hb-ot-math: HarfBuzz Manual

## hb-ot-math hb-ot-math — OpenType Math information |

## Functions

hb_bool_t | hb_ot_math_has_data ()
hb_position_t | hb_ot_math_get_constant ()
hb_position_t | hb_ot_math_get_glyph_italics_correction ()
hb_position_t | hb_ot_math_get_glyph_top_accent_attachment ()
hb_position_t | hb_ot_math_get_glyph_kerning ()
hb_bool_t | hb_ot_math_is_glyph_extended_shape ()
unsigned int | hb_ot_math_get_glyph_variants ()
hb_position_t | hb_ot_math_get_min_connector_overlap ()
unsigned int | hb_ot_math_get_glyph_assembly ()

## Types and Values

#define | HB_OT_TAG_MATH
#define | HB_OT_MATH_SCRIPT
enum | hb_ot_math_constant_t
enum | hb_ot_math_kern_t
| hb_ot_math_glyph_variant_t
enum | hb_ot_math_glyph_part_flags_t
| hb_ot_math_glyph_part_t

## Object Hierarchy

        GBoxed
        ├── hb_ot_math_glyph_part_t
        ╰── hb_ot_math_glyph_variant_t
        GEnum
        ├── hb_ot_math_constant_t
        ╰── hb_ot_math_kern_t
        GFlags
        ╰── hb_ot_math_glyph_part_flags_t

## Includes

    #include <hb-ot.h>

## Description

Functions for fetching mathematics layout data from OpenType fonts.

HarfBuzz itself does not implement a math layout solution. The functions and types provided can be used by client programs to access the font data necessary for typesetting OpenType Math layout.

## Functions

### hb_ot_math_has_data ()

    hb_bool_t
    hb_ot_math_has_data (hb_face_t *face);

Tests whether a face has a `MATH` table.

#### Parameters

face | hb_face_t to test |

#### Returns

true if the table is found, false otherwise

Since: 1.3.3

### hb_ot_math_get_constant ()

    hb_position_t
    hb_ot_math_get_constant (hb_font_t *font,
                             hb_ot_math_constant_t constant);

Fetches the specified math constant. For most constants, the value returned is an hb_position_t.

However, if the requested constant is HB_OT_MATH_CONSTANT_SCRIPT_PERCENT_SCALE_DOWN, HB_OT_MATH_CONSTANT_SCRIPT_SCRIPT_PERCENT_SCALE_DOWN or HB_OT_MATH_CONSTANT_SCRIPT_PERCENT_SCALE_DOWN, then the return value is an integer between 0 and 100 representing that percentage.

#### Parameters

font | hb_font_t to work upon |
constant | hb_ot_math_constant_t the constant to retrieve |

#### Returns

the requested constant or zero

Since: 1.3.3

### hb_ot_math_get_glyph_italics_correction ()

    hb_position_t
    hb_ot_math_get_glyph_italics_correction
                                   (hb_font_t *font,
                                    hb_codepoint_t glyph);

Fetches an italics-correction value (if one exists) for the specified glyph index.

#### Parameters

font | hb_font_t to work upon |
glyph | The glyph index from which to retrieve the value |

#### Returns

the italics correction of the glyph or zero

Since: 1.3.3

### hb_ot_math_get_glyph_top_accent_attachment ()

    hb_position_t
    hb_ot_math_get_glyph_top_accent_attachment
                                   (hb_font_t *font,
                                    hb_codepoint_t glyph);

Fetches a top-accent-attachment value (if one exists) for the specified glyph index.

For any glyph that does not have a top-accent-attachment value - that is, a glyph not covered by the `MathTopAccentAttachment` table (or, when `font` has no `MathTopAccentAttachment` table or no `MATH` table, any glyph) - the function synthesizes a value, returning the position at one-half the glyph's advance width.

#### Parameters

font | hb_font_t to work upon |
glyph | The glyph index from which to retrieve the value |

#### Returns

the top accent attachment of the glyph or 0.5 * the advance width of `glyph`

Since: 1.3.3

### hb_ot_math_get_glyph_kerning ()

    hb_position_t
    hb_ot_math_get_glyph_kerning (hb_font_t *font,
                                  hb_codepoint_t glyph,
                                  hb_ot_math_kern_t kern,
                                  hb_position_t correction_height);

Fetches the math kerning (cut-ins) value for the specified font, glyph index, and `kern` .

If the MathKern table is found, the function examines it to find a height value that is greater or equal to `correction_height` . If such a height value is found, corresponding kerning value from the table is returned. If no such height value is found, the last kerning value is returned.

#### Parameters

font | hb_font_t to work upon |
glyph | The glyph index from which to retrieve the value |
kern | The hb_ot_math_kern_t from which to retrieve the value |
correction_height | the correction height to use to determine the kerning. |

#### Returns

requested kerning value or zero

Since: 1.3.3

### hb_ot_math_is_glyph_extended_shape ()

    hb_bool_t
    hb_ot_math_is_glyph_extended_shape (hb_face_t *face,
                                        hb_codepoint_t glyph);

Tests whether the given glyph index is an extended shape in the face.

#### Parameters

face | hb_face_t to work upon |
glyph | The glyph index to test |

#### Returns

true if the glyph is an extended shape, false otherwise

Since: 1.3.3

### hb_ot_math_get_glyph_variants ()

    unsigned int
    hb_ot_math_get_glyph_variants (hb_font_t *font,
                                   hb_codepoint_t glyph,
                                   hb_direction_t direction,
                                   unsigned int start_offset,
                                   unsigned int *variants_count,
                                   hb_ot_math_glyph_variant_t *variants);

Fetches the MathGlyphConstruction for the specified font, glyph index, and direction. The corresponding list of size variants is returned as a list of hb_ot_math_glyph_variant_t structs.

The `direction` parameter is only used to select between horizontal or vertical directions for the construction. Even though all hb_direction_t values are accepted, only the result of HB_DIRECTION_IS_HORIZONTAL is considered.

#### Parameters

font | hb_font_t to work upon |
glyph | The index of the glyph to stretch |
direction | The direction of the stretching (horizontal or vertical) |
start_offset | offset of the first variant to retrieve |
variants_count | Input = the maximum number of variants to return; Output = the actual number of variants returned. | [inout]
variants | array of variants returned. | [out][array length=variants_count]

#### Returns

the total number of size variants available or zero

Since: 1.3.3

### hb_ot_math_get_min_connector_overlap ()

    hb_position_t
    hb_ot_math_get_min_connector_overlap (hb_font_t *font,
                                          hb_direction_t direction);

Fetches the MathVariants table for the specified font and returns the minimum overlap of connecting glyphs that are required to draw a glyph assembly in the specified direction.

The `direction` parameter is only used to select between horizontal or vertical directions for the construction. Even though all hb_direction_t values are accepted, only the result of HB_DIRECTION_IS_HORIZONTAL is considered.

#### Parameters

font | hb_font_t to work upon |
direction | direction of the stretching (horizontal or vertical) |

#### Returns

requested minimum connector overlap or zero

Since: 1.3.3

### hb_ot_math_get_glyph_assembly ()

    unsigned int
    hb_ot_math_get_glyph_assembly (hb_font_t *font,
                                   hb_codepoint_t glyph,
                                   hb_direction_t direction,
                                   unsigned int start_offset,
                                   unsigned int *parts_count,
                                   hb_ot_math_glyph_part_t *parts,
                                   hb_position_t *italics_correction);

Fetches the GlyphAssembly for the specified font, glyph index, and direction. Returned are a list of hb_ot_math_glyph_part_t glyph parts that can be used to draw the glyph and an italics-correction value (if one is defined in the font).

The `direction` parameter is only used to select between horizontal or vertical directions for the construction. Even though all hb_direction_t values are accepted, only the result of HB_DIRECTION_IS_HORIZONTAL is considered.

#### Parameters

font | hb_font_t to work upon |
glyph | The index of the glyph to stretch |
direction | direction of the stretching (horizontal or vertical) |
start_offset | offset of the first glyph part to retrieve |
parts_count | Input = maximum number of glyph parts to return; Output = actual number of parts returned. | [inout]
parts | the glyph parts returned. | [out][array length=parts_count]
italics_correction | italics correction of the glyph assembly. | [out]

#### Returns

the total number of parts in the glyph assembly

Since: 1.3.3

## Types and Values

### HB_OT_TAG_MATH

    #define HB_OT_TAG_MATH HB_TAG('M','A','T','H')

### HB_OT_MATH_SCRIPT

    #define HB_OT_MATH_SCRIPT HB_TAG('m','a','t','h')

### enum hb_ot_math_constant_t

The 'MATH' table constants specified at https://docs.microsoft.com/en-us/typography/opentype/spec/math

#### Members

HB_OT_MATH_CONSTANT_SCRIPT_PERCENT_SCALE_DOWN |  |
HB_OT_MATH_CONSTANT_SCRIPT_SCRIPT_PERCENT_SCALE_DOWN |  |
HB_OT_MATH_CONSTANT_DELIMITED_SUB_FORMULA_MIN_HEIGHT |  |
HB_OT_MATH_CONSTANT_DISPLAY_OPERATOR_MIN_HEIGHT |  |
HB_OT_MATH_CONSTANT_MATH_LEADING |  |
HB_OT_MATH_CONSTANT_AXIS_HEIGHT |  |
HB_OT_MATH_CONSTANT_ACCENT_BASE_HEIGHT |  |
HB_OT_MATH_CONSTANT_FLATTENED_ACCENT_BASE_HEIGHT |  |
HB_OT_MATH_CONSTANT_SUBSCRIPT_SHIFT_DOWN |  |
HB_OT_MATH_CONSTANT_SUBSCRIPT_TOP_MAX |  |
HB_OT_MATH_CONSTANT_SUBSCRIPT_BASELINE_DROP_MIN |  |
HB_OT_MATH_CONSTANT_SUPERSCRIPT_SHIFT_UP |  |
HB_OT_MATH_CONSTANT_SUPERSCRIPT_SHIFT_UP_CRAMPED |  |
HB_OT_MATH_CONSTANT_SUPERSCRIPT_BOTTOM_MIN |  |
HB_OT_MATH_CONSTANT_SUPERSCRIPT_BASELINE_DROP_MAX |  |
HB_OT_MATH_CONSTANT_SUB_SUPERSCRIPT_GAP_MIN |  |
HB_OT_MATH_CONSTANT_SUPERSCRIPT_BOTTOM_MAX_WITH_SUBSCRIPT |  |
HB_OT_MATH_CONSTANT_SPACE_AFTER_SCRIPT |  |
HB_OT_MATH_CONSTANT_UPPER_LIMIT_GAP_MIN |  |
HB_OT_MATH_CONSTANT_UPPER_LIMIT_BASELINE_RISE_MIN |  |
HB_OT_MATH_CONSTANT_LOWER_LIMIT_GAP_MIN |  |
HB_OT_MATH_CONSTANT_LOWER_LIMIT_BASELINE_DROP_MIN |  |
HB_OT_MATH_CONSTANT_STACK_TOP_SHIFT_UP |  |
HB_OT_MATH_CONSTANT_STACK_TOP_DISPLAY_STYLE_SHIFT_UP |  |
HB_OT_MATH_CONSTANT_STACK_BOTTOM_SHIFT_DOWN |  |
HB_OT_MATH_CONSTANT_STACK_BOTTOM_DISPLAY_STYLE_SHIFT_DOWN |  |
HB_OT_MATH_CONSTANT_STACK_GAP_MIN |  |
HB_OT_MATH_CONSTANT_STACK_DISPLAY_STYLE_GAP_MIN |  |
HB_OT_MATH_CONSTANT_STRETCH_STACK_TOP_SHIFT_UP |  |
HB_OT_MATH_CONSTANT_STRETCH_STACK_BOTTOM_SHIFT_DOWN |  |
HB_OT_MATH_CONSTANT_STRETCH_STACK_GAP_ABOVE_MIN |  |
HB_OT_MATH_CONSTANT_STRETCH_STACK_GAP_BELOW_MIN |  |
HB_OT_MATH_CONSTANT_FRACTION_NUMERATOR_SHIFT_UP |  |
HB_OT_MATH_CONSTANT_FRACTION_NUMERATOR_DISPLAY_STYLE_SHIFT_UP |  |
HB_OT_MATH_CONSTANT_FRACTION_DENOMINATOR_SHIFT_DOWN |  |
HB_OT_MATH_CONSTANT_FRACTION_DENOMINATOR_DISPLAY_STYLE_SHIFT_DOWN |  |
HB_OT_MATH_CONSTANT_FRACTION_NUMERATOR_GAP_MIN |  |
HB_OT_MATH_CONSTANT_FRACTION_NUM_DISPLAY_STYLE_GAP_MIN |  |
HB_OT_MATH_CONSTANT_FRACTION_RULE_THICKNESS |  |
HB_OT_MATH_CONSTANT_FRACTION_DENOMINATOR_GAP_MIN |  |
HB_OT_MATH_CONSTANT_FRACTION_DENOM_DISPLAY_STYLE_GAP_MIN |  |
HB_OT_MATH_CONSTANT_SKEWED_FRACTION_HORIZONTAL_GAP |  |
HB_OT_MATH_CONSTANT_SKEWED_FRACTION_VERTICAL_GAP |  |
HB_OT_MATH_CONSTANT_OVERBAR_VERTICAL_GAP |  |
HB_OT_MATH_CONSTANT_OVERBAR_RULE_THICKNESS |  |
HB_OT_MATH_CONSTANT_OVERBAR_EXTRA_ASCENDER |  |
HB_OT_MATH_CONSTANT_UNDERBAR_VERTICAL_GAP |  |
HB_OT_MATH_CONSTANT_UNDERBAR_RULE_THICKNESS |  |
HB_OT_MATH_CONSTANT_UNDERBAR_EXTRA_DESCENDER |  |
HB_OT_MATH_CONSTANT_RADICAL_VERTICAL_GAP |  |
HB_OT_MATH_CONSTANT_RADICAL_DISPLAY_STYLE_VERTICAL_GAP |  |
HB_OT_MATH_CONSTANT_RADICAL_RULE_THICKNESS |  |
HB_OT_MATH_CONSTANT_RADICAL_EXTRA_ASCENDER |  |
HB_OT_MATH_CONSTANT_RADICAL_KERN_BEFORE_DEGREE |  |
HB_OT_MATH_CONSTANT_RADICAL_KERN_AFTER_DEGREE |  |
HB_OT_MATH_CONSTANT_RADICAL_DEGREE_BOTTOM_RAISE_PERCENT |  |

Since: 1.3.3

### enum hb_ot_math_kern_t

The math kerning-table types defined for the four corners of a glyph.

#### Members

HB_OT_MATH_KERN_TOP_RIGHT |  |
HB_OT_MATH_KERN_TOP_LEFT |  |
HB_OT_MATH_KERN_BOTTOM_RIGHT |  |
HB_OT_MATH_KERN_BOTTOM_LEFT |  |

Since: 1.3.3

### hb_ot_math_glyph_variant_t

    typedef struct {
      hb_codepoint_t glyph;
      hb_position_t advance;
    } hb_ot_math_glyph_variant_t;

Data type to hold math-variant information for a glyph.

#### Members

hb_codepoint_t `glyph`; | The glyph index of the variant |
hb_position_t `advance`; | The advance width of the variant |

Since: 1.3.3

### enum hb_ot_math_glyph_part_flags_t

Flags for math glyph parts.

#### Members

HB_OT_MATH_GLYPH_PART_FLAG_EXTENDER |  |

Since: 1.3.3

### hb_ot_math_glyph_part_t

    typedef struct {
      hb_codepoint_t glyph;
      hb_position_t start_connector_length;
      hb_position_t end_connector_length;
      hb_position_t full_advance;
      hb_ot_math_glyph_part_flags_t flags;
    } hb_ot_math_glyph_part_t;

Data type to hold information for a "part" component of a math-variant glyph. Large variants for stretchable math glyphs (such as parentheses) can be constructed on the fly from parts.

#### Members

hb_codepoint_t `glyph`; | The glyph index of the variant part |
hb_position_t `start_connector_length`; | The length of the connector on the starting side of the variant part |
hb_position_t `end_connector_length`; | The length of the connector on the ending side of the variant part |
hb_position_t `full_advance`; | The total advance of the part |
hb_ot_math_glyph_part_flags_t `flags`; | hb_ot_math_glyph_part_flags_t flags for the part |

Since: 1.3.3