fixes for Qt6 and building without sound

frontend/audio.cpp

@@ -43,11 +43,15 @@ void MainWindow::audioStateChanged(QAudio::State state) {
 #endif
 
 void MainWindow::onAudioSample(int16_t left, int16_t right) {
+#ifndef NO_SOUND
   m_audioStream->write(reinterpret_cast<const char*>(left), sizeof(int16_t));
   m_audioStream->write(reinterpret_cast<const char*>(right), sizeof(int16_t));
+#endif
 }
 
 void MainWindow::onAudioSampleBatch(const int16_t *data, size_t frames) {
+#ifndef NO_SOUND
   // each "frame" is two int16_t's (one for each channel of a stereo track)
   m_audioStream->write(reinterpret_cast<const char*>(data), frames * sizeof(int16_t) * 2);
+#endif
 }

reference_frontend.pro

@@ -16,7 +16,11 @@
 
 TEMPLATE = app
 
-QT += gui widgets
+QT += gui widgets opengl
+
+greaterThan(QT_MAJOR_VERSION, 5) {
+  QT += openglwidgets
+}
 
 TARGET = reference_frontend