head - Font Header Table (OpenType 1.4)
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.
|Fixed||Table version number||0x00010000 for version 1.0.|
|Fixed||fontRevision||Set by font manufacturer.|
|ULONG||checkSumAdjustment||To compute: set it to 0, sum the entire font as ULONG, then store 0xB1B0AFBA - sum.|
|ULONG||magicNumber||Set to 0x5F0F3CF5.|
|USHORT||flags||Bit 0: Baseline for font at y=0;|
Bit 1: Left sidebearing point at x=0;
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);
Bits 5-10: These should be set according to Apple’s specification. However, they are not implemented in OpenType.
Bit 11: Font data is ‘lossless,’ as a result of having been compressed and decompressed with the Agfa MicroType Express engine.
Bit 12: Font converted (produce compatible metrics)
Bit 13: Font optimised for ClearType
Bit 14: Reserved, set to 0
Bit 15: Reserved, set to 0
|USHORT||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, January 1, 1904. 64-bit integer|
|LONGDATETIME||modified||Number of seconds since 12:00 midnight, January 1, 1904. 64-bit integer|
|SHORT||xMin||For all glyph bounding boxes.|
|SHORT||yMin||For all glyph bounding boxes.|
|SHORT||xMax||For all glyph bounding boxes.|
|SHORT||yMax||For all glyph bounding boxes.|
|USHORT||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).
|USHORT||lowestRecPPEM||Smallest readable size in pixels.|
|SHORT||fontDirectionHint|| 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
|SHORT||indexToLocFormat||0 for short offsets, 1 for long.|
|SHORT||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.