+ if (fonts.empty()) {
+ return;
+ }
+
+ /* Fonts may come in with empty IDs but we don't want to put those in the DCP */
+ auto fix_id = [](string id) {
+ return id.empty() ? "font" : id;
+ };
+
+ if (film()->interop()) {
+ /* Interop will ignore second and subsequent <LoadFont>s so we don't want to
+ * even write them as they upset some validators. Set up _fonts so that every
+ * font used by any subtitle will be written with the same ID.
+ */
+ for (size_t i = 0; i < fonts.size(); ++i) {
+ _fonts.put(fonts[i], fix_id(fonts[0]->id()));
+ }
+ _chosen_interop_font = fonts[0];
+ } else {
+ set<string> used_ids;
+
+ /* Return the index of a _N at the end of a string, or string::npos */
+ auto underscore_number_position = [](string s) {
+ auto last_underscore = s.find_last_of("_");
+ if (last_underscore == string::npos) {
+ return string::npos;
+ }
+
+ for (auto i = last_underscore + 1; i < s.size(); ++i) {
+ if (!isdigit(s[i])) {
+ return string::npos;
+ }
+ }
+
+ return last_underscore;
+ };
+
+ /* Write fonts to _fonts, changing any duplicate IDs so that they are unique */
+ for (auto font: fonts) {
+ auto id = fix_id(font->id());
+ if (used_ids.find(id) == used_ids.end()) {
+ /* This ID is unique so we can just use it as-is */
+ _fonts.put(font, id);
+ used_ids.insert(id);
+ } else {
+ auto end = underscore_number_position(id);
+ if (end == string::npos) {
+ /* This string has no _N suffix, so add one */
+ id += "_0";
+ end = underscore_number_position(id);
+ }
+
+ ++end;
+
+ /* Increment the suffix until we find a unique one */
+ auto number = dcp::raw_convert<int>(id.substr(end));
+ while (used_ids.find(id) != used_ids.end()) {
+ ++number;
+ id = String::compose("%1_%2", id.substr(0, end - 1), number);
+ }
+ used_ids.insert(id);
+ }
+ _fonts.put(font, id);
+ }
+
+ DCPOMATIC_ASSERT(_fonts.map().size() == used_ids.size());
+ }