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  1. Qt
  2. QTBUG-104986

QTextLayout::maximumWidth() is not correct for multi-line text

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    • Icon: Bug Bug
    • Resolution: Fixed
    • Icon: P2: Important P2: Important
    • 6.5.0 Beta1
    • 5.15.2, 6.2.4, 6.3.1
    • GUI: Text handling
    • None
    • All
    • 013c346a8d (qt/qtbase/dev) 013c346a8d (qt/tqtc-qtbase/dev) 70e33a585c (qt/qtbase/6.4) 70e33a585c (qt/tqtc-qtbase/6.4) 07bde1cadf (qt/tqtc-qtbase/6.2) 991c056438 (qt/tqtc-qtbase/dev)

      Found this while investigating QTBUG-89557.

      QTextLayout::maximumWidth() doesn't take into account line separator for multi-line text.
      Reproduced on the current Dev as well.

      Code sample:

      #include <QGuiApplication>
#include <QTextLayout>

qreal layoutMaximumWidth(const QString &text)
{
    QTextLayout layout(text);
    layout.beginLayout();
    while (layout.createLine().isValid()) { }
    layout.endLayout();

    return layout.maximumWidth();
}

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    qreal w1 = layoutMaximumWidth("test");
    qDebug() << "singleline maxwidth:" << w1;

    qreal w2 = layoutMaximumWidth("test\ntest");
    qDebug() << "multiline maxwidth:" << w2;

    Q_ASSERT(qFuzzyCompare(w1, w2));

    return 0;
}

      Output:

      singleline maxwidth: 19.4688
multiline maxwidth: 38.9375
ASSERT: "qFuzzyCompare(w1, w2)" in file ..\textLayout\main.cpp, line 24

      For the test case above w1 should be equal to w2, and the ASSERT should not fire.
      See full example textLayout.zip
       

        1. textLayout.zip
          0.8 kB
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            esabraha Eskil Abrahamsen Blomfeldt
            studiosus Vladimir Belyavsky
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              Created:
              Updated:
              Resolved: