it is done

.gitignore

@@ -2,4 +2,6 @@ zig-cache
 zig-out
 *.bdf
 out
-*.font.json
+*.font.json
+*.exe
+*.bin

src/bdf.zig

@@ -16,7 +16,7 @@ const Character = struct {
 };
 const CharacterMap = std.AutoHashMap(u16, Character);
 
-const Font = struct {
+pub const Font = struct {
     name: []const u8,
     height: u8,
     width: u8,

src/bin.zig

@@ -0,0 +1,17 @@
+const std = @import("std");
+const bdf = @import("bdf.zig");
+
+const WriteError = error{UnknownGlyph};
+
+pub fn writeGlyphs(output: anytype, font: bdf.Font, glyphs: []const u16) !void {
+    for (glyphs) |glyph| {
+        const character = font.characters.get(glyph) orelse {
+            std.log.err("Unknown glyph: {d}", .{glyph});
+            return WriteError.UnknownGlyph;
+        };
+
+        for (character.bitmap) |line| {
+            _ = try output.write(line);
+        }
+    }
+}

src/main.zig

@@ -1,9 +1,11 @@
 const std = @import("std");
 const bdf = @import("bdf.zig");
+const bin = @import("bin.zig");
 
 const FontConfig = struct {
     inputFile: []const u8,
     outputFile: []const u8,
+    glyphs: []const u16,
 };
 
 pub fn main() !void {
@@ -30,11 +32,18 @@ pub fn main() !void {
     const fontConfig = try readConfig(allocator, configFile);
     defer fontConfig.deinit();
 
+    // Open and parse BDF font
     const input = try std.fs.cwd().openFile(fontConfig.value.inputFile, .{});
     defer input.close();
 
     var font = try bdf.parse(allocator, input.reader());
     defer font.deinit(allocator);
+
+    // Write output
+    const output = try std.fs.cwd().createFile(fontConfig.value.outputFile, .{});
+    defer output.close();
+
+    try bin.writeGlyphs(output.writer(), font, fontConfig.value.glyphs);
 }
 
 fn readConfig(allocator: std.mem.Allocator, input: []u8) !std.json.Parsed(FontConfig) {