Multilingual QPlainTextEdit: Different font height



  • I use QPlainTextEdit to implement a code editor, but english and CJK characters have different line height.

    I set the font as Ubuntu Mono which does not contain CJK characters, so Qt fallback to the WenQuanYi Zen Hei on my machine. I used the following code to inspect these two fonts.

    @QFont f1("Ubuntu Mono", 12);
    QFont f2("WenQuanYi Zen Hei", 12);
    fontInfo(f1);
    fontInfo(f2);@

    The function fontInfo is defined as

    @void fontInfo(QFont &f) {
    QFontMetrics m(f);
    cout << "Ascent: " << m.ascent() << ", Descent: " << m.descent() << ", Height: " << m.height() << ", Leading: " << m.leading() << ", LineSpacing: " << m.lineSpacing() << endl;
    cout << "Underline pos: " << m.underlinePos() << ", Overline pos: " << m.overlinePos() << ", Strikeline pos: " << m.strikeOutPos() << endl;
    }@

    The result is:

    Ubuntu Mono:
    Ascent: 14, Descent: 3, Height: 17, Leading: -1, LineSpacing: 16
    Underline pos: 2, Overline pos: 15, Strikeline pos: 4

    WenQuanYi Zen Hei
    Ascent: 16, Descent: 5, Height: 21, Leading: 1, LineSpacing: 22
    Underline pos: 4, Overline pos: 17, Strikeline pos: 5

    How can I set the line spacing to the same value so English and CJK characters would be same height.


  • Lifetime Qt Champion

    Hi and welcome to devnet,

    Did you try with QTextFormat and setting the property QTextFormat::LineHeight ?

    Hope it helps



  • I looked at the doc of QTextFormat and discovered that I have to implement a QSyntaxHighlighter to apply the format, so I came out with this:

    @class HighLighter : public QSyntaxHighlighter {
    Q_OBJECT
    public:
    explicit HighLighter(QObject *parent = 0) : QSyntaxHighlighter(parent) {}
    protected:
    void highlightBlock(const QString &text) {
    QTextCharFormat format;
    format.setProperty(QTextFormat::LineHeight, 50);
    this->setFormat(0, text.length(), format);
    this->setFormat(0, text.length(), Qt::blue);
    }
    };@

    The text successfully turned into blue, but the line height still not change.


  • Lifetime Qt Champion

    I might be wrong but I don't think you can set a line height like that. Why don't you set that line height document wide ?


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