font: CodepointMap

src/font/CodepointMap.zig

@@ -0,0 +1,48 @@
+/// CodepointMap is a map of codepoints to a discovery descriptor of a font
+/// to use for that codepoint. If the descriptor doesn't return any matching
+/// font, the codepoint is rendered using the default font.
+const CodepointMap = @This();
+
+const std = @import("std");
+const assert = std.debug.assert;
+const Allocator = std.mem.Allocator;
+const discovery = @import("discovery.zig");
+
+pub const Entry = struct {
+    /// Unicode codepoint range. Asserts range[0] <= range[1].
+    range: [2]u21,
+
+    /// The discovery descriptor of the font to use for this range.
+    descriptor: discovery.Descriptor,
+};
+
+/// The list of entries. We use a multiarraylist because Descriptors are
+/// quite large and we will very rarely match, so we'd rather pack our
+/// ranges together to make everything more cache friendly for lookups.
+///
+/// Note: we just do a linear search because we expect to always have very
+/// few entries, so the overhead of a binary search is not worth it. This is
+/// possible to defeat with some pathological inputs, but there is no realistic
+/// scenario where this will be a problem except people trying to fuck around.
+list: std.MultiArrayList(Entry) = .{},
+
+/// Add an entry to the map.
+///
+/// For conflicting codepoints, entries added later take priority over
+/// entries added earlier.
+pub fn add(self: *CodepointMap, alloc: Allocator, entry: Entry) !void {
+    assert(entry.range[0] <= entry.range[1]);
+    try self.list.append(alloc, entry);
+}
+
+/// Get a descriptor for a codepoint.
+pub fn get(self: *const CodepointMap, cp: u21) ?discovery.Descriptor {
+    for (self.list.items(.range), 0..) |range, i| {
+        if (range[0] <= cp and cp <= range[1]) {
+            const descs = self.list.items(.descriptor);
+            return descs[i];
+        }
+    }
+
+    return null;
+}

src/font/Group.zig

@@ -32,6 +32,7 @@ const log = std.log.scoped(.font_group);
 // most important memory efficiency we can look for. This is totally opaque
 // to the user so we can change this later.
 const StyleArray = std.EnumArray(Style, std.ArrayListUnmanaged(GroupFace));
+
 /// The allocator for this group
 alloc: Allocator,