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 ()
unsigned int | hb_ot_math_get_glyph_kernings ()
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_TAG_MATH_SCRIPT
enum | hb_ot_math_constant_t
enum | hb_ot_math_kern_t
| hb_ot_math_kern_entry_t
| hb_ot_math_glyph_variant_t
enum | hb_ot_math_glyph_part_flags_t
| hb_ot_math_glyph_part_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_get_glyph_kernings ()

    unsigned int
    hb_ot_math_get_glyph_kernings (hb_font_t *font,
                                   hb_codepoint_t glyph,
                                   hb_ot_math_kern_t kern,
                                   unsigned int start_offset,
                                   unsigned int *entries_count,
                                   hb_ot_math_kern_entry_t *kern_entries);

Fetches the raw MathKern (cut-in) data for the specified font, glyph index, and `kern` . The corresponding list of kern values and correction heights is returned as a list of hb_ot_math_kern_entry_t structs.

See also hb_ot_math_get_glyph_kerning, which handles selecting the appropriate kern value for a given correction height.

For a glyph with `n` defined kern values (where `n` > 0), there are only `n`−1 defined correction heights, as each correction height defines a boundary past which the next kern value should be selected. Therefore, only the hb_ot_math_kern_entry_t.kern_value of the uppermost hb_ot_math_kern_entry_t actually comes from the font; its corresponding hb_ot_math_kern_entry_t.max_correction_height is always set to `INT32_MAX`.

#### Parameters

font | hb_font_t to work upon |
glyph | The glyph index from which to retrieve the kernings |
kern | The hb_ot_math_kern_t from which to retrieve the kernings |
start_offset | offset of the first kern entry to retrieve |
entries_count | Input = the maximum number of kern entries to return; Output = the actual number of kern entries returned. | [inout][optional]
kern_entries | array of kern entries returned. | [out caller-allocates][array length=entries_count]

#### Returns

the total number of kern values available or zero

Since: 3.4.0

### 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')

OpenType Mathematical Typesetting Table.

Since: 1.3.3

### HB_OT_TAG_MATH_SCRIPT

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

OpenType script tag, `math`, for features specific to math shaping.

HB_OT_TAG_MATH_SCRIPT is not a valid hb_script_t and should only be used with functions that accept raw OpenType script tags, such as hb_ot_layout_collect_features. In other cases, HB_SCRIPT_MATH should be used instead.

Since: 3.4.0

### enum hb_ot_math_constant_t

The 'MATH' table constants, refer to OpenType documentation For more explanations.

#### Members

HB_OT_MATH_CONSTANT_SCRIPT_PERCENT_SCALE_DOWN | scriptPercentScaleDown |
HB_OT_MATH_CONSTANT_SCRIPT_SCRIPT_PERCENT_SCALE_DOWN | scriptScriptPercentScaleDown |
HB_OT_MATH_CONSTANT_DELIMITED_SUB_FORMULA_MIN_HEIGHT | delimitedSubFormulaMinHeight |
HB_OT_MATH_CONSTANT_DISPLAY_OPERATOR_MIN_HEIGHT | displayOperatorMinHeight |
HB_OT_MATH_CONSTANT_MATH_LEADING | mathLeading |
HB_OT_MATH_CONSTANT_AXIS_HEIGHT | axisHeight |
HB_OT_MATH_CONSTANT_ACCENT_BASE_HEIGHT | accentBaseHeight |
HB_OT_MATH_CONSTANT_FLATTENED_ACCENT_BASE_HEIGHT | flattenedAccentBaseHeight |
HB_OT_MATH_CONSTANT_SUBSCRIPT_SHIFT_DOWN | subscriptShiftDown |
HB_OT_MATH_CONSTANT_SUBSCRIPT_TOP_MAX | subscriptTopMax |
HB_OT_MATH_CONSTANT_SUBSCRIPT_BASELINE_DROP_MIN | subscriptBaselineDropMin |
HB_OT_MATH_CONSTANT_SUPERSCRIPT_SHIFT_UP | superscriptShiftUp |
HB_OT_MATH_CONSTANT_SUPERSCRIPT_SHIFT_UP_CRAMPED | superscriptShiftUpCramped |
HB_OT_MATH_CONSTANT_SUPERSCRIPT_BOTTOM_MIN | superscriptBottomMin |
HB_OT_MATH_CONSTANT_SUPERSCRIPT_BASELINE_DROP_MAX | superscriptBaselineDropMax |
HB_OT_MATH_CONSTANT_SUB_SUPERSCRIPT_GAP_MIN | subSuperscriptGapMin |
HB_OT_MATH_CONSTANT_SUPERSCRIPT_BOTTOM_MAX_WITH_SUBSCRIPT | superscriptBottomMaxWithSubscript |
HB_OT_MATH_CONSTANT_SPACE_AFTER_SCRIPT | spaceAfterScript |
HB_OT_MATH_CONSTANT_UPPER_LIMIT_GAP_MIN | upperLimitGapMin |
HB_OT_MATH_CONSTANT_UPPER_LIMIT_BASELINE_RISE_MIN | upperLimitBaselineRiseMin |
HB_OT_MATH_CONSTANT_LOWER_LIMIT_GAP_MIN | lowerLimitGapMin |
HB_OT_MATH_CONSTANT_LOWER_LIMIT_BASELINE_DROP_MIN | lowerLimitBaselineDropMin |
HB_OT_MATH_CONSTANT_STACK_TOP_SHIFT_UP | stackTopShiftUp |
HB_OT_MATH_CONSTANT_STACK_TOP_DISPLAY_STYLE_SHIFT_UP | stackTopDisplayStyleShiftUp |
HB_OT_MATH_CONSTANT_STACK_BOTTOM_SHIFT_DOWN | stackBottomShiftDown |
HB_OT_MATH_CONSTANT_STACK_BOTTOM_DISPLAY_STYLE_SHIFT_DOWN | stackBottomDisplayStyleShiftDown |
HB_OT_MATH_CONSTANT_STACK_GAP_MIN | stackGapMin |
HB_OT_MATH_CONSTANT_STACK_DISPLAY_STYLE_GAP_MIN | stackDisplayStyleGapMin |
HB_OT_MATH_CONSTANT_STRETCH_STACK_TOP_SHIFT_UP | stretchStackTopShiftUp |
HB_OT_MATH_CONSTANT_STRETCH_STACK_BOTTOM_SHIFT_DOWN | stretchStackBottomShiftDown |
HB_OT_MATH_CONSTANT_STRETCH_STACK_GAP_ABOVE_MIN | stretchStackGapAboveMin |
HB_OT_MATH_CONSTANT_STRETCH_STACK_GAP_BELOW_MIN | stretchStackGapBelowMin |
HB_OT_MATH_CONSTANT_FRACTION_NUMERATOR_SHIFT_UP | fractionNumeratorShiftUp |
HB_OT_MATH_CONSTANT_FRACTION_NUMERATOR_DISPLAY_STYLE_SHIFT_UP | fractionNumeratorDisplayStyleShiftUp |
HB_OT_MATH_CONSTANT_FRACTION_DENOMINATOR_SHIFT_DOWN | fractionDenominatorShiftDown |
HB_OT_MATH_CONSTANT_FRACTION_DENOMINATOR_DISPLAY_STYLE_SHIFT_DOWN | fractionDenominatorDisplayStyleShiftDown |
HB_OT_MATH_CONSTANT_FRACTION_NUMERATOR_GAP_MIN | fractionNumeratorGapMin |
HB_OT_MATH_CONSTANT_FRACTION_NUM_DISPLAY_STYLE_GAP_MIN | fractionNumDisplayStyleGapMin |
HB_OT_MATH_CONSTANT_FRACTION_RULE_THICKNESS | fractionRuleThickness |
HB_OT_MATH_CONSTANT_FRACTION_DENOMINATOR_GAP_MIN | fractionDenominatorGapMin |
HB_OT_MATH_CONSTANT_FRACTION_DENOM_DISPLAY_STYLE_GAP_MIN | fractionDenomDisplayStyleGapMin |
HB_OT_MATH_CONSTANT_SKEWED_FRACTION_HORIZONTAL_GAP | skewedFractionHorizontalGap |
HB_OT_MATH_CONSTANT_SKEWED_FRACTION_VERTICAL_GAP | skewedFractionVerticalGap |
HB_OT_MATH_CONSTANT_OVERBAR_VERTICAL_GAP | overbarVerticalGap |
HB_OT_MATH_CONSTANT_OVERBAR_RULE_THICKNESS | overbarRuleThickness |
HB_OT_MATH_CONSTANT_OVERBAR_EXTRA_ASCENDER | overbarExtraAscender |
HB_OT_MATH_CONSTANT_UNDERBAR_VERTICAL_GAP | underbarVerticalGap |
HB_OT_MATH_CONSTANT_UNDERBAR_RULE_THICKNESS | underbarRuleThickness |
HB_OT_MATH_CONSTANT_UNDERBAR_EXTRA_DESCENDER | underbarExtraDescender |
HB_OT_MATH_CONSTANT_RADICAL_VERTICAL_GAP | radicalVerticalGap |
HB_OT_MATH_CONSTANT_RADICAL_DISPLAY_STYLE_VERTICAL_GAP | radicalDisplayStyleVerticalGap |
HB_OT_MATH_CONSTANT_RADICAL_RULE_THICKNESS | radicalRuleThickness |
HB_OT_MATH_CONSTANT_RADICAL_EXTRA_ASCENDER | radicalExtraAscender |
HB_OT_MATH_CONSTANT_RADICAL_KERN_BEFORE_DEGREE | radicalKernBeforeDegree |
HB_OT_MATH_CONSTANT_RADICAL_KERN_AFTER_DEGREE | radicalKernAfterDegree |
HB_OT_MATH_CONSTANT_RADICAL_DEGREE_BOTTOM_RAISE_PERCENT | radicalDegreeBottomRaisePercent |

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 | The top right corner of the glyph. |
HB_OT_MATH_KERN_TOP_LEFT | The top left corner of the glyph. |
HB_OT_MATH_KERN_BOTTOM_RIGHT | The bottom right corner of the glyph. |
HB_OT_MATH_KERN_BOTTOM_LEFT | The bottom left corner of the glyph. |

Since: 1.3.3

### hb_ot_math_kern_entry_t

    typedef struct {
      hb_position_t max_correction_height;
      hb_position_t kern_value;
    } hb_ot_math_kern_entry_t;

Data type to hold math kerning (cut-in) information for a glyph.

#### Members

hb_position_t `max_correction_height`; | The maximum height at which this entry should be used |
hb_position_t `kern_value`; | The kern value of the entry |

Since: 3.4.0

### 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 | This is an extender glyph part that can be repeated to reach the desired length. |

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