyphs.

The input buffer is a sequence of Unicode codepoints, with associated attributes such as direction and script. The output buffer is a sequence of glyphs, with associated attributes such as position and cluster.

hb_bool_t
hb_buffer_allocation_successful (hb_buffer_t *buffer);

Check if allocating memory for the buffer succeeded.

true if buffer memory allocation succeeded, false otherwise.

Since: 0.9.2

hb_buffer_t *
hb_buffer_get_empty (void);

Fetches an empty hb_buffer_t.

The empty buffer.

[transfer full]

Since: 0.9.2

hb_buffer_t *
hb_buffer_reference (hb_buffer_t *buffer);

Increases the reference count on buffer by one. This prevents buffer from being destroyed until a matching call to hb_buffer_destroy() is made.

[skip]

Since: 0.9.2

void
hb_buffer_destroy (hb_buffer_t *buffer);

Deallocate the buffer . Decreases the reference count on buffer by one. If the result is zero, then buffer and all associated resources are freed. See hb_buffer_reference().

[skip]

Since: 0.9.2

hb_bool_t
hb_buffer_set_user_data (hb_buffer_t *buffer,
                         hb_user_data_key_t *key,
                         void *data,
                         hb_destroy_func_t destroy,
                         hb_bool_t replace);

Attaches a user-data key/data pair to the specified buffer.

[skip]

buffer

An hb_buffer_t

key

The user-data key

data

A pointer to the user data

destroy

A callback to call when data is not needed anymore.

replace

Whether to replace an existing data with the same key

true if success, false otherwise

Since: 0.9.2

void *
hb_buffer_get_user_data (const hb_buffer_t *buffer,
                         hb_user_data_key_t *key);

Fetches the user data associated with the specified key, attached to the specified buffer.

[skip]

A pointer to the user data.

[transfer none]

Since: 0.9.2

void
hb_buffer_reset (hb_buffer_t *buffer);

Resets the buffer to its initial status, as if it was just newly created with hb_buffer_create().

Since: 0.9.2

void
hb_buffer_clear_contents (hb_buffer_t *buffer);

Similar to hb_buffer_reset(), but does not clear the Unicode functions and the replacement code point.

Since: 0.9.11

hb_bool_t
hb_buffer_pre_allocate (hb_buffer_t *buffer,
                        unsigned int size);

Pre allocates memory for buffer to fit at least size number of items.

buffer

An hb_buffer_t

size

Number of items to pre allocate.

true if buffer memory allocation succeeded, false otherwise

Since: 0.9.2

void
hb_buffer_add (hb_buffer_t *buffer,
               hb_codepoint_t codepoint,
               unsigned int cluster);

Appends a character with the Unicode value of codepoint to buffer , and gives it the initial cluster value of cluster . Clusters can be any thing the client wants, they are usually used to refer to the index of the character in the input text stream and are output in hb_glyph_info_t.cluster field.

This function does not check the validity of codepoint , it is up to the caller to ensure it is a valid Unicode code point.

buffer

An hb_buffer_t

codepoint

A Unicode code point.

cluster

The cluster value of codepoint .

Since: 0.9.7

void
hb_buffer_add_codepoints (hb_buffer_t *buffer,
                          const hb_codepoint_t *text,
                          int text_length,
                          unsigned int item_offset,
                          int item_length);

Appends characters from text array to buffer . The item_offset is the position of the first character from text that will be appended, and item_length is the number of character. When shaping part of a larger text (e.g. a run of text from a paragraph), instead of passing just the substring corresponding to the run, it is preferable to pass the whole paragraph and specify the run start and length as item_offset and item_length , respectively, to give HarfBuzz the full context to be able, for example, to do cross-run Arabic shaping or properly handle combining marks at stat of run.

This function does not check the validity of text , it is up to the caller to ensure it contains a valid Unicode scalar values. In contrast, hb_buffer_add_utf32() can be used that takes similar input but performs sanity-check on the input.

buffer

a hb_buffer_t to append characters to.

text

an array of Unicode code points to append.

text_length

the length of the text , or -1 if it is NULL terminated.

item_offset

the offset of the first code point to add to the buffer .

item_length

the number of code points to add to the buffer , or -1 for the end of text (assuming it is NULL terminated).

Since: 0.9.31

void
hb_buffer_add_utf32 (hb_buffer_t *buffer,
                     const uint32_t *text,
                     int text_length,
                     unsigned int item_offset,
                     int item_length);

See hb_buffer_add_codepoints().

Replaces invalid UTF-32 characters with the buffer replacement code point, see hb_buffer_set_replacement_codepoint().

buffer

An hb_buffer_t

text

An array of UTF-32 characters to append.

text_length

The length of the text , or -1 if it is NULL terminated

item_offset

The offset of the first character to add to the buffer

item_length

The number of characters to add to the buffer , or -1 for the end of text (assuming it is NULL terminated)

Since: 0.9.2

void
hb_buffer_add_utf16 (hb_buffer_t *buffer,
                     const uint16_t *text,
                     int text_length,
                     unsigned int item_offset,
                     int item_length);

See hb_buffer_add_codepoints().

Replaces invalid UTF-16 characters with the buffer replacement code point, see hb_buffer_set_replacement_codepoint().

buffer

An hb_buffer_t

text

An array of UTF-16 characters to append.

text_length

The length of the text , or -1 if it is NULL terminated

item_offset

The offset of the first character to add to the buffer

item_length

The number of characters to add to the buffer , or -1 for the end of text (assuming it is NULL terminated)

Since: 0.9.2

void
hb_buffer_add_utf8 (hb_buffer_t *buffer,
                    const char *text,
                    int text_length,
                    unsigned int item_offset,
                    int item_length);

See hb_buffer_add_codepoints().

Replaces invalid UTF-8 characters with the buffer replacement code point, see hb_buffer_set_replacement_codepoint().

buffer

An hb_buffer_t

text

An array of UTF-8 characters to append.

text_length

The length of the text , or -1 if it is NULL terminated.

item_offset

The offset of the first character to add to the buffer .

item_length

The number of characters to add to the buffer , or -1 for the end of text (assuming it is NULL terminated).

Since: 0.9.2

void
hb_buffer_add_latin1 (hb_buffer_t *buffer,
                      const uint8_t *text,
                      int text_length,
                      unsigned int item_offset,
                      int item_length);

Similar to hb_buffer_add_codepoints(), but allows only access to first 256 Unicode code points that can fit in 8-bit strings.

Has nothing to do with non-Unicode Latin-1 encoding.

buffer

An hb_buffer_t

text

an array of UTF-8 characters to append.

text_length

the length of the text , or -1 if it is NULL terminated

item_offset

the offset of the first character to add to the buffer

item_length

the number of characters to add to the buffer , or -1 for the end of text (assuming it is NULL terminated)

Since: 0.9.39

void
hb_buffer_append (hb_buffer_t *buffer,
                  const hb_buffer_t *source,
                  unsigned int start,
                  unsigned int end);

Append (part of) contents of another buffer to this buffer.

buffer

An hb_buffer_t

source

source hb_buffer_t

start

start index into source buffer to copy. Use 0 to copy from start of buffer.

end

end index into source buffer to copy. Use UINT_MAX (or ((unsigned int) -1)) to copy to end of buffer.

Since: 1.5.0

void
hb_buffer_set_content_type (hb_buffer_t *buffer,
                            hb_buffer_content_type_t content_type);

Sets the type of buffer contents. Buffers are either empty, contain characters (before shaping), or contain glyphs (the result of shaping).

You rarely need to call this function, since a number of other functions transition the content type for you. Namely:

The above transitions are designed such that one can use a buffer in a loop of "reset : add-text : shape" without needing to ever modify the content type manually.

buffer

An hb_buffer_t

content_type

The type of buffer contents to set

Since: 0.9.5

hb_buffer_content_type_t
hb_buffer_get_content_type (const hb_buffer_t *buffer);

Fetches the type of buffer contents. Buffers are either empty, contain characters (before shaping), or contain glyphs (the result of shaping).

The type of buffer contents

Since: 0.9.5

void
hb_buffer_set_direction (hb_buffer_t *buffer,
                         hb_direction_t direction);

Set the text flow direction of the buffer. No shaping can happen without setting buffer direction, and it controls the visual direction for the output glyphs; for RTL direction the glyphs will be reversed. Many layout features depend on the proper setting of the direction, for example, reversing RTL text before shaping, then shaping with LTR direction is not the same as keeping the text in logical order and shaping with RTL direction.

Since: 0.9.2

void
hb_buffer_set_script (hb_buffer_t *buffer,
                      hb_script_t script);

Sets the script of buffer to script .

Script is crucial for choosing the proper shaping behaviour for scripts that require it (e.g. Arabic) and the which OpenType features defined in the font to be applied.

You can pass one of the predefined hb_script_t values, or use hb_script_from_string() or hb_script_from_iso15924_tag() to get the corresponding script from an ISO 15924 script tag.

Since: 0.9.2

void
hb_buffer_set_language (hb_buffer_t *buffer,
                        hb_language_t language);

Sets the language of buffer to language .

Languages are crucial for selecting which OpenType feature to apply to the buffer which can result in applying language-specific behaviour. Languages are orthogonal to the scripts, and though they are related, they are different concepts and should not be confused with each other.

Use hb_language_from_string() to convert from BCP 47 language tags to hb_language_t.

Since: 0.9.2

hb_bool_t
hb_buffer_set_length (hb_buffer_t *buffer,
                      unsigned int length);

Similar to hb_buffer_pre_allocate(), but clears any new items added at the end.

true if buffer memory allocation succeeded, false otherwise.

Since: 0.9.2

unsigned int
hb_buffer_get_length (const hb_buffer_t *buffer);

Returns the number of items in the buffer.

The buffer length. The value valid as long as buffer has not been modified.

Since: 0.9.2

void
hb_buffer_set_unicode_funcs (hb_buffer_t *buffer,
                             hb_unicode_funcs_t *unicode_funcs);

Sets the Unicode-functions structure of a buffer to unicode_funcs .

buffer

An hb_buffer_t

unicode_funcs

The Unicode-functions structure

Since: 0.9.2

hb_unicode_funcs_t *
hb_buffer_get_unicode_funcs (const hb_buffer_t *buffer);

Fetches the Unicode-functions structure of a buffer.

The Unicode-functions structure

Since: 0.9.2

hb_glyph_info_t *
hb_buffer_get_glyph_infos (hb_buffer_t *buffer,
                           unsigned int *length);

Returns buffer glyph information array. Returned pointer is valid as long as buffer contents are not modified.

buffer

An hb_buffer_t

length

The output-array length.

The buffer glyph information array. The value valid as long as buffer has not been modified.

[transfer none][array length=length]

Since: 0.9.2

hb_glyph_position_t *
hb_buffer_get_glyph_positions (hb_buffer_t *buffer,
                               unsigned int *length);

Returns buffer glyph position array. Returned pointer is valid as long as buffer contents are not modified.

If buffer did not have positions before, the positions will be initialized to zeros, unless this function is called from within a buffer message callback (see hb_buffer_set_message_func()), in which case NULL is returned.

The buffer glyph position array. The value valid as long as buffer has not been modified.

[transfer none][array length=length]

Since: 0.9.2

void
hb_buffer_set_invisible_glyph (hb_buffer_t *buffer,
                               hb_codepoint_t invisible);

Sets the hb_codepoint_t that replaces invisible characters in the shaping result. If set to zero (default), the glyph for the U+0020 SPACE character is used. Otherwise, this value is used verbatim.

Since: 2.0.0

void
hb_buffer_set_not_found_glyph (hb_buffer_t *buffer,
                               hb_codepoint_t not_found);

Sets the hb_codepoint_t that replaces characters not found in the font during shaping.

The not-found glyph defaults to zero, sometimes known as the ".notdef" glyph. This API allows for differentiating the two.

Since: 3.1.0

void
hb_buffer_set_not_found_variation_selector_glyph
                               (hb_buffer_t *buffer,
                                hb_codepoint_t not_found_variation_selector);

Sets the hb_codepoint_t that replaces variation-selector characters not resolved in the font during shaping.

The not-found-variation-selector glyph defaults to HB_CODEPOINT_INVALID, in which case an unresolved variation-selector will be removed from the glyph string during shaping. This API allows for changing that and retaining a glyph, such that the situation can be detected by the client and handled accordingly (e.g. by using a different font).

Since: 10.0.0

hb_codepoint_t
hb_buffer_get_replacement_codepoint (const hb_buffer_t *buffer);

Fetches the hb_codepoint_t that replaces invalid entries for a given encoding when adding text to buffer .

Since: 0.9.31

void
hb_buffer_set_random_state (hb_buffer_t *buffer,
                            unsigned  state);

Sets the random state of the buffer. The state changes every time a glyph uses randomness (eg. the rand OpenType feature). This function together with hb_buffer_get_random_state() allow for transferring the current random state to a subsequent buffer, to get better randomness distribution.

Defaults to 1 and when buffer contents are cleared. A value of 0 disables randomness during shaping.

Since: 8.4.0

void
hb_buffer_normalize_glyphs (hb_buffer_t *buffer);

Reorders a glyph buffer to have canonical in-cluster glyph order / position. The resulting clusters should behave identical to pre-reordering clusters.

This has nothing to do with Unicode normalization.

Since: 0.9.2

void
hb_buffer_reverse (hb_buffer_t *buffer);

Reverses buffer contents.

Since: 0.9.2

void
hb_buffer_reverse_range (hb_buffer_t *buffer,
                         unsigned int start,
                         unsigned int end);

Reverses buffer contents between start and end .

Since: 0.9.41

void
hb_buffer_reverse_clusters (hb_buffer_t *buffer);

Reverses buffer clusters. That is, the buffer contents are reversed, then each cluster (consecutive items having the same cluster number) are reversed again.

Since: 0.9.2

unsigned int
hb_buffer_serialize (hb_buffer_t *buffer,
                     unsigned int start,
                     unsigned int end,
                     char *buf,
                     unsigned int buf_size,
                     unsigned int *buf_consumed,
                     hb_font_t *font,
                     hb_buffer_serialize_format_t format,
                     hb_buffer_serialize_flags_t flags);

Serializes buffer into a textual representation of its content, whether Unicode codepoints or glyph identifiers and positioning information. This is useful for showing the contents of the buffer, for example during debugging. See the documentation of hb_buffer_serialize_unicode() and hb_buffer_serialize_glyphs() for a description of the output format.

buffer

an hb_buffer_t buffer.

start

the first item in buffer to serialize.

end

the last item in buffer to serialize.

buf

output string to write serialized buffer into.

buf_size

the size of buf .

buf_consumed

if not NULL, will be set to the number of bytes written into buf .

font

the hb_font_t used to shape this buffer, needed to read glyph names and extents. If NULL, an empty font will be used.

format

the hb_buffer_serialize_format_t to use for formatting the output.

flags

the hb_buffer_serialize_flags_t that control what glyph properties to serialize.

The number of serialized items.

Since: 2.7.3

unsigned int
hb_buffer_serialize_glyphs (hb_buffer_t *buffer,
                            unsigned int start,
                            unsigned int end,
                            char *buf,
                            unsigned int buf_size,
                            unsigned int *buf_consumed,
                            hb_font_t *font,
                            hb_buffer_serialize_format_t format,
                            hb_buffer_serialize_flags_t flags);

Serializes buffer into a textual representation of its glyph content, useful for showing the contents of the buffer, for example during debugging. There are currently two supported serialization formats:

A human-readable, plain text format. The serialized glyphs will look something like:

[uni0651=0@518,0+0|uni0628=0+1897]

A machine-readable, structured format. The serialized glyphs will look something like:

[{"g":"uni0651","cl":0,"dx":518,"dy":0,"ax":0,"ay":0}, {"g":"uni0628","cl":0,"dx":0,"dy":0,"ax":1897,"ay":0}]

Each glyph is a JSON object, with the following properties:

• g: the glyph name or glyph index if HB_BUFFER_SERIALIZE_FLAG_NO_GLYPH_NAMES flag is set.

• cl: hb_glyph_info_t.cluster if HB_BUFFER_SERIALIZE_FLAG_NO_CLUSTERS is not set.

• dx,dy,ax,ay: hb_glyph_position_t.x_offset, hb_glyph_position_t.y_offset, hb_glyph_position_t.x_advance and hb_glyph_position_t.y_advance respectively, if HB_BUFFER_SERIALIZE_FLAG_NO_POSITIONS is not set.

• xb,yb,w,h: hb_glyph_extents_t.x_bearing, hb_glyph_extents_t.y_bearing, hb_glyph_extents_t.width and hb_glyph_extents_t.height respectively if HB_BUFFER_SERIALIZE_FLAG_GLYPH_EXTENTS is set.

buffer

an hb_buffer_t buffer.

start

the first item in buffer to serialize.

end

the last item in buffer to serialize.

buf

output string to write serialized buffer into.

buf_size

the size of buf .

buf_consumed

if not NULL, will be set to the number of bytes written into buf .

font

the hb_font_t used to shape this buffer, needed to read glyph names and extents. If NULL, an empty font will be used.

format

the hb_buffer_serialize_format_t to use for formatting the output.

flags

the hb_buffer_serialize_flags_t that control what glyph properties to serialize.

The number of serialized items.

Since: 0.9.7

hb_bool_t
hb_buffer_deserialize_glyphs (hb_buffer_t *buffer,
                              const char *buf,
                              int buf_len,
                              const char **end_ptr,
                              hb_font_t *font,
                              hb_buffer_serialize_format_t format);

Deserializes glyphs buffer from textual representation in the format produced by hb_buffer_serialize_glyphs().

buffer

an hb_buffer_t buffer.

buf

string to deserialize.

buf_len

the size of buf , or -1 if it is NULL-terminated

end_ptr

output pointer to the character after last consumed one.

font

font for getting glyph IDs.

format

the hb_buffer_serialize_format_t of the input buf

true if the full string was parsed, false otherwise.

Since: 0.9.7

unsigned int
hb_buffer_serialize_unicode (hb_buffer_t *buffer,
                             unsigned int start,
                             unsigned int end,
                             char *buf,
                             unsigned int buf_size,
                             unsigned int *buf_consumed,
                             hb_buffer_serialize_format_t format,
                             hb_buffer_serialize_flags_t flags);

Serializes buffer into a textual representation of its content, when the buffer contains Unicode codepoints (i.e., before shaping). This is useful for showing the contents of the buffer, for example during debugging. There are currently two supported serialization formats:

A human-readable, plain text format. The serialized codepoints will look something like:

 <U+0651=0|U+0628=1>

A machine-readable, structured format. The serialized codepoints will be a list of objects with the following properties:

For example:

[{u:1617,cl:0},{u:1576,cl:1}]

buffer

an hb_buffer_t buffer.

start

the first item in buffer to serialize.

end

the last item in buffer to serialize.

buf

output string to write serialized buffer into.

buf_size

the size of buf .

buf_consumed

if not NULL, will be set to the number of bytes written into buf .

format

the hb_buffer_serialize_format_t to use for formatting the output.

flags

the hb_buffer_serialize_flags_t that control what glyph properties to serialize.

The number of serialized items.

Since: 2.7.3

hb_bool_t
hb_buffer_deserialize_unicode (hb_buffer_t *buffer,
                               const char *buf,
                               int buf_len,
                               const char **end_ptr,
                               hb_buffer_serialize_format_t format);

Deserializes Unicode buffer from textual representation in the format produced by hb_buffer_serialize_unicode().

buffer

an hb_buffer_t buffer.

buf

string to deserialize.

buf_len

the size of buf , or -1 if it is NULL-terminated

end_ptr

output pointer to the character after last consumed one.

format

the hb_buffer_serialize_format_t of the input buf

true if the full string was parsed, false otherwise.

Since: 2.7.3

const char *
hb_buffer_serialize_format_to_string (hb_buffer_serialize_format_t format);

Converts format to the string corresponding it, or NULL if it is not a valid hb_buffer_serialize_format_t.

A NULL terminated string corresponding to format . Should not be freed.

[transfer none]

Since: 0.9.7

const char **
hb_buffer_serialize_list_formats (void);

Returns a list of supported buffer serialization formats.

A string array of buffer serialization formats. Should not be freed.

[transfer none]

Since: 0.9.7

unsigned int
hb_segment_properties_hash (const hb_segment_properties_t *p);

Creates a hash representing p .

Since: 0.9.7

void
hb_segment_properties_overlay (hb_segment_properties_t *p,
                               const hb_segment_properties_t *src);

Fills in missing fields of p from src in a considered manner.

First, if p does not have direction set, direction is copied from src .

Next, if p and src have the same direction (which can be unset), if p does not have script set, script is copied from src .

Finally, if p and src have the same direction and script (which either can be unset), if p does not have language set, language is copied from src .

Since: 3.3.0

hb_bool_t
(*hb_buffer_message_func_t) (hb_buffer_t *buffer,
                             hb_font_t *font,
                             const char *message,
                             void *user_data);

A callback method for hb_buffer_t. The method gets called with the hb_buffer_t it was set on, the hb_font_t the buffer is shaped with and a message describing what step of the shaping process will be performed. Returning false from this method will skip this shaping step and move to the next one.

buffer

An hb_buffer_t to work upon

font

The hb_font_t the buffer is shaped with

message

NULL-terminated message passed to the function

user_data

User data pointer passed by the caller

true to perform the shaping step, false to skip it.

Since: 1.1.3

void
hb_buffer_set_message_func (hb_buffer_t *buffer,
                            hb_buffer_message_func_t func,
                            void *user_data,
                            hb_destroy_func_t destroy);

Sets the implementation function for hb_buffer_message_func_t.

buffer

An hb_buffer_t

func

Callback function.

user_data

Data to pass to func .

destroy

The function to call when user_data is not needed anymore.

Since: 1.1.3

#define             HB_BUFFER_CLUSTER_LEVEL_IS_CHARACTERS(level)

Tests whether a cluster level does not group cluster values by graphemes. Requires that the level be valid.

Since: 11.0.0

#define             HB_BUFFER_CLUSTER_LEVEL_IS_GRAPHEMES(level)

Tests whether a cluster level groups cluster values by graphemes. Requires that the level be valid.

Since: 11.0.0

#define             HB_BUFFER_CLUSTER_LEVEL_IS_MONOTONE(level)

Tests whether a cluster level groups cluster values into monotone order. Requires that the level be valid.

Since: 11.0.0

#define HB_BUFFER_REPLACEMENT_CODEPOINT_DEFAULT 0xFFFDu

The default code point for replacing invalid characters in a given encoding. Set to U+FFFD REPLACEMENT CHARACTER.

Since: 0.9.31

typedef struct hb_buffer_t hb_buffer_t;

The main structure holding the input text and its properties before shaping, and output glyphs and their information after shaping.

typedef struct {
  hb_codepoint_t codepoint;
  uint32_t       cluster;
} hb_glyph_info_t;

The hb_glyph_info_t is the structure that holds information about the glyphs and their relation to input text.

hb_codepoint_t codepoint;

either a Unicode code point (before shaping) or a glyph index (after shaping).

uint32_t cluster;

the index of the character in the original text that corresponds to this hb_glyph_info_t, or whatever the client passes to hb_buffer_add(). More than one hb_glyph_info_t can have the same cluster value, if they resulted from the same character (e.g. one to many glyph substitution), and when more than one character gets merged in the same glyph (e.g. many to one glyph substitution) the hb_glyph_info_t will have the smallest cluster value of them. By default some characters are merged into the same cluster (e.g. combining marks have the same cluster as their bases) even if they are separate glyphs, hb_buffer_set_cluster_level() allow selecting more fine-grained cluster handling.

Flags for hb_glyph_info_t.

HB_GLYPH_FLAG_UNSAFE_TO_BREAK

Indicates that if input text is broken at the beginning of the cluster this glyph is part of, then both sides need to be re-shaped, as the result might be different. On the flip side, it means that when this flag is not present, then it is safe to break the glyph-run at the beginning of this cluster, and the two sides will represent the exact same result one would get if breaking input text at the beginning of this cluster and shaping the two sides separately. This can be used to optimize paragraph layout, by avoiding re-shaping of each line after line-breaking.

HB_GLYPH_FLAG_UNSAFE_TO_CONCAT

Indicates that if input text is changed on one side of the beginning of the cluster this glyph is part of, then the shaping results for the other side might change. Note that the absence of this flag will NOT by itself mean that it IS safe to concat text. Only two pieces of text both of which clear of this flag can be concatenated safely. This can be used to optimize paragraph layout, by avoiding re-shaping of each line after line-breaking, by limiting the reshaping to a small piece around the breaking position only, even if the breaking position carries the HB_GLYPH_FLAG_UNSAFE_TO_BREAK or when hyphenation or other text transformation happens at line-break position, in the following way: 1. Iterate back from the line-break position until the first cluster start position that is NOT unsafe-to-concat, 2. shape the segment from there till the end of line, 3. check whether the resulting glyph-run also is clear of the unsafe-to-concat at its start-of-text position; if it is, just splice it into place and the line is shaped; If not, move on to a position further back that is clear of unsafe-to-concat and retry from there, and repeat. At the start of next line a similar algorithm can be implemented. That is: 1. Iterate forward from the line-break position until the first cluster start position that is NOT unsafe-to-concat, 2. shape the segment from beginning of the line to that position, 3. check whether the resulting glyph-run also is clear of the unsafe-to-concat at its end-of-text position; if it is, just splice it into place and the beginning is shaped; If not, move on to a position further forward that is clear of unsafe-to-concat and retry up to there, and repeat. A slight complication will arise in the implementation of the algorithm above, because while our buffer API has a way to return flags for position corresponding to start-of-text, there is currently no position corresponding to end-of-text. This limitation can be alleviated by shaping more text than needed and looking for unsafe-to-concat flag within text clusters. The HB_GLYPH_FLAG_UNSAFE_TO_BREAK flag will always imply this flag. To use this flag, you must enable the buffer flag HB_BUFFER_FLAG_PRODUCE_UNSAFE_TO_CONCAT during shaping, otherwise the buffer flag will not be reliably produced. Since: 4.0.0

HB_GLYPH_FLAG_SAFE_TO_INSERT_TATWEEL

In scripts that use elongation (Arabic, Mongolian, Syriac, etc.), this flag signifies that it is safe to insert a U+0640 TATWEEL character before this cluster for elongation. This flag does not determine the script-specific elongation places, but only when it is safe to do the elongation without interrupting text shaping. Since: 5.1.0

HB_GLYPH_FLAG_DEFINED

All the currently defined flags.

Since: 1.5.0

typedef struct {
  hb_position_t  x_advance;
  hb_position_t  y_advance;
  hb_position_t  x_offset;
  hb_position_t  y_offset;
} hb_glyph_position_t;

The hb_glyph_position_t is the structure that holds the positions of the glyph in both horizontal and vertical directions. All positions in hb_glyph_position_t are relative to the current point.

hb_position_t x_advance;

how much the line advances after drawing this glyph when setting text in horizontal direction.

hb_position_t y_advance;

how much the line advances after drawing this glyph when setting text in vertical direction.

hb_position_t x_offset;

how much the glyph moves on the X-axis before drawing it, this should not affect how much the line advances.

hb_position_t y_offset;

how much the glyph moves on the Y-axis before drawing it, this should not affect how much the line advances.

The type of hb_buffer_t contents.

HB_BUFFER_CONTENT_TYPE_INVALID

Initial value for new buffer.

HB_BUFFER_CONTENT_TYPE_UNICODE

The buffer contains input characters (before shaping).

HB_BUFFER_CONTENT_TYPE_GLYPHS

The buffer contains output glyphs (after shaping).

Flags for hb_buffer_t.

HB_BUFFER_FLAG_DEFAULT

the default buffer flag.

HB_BUFFER_FLAG_BOT

flag indicating that special handling of the beginning of text paragraph can be applied to this buffer. Should usually be set, unless you are passing to the buffer only part of the text without the full context.

HB_BUFFER_FLAG_EOT

flag indicating that special handling of the end of text paragraph can be applied to this buffer, similar to HB_BUFFER_FLAG_BOT .

HB_BUFFER_FLAG_PRESERVE_DEFAULT_IGNORABLES

flag indication that character with Default_Ignorable Unicode property should use the corresponding glyph from the font, instead of hiding them (done by replacing them with the space glyph and zeroing the advance width.) This flag takes precedence over HB_BUFFER_FLAG_REMOVE_DEFAULT_IGNORABLES .

HB_BUFFER_FLAG_REMOVE_DEFAULT_IGNORABLES

flag indication that character with Default_Ignorable Unicode property should be removed from glyph string instead of hiding them (done by replacing them with the space glyph and zeroing the advance width.) HB_BUFFER_FLAG_PRESERVE_DEFAULT_IGNORABLES takes precedence over this flag. Since: 1.8.0

HB_BUFFER_FLAG_DO_NOT_INSERT_DOTTED_CIRCLE

flag indicating that a dotted circle should not be inserted in the rendering of incorrect character sequences (such at <0905 093E>). Since: 2.4.0

HB_BUFFER_FLAG_VERIFY

flag indicating that the hb_shape() call and its variants should perform various verification processes on the results of the shaping operation on the buffer. If the verification fails, then either a buffer message is sent, if a message handler is installed on the buffer, or a message is written to standard error. In either case, the shaping result might be modified to show the failed output. Since: 3.4.0

HB_BUFFER_FLAG_PRODUCE_UNSAFE_TO_CONCAT

flag indicating that the HB_GLYPH_FLAG_UNSAFE_TO_CONCAT glyph-flag should be produced by the shaper. By default it will not be produced since it incurs a cost. Since: 4.0.0

HB_BUFFER_FLAG_PRODUCE_SAFE_TO_INSERT_TATWEEL

flag indicating that the HB_GLYPH_FLAG_SAFE_TO_INSERT_TATWEEL glyph-flag should be produced by the shaper. By default it will not be produced. Since: 5.1.0

HB_BUFFER_FLAG_DEFINED

All currently defined flags: Since: 4.4.0

Since: 0.9.20

Data type for holding HarfBuzz's clustering behavior options. The cluster level dictates one aspect of how HarfBuzz will treat non-base characters during shaping.

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 every time 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. 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 do not need to maintain such backward compatibility are recommended to use HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS instead of the default.

HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES

Return cluster values grouped by graphemes into monotone order.

HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS

Return cluster values grouped into monotone order.

HB_BUFFER_CLUSTER_LEVEL_CHARACTERS

Don't group cluster values.

HB_BUFFER_CLUSTER_LEVEL_GRAPHEMES

Only group clusters, but don't enforce monotone order.

HB_BUFFER_CLUSTER_LEVEL_DEFAULT

Default cluster level, equal to HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES .

Since: 0.9.42

The buffer serialization and de-serialization format used in hb_buffer_serialize_glyphs() and hb_buffer_deserialize_glyphs().

HB_BUFFER_SERIALIZE_FORMAT_TEXT

a human-readable, plain text format.

HB_BUFFER_SERIALIZE_FORMAT_JSON

a machine-readable JSON format.

HB_BUFFER_SERIALIZE_FORMAT_INVALID

invalid format.

Since: 0.9.2

Flags that control what glyph information are serialized in hb_buffer_serialize_glyphs().

HB_BUFFER_SERIALIZE_FLAG_DEFAULT

serialize glyph names, clusters and positions.

HB_BUFFER_SERIALIZE_FLAG_NO_CLUSTERS

do not serialize glyph cluster.

HB_BUFFER_SERIALIZE_FLAG_NO_POSITIONS

do not serialize glyph position information.

HB_BUFFER_SERIALIZE_FLAG_NO_GLYPH_NAMES

do no serialize glyph name.

HB_BUFFER_SERIALIZE_FLAG_GLYPH_EXTENTS

serialize glyph extents.

HB_BUFFER_SERIALIZE_FLAG_GLYPH_FLAGS

serialize glyph flags. Since: 1.5.0

HB_BUFFER_SERIALIZE_FLAG_NO_ADVANCES

do not serialize glyph advances, glyph offsets will reflect absolute glyph positions. Since: 1.8.0

HB_BUFFER_SERIALIZE_FLAG_DEFINED

All currently defined flags. Since: 4.4.0

Since: 0.9.20

Flags from comparing two hb_buffer_t's.

Buffer with different hb_buffer_content_type_t cannot be meaningfully compared in any further detail.

For buffers with differing length, the per-glyph comparison is not attempted, though we do still scan reference buffer for dotted circle and .notdef glyphs.

If the buffers have the same length, we compare them glyph-by-glyph and report which aspect(s) of the glyph info/position are different.

HB_BUFFER_DIFF_FLAG_EQUAL

equal buffers.

HB_BUFFER_DIFF_FLAG_CONTENT_TYPE_MISMATCH

buffers with different hb_buffer_content_type_t.

HB_BUFFER_DIFF_FLAG_LENGTH_MISMATCH

buffers with differing length.

HB_BUFFER_DIFF_FLAG_NOTDEF_PRESENT

.notdef glyph is present in the reference buffer.

HB_BUFFER_DIFF_FLAG_DOTTED_CIRCLE_PRESENT

dotted circle glyph is present in the reference buffer.

HB_BUFFER_DIFF_FLAG_CODEPOINT_MISMATCH

difference in hb_glyph_info_t.codepoint

HB_BUFFER_DIFF_FLAG_CLUSTER_MISMATCH

difference in hb_glyph_info_t.cluster

HB_BUFFER_DIFF_FLAG_GLYPH_FLAGS_MISMATCH

difference in hb_glyph_flags_t.

HB_BUFFER_DIFF_FLAG_POSITION_MISMATCH

difference in hb_glyph_position_t.

Since: 1.5.0

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