Grey-out stop button when not speaking

resources/css/style.css

@@ -352,3 +352,7 @@ TextToSpeechBar > #closeButton:pressed {
     background-color: #D9E9FF;
     border: 1px solid #3366CC;
 }
+
+TextToSpeechBar > #stopButton:disabled {
+    color: grey;
+}

src/texttospeechbar.cpp

@@ -10,6 +10,7 @@ TextToSpeechBar::TextToSpeechBar(QWidget *parent)
     close();
     mp_ui->setupUi(this);
     mp_ui->stopButton->setText(gt("stop"));
+    connect(mp_speech, &QTextToSpeech::stateChanged, this, &TextToSpeechBar::onStateChanged);
     connect(mp_ui->stopButton, &QPushButton::released, [=](){
         mp_speech->stop();
     });
@@ -71,6 +72,14 @@ void TextToSpeechBar::voiceSelected(int index)
     mp_speech->setVoice(m_voices.at(index));
 }
 
+void TextToSpeechBar::onStateChanged(QTextToSpeech::State state)
+{
+    if (state == QTextToSpeech::Ready)
+        mp_ui->stopButton->setDisabled(true);
+    else
+        mp_ui->stopButton->setDisabled(false);
+}
+
 void TextToSpeechBar::speechBarClose()
 {
     /* Prevent webview from scrolling to up to the top after losing focus. */

src/texttospeechbar.h

@@ -20,6 +20,7 @@ public slots:
     void speechBarClose();
     void languageSelected(int index);
     void voiceSelected(int index);
+    void onStateChanged(QTextToSpeech::State state);
 
 private:
     QTextToSpeech *mp_speech;