It seems that the internal Qt5 caching does not work well here,
especially in the case of Herbrew documents.
int cache_metrics_width_size = 1 << 19;
int cache_metrics_breakat_size = 1 << 19;
// Qt 5.x already has its own caching of QTextLayout objects
int cache_metrics_width_size = 1 << 19;
int cache_metrics_breakat_size = 1 << 19;
// Qt 5.x already has its own caching of QTextLayout objects
-#if (QT_VERSION < 0x050000)
+// but it does not seem to work well on MacOS X.
+#if (QT_VERSION < 0x050000) || defined(Q_OS_MAC)
int cache_metrics_qtextlayout_size = 500;
#else
int cache_metrics_qtextlayout_size = 0;
int cache_metrics_qtextlayout_size = 500;
#else
int cache_metrics_qtextlayout_size = 0;