ascender
return m_cur_face->ascender * height() / m_cur_face->height;
double ascender() const;
fHeight.ascent = (double)face->ascender / face->units_per_EM;
fHeight.leading = (double)(face->height - face->ascender
fHeight.ascent = (double)metrics.ascender / size;
fHeight.leading = (double)(metrics.height - metrics.ascender