tiny.filigree.font.lookups

1const std = @import("std");2const gdef_table = @import("gdef.zig");3const model = @import("model.zig");45const FontError = model.FontError;6const Gdef = gdef_table.Gdef;7const LayoutSelection = model.LayoutSelection;8const Tag = model.Tag;9const VariationSetting = model.VariationSetting;1011pub const Kind = enum {12    gsub,13    gpos,14};1516pub const VariationContext = struct {17    ptr: *const anyopaque,18    variation_axis_count: *const fn (*const anyopaque) u16,19    normalized_coordinate_at: *const fn (*const anyopaque, []const VariationSetting, usize) FontError!i16,2021    pub fn variationAxisCount(self: VariationContext) u16 {22        return self.variation_axis_count(self.ptr);23    }2425    pub fn normalizedCoordinateAt(self: VariationContext, settings: []const VariationSetting, axis_index: usize) FontError!i16 {26        return self.normalized_coordinate_at(self.ptr, settings, axis_index);27    }28};2930pub const ignore_base_glyphs: u16 = 0x0002;31pub const ignore_ligatures: u16 = 0x0004;32pub const ignore_marks: u16 = 0x0008;33pub const use_mark_filtering_set: u16 = 0x0010;34pub const reserved_flags: u16 = 0x00e0;35pub const mark_attachment_type: u16 = 0xff00;3637pub const LookupFilter = struct {38    flags: u16,39    mark_filtering_set: ?u16 = null,40};4142pub fn matchingFeatureSubstitutionOffset(comptime kind: Kind, bytes: []const u8, feature_variations_offset: ?usize, face: anytype, selection: LayoutSelection) FontError!?usize {43    const offset = feature_variations_offset orelse return null;44    if (!hasBytes(kind, bytes, offset, 8)) return invalid(kind);45    if (try readU16(kind, bytes, offset) != 1 or try readU16(kind, bytes, offset + 2) != 0) return null;46    const record_count = try readU32(kind, bytes, offset + 4);47    if (@as(u64, record_count) * 8 > @as(u64, bytes.len - offset - 8)) return invalid(kind);4849    for (0..record_count) |record_index| {50        const record_offset = offset + 8 + @as(usize, @intCast(record_index)) * 8;51        const condition_set_offset = try readU32(kind, bytes, record_offset);52        if (!try featureConditionSetMatches(kind, bytes, offset, condition_set_offset, face, selection)) continue;5354        const substitution_relative = try readU32(kind, bytes, record_offset + 4);55        if (substitution_relative == 0) return null;56        const substitution_offset = try childOffset32(kind, bytes, offset, substitution_relative, 6);57        if (try readU16(kind, bytes, substitution_offset) == 1 and try readU16(kind, bytes, substitution_offset + 2) == 0) {58            return substitution_offset;59        }60    }61    return null;62}6364fn featureConditionSetMatches(comptime kind: Kind, bytes: []const u8, feature_variations_offset: usize, relative_offset: u32, face: anytype, selection: LayoutSelection) FontError!bool {65    if (relative_offset == 0) return true;66    const offset = try childOffset32(kind, bytes, feature_variations_offset, relative_offset, 2);67    const condition_count = try readU16(kind, bytes, offset);68    if (@as(u64, condition_count) * 4 > @as(u64, bytes.len - offset - 2)) return invalid(kind);69    const condition_offsets = offset + 2;70    for (0..condition_count) |condition_index| {71        const condition_relative = try readU32(kind, bytes, condition_offsets + condition_index * 4);72        const condition_offset = try childOffset32(kind, bytes, offset, condition_relative, 2);73        if (!try featureConditionMatches(kind, bytes, condition_offset, face, selection)) return false;74    }75    return true;76}7778fn featureConditionMatches(comptime kind: Kind, bytes: []const u8, condition_offset: usize, face: anytype, selection: LayoutSelection) FontError!bool {79    const format = try readU16(kind, bytes, condition_offset);80    if (format != 1) return false;81    if (!hasBytes(kind, bytes, condition_offset, 8)) return invalid(kind);82    const axis_index = try readU16(kind, bytes, condition_offset + 2);83    const min_value = try readI16(kind, bytes, condition_offset + 4);84    const max_value = try readI16(kind, bytes, condition_offset + 6);85    if (min_value > max_value) return false;86    const found_face = face orelse return false;87    if (axis_index >= found_face.variationAxisCount()) return false;88    const value = found_face.normalizedCoordinateAt(selection.variations, axis_index) catch return false;89    return value >= min_value and value <= max_value;90}9192pub fn substitutedFeatureOffset(comptime kind: Kind, bytes: []const u8, substitution_offset: usize, feature_index: u16) FontError!?usize {93    if (try readU16(kind, bytes, substitution_offset) != 1 or try readU16(kind, bytes, substitution_offset + 2) != 0) return null;94    const substitution_count = try readU16(kind, bytes, substitution_offset + 4);95    if (@as(u64, substitution_count) * 6 > @as(u64, bytes.len - substitution_offset - 6)) return invalid(kind);96    const records = substitution_offset + 6;97    for (0..substitution_count) |record_index| {98        const record_offset = records + record_index * 6;99        const current_feature_index = try readU16(kind, bytes, record_offset);100        if (current_feature_index > feature_index) return null;101        if (current_feature_index != feature_index) continue;102        const alternate_relative = try readU32(kind, bytes, record_offset + 2);103        return try childOffset32(kind, bytes, substitution_offset, alternate_relative, 4);104    }105    return null;106}107108pub fn featureTableContainsLookup(comptime kind: Kind, bytes: []const u8, feature_offset: usize, lookup_index: u16) FontError!bool {109    if (!hasBytes(kind, bytes, feature_offset, 4)) return invalid(kind);110    const lookup_index_count = try readU16(kind, bytes, feature_offset + 2);111    if (@as(u64, lookup_index_count) * 2 > @as(u64, bytes.len - feature_offset - 4)) return invalid(kind);112    for (0..lookup_index_count) |i| {113        if (try readU16(kind, bytes, feature_offset + 4 + i * 2) == lookup_index) return true;114    }115    return false;116}117118pub fn baseOffset(comptime kind: Kind, data: []const u8, relative_offset: u16) FontError!usize {119    const relative: usize = relative_offset;120    if (relative == 0 or relative >= data.len) return invalid(kind);121    if (data.len - relative < 2) return invalid(kind);122    return relative;123}124125pub fn childOffset(comptime kind: Kind, data: []const u8, base: usize, relative_offset: u16, min_len: usize) FontError!usize {126    const relative: usize = relative_offset;127    if (relative == 0 or base > data.len or relative > data.len - base) return invalid(kind);128    const child = base + relative;129    if (!hasBytes(kind, data, child, min_len)) return invalid(kind);130    return child;131}132133pub fn childOffset32(comptime kind: Kind, data: []const u8, base: usize, relative_offset: u32, min_len: usize) FontError!usize {134    if (relative_offset == 0 or relative_offset > std.math.maxInt(usize)) return invalid(kind);135    const relative: usize = @intCast(relative_offset);136    if (base > data.len or relative > data.len - base) return invalid(kind);137    const child = base + relative;138    if (!hasBytes(kind, data, child, min_len)) return invalid(kind);139    return child;140}141142pub fn hasBytes(comptime kind: Kind, data: []const u8, offset_value: usize, len: usize) bool {143    _ = kind;144    return offset_value <= data.len and len <= data.len - offset_value;145}146147pub fn readU16(comptime kind: Kind, data: []const u8, offset_value: usize) FontError!u16 {148    if (!hasBytes(kind, data, offset_value, 2)) return invalid(kind);149    return std.mem.readInt(u16, data[offset_value..][0..2], .big);150}151152pub fn readI16(comptime kind: Kind, data: []const u8, offset_value: usize) FontError!i16 {153    return @bitCast(try readU16(kind, data, offset_value));154}155156pub fn readU32(comptime kind: Kind, data: []const u8, offset_value: usize) FontError!u32 {157    if (!hasBytes(kind, data, offset_value, 4)) return invalid(kind);158    return std.mem.readInt(u32, data[offset_value..][0..4], .big);159}160161pub fn invalid(comptime kind: Kind) FontError {162    return switch (kind) {163        .gsub => error.InvalidGsub,164        .gpos => error.InvalidGpos,165    };166}167168pub fn lookupFilterSkipsGlyphs(filter: LookupFilter) bool {169    return filter.flags != 0 or filter.mark_filtering_set != null;170}171172pub fn gsubLookupFilter(data: []const u8, lookup_offset: usize) FontError!LookupFilter {173    const flags = try gsubReadU16(data, lookup_offset + 2);174    if ((flags & reserved_flags) != 0) return error.InvalidGsub;175    const subtable_count = try gsubReadU16(data, lookup_offset + 4);176    const mark_filtering_set_offset = lookup_offset + 6 + @as(usize, subtable_count) * 2;177    if ((flags & use_mark_filtering_set) == 0) {178        return .{ .flags = flags };179    }180    if (!gsubHasBytes(data, mark_filtering_set_offset, 2)) return error.InvalidGsub;181    return .{182        .flags = flags,183        .mark_filtering_set = try gsubReadU16(data, mark_filtering_set_offset),184    };185}186187pub fn gposLookupFilter(data: []const u8, lookup_offset: usize) FontError!LookupFilter {188    const flags = try gposReadU16(data, lookup_offset + 2);189    if ((flags & reserved_flags) != 0) return error.InvalidGpos;190    const subtable_count = try gposReadU16(data, lookup_offset + 4);191    const mark_filtering_set_offset = lookup_offset + 6 + @as(usize, subtable_count) * 2;192    if ((flags & use_mark_filtering_set) == 0) {193        return .{ .flags = flags };194    }195    if (!gposHasBytes(data, mark_filtering_set_offset, 2)) return error.InvalidGpos;196    return .{197        .flags = flags,198        .mark_filtering_set = try gposReadU16(data, mark_filtering_set_offset),199    };200}201202pub fn lookupGlyphIgnored(data: []const u8, gdef: ?Gdef, filter: LookupFilter, glyph_id: u16) FontError!bool {203    const needs_gdef =204        (filter.flags & (ignore_base_glyphs | ignore_ligatures | ignore_marks | mark_attachment_type)) != 0 or205        filter.mark_filtering_set != null;206    const definition = gdef orelse return needs_gdef;207    const class = try definition.glyphClass(data, glyph_id);208209    if (class == .base and (filter.flags & ignore_base_glyphs) != 0) return true;210    if (class == .ligature and (filter.flags & ignore_ligatures) != 0) return true;211    if (class != .mark) return false;212    if ((filter.flags & ignore_marks) != 0) return true;213214    if (filter.mark_filtering_set) |set_index| {215        return !try definition.markGlyphSetContains(data, set_index, glyph_id);216    }217218    const attachment_type = (filter.flags & mark_attachment_type) >> 8;219    if (attachment_type == 0) return false;220    return try definition.markAttachmentClass(data, glyph_id) != attachment_type;221}222223pub fn scriptTagListContains(script_tags: []const Tag, wanted: Tag) bool {224    for (script_tags) |script_tag| {225        if (script_tag == wanted) return true;226    }227    return false;228}229230pub fn gsubOffset(data: []const u8, relative_offset: u16) FontError!usize {231    return baseOffset(.gsub, data, relative_offset);232}233234pub fn gsubChildOffset(data: []const u8, base: usize, relative_offset: u16, min_len: usize) FontError!usize {235    return childOffset(.gsub, data, base, relative_offset, min_len);236}237238pub fn gsubChildOffset32(data: []const u8, base: usize, relative_offset: u32, min_len: usize) FontError!usize {239    return childOffset32(.gsub, data, base, relative_offset, min_len);240}241242pub fn gsubHasBytes(data: []const u8, offset_value: usize, len: usize) bool {243    return hasBytes(.gsub, data, offset_value, len);244}245246pub fn gsubReadU16(data: []const u8, offset_value: usize) FontError!u16 {247    return readU16(.gsub, data, offset_value);248}249250pub fn gsubReadI16(data: []const u8, offset_value: usize) FontError!i16 {251    return readI16(.gsub, data, offset_value);252}253254pub fn gsubReadU32(data: []const u8, offset_value: usize) FontError!u32 {255    return readU32(.gsub, data, offset_value);256}257258pub fn gposOffset(data: []const u8, relative_offset: u16) FontError!usize {259    return baseOffset(.gpos, data, relative_offset);260}261262pub fn gposChildOffset(data: []const u8, base: usize, relative_offset: u16, min_len: usize) FontError!usize {263    return childOffset(.gpos, data, base, relative_offset, min_len);264}265266pub fn gposChildOffset32(data: []const u8, base: usize, relative_offset: u32, min_len: usize) FontError!usize {267    return childOffset32(.gpos, data, base, relative_offset, min_len);268}269270pub fn gposHasBytes(data: []const u8, offset_value: usize, len: usize) bool {271    return hasBytes(.gpos, data, offset_value, len);272}273274pub fn gposReadU16(data: []const u8, offset_value: usize) FontError!u16 {275    return readU16(.gpos, data, offset_value);276}277278pub fn gposReadI16(data: []const u8, offset_value: usize) FontError!i16 {279    return readI16(.gpos, data, offset_value);280}281282pub fn gposReadU32(data: []const u8, offset_value: usize) FontError!u32 {283    return readU32(.gpos, data, offset_value);284}

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