Change how getting the current title works, and fix ZSM backend not setting itself as opened.

backends/playback/sdl_mixer_x/sdl_mixer_x.cpp

@@ -62,10 +62,7 @@ void SDLMixerXBackend::load(const char *filename) {
     current_file = std::string(filename);
     const char *title_tag = Mix_GetMusicTitleTag(output);
     // Check for an empty string, which indicates there's no title tag.
-    if (title_tag[0] == '\0') {
-        std::filesystem::path path(current_file);
-        current_title = path.stem().string();
-    } else {
+    if (title_tag[0] != '\0') {
         current_title = std::string(title_tag);
     }
     this->music = output;
@@ -73,9 +70,9 @@ void SDLMixerXBackend::load(const char *filename) {
     PlaybackStream stream;
     stream.id = 0;
     stream.length = Mix_MusicDuration(output);
-    stream.name = current_title;
-    streams.push_back(stream);
     open = true;
+    stream.name = get_title.value();
+    streams.push_back(stream);
     initial = true;
 }
 void SDLMixerXBackend::switch_stream(int idx) {

backends/playback/zsm/zsm_backend.cpp

@@ -40,7 +40,7 @@ std::vector<Property> ZsmBackend::get_property_list() {
 	return properties;
 }
 void ZsmBackend::load(const char *filename) {
-	memset(&spec, 0, sizeof(spec));
+    memset(&spec, 0, sizeof(spec));
     current_file = filename;
     spec.format = AUDIO_S16SYS;
     spec.samples = 100;
@@ -157,6 +157,7 @@ void ZsmBackend::load(const char *filename) {
 		property_defaults[#name] = value; \
 	}
 #include "properties.inc"
+    PlaybackStream stream;
 }
 extern SDL_AudioSpec obtained;
 void ZsmBackend::switch_stream(int idx) {
@@ -172,6 +173,7 @@ void ZsmBackend::switch_stream(int idx) {
     this->cpuClocks = 0.0;
     this->delayTicks = 0.0;
     this->ticks = 0.0;
+    open = true;
 }
 void ZsmBackend::cleanup() {
     delete file;

playback_backend.hpp

@@ -24,7 +24,7 @@ class PlaybackBackend {
     uint64_t length;
     std::vector<PlaybackStream> streams;
     std::string current_file;
-    std::string current_title;
+    std::optional<std::string> current_title;
     bool open;
     SDL_AudioSpec spec;
     uint64_t position;
@@ -134,7 +134,21 @@ class PlaybackBackend {
         return open ? current_file : std::optional<std::string>();
     }
     inline virtual std::optional<std::string> get_title() {
-        return open ? current_title : std::optional<std::string>();
+        if (open) {
+            if (current_title.has_value()) {
+                return current_title;
+            } else {
+                auto file = get_current_file();
+                if (file.has_value()) {
+                    std::filesystem::path path(file.value());
+                    return path.stem().string();
+                } else {
+                    return {};
+                }
+            }
+        } else {
+            return {};
+        }
     }
     inline virtual int get_stream_idx() {return 0;}
     inline virtual ~PlaybackBackend() { }