hb-buffer: HarfBuzz Manual

## hb-buffer hb-buffer — Input and output buffers |

## Functions

hb_buffer_t * | hb_buffer_create ()
hb_bool_t | hb_buffer_allocation_successful ()
hb_buffer_t * | hb_buffer_create_similar ()
hb_buffer_t * | hb_buffer_get_empty ()
hb_buffer_t * | hb_buffer_reference ()
void | hb_buffer_destroy ()
hb_bool_t | hb_buffer_set_user_data ()
void * | hb_buffer_get_user_data ()
void | hb_buffer_reset ()
void | hb_buffer_clear_contents ()
hb_bool_t | hb_buffer_pre_allocate ()
void | hb_buffer_add ()
void | hb_buffer_add_codepoints ()
void | hb_buffer_add_utf32 ()
void | hb_buffer_add_utf16 ()
void | hb_buffer_add_utf8 ()
void | hb_buffer_add_latin1 ()
void | hb_buffer_append ()
void | hb_buffer_set_content_type ()
hb_buffer_content_type_t | hb_buffer_get_content_type ()
void | hb_buffer_set_direction ()
hb_direction_t | hb_buffer_get_direction ()
void | hb_buffer_set_script ()
hb_script_t | hb_buffer_get_script ()
void | hb_buffer_set_language ()
hb_language_t | hb_buffer_get_language ()
void | hb_buffer_set_flags ()
hb_buffer_flags_t | hb_buffer_get_flags ()
void | hb_buffer_set_cluster_level ()
hb_buffer_cluster_level_t | hb_buffer_get_cluster_level ()
hb_bool_t | hb_buffer_set_length ()
unsigned int | hb_buffer_get_length ()
void | hb_buffer_set_segment_properties ()
void | hb_buffer_get_segment_properties ()
void | hb_buffer_guess_segment_properties ()
void | hb_buffer_set_unicode_funcs ()
hb_unicode_funcs_t * | hb_buffer_get_unicode_funcs ()
hb_glyph_info_t * | hb_buffer_get_glyph_infos ()
hb_glyph_flags_t | hb_glyph_info_get_glyph_flags ()
hb_glyph_position_t * | hb_buffer_get_glyph_positions ()
hb_bool_t | hb_buffer_has_positions ()
void | hb_buffer_set_invisible_glyph ()
hb_codepoint_t | hb_buffer_get_invisible_glyph ()
void | hb_buffer_set_not_found_glyph ()
hb_codepoint_t | hb_buffer_get_not_found_glyph ()
void | hb_buffer_set_not_found_variation_selector_glyph ()
hb_codepoint_t | hb_buffer_get_not_found_variation_selector_glyph ()
void | hb_buffer_set_replacement_codepoint ()
hb_codepoint_t | hb_buffer_get_replacement_codepoint ()
void | hb_buffer_set_random_state ()
unsigned | hb_buffer_get_random_state ()
void | hb_buffer_normalize_glyphs ()
void | hb_buffer_reverse ()
void | hb_buffer_reverse_range ()
void | hb_buffer_reverse_clusters ()
unsigned int | hb_buffer_serialize ()
unsigned int | hb_buffer_serialize_glyphs ()
hb_bool_t | hb_buffer_deserialize_glyphs ()
unsigned int | hb_buffer_serialize_unicode ()
hb_bool_t | hb_buffer_deserialize_unicode ()
hb_buffer_serialize_format_t | hb_buffer_serialize_format_from_string ()
const char * | hb_buffer_serialize_format_to_string ()
const char ** | hb_buffer_serialize_list_formats ()
hb_bool_t | hb_segment_properties_equal ()
unsigned int | hb_segment_properties_hash ()
void | hb_segment_properties_overlay ()
hb_buffer_diff_flags_t | hb_buffer_diff ()
hb_bool_t | (*hb_buffer_message_func_t) ()
void | hb_buffer_set_message_func ()
void | hb_buffer_changed ()
#define | HB_BUFFER_CLUSTER_LEVEL_IS_CHARACTERS()
#define | HB_BUFFER_CLUSTER_LEVEL_IS_GRAPHEMES()
#define | HB_BUFFER_CLUSTER_LEVEL_IS_MONOTONE()

## Types and Values

#define | HB_SEGMENT_PROPERTIES_DEFAULT
#define | HB_BUFFER_REPLACEMENT_CODEPOINT_DEFAULT
typedef | hb_buffer_t
| hb_glyph_info_t
enum | hb_glyph_flags_t
| hb_glyph_position_t
enum | hb_buffer_content_type_t
enum | hb_buffer_flags_t
enum | hb_buffer_cluster_level_t
| hb_segment_properties_t
enum | hb_buffer_serialize_format_t
enum | hb_buffer_serialize_flags_t
enum | hb_buffer_diff_flags_t

## Includes

    #include <hb.h>

## Description

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.

## Functions

### hb_buffer_create ()

    hb_buffer_t *
    hb_buffer_create (void);

Creates a new hb_buffer_t with all properties to defaults.

#### Returns

A newly allocated hb_buffer_t with a reference count of 1. The initial reference count should be released with `hb_buffer_destroy()` when you are done using the hb_buffer_t. This function never returns `NULL`. If memory cannot be allocated, a special hb_buffer_t object will be returned on which `hb_buffer_allocation_successful()` returns `false`.

[transfer full]

Since: 0.9.2

### hb_buffer_allocation_successful ()

    hb_bool_t
    hb_buffer_allocation_successful (hb_buffer_t *buffer);

Check if allocating memory for the buffer succeeded.

#### Parameters

buffer | An hb_buffer_t |

#### Returns

`true` if `buffer` memory allocation succeeded, `false` otherwise.

Since: 0.9.2

### hb_buffer_create_similar ()

    hb_buffer_t *
    hb_buffer_create_similar (const hb_buffer_t *src);

Creates a new hb_buffer_t, similar to `hb_buffer_create()`. The only difference is that the buffer is configured similarly to `src` .

#### Parameters

src | An hb_buffer_t |

#### Returns

A newly allocated hb_buffer_t, similar to `hb_buffer_create()`.

[transfer full]

Since: 3.3.0

### hb_buffer_get_empty ()

    hb_buffer_t *
    hb_buffer_get_empty (void);

Fetches an empty hb_buffer_t.

#### Returns

The empty buffer.

[transfer full]

Since: 0.9.2

### hb_buffer_reference ()

    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]

#### Parameters

buffer | An hb_buffer_t |

#### Returns

The referenced hb_buffer_t.

[transfer full]

Since: 0.9.2

### hb_buffer_destroy ()

    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]

#### Parameters

buffer | An hb_buffer_t |

Since: 0.9.2

### hb_buffer_set_user_data ()

    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]

#### Parameters

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. | [nullable]
replace | Whether to replace an existing data with the same key |

#### Returns

`true` if success, `false` otherwise

Since: 0.9.2

### hb_buffer_get_user_data ()

    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]

#### Parameters

buffer | An hb_buffer_t |
key | The user-data key to query |

#### Returns

A pointer to the user data.

[transfer none]

Since: 0.9.2

### hb_buffer_reset ()

    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()`.

#### Parameters

buffer | An hb_buffer_t |

Since: 0.9.2

### hb_buffer_clear_contents ()

    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.

#### Parameters

buffer | An hb_buffer_t |

Since: 0.9.11

### hb_buffer_pre_allocate ()

    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.

#### Parameters

buffer | An hb_buffer_t |
size | Number of items to pre allocate. |

#### Returns

`true` if `buffer` memory allocation succeeded, `false` otherwise

Since: 0.9.2

### hb_buffer_add ()

    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.

#### Parameters

buffer | An hb_buffer_t |
codepoint | A Unicode code point. |
cluster | The cluster value of `codepoint` . |

Since: 0.9.7

### hb_buffer_add_codepoints ()

    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.

#### Parameters

buffer | a hb_buffer_t to append characters to. |
text | an array of Unicode code points to append. | [array length=text_length]
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

### hb_buffer_add_utf32 ()

    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()`.

#### Parameters

buffer | An hb_buffer_t |
text | An array of UTF-32 characters to append. | [array length=text_length]
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

### hb_buffer_add_utf16 ()

    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()`.

#### Parameters

buffer | An hb_buffer_t |
text | An array of UTF-16 characters to append. | [array length=text_length]
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

### hb_buffer_add_utf8 ()

    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()`.

#### Parameters

buffer | An hb_buffer_t |
text | An array of UTF-8 characters to append. | [array length=text_length][element-type uint8_t]
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

### hb_buffer_add_latin1 ()

    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.

#### Parameters

buffer | An hb_buffer_t |
text | an array of UTF-8 characters to append. | [array length=text_length][element-type uint8_t]
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

### hb_buffer_append ()

    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.

#### Parameters

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

### hb_buffer_set_content_type ()

    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:

- A newly created buffer starts with content type `HB_BUFFER_CONTENT_TYPE_INVALID`. Calling `hb_buffer_reset()`, `hb_buffer_clear_contents()`, as well as calling `hb_buffer_set_length()` with an argument of zero all set the buffer content type to invalid as well.

- Calling `hb_buffer_add_utf8()`, `hb_buffer_add_utf16()`, `hb_buffer_add_utf32()`, `hb_buffer_add_codepoints()` and `hb_buffer_add_latin1()` expect that buffer is either empty and have a content type of invalid, or that buffer content type is `HB_BUFFER_CONTENT_TYPE_UNICODE`, and they also set the content type to Unicode if they added anything to an empty buffer.

- Finally `hb_shape()` and `hb_shape_full()` expect that the buffer is either empty and have content type of invalid, or that buffer content type is `HB_BUFFER_CONTENT_TYPE_UNICODE`, and upon success they set the buffer content type to `HB_BUFFER_CONTENT_TYPE_GLYPHS`.

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.

#### Parameters

buffer | An hb_buffer_t |
content_type | The type of buffer contents to set |

Since: 0.9.5

### hb_buffer_get_content_type ()

    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).

#### Parameters

buffer | An hb_buffer_t |

#### Returns

The type of `buffer` contents

Since: 0.9.5

### hb_buffer_set_direction ()

    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.

#### Parameters

buffer | An hb_buffer_t |
direction | the hb_direction_t of the `buffer` |

Since: 0.9.2

### hb_buffer_get_direction ()

    hb_direction_t
    hb_buffer_get_direction (const hb_buffer_t *buffer);

See `hb_buffer_set_direction()`

#### Parameters

buffer | An hb_buffer_t |

#### Returns

The direction of the `buffer` .

Since: 0.9.2

### hb_buffer_set_script ()

    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.

#### Parameters

buffer | An hb_buffer_t |
script | An hb_script_t to set. |

Since: 0.9.2

### hb_buffer_get_script ()

    hb_script_t
    hb_buffer_get_script (const hb_buffer_t *buffer);

Fetches the script of `buffer` .

#### Parameters

buffer | An hb_buffer_t |

#### Returns

The hb_script_t of the `buffer`

Since: 0.9.2

### hb_buffer_set_language ()

    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.

#### Parameters

buffer | An hb_buffer_t |
language | An hb_language_t to set |

Since: 0.9.2

### hb_buffer_get_language ()

    hb_language_t
    hb_buffer_get_language (const hb_buffer_t *buffer);

See `hb_buffer_set_language()`.

#### Parameters

buffer | An hb_buffer_t |

#### Returns

The hb_language_t of the buffer. Must not be freed by the caller.

[transfer none]

Since: 0.9.2

### hb_buffer_set_flags ()

    void
    hb_buffer_set_flags (hb_buffer_t *buffer,
                         hb_buffer_flags_t flags);

Sets `buffer` flags to `flags` . See hb_buffer_flags_t.

#### Parameters

buffer | An hb_buffer_t |
flags | The buffer flags to set |

Since: 0.9.7

### hb_buffer_get_flags ()

    hb_buffer_flags_t
    hb_buffer_get_flags (const hb_buffer_t *buffer);

Fetches the hb_buffer_flags_t of `buffer` .

#### Parameters

buffer | An hb_buffer_t |

#### Returns

The `buffer` flags

Since: 0.9.7

### hb_buffer_set_cluster_level ()

    void
    hb_buffer_set_cluster_level (hb_buffer_t *buffer,
                                 hb_buffer_cluster_level_t cluster_level);

Sets the cluster level of a buffer. The hb_buffer_cluster_level_t dictates one aspect of how HarfBuzz will treat non-base characters during shaping.

#### Parameters

buffer | An hb_buffer_t |
cluster_level | The cluster level to set on the buffer |

Since: 0.9.42

### hb_buffer_get_cluster_level ()

    hb_buffer_cluster_level_t
    hb_buffer_get_cluster_level (const hb_buffer_t *buffer);

Fetches the cluster level of a buffer. The hb_buffer_cluster_level_t dictates one aspect of how HarfBuzz will treat non-base characters during shaping.

#### Parameters

buffer | An hb_buffer_t |

#### Returns

The cluster level of `buffer`

Since: 0.9.42

### hb_buffer_set_length ()

    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.

#### Parameters

buffer | An hb_buffer_t |
length | The new length of `buffer` |

#### Returns

`true` if `buffer` memory allocation succeeded, `false` otherwise.

Since: 0.9.2

### hb_buffer_get_length ()

    unsigned int
    hb_buffer_get_length (const hb_buffer_t *buffer);

Returns the number of items in the buffer.

#### Parameters

buffer | An hb_buffer_t |

#### Returns

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

Since: 0.9.2

### hb_buffer_set_segment_properties ()

    void
    hb_buffer_set_segment_properties (hb_buffer_t *buffer,
                                      const hb_segment_properties_t *props);

Sets the segment properties of the buffer, a shortcut for calling `hb_buffer_set_direction()`, `hb_buffer_set_script()` and `hb_buffer_set_language()` individually.

#### Parameters

buffer | An hb_buffer_t |
props | An hb_segment_properties_t to use |

Since: 0.9.7

### hb_buffer_get_segment_properties ()

    void
    hb_buffer_get_segment_properties (const hb_buffer_t *buffer,
                                      hb_segment_properties_t *props);

Sets `props` to the hb_segment_properties_t of `buffer` .

#### Parameters

buffer | An hb_buffer_t |
props | The output hb_segment_properties_t. | [out]

Since: 0.9.7

### hb_buffer_guess_segment_properties ()

    void
    hb_buffer_guess_segment_properties (hb_buffer_t *buffer);

Sets unset buffer segment properties based on buffer Unicode contents. If buffer is not empty, it must have content type HB_BUFFER_CONTENT_TYPE_UNICODE.

If buffer script is not set (ie. is HB_SCRIPT_INVALID), it will be set to the Unicode script of the first character in the buffer that has a script other than HB_SCRIPT_COMMON, HB_SCRIPT_INHERITED, and HB_SCRIPT_UNKNOWN.

Next, if buffer direction is not set (ie. is HB_DIRECTION_INVALID), it will be set to the natural horizontal direction of the buffer script as returned by `hb_script_get_horizontal_direction()`. If `hb_script_get_horizontal_direction()` returns HB_DIRECTION_INVALID, then HB_DIRECTION_LTR is used.

Finally, if buffer language is not set (ie. is HB_LANGUAGE_INVALID), it will be set to the process's default language as returned by `hb_language_get_default()`. This may change in the future by taking buffer script into consideration when choosing a language. Note that `hb_language_get_default()` is NOT threadsafe the first time it is called. See documentation for that function for details.

#### Parameters

buffer | An hb_buffer_t |

Since: 0.9.7

### hb_buffer_set_unicode_funcs ()

    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` .

#### Parameters

buffer | An hb_buffer_t |
unicode_funcs | The Unicode-functions structure |

Since: 0.9.2

### hb_buffer_get_unicode_funcs ()

    hb_unicode_funcs_t *
    hb_buffer_get_unicode_funcs (const hb_buffer_t *buffer);

Fetches the Unicode-functions structure of a buffer.

#### Parameters

buffer | An hb_buffer_t |

#### Returns

The Unicode-functions structure

Since: 0.9.2

### hb_buffer_get_glyph_infos ()

    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.

#### Parameters

buffer | An hb_buffer_t |
length | The output-array length. | [out]

#### Returns

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_info_get_glyph_flags ()

    hb_glyph_flags_t
    hb_glyph_info_get_glyph_flags (const hb_glyph_info_t *info);

Returns glyph flags encoded within a hb_glyph_info_t.

#### Parameters

info | a hb_glyph_info_t |

#### Returns

The hb_glyph_flags_t encoded within `info`

Since: 1.5.0

### hb_buffer_get_glyph_positions ()

    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.

#### Parameters

buffer | An hb_buffer_t |
length | The output length. | [out]

#### Returns

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

### hb_buffer_has_positions ()

    hb_bool_t
    hb_buffer_has_positions (hb_buffer_t *buffer);

Returns whether `buffer` has glyph position data. A buffer gains position data when `hb_buffer_get_glyph_positions()` is called on it, and cleared of position data when `hb_buffer_clear_contents()` is called.

#### Parameters

buffer | an hb_buffer_t. |

#### Returns

`true` if the `buffer` has position array, `false` otherwise.

Since: 2.7.3

### hb_buffer_set_invisible_glyph ()

    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.

#### Parameters

buffer | An hb_buffer_t |
invisible | the invisible hb_codepoint_t |

Since: 2.0.0

### hb_buffer_get_invisible_glyph ()

    hb_codepoint_t
    hb_buffer_get_invisible_glyph (const hb_buffer_t *buffer);

See `hb_buffer_set_invisible_glyph()`.

#### Parameters

buffer | An hb_buffer_t |

#### Returns

The `buffer` invisible hb_codepoint_t

Since: 2.0.0

### hb_buffer_set_not_found_glyph ()

    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.

#### Parameters

buffer | An hb_buffer_t |
not_found | the not-found hb_codepoint_t |

Since: 3.1.0

### hb_buffer_get_not_found_glyph ()

    hb_codepoint_t
    hb_buffer_get_not_found_glyph (const hb_buffer_t *buffer);

See `hb_buffer_set_not_found_glyph()`.

#### Parameters

buffer | An hb_buffer_t |

#### Returns

The `buffer` not-found hb_codepoint_t

Since: 3.1.0

### hb_buffer_set_not_found_variation_selector_glyph ()

    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).

#### Parameters

buffer | An hb_buffer_t |
not_found_variation_selector | the not-found-variation-selector hb_codepoint_t |

Since: 10.0.0

### hb_buffer_get_not_found_variation_selector_glyph ()

    hb_codepoint_t
    hb_buffer_get_not_found_variation_selector_glyph
                                   (const hb_buffer_t *buffer);

See `hb_buffer_set_not_found_variation_selector_glyph()`.

#### Parameters

buffer | An hb_buffer_t |

#### Returns

The `buffer` not-found-variation-selector hb_codepoint_t

Since: 10.0.0

### hb_buffer_set_replacement_codepoint ()

    void
    hb_buffer_set_replacement_codepoint (hb_buffer_t *buffer,
                                         hb_codepoint_t replacement);

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

Default is HB_BUFFER_REPLACEMENT_CODEPOINT_DEFAULT.

#### Parameters

buffer | An hb_buffer_t |
replacement | the replacement hb_codepoint_t |

Since: 0.9.31

### hb_buffer_get_replacement_codepoint ()

    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` .

#### Parameters

buffer | An hb_buffer_t |

#### Returns

The `buffer` replacement hb_codepoint_t

Since: 0.9.31

### hb_buffer_set_random_state ()

    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.

#### Parameters

buffer | An hb_buffer_t |
state | the new random state |

Since: 8.4.0

### hb_buffer_get_random_state ()

    unsigned
    hb_buffer_get_random_state (const hb_buffer_t *buffer);

See `hb_buffer_set_random_state()`.

#### Parameters

buffer | An hb_buffer_t |

#### Returns

The `buffer` random state

Since: 8.4.0

### hb_buffer_normalize_glyphs ()

    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.

#### Parameters

buffer | An hb_buffer_t |

Since: 0.9.2

### hb_buffer_reverse ()

    void
    hb_buffer_reverse (hb_buffer_t *buffer);

Reverses buffer contents.

#### Parameters

buffer | An hb_buffer_t |

Since: 0.9.2

### hb_buffer_reverse_range ()

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

Reverses buffer contents between `start` and `end` .

#### Parameters

buffer | An hb_buffer_t |
start | start index |
end | end index |

Since: 0.9.41

### hb_buffer_reverse_clusters ()

    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.

#### Parameters

buffer | An hb_buffer_t |

Since: 0.9.2

### hb_buffer_serialize ()

    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.

#### Parameters

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. | [out][array length=buf_size][element-type uint8_t]
buf_size | the size of `buf` . |
buf_consumed | if not `NULL`, will be set to the number of bytes written into `buf` . | [out][optional]
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. | [nullable]
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. |

#### Returns

The number of serialized items.

Since: 2.7.3

### hb_buffer_serialize_glyphs ()

    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:

#### text

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

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

- The serialized glyphs are delimited with `[` and `]`.

- Glyphs are separated with `|`

- Each glyph starts with glyph name, or glyph index if HB_BUFFER_SERIALIZE_FLAG_NO_GLYPH_NAMES flag is set. Then,

  - If HB_BUFFER_SERIALIZE_FLAG_NO_CLUSTERS is not set, `=` then hb_glyph_info_t.cluster.

  - If HB_BUFFER_SERIALIZE_FLAG_NO_POSITIONS is not set, the hb_glyph_position_t in the format:

    - If hb_glyph_position_t.x_offset and hb_glyph_position_t.y_offset are not both 0, `@x_offset,y_offset`. Then,

    - `+x_advance`, then `,y_advance` if hb_glyph_position_t.y_advance is not 0. Then,

  - If HB_BUFFER_SERIALIZE_FLAG_GLYPH_EXTENTS is set, the hb_glyph_extents_t in the format `<x_bearing,y_bearing,width,height>`

#### json

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.

#### Parameters

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. | [out][array length=buf_size][element-type uint8_t]
buf_size | the size of `buf` . |
buf_consumed | if not `NULL`, will be set to the number of bytes written into `buf` . | [out][optional]
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. | [nullable]
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. |

#### Returns

The number of serialized items.

Since: 0.9.7

### hb_buffer_deserialize_glyphs ()

    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()`.

#### Parameters

buffer | an hb_buffer_t buffer. |
buf | string to deserialize. | [array length=buf_len]
buf_len | the size of `buf` , or -1 if it is `NULL`-terminated |
end_ptr | output pointer to the character after last consumed one. | [out][optional]
font | font for getting glyph IDs. | [nullable]
format | the hb_buffer_serialize_format_t of the input `buf` |

#### Returns

`true` if the full string was parsed, `false` otherwise.

Since: 0.9.7

### hb_buffer_serialize_unicode ()

    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:

#### text

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

     <U+0651=0|U+0628=1>

- Glyphs are separated with `|`

- Unicode codepoints are expressed as zero-padded four (or more) digit hexadecimal numbers preceded by `U+`

- If HB_BUFFER_SERIALIZE_FLAG_NO_CLUSTERS is not set, the cluster will be indicated with a `=` then hb_glyph_info_t.cluster.

#### json

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

- `u`: the Unicode codepoint as a decimal integer

- `cl`: hb_glyph_info_t.cluster if HB_BUFFER_SERIALIZE_FLAG_NO_CLUSTERS is not set.

For example:

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

#### Parameters

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. | [out][array length=buf_size][element-type uint8_t]
buf_size | the size of `buf` . |
buf_consumed | if not `NULL`, will be set to the number of bytes written into `buf` . | [out][optional]
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. |

#### Returns

The number of serialized items.

Since: 2.7.3

### hb_buffer_deserialize_unicode ()

    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()`.

#### Parameters

buffer | an hb_buffer_t buffer. |
buf | string to deserialize. | [array length=buf_len]
buf_len | the size of `buf` , or -1 if it is `NULL`-terminated |
end_ptr | output pointer to the character after last consumed one. | [out][optional]
format | the hb_buffer_serialize_format_t of the input `buf` |

#### Returns

`true` if the full string was parsed, `false` otherwise.

Since: 2.7.3

### hb_buffer_serialize_format_from_string ()

    hb_buffer_serialize_format_t
    hb_buffer_serialize_format_from_string
                                   (const char *str,
                                    int len);

Parses a string into an hb_buffer_serialize_format_t. Does not check if `str` is a valid buffer serialization format, use `hb_buffer_serialize_list_formats()` to get the list of supported formats.

#### Parameters

str | a string to parse. | [array length=len][element-type uint8_t]
len | length of `str` , or -1 if string is `NULL` terminated |

#### Returns

The parsed hb_buffer_serialize_format_t.

Since: 0.9.7

### hb_buffer_serialize_format_to_string ()

    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.

#### Parameters

format | an hb_buffer_serialize_format_t to convert. |

#### Returns

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

[transfer none]

Since: 0.9.7

### hb_buffer_serialize_list_formats ()

    const char **
    hb_buffer_serialize_list_formats (void);

Returns a list of supported buffer serialization formats.

#### Returns

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

[transfer none]

Since: 0.9.7

### hb_segment_properties_equal ()

    hb_bool_t
    hb_segment_properties_equal (const hb_segment_properties_t *a,
                                 const hb_segment_properties_t *b);

Checks the equality of two hb_segment_properties_t's.

#### Parameters

a | first hb_segment_properties_t to compare. |
b | second hb_segment_properties_t to compare. |

#### Returns

`true` if all properties of `a` equal those of `b` , `false` otherwise.

Since: 0.9.7

### hb_segment_properties_hash ()

    unsigned int
    hb_segment_properties_hash (const hb_segment_properties_t *p);

Creates a hash representing `p` .

#### Parameters

p | hb_segment_properties_t to hash. |

#### Returns

A hash of `p` .

Since: 0.9.7

### hb_segment_properties_overlay ()

    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` .

#### Parameters

p | hb_segment_properties_t to fill in. |
src | hb_segment_properties_t to fill in from. |

Since: 3.3.0

### hb_buffer_diff ()

    hb_buffer_diff_flags_t
    hb_buffer_diff (hb_buffer_t *buffer,
                    hb_buffer_t *reference,
                    hb_codepoint_t dottedcircle_glyph,
                    unsigned int position_fuzz);

If dottedcircle_glyph is (hb_codepoint_t) -1 then HB_BUFFER_DIFF_FLAG_DOTTED_CIRCLE_PRESENT and HB_BUFFER_DIFF_FLAG_NOTDEF_PRESENT are never returned. This should be used by most callers if just comparing two buffers is needed.

#### Parameters

buffer | a buffer. |
reference | other buffer to compare to. |
dottedcircle_glyph | glyph id of U+25CC DOTTED CIRCLE, or (hb_codepoint_t) -1. |
position_fuzz | allowed absolute difference in position values. |

Since: 1.5.0

### hb_buffer_message_func_t ()

    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.

#### Parameters

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 |

#### Returns

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

Since: 1.1.3

### hb_buffer_set_message_func ()

    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.

#### Parameters

buffer | An hb_buffer_t |
func | Callback function. | [closure user_data][destroy destroy][scope notified]
user_data | Data to pass to `func` . | [nullable]
destroy | The function to call when `user_data` is not needed anymore. | [nullable]

Since: 1.1.3

### hb_buffer_changed ()

    void
    hb_buffer_changed (hb_buffer_t *buffer);

Called by a message callback after modifying buffer glyph indices, to update internal caches.

If not called from inside a message callback, does nothing.

#### Parameters

buffer | An hb_buffer_t |

Since: 13.0.0

### HB_BUFFER_CLUSTER_LEVEL_IS_CHARACTERS()

    #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.

#### Parameters

level | hb_buffer_cluster_level_t to test |

Since: 11.0.0

### HB_BUFFER_CLUSTER_LEVEL_IS_GRAPHEMES()

    #define             HB_BUFFER_CLUSTER_LEVEL_IS_GRAPHEMES(level)

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

#### Parameters

level | hb_buffer_cluster_level_t to test |

Since: 11.0.0

### HB_BUFFER_CLUSTER_LEVEL_IS_MONOTONE()

    #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.

#### Parameters

level | hb_buffer_cluster_level_t to test |

Since: 11.0.0

## Types and Values

### HB_SEGMENT_PROPERTIES_DEFAULT

    #define             HB_SEGMENT_PROPERTIES_DEFAULT

The default hb_segment_properties_t of of freshly created hb_buffer_t.

### HB_BUFFER_REPLACEMENT_CODEPOINT_DEFAULT

    #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

### hb_buffer_t

    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.

### hb_glyph_info_t

    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.

#### Members

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. |

### enum hb_glyph_flags_t

Flags for hb_glyph_info_t.

#### Members

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

### hb_glyph_position_t

    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.

#### Members

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. |

### enum hb_buffer_content_type_t

The type of hb_buffer_t contents.

#### Members

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). |

### enum hb_buffer_flags_t

Flags for hb_buffer_t.

#### Members

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

### enum hb_buffer_cluster_level_t

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.

#### Members

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

### hb_segment_properties_t

    typedef struct {
      hb_direction_t  direction;
      hb_script_t     script;
      hb_language_t   language;
    } hb_segment_properties_t;

The structure that holds various text properties of an hb_buffer_t. Can be set and retrieved using `hb_buffer_set_segment_properties()` and `hb_buffer_get_segment_properties()`, respectively.

#### Members

hb_direction_t `direction`; | the hb_direction_t of the buffer, see `hb_buffer_set_direction()`. |
hb_script_t `script`; | the hb_script_t of the buffer, see `hb_buffer_set_script()`. |
hb_language_t `language`; | the hb_language_t of the buffer, see `hb_buffer_set_language()`. |

### enum hb_buffer_serialize_format_t

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

#### Members

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

### enum hb_buffer_serialize_flags_t

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

#### Members

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. Note: when this flag is used with a partial range of the buffer (i.e. `start` is not 0), calculating the absolute positions has a cost proportional to `start` . If the buffer is serialized in many small chunks, this can lead to quadratic behavior. It is recommended to use a larger `buf_size` to minimize this cost. |
HB_BUFFER_SERIALIZE_FLAG_DEFINED | All currently defined flags. Since: 4.4.0 |

Since: 0.9.20

### enum hb_buffer_diff_flags_t

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.

#### Members

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