QTextEdit and colored bash-like output emulation

Finally, I found the approach (it is understood, that QTextEdit::setReadOnly(true)):

// based on information: http://en.m.wikipedia.org/wiki/ANSI_escape_code http://misc.flogisoft.com/bash/tip_colors_and_formatting http://invisible-island.net/xterm/ctlseqs/ctlseqs.html
void MainWindow::parseEscapeSequence(int attribute, QListIterator< QString > & i, QTextCharFormat & textCharFormat, QTextCharFormat const & defaultTextCharFormat)
{
    switch (attribute) {
    case 0 : { // Normal/Default (reset all attributes)
        textCharFormat = defaultTextCharFormat;
        break;
    }
    case 1 : { // Bold/Bright (bold or increased intensity)
        textCharFormat.setFontWeight(QFont::Bold);
        break;
    }
    case 2 : { // Dim/Faint (decreased intensity)
        textCharFormat.setFontWeight(QFont::Light);
        break;
    }
    case 3 : { // Italicized (italic on)
        textCharFormat.setFontItalic(true);
        break;
    }
    case 4 : { // Underscore (single underlined)
        textCharFormat.setUnderlineStyle(QTextCharFormat::SingleUnderline);
        textCharFormat.setFontUnderline(true);
        break;
    }
    case 5 : { // Blink (slow, appears as Bold)
        textCharFormat.setFontWeight(QFont::Bold);
        break;
    }
    case 6 : { // Blink (rapid, appears as very Bold)
        textCharFormat.setFontWeight(QFont::Black);
        break;
    }
    case 7 : { // Reverse/Inverse (swap foreground and background)
        QBrush foregroundBrush = textCharFormat.foreground();
        textCharFormat.setForeground(textCharFormat.background());
        textCharFormat.setBackground(foregroundBrush);
        break;
    }
    case 8 : { // Concealed/Hidden/Invisible (usefull for passwords)
        textCharFormat.setForeground(textCharFormat.background());
        break;
    }
    case 9 : { // Crossed-out characters
        textCharFormat.setFontStrikeOut(true);
        break;
    }
    case 10 : { // Primary (default) font
        textCharFormat.setFont(defaultTextCharFormat.font());
        break;
    }
    case 11 ... 19 : {
        QFontDatabase fontDatabase;
        QString fontFamily = textCharFormat.fontFamily();
        QStringList fontStyles = fontDatabase.styles(fontFamily);
        int fontStyleIndex = attribute - 11;
        if (fontStyleIndex < fontStyles.length()) {
            textCharFormat.setFont(fontDatabase.font(fontFamily, fontStyles.at(fontStyleIndex), textCharFormat.font().pointSize()));
        }
        break;
    }
    case 20 : { // Fraktur (unsupported)
        break;
    }
    case 21 : { // Set Bold off
        textCharFormat.setFontWeight(QFont::Normal);
        break;
    }
    case 22 : { // Set Dim off
        textCharFormat.setFontWeight(QFont::Normal);
        break;
    }
    case 23 : { // Unset italic and unset fraktur
        textCharFormat.setFontItalic(false);
        break;
    }
    case 24 : { // Unset underlining
        textCharFormat.setUnderlineStyle(QTextCharFormat::NoUnderline);
        textCharFormat.setFontUnderline(false);
        break;
    }
    case 25 : { // Unset Blink/Bold
        textCharFormat.setFontWeight(QFont::Normal);
        break;
    }
    case 26 : { // Reserved
        break;
    }
    case 27 : { // Positive (non-inverted)
        QBrush backgroundBrush = textCharFormat.background();
        textCharFormat.setBackground(textCharFormat.foreground());
        textCharFormat.setForeground(backgroundBrush);
        break;
    }
    case 28 : {
        textCharFormat.setForeground(defaultTextCharFormat.foreground());
        textCharFormat.setBackground(defaultTextCharFormat.background());
        break;
    }
    case 29 : {
        textCharFormat.setUnderlineStyle(QTextCharFormat::NoUnderline);
        textCharFormat.setFontUnderline(false);
        break;
    }
    case 30 ... 37 : {
        int colorIndex = attribute - 30;
        QColor color;
        if (QFont::Normal < textCharFormat.fontWeight()) {
            switch (colorIndex) {
            case 0 : {
                color = Qt::darkGray;
                break;
            }
            case 1 : {
                color = Qt::red;
                break;
            }
            case 2 : {
                color = Qt::green;
                break;
            }
            case 3 : {
                color = Qt::yellow;
                break;
            }
            case 4 : {
                color = Qt::blue;
                break;
            }
            case 5 : {
                color = Qt::magenta;
                break;
            }
            case 6 : {
                color = Qt::cyan;
                break;
            }
            case 7 : {
                color = Qt::white;
                break;
            }
            default : {
                Q_ASSERT(false);
            }
            }
        } else {
            switch (colorIndex) {
            case 0 : {
                color = Qt::black;
                break;
            }
            case 1 : {
                color = Qt::darkRed;
                break;
            }
            case 2 : {
                color = Qt::darkGreen;
                break;
            }
            case 3 : {
                color = Qt::darkYellow;
                break;
            }
            case 4 : {
                color = Qt::darkBlue;
                break;
            }
            case 5 : {
                color = Qt::darkMagenta;
                break;
            }
            case 6 : {
                color = Qt::darkCyan;
                break;
            }
            case 7 : {
                color = Qt::lightGray;
                break;
            }
            default : {
                Q_ASSERT(false);
            }
            }
        }
        textCharFormat.setForeground(color);
        break;
    }
    case 38 : {
        if (i.hasNext()) {
            bool ok = false;
            int selector = i.next().toInt(&ok);
            Q_ASSERT(ok);
            QColor color;
            switch (selector) {
            case 2 : {
                if (!i.hasNext()) {
                    break;
                }
                int red = i.next().toInt(&ok);
                Q_ASSERT(ok);
                if (!i.hasNext()) {
                    break;
                }
                int green = i.next().toInt(&ok);
                Q_ASSERT(ok);
                if (!i.hasNext()) {
                    break;
                }
                int blue = i.next().toInt(&ok);
                Q_ASSERT(ok);
                color.setRgb(red, green, blue);
                break;
            }
            case 5 : {
                if (!i.hasNext()) {
                    break;
                }
                int index = i.next().toInt(&ok);
                Q_ASSERT(ok);
                switch (index) {
                case 0x00 ... 0x07 : { // 0x00-0x07:  standard colors (as in ESC [ 30..37 m)
                    return parseEscapeSequence(index - 0x00 + 30, i, textCharFormat, defaultTextCharFormat);
                }
                case 0x08 ... 0x0F : { // 0x08-0x0F:  high intensity colors (as in ESC [ 90..97 m)
                    return parseEscapeSequence(index - 0x08 + 90, i, textCharFormat, defaultTextCharFormat);
                }
                case 0x10 ... 0xE7 : { // 0x10-0xE7:  6*6*6=216 colors: 16 + 36*r + 6*g + b (0≤r,g,b≤5)
                    index -= 0x10;
                    int red = index % 6;
                    index /= 6;
                    int green = index % 6;
                    index /= 6;
                    int blue = index % 6;
                    index /= 6;
                    Q_ASSERT(index == 0);
                    color.setRgb(red, green, blue);
                    break;
                }
                case 0xE8 ... 0xFF : { // 0xE8-0xFF:  grayscale from black to white in 24 steps
                    qreal intensity = qreal(index - 0xE8) / (0xFF - 0xE8);
                    color.setRgbF(intensity, intensity, intensity);
                    break;
                }
                }
                textCharFormat.setForeground(color);
                break;
            }
            default : {
                break;
            }
            }
        }
        break;
    }
    case 39 : {
        textCharFormat.setForeground(defaultTextCharFormat.foreground());
        break;
    }
    case 40 ... 47 : {
        int colorIndex = attribute - 40;
        QColor color;
        switch (colorIndex) {
        case 0 : {
            color = Qt::darkGray;
            break;
        }
        case 1 : {
            color = Qt::red;
            break;
        }
        case 2 : {
            color = Qt::green;
            break;
        }
        case 3 : {
            color = Qt::yellow;
            break;
        }
        case 4 : {
            color = Qt::blue;
            break;
        }
        case 5 : {
            color = Qt::magenta;
            break;
        }
        case 6 : {
            color = Qt::cyan;
            break;
        }
        case 7 : {
            color = Qt::white;
            break;
        }
        default : {
            Q_ASSERT(false);
        }
        }
        textCharFormat.setBackground(color);
        break;
    }
    case 48 : {
        if (i.hasNext()) {
            bool ok = false;
            int selector = i.next().toInt(&ok);
            Q_ASSERT(ok);
            QColor color;
            switch (selector) {
            case 2 : {
                if (!i.hasNext()) {
                    break;
                }
                int red = i.next().toInt(&ok);
                Q_ASSERT(ok);
                if (!i.hasNext()) {
                    break;
                }
                int green = i.next().toInt(&ok);
                Q_ASSERT(ok);
                if (!i.hasNext()) {
                    break;
                }
                int blue = i.next().toInt(&ok);
                Q_ASSERT(ok);
                color.setRgb(red, green, blue);
                break;
            }
            case 5 : {
                if (!i.hasNext()) {
                    break;
                }
                int index = i.next().toInt(&ok);
                Q_ASSERT(ok);
                switch (index) {
                case 0x00 ... 0x07 : { // 0x00-0x07:  standard colors (as in ESC [ 40..47 m)
                    return parseEscapeSequence(index - 0x00 + 40, i, textCharFormat, defaultTextCharFormat);
                }
                case 0x08 ... 0x0F : { // 0x08-0x0F:  high intensity colors (as in ESC [ 100..107 m)
                    return parseEscapeSequence(index - 0x08 + 100, i, textCharFormat, defaultTextCharFormat);
                }
                case 0x10 ... 0xE7 : { // 0x10-0xE7:  6*6*6=216 colors: 16 + 36*r + 6*g + b (0≤r,g,b≤5)
                    index -= 0x10;
                    int red = index % 6;
                    index /= 6;
                    int green = index % 6;
                    index /= 6;
                    int blue = index % 6;
                    index /= 6;
                    Q_ASSERT(index == 0);
                    color.setRgb(red, green, blue);
                    break;
                }
                case 0xE8 ... 0xFF : { // 0xE8-0xFF:  grayscale from black to white in 24 steps
                    qreal intensity = qreal(index - 0xE8) / (0xFF - 0xE8);
                    color.setRgbF(intensity, intensity, intensity);
                    break;
                }
                }
                textCharFormat.setBackground(color);
                break;
            }
            default : {
                break;
            }
            }
        }
        break;
    }
    case 49 : {
        textCharFormat.setBackground(defaultTextCharFormat.background());
        break;
    }
    case 90 ... 97 : {
        int colorIndex = attribute - 90;
        QColor color;
        switch (colorIndex) {
        case 0 : {
            color = Qt::darkGray;
            break;
        }
        case 1 : {
            color = Qt::red;
            break;
        }
        case 2 : {
            color = Qt::green;
            break;
        }
        case 3 : {
            color = Qt::yellow;
            break;
        }
        case 4 : {
            color = Qt::blue;
            break;
        }
        case 5 : {
            color = Qt::magenta;
            break;
        }
        case 6 : {
            color = Qt::cyan;
            break;
        }
        case 7 : {
            color = Qt::white;
            break;
        }
        default : {
            Q_ASSERT(false);
        }
        }
        color.setRedF(color.redF() * 0.8);
        color.setGreenF(color.greenF() * 0.8);
        color.setBlueF(color.blueF() * 0.8);
        textCharFormat.setForeground(color);
        break;
    }
    case 100 ... 107 : {
        int colorIndex = attribute - 100;
        QColor color;
        switch (colorIndex) {
        case 0 : {
            color = Qt::darkGray;
            break;
        }
        case 1 : {
            color = Qt::red;
            break;
        }
        case 2 : {
            color = Qt::green;
            break;
        }
        case 3 : {
            color = Qt::yellow;
            break;
        }
        case 4 : {
            color = Qt::blue;
            break;
        }
        case 5 : {
            color = Qt::magenta;
            break;
        }
        case 6 : {
            color = Qt::cyan;
            break;
        }
        case 7 : {
            color = Qt::white;
            break;
        }
        default : {
            Q_ASSERT(false);
        }
        }
        color.setRedF(color.redF() * 0.8);
        color.setGreenF(color.greenF() * 0.8);
        color.setBlueF(color.blueF() * 0.8);
        textCharFormat.setBackground(color);
        break;
    }
    default : {
        break;
    }
    }
}

void MainWindow::setTextTermFormatting(QTextEdit * textEdit, QString const & text)
{
    QTextDocument * document = textEdit->document();
    QRegExp const escapeSequenceExpression(R"(\x1B\[([\d;]+)m)");
    QTextCursor cursor(document);
    QTextCharFormat const defaultTextCharFormat = cursor.charFormat();
    cursor.beginEditBlock();
    int offset = escapeSequenceExpression.indexIn(text);
    cursor.insertText(text.mid(0, offset));
    QTextCharFormat textCharFormat = defaultTextCharFormat;
    while (!(offset < 0)) {
        int previousOffset = offset + escapeSequenceExpression.matchedLength();
        QStringList capturedTexts = escapeSequenceExpression.capturedTexts().back().split(';');
        QListIterator< QString > i(capturedTexts);
        while (i.hasNext()) {
            bool ok = false;
            int attribute = i.next().toInt(&ok);
            Q_ASSERT(ok);
            parseEscapeSequence(attribute, i, textCharFormat, defaultTextCharFormat);
        }
        offset = escapeSequenceExpression.indexIn(text, previousOffset);
        if (offset < 0) {
            cursor.insertText(text.mid(previousOffset), textCharFormat);
        } else {
            cursor.insertText(text.mid(previousOffset, offset - previousOffset), textCharFormat);
        }
    }
    cursor.setCharFormat(defaultTextCharFormat);
    cursor.endEditBlock();
    //cursor.movePosition(QTextCursor::Start);
    textEdit->setTextCursor(cursor);
}

It is not fully tested at the moment, but quite workable. It is exact what I wanted.

Those are ANSI escape codes. They are very simple to parse, especially if you have just a small fixed subset you control. There probably are libraries which could also help you parse the escape codes, and if you see a need to support more codes than just colors, then it might make sense to try and find one, but if you just need simple color codes and have full control of the original strings, then writing your own is probably quicker.

So what you need to do, is parse those escape codes from the strings, and replace them with Qt rich text markup, which is a subset of HTML markup.

---

Another approach might be to do the reverse: store your strings using HTML (or some other) markup, then convert that to ANSI codes for colored console output. With luck you might even find a library which can convert HTML to text with ANSI escape codes.