tiny.filigree.font.description

1const std = @import("std");2const binary = @import("binary.zig");3const directory = @import("directory.zig");4const model = @import("model.zig");5const names = @import("names.zig");6const cmap_owner = @import("cmap.zig");78/// Coverage beyond the four OS/2 Unicode-range words.9pub const extended_emoji_word: usize = 4;10pub const extended_emoji_bit: u5 = 0;1112pub const Description = struct {13    family: []u8,14    weight_class: u16,15    width_class: u16,16    selection: u16,17    units_per_em: u16,18    ascent: f32,19    descent: f32,20    line_gap: f32,21    coverage: [8]u32,22    fixed_pitch: bool,23    color: bool,24    face_index: u32,2526    pub fn deinit(self: *Description, allocator: std.mem.Allocator) void {27        allocator.free(self.family);28        self.* = undefined;29    }30};3132pub fn describeAlloc(allocator: std.mem.Allocator, data: []const u8) (model.FontError || error{OutOfMemory})!Description {33    return describeAtAlloc(allocator, data, 0);34}3536pub fn describeAtAlloc(allocator: std.mem.Allocator, data: []const u8, face_index: u32) (model.FontError || error{OutOfMemory})!Description {37    const offset = try directory.fontDirectoryOffset(data, face_index);38    const os2 = try directory.tableAt(data, offset, "OS/2");39    if (os2.len < 64) return error.InvalidFont;40    const head = try directory.tableAt(data, offset, "head");41    const hhea = try directory.tableAt(data, offset, "hhea");42    if (head.len < 54 or hhea.len < 10) return error.InvalidFont;43    const units_per_em = try binary.readU16(data, head.offset + 18);44    if (units_per_em == 0) return error.InvalidFont;45    const selection = try binary.readU16(data, os2.offset + 62);46    const metric_source = if (selection & 0x80 != 0) os2 else hhea;47    if (selection & 0x80 != 0 and os2.len < 78) return error.InvalidFont;48    const metric_offset: usize = if (selection & 0x80 != 0) 68 else 4;49    const scale = @as(f32, @floatFromInt(units_per_em));50    const cmap_table = try directory.tableAt(data, offset, "cmap");51    const cmap = try cmap_owner.Cmap.init(data, cmap_table);52    var coverage: [8]u32 = @splat(0);53    inline for (0..4) |word| {54        coverage[word] = try binary.readU32(data, os2.offset + 42 + word * 4);55    }56    if (try hasEmoji(data, cmap)) coverage[extended_emoji_word] |= @as(u32, 1) << extended_emoji_bit;57    const post = directory.tableAt(data, offset, "post") catch |err| switch (err) {58        error.MissingTable => null,59        else => return err,60    };61    const name_table = try directory.tableAt(data, offset, "name");62    const record = (try names.bestNameRecord(data, name_table, 16)) orelse63        (try names.bestNameRecord(data, name_table, 1)) orelse return error.InvalidFont;64    const family = names.utf16BeToUtf8Alloc(allocator, record.bytes) catch |err| switch (err) {65        error.OutOfMemory => return error.OutOfMemory,66        else => return error.InvalidFont,67    };68    errdefer allocator.free(family);69    return .{70        .family = family,71        .weight_class = try binary.readU16(data, os2.offset + 4),72        .width_class = try binary.readU16(data, os2.offset + 6),73        .selection = selection,74        .units_per_em = units_per_em,75        .ascent = @as(f32, @floatFromInt(try binary.readI16(data, metric_source.offset + metric_offset))) / scale,76        .descent = @as(f32, @floatFromInt(try binary.readI16(data, metric_source.offset + metric_offset + 2))) / scale,77        .line_gap = @as(f32, @floatFromInt(try binary.readI16(data, metric_source.offset + metric_offset + 4))) / scale,78        .coverage = coverage,79        .fixed_pitch = if (post) |table| try readFixedPitch(data, table) else false,80        .color = directory.optionalAt(data, offset, "COLR") != null or81            directory.optionalAt(data, offset, "CBDT") != null or82            directory.optionalAt(data, offset, "sbix") != null or83            directory.optionalAt(data, offset, "SVG ") != null,84        .face_index = face_index,85    };86}8788fn hasEmoji(data: []const u8, cmap: cmap_owner.Cmap) model.FontError!bool {89    for (0x1f300..0x1fb00) |codepoint| {90        if (try cmap.map(data, @intCast(codepoint)) != 0) return true;91    }92    return false;93}9495fn readFixedPitch(data: []const u8, table: binary.Table) model.FontError!bool {96    if (table.len < 16) return error.InvalidFont;97    return (try binary.readU32(data, table.offset + 12)) != 0;98}99100test "face description reads family and OS/2 fields" {101    const fixture = @import("../fixture/root.zig");102    const allocator = std.testing.allocator;103    const bytes = try fixture.createWithMetricVariations(allocator);104    defer allocator.free(bytes);105    const os2 = try directory.table(bytes, "OS/2");106    std.mem.writeInt(u16, bytes[os2.offset + 4 ..][0..2], 700, .big);107    std.mem.writeInt(u16, bytes[os2.offset + 6 ..][0..2], 3, .big);108    std.mem.writeInt(u32, bytes[os2.offset + 42 ..][0..4], 0x201, .big);109    std.mem.writeInt(u16, bytes[os2.offset + 62 ..][0..2], 0x21, .big);110    var result = try describeAlloc(allocator, bytes);111    defer result.deinit(allocator);112    try std.testing.expectEqualStrings("Tiny Fixture", result.family);113    try std.testing.expectEqual(@as(u16, 700), result.weight_class);114    try std.testing.expectEqual(@as(u16, 3), result.width_class);115    try std.testing.expectEqual(@as(u16, 0x21), result.selection);116    try std.testing.expectEqual(@as(u32, 0x201), result.coverage[0]);117    try std.testing.expectEqual(@as(u16, 1000), result.units_per_em);118    try std.testing.expectEqual(@as(f32, 0.8), result.ascent);119    try std.testing.expectEqual(@as(f32, -0.2), result.descent);120    try std.testing.expectEqual(@as(f32, 0), result.line_gap);121    try std.testing.expect(!result.fixed_pitch);122    try std.testing.expect(!result.color);123    try std.testing.expectEqual(@as(u32, 0), result.face_index);124}125126test "face description selects OS/2 typo metrics when requested" {127    const fixture = @import("../fixture/root.zig");128    const allocator = std.testing.allocator;129    const bytes = try fixture.createWithMetricVariations(allocator);130    defer allocator.free(bytes);131    var result = try describeAlloc(allocator, bytes);132    defer result.deinit(allocator);133    try std.testing.expectEqual(@as(f32, 0.8), result.ascent);134    try std.testing.expectEqual(@as(f32, -0.2), result.descent);135    try std.testing.expectEqual(@as(f32, 0.04), result.line_gap);136}137138test "face description derives extended emoji coverage from cmap" {139    var bytes: [40]u8 = @splat(0);140    std.mem.writeInt(u16, bytes[2..4], 1, .big);141    std.mem.writeInt(u16, bytes[4..6], 3, .big);142    std.mem.writeInt(u16, bytes[6..8], 10, .big);143    std.mem.writeInt(u32, bytes[8..12], 12, .big);144    std.mem.writeInt(u16, bytes[12..14], 12, .big);145    std.mem.writeInt(u32, bytes[16..20], 28, .big);146    std.mem.writeInt(u32, bytes[24..28], 1, .big);147    std.mem.writeInt(u32, bytes[28..32], 0x1f600, .big);148    std.mem.writeInt(u32, bytes[32..36], 0x1f600, .big);149    std.mem.writeInt(u32, bytes[36..40], 1, .big);150    const cmap = try cmap_owner.Cmap.init(&bytes, .{ .offset = 0, .len = bytes.len });151    try std.testing.expect(try hasEmoji(&bytes, cmap));152}153154test "face description reads post fixed pitch and rejects a short table" {155    var bytes: [16]u8 = @splat(0);156    std.mem.writeInt(u32, bytes[12..16], 1, .big);157    try std.testing.expect(try readFixedPitch(&bytes, .{ .offset = 0, .len = bytes.len }));158    try std.testing.expectError(error.InvalidFont, readFixedPitch(&bytes, .{ .offset = 0, .len = 15 }));159}160161test "face description rejects missing and truncated OS/2" {162    const fixture = @import("../fixture/root.zig");163    const allocator = std.testing.allocator;164    const missing = try fixture.create(allocator);165    defer allocator.free(missing);166    try std.testing.expectError(error.MissingTable, describeAlloc(allocator, missing));167    const bytes = try fixture.createWithMetricVariations(allocator);168    defer allocator.free(bytes);169    const os2 = try directory.table(bytes, "OS/2");170    const records = try binary.readU16(bytes, 4);171    for (0..records) |index| {172        const row = 12 + index * 16;173        if (try binary.readU32(bytes, row) != model.tag("OS/2")) continue;174        std.mem.writeInt(u32, bytes[row + 12 ..][0..4], 63, .big);175        break;176    }177    _ = os2;178    try std.testing.expectError(error.InvalidFont, describeAlloc(allocator, bytes));179}

1pub const description = @import("description.zig");