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const std = @import("std");
const assert = std.debug.assert;
const sfnt = @import("sfnt.zig");
/// Font Header Table
///
/// References:
/// - https://learn.microsoft.com/en-us/typography/opentype/spec/head
///
/// Field names are in camelCase to match names in spec.
pub const Head = extern struct {
/// Major version number of the font header table — set to 1.
majorVersion: sfnt.uint16 align(1),
/// Minor version number of the font header table — set to 0.
minorVersion: sfnt.uint16 align(1),
/// Set by font manufacturer.
fontRevision: sfnt.Fixed align(1),
/// 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.
checksumAdjustment: sfnt.uint32 align(1),
/// Set to 0x5F0F3CF5.
magicNumber: sfnt.uint32 align(1),
/// Bit 0: Baseline for font at y=0.
///
/// Bit 1: Left sidebearing point at x=0
/// (relevant only for TrueType rasterizers)
///
/// 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. It is strongly
/// recommended that this be set in hinted fonts.
///
/// 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 use in Apple platforms.)
///
/// Bit 11: Font data is “lossless” as a result of having been
/// subjected to optimizing transformation and/or compression
/// (such as 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 do not 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.
flags: sfnt.uint16 align(1),
/// Set to a value from 16 to 16384. Any value in this range is valid.
///
/// In fonts that have TrueType outlines, a power of 2 is recommended
/// as this allows performance optimization in some rasterizers.
unitsPerEm: sfnt.uint16 align(1),
/// Number of seconds since 12:00 midnight that started
/// January 1st, 1904, in GMT/UTC time zone.
created: sfnt.LONGDATETIME align(1),
/// Number of seconds since 12:00 midnight that started
/// January 1st, 1904, in GMT/UTC time zone.
modified: sfnt.LONGDATETIME align(1),
/// Minimum x coordinate across all glyph bounding boxes.
xMin: sfnt.int16 align(1),
/// Minimum y coordinate across all glyph bounding boxes.
yMin: sfnt.int16 align(1),
/// Maximum x coordinate across all glyph bounding boxes.
xMax: sfnt.int16 align(1),
/// Maximum y coordinate across all glyph bounding boxes.
yMax: sfnt.int16 align(1),
/// 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).
macStyle: sfnt.uint16 align(1),
/// Smallest readable size in pixels.
lowestRecPPEM: sfnt.uint16 align(1),
/// 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.
fontDirectionHint: sfnt.int16 align(1),
/// 0 for short offsets (Offset16), 1 for long (Offset32).
indexToLocFormat: sfnt.int16 align(1),
/// 0 for current format.
glyphDataFormat: sfnt.int16 align(1),
/// Parse the table from raw data.
pub fn init(data: []const u8) error{EndOfStream}!Head {
var fbs = std.io.fixedBufferStream(data);
const reader = fbs.reader();
return try reader.readStructEndian(Head, .big);
}
};
test "head" {
const testing = std.testing;
const alloc = testing.allocator;
const test_font = @import("../embedded.zig").julia_mono;
const font = try sfnt.SFNT.init(test_font, alloc);
defer font.deinit(alloc);
const table = font.getTable("head").?;
const head = try Head.init(table);
try testing.expectEqualDeep(
Head{
.majorVersion = 1,
.minorVersion = 0,
.fontRevision = sfnt.Fixed.from(0.05499267578125),
.checksumAdjustment = 1007668681,
.magicNumber = 1594834165,
.flags = 7,
.unitsPerEm = 2000,
.created = 3797757830,
.modified = 3797760444,
.xMin = -1000,
.yMin = -1058,
.xMax = 3089,
.yMax = 2400,
.macStyle = 0,
.lowestRecPPEM = 7,
.fontDirectionHint = 2,
.indexToLocFormat = 1,
.glyphDataFormat = 0,
},
head,
);
}
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