head — Font Header Table (OpenType 1.8.1)

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This table gives global information about the font. The bounding box values should be computed using only glyphs that have contours. Glyphs with no contours should be ignored for the purposes of these calculations.

Type Name Description
uint16 majorVersion Major version number of the font header table — set to 1.
uint16 minorVersion Minor version number of the font header table — set to 0.
Fixed fontRevision Set by font manufacturer.
uint32 checkSumAdjustment To compute: set it to 0, sum the entire font as uint32, then store 0xB1B0AFBA - sum. If the font is used as a component in a font collection file, the value of this field will be invalidated by changes to the file structure and font table directory, and must be ignored.
uint32 magicNumber Set to 0x5F0F3CF5.
uint16 flags Bit 0: Baseline for font at y=0;
Bit 1: Left sidebearing point at x=0 (relevant only for TrueType rasterizers) — see the note below regarding variable fonts;

Bit 2: Instructions may depend on point size;

Bit 3: Force ppem to integer values for all internal scaler math; may use fractional ppem sizes if this bit is clear;

Bit 4: Instructions may alter advance width (the advance widths might not scale linearly);

Bit 5: This bit is not used in OpenType, and should not be set in order to ensure compatible behavior on all platforms. If set, it may result in different behavior for vertical layout in some platforms. (See Apple’s specification for details regarding behavior in Apple platforms.)

Bits 6–10: These bits are not used in Opentype and should always be cleared. (See Apple’s specification for details regarding legacy used in Apple platforms.)

Bit 11: Font data is ‘lossless’ as a results of having been subjected to optimizing transformation and/or compression (such as e.g. compression mechanisms defined by ISO/IEC 14496-18, MicroType Express, WOFF 2.0 or similar) where the original font functionality and features are retained but the binary compatibility between input and output font files is not guaranteed. As a result of the applied transform, the 'DSIG' Table may also be invalidated.

Bit 12: Font converted (produce compatible metrics)

Bit 13: Font optimized for ClearType™. Note, fonts that rely on embedded bitmaps (EBDT) for rendering should not be considered optimized for ClearType, and therefore should keep this bit cleared.

Bit 14: Last Resort font. If set, indicates that the glyphs encoded in the cmap subtables are simply generic symbolic representations of code point ranges and don’t truly represent support for those code points. If unset, indicates that the glyphs encoded in the cmap subtables represent proper support for those code points.

Bit 15: Reserved, set to 0
uint16 unitsPerEm Valid range is from 16 to 16384. This value should be a power of 2 for fonts that have TrueType outlines.
LONGDATETIME created Number of seconds since 12:00 midnight that started January 1st 1904 in GMT/UTC time zone. 64-bit integer
LONGDATETIME modified Number of seconds since 12:00 midnight that started January 1st 1904 in GMT/UTC time zone. 64-bit integer
int16 xMin For all glyph bounding boxes.
int16 yMin For all glyph bounding boxes.
int16 xMax For all glyph bounding boxes.
int16 yMax For all glyph bounding boxes.
uint16 macStyle Bit 0: Bold (if set to 1);
Bit 1: Italic (if set to 1)
Bit 2: Underline (if set to 1)
Bit 3: Outline (if set to 1)
Bit 4: Shadow (if set to 1)
Bit 5: Condensed (if set to 1)
Bit 6: Extended (if set to 1)
Bits 7–15: Reserved (set to 0).
uint16 lowestRecPPEM Smallest readable size in pixels.
int16 fontDirectionHint Deprecated (Set to 2).
0: Fully mixed directional glyphs;
1: Only strongly left to right;
2: Like 1 but also contains neutrals;
-1: Only strongly right to left;
-2: Like -1 but also contains neutrals.1
int16 indexToLocFormat 0 for short offsets (Offset16), 1 for long (Offset32).
int16 glyphDataFormat 0 for current format.
1 A neutral character has no inherent directionality; it is not a character with zero (0) width. Spaces and punctuation are examples of neutral characters. Non-neutral characters are those with inherent directionality. For example, Roman letters (left-to-right) and Arabic letters (right-to-left) have directionality. In a “normal” Roman font where spaces and punctuation are present, the font direction hints should be set to two (2).

Note that the macStyle bits must agree with the 'OS/2' table fsSelection bits. The fsSelection bits are used over the macStyle bits in Microsoft Windows. The PANOSE values and 'post' table values are ignored for determining bold or italic fonts.

For historical reasons, the fontRevision value contained in this table is not used by Windows to determine the version of a font. Instead, Windows evaluates the version string (id 5) in the 'name' table.

Note that, in a variable font with TrueType outlines, the left side bearing for each glyph must equal xMin, and bit 1 in the flags field must be set. Also, bit 5 must be cleared in all variable fonts. For general information on OpenType Font Variations, see the chapter, OpenType Font Variations Overview.