about QFontMetrics elidedText, sort of difficult to realize

[opengpu2]

i use QAbstractItemDelegate, and in the pain(), i draw the fileName use drawText().
when the fileName is very very long, i want at most 4 lines are shown, and if the title is still not shown all, then ElideRight the rest.
which means, 4 lines is the most. if still not enough, elide the rest.