QtQuick using QQuickTextNode

Question

I tried to use QQuickTextNode in a custom QQuickitem but ended up not seeing anything on the screen (I know it is a private API)...

Could anyone tell me what I am doing wrong?

Header:

#pragma once

#include <QQuickItem>
#include <QTextLayout>

class TextItem: public QQuickItem {

    Q_OBJECT

    Q_PROPERTY(QString text READ text WRITE setText NOTIFY textChanged)

public:

    TextItem(QQuickItem *parent = nullptr);
    ~TextItem();

    QString text() const;

public slots:

    void setText(QString text);

signals:

    void textChanged(QString text);

protected:

    QSGNode *updatePaintNode(QSGNode *oldNode, UpdatePaintNodeData *data) override;

private:

    QString         _text;
    QTextLayout    *_layout;
};

Implementation:

#include "text_item.h"

#include <QTextLayout>

#include <private/qquicktextnode_p.h>

TextItem::TextItem(QQuickItem *parent)
    : QQuickItem(parent)
    , _layout(new QTextLayout)
{
    setFlag(ItemHasContents, true);
}

TextItem::~TextItem()
{
    delete _layout;
}

QString TextItem::text() const
{
    return _text;
}

void TextItem::setText(QString text)
{
    if (_text == text)
        return;

    _text = text;
    emit textChanged(_text);
}
QSGNode *TextItem::updatePaintNode(QSGNode *oldNode, QQuickItem::UpdatePaintNodeData *data)
{
    QQuickTextNode *node = nullptr;
    if (!oldNode) {
        node = new QQuickTextNode(this);
    } else {
        node = static_cast<QQuickTextNode *>(oldNode);
    }
    _layout->setText(_text);
    QQuickText::TextStyle textStyle;
    node->addTextLayout(QPointF(5, 5), _layout);
    return node;
}

Answer 1

You have to create the QTextLine of the QTextLayout, in the following example I have added the lines with an increasing width:

textitem.h

#ifndef TEXTITEM_H
#define TEXTITEM_H

#include <QQuickItem>
class QTextLayout;

class TextItem : public QQuickItem
{
    Q_OBJECT
    Q_PROPERTY(QString text READ text WRITE setText NOTIFY textChanged)
    Q_PROPERTY(QFont font READ font WRITE setFont NOTIFY fontChanged)
public:
    TextItem(QQuickItem *parent = nullptr);
    ~TextItem();
    QString text() const;
    void setText(const QString &text);
    QFont font() const;
    void setFont(const QFont &font);
signals:
    void textChanged(const QString &);
    void fontChanged();
protected:
    QSGNode *updatePaintNode(QSGNode *, UpdatePaintNodeData *);
private:
    QString m_text;
    QFont m_font;
    QTextLayout *m_layout;
};

#endif // TEXTITEM_H

textitem.cpp

#include "textitem.h"
#include <private/qquicktextnode_p.h>
#include <QFontMetrics>

TextItem::TextItem(QQuickItem *parent):
    QQuickItem(parent),
    m_layout(new QTextLayout)
{
    setFlag(ItemHasContents, true);
}

TextItem::~TextItem(){ delete m_layout;}

QString TextItem::text() const{ return m_text; }

void TextItem::setText(const QString &text)
{
    if(m_text == text) return;
    m_text = text;
    emit textChanged(m_text);
    update();
}

QFont TextItem::font() const { return m_font;}

void TextItem::setFont(const QFont &font)
{
    if(m_font == font) return;
    m_font = font;
    emit fontChanged();
    update();
}

QSGNode *TextItem::updatePaintNode(QSGNode *node, QQuickItem::UpdatePaintNodeData *data)
{
    Q_UNUSED(data)
    QFontMetrics fontMetrics(font());
    int height = 0;
    int lineWidth = 40;
    int leading = fontMetrics.leading();
    m_layout->setText(m_text);
    m_layout->beginLayout();
    int counter = 1;
    while (1) {
        QTextLine line = m_layout->createLine();
        if (!line.isValid())
            break;
        line.setLineWidth(counter*lineWidth);
        height += leading;
        line.setPosition(QPointF(0, height));
        height += line.height();
        counter++;
    }
    m_layout->endLayout();

    QQuickTextNode *n = static_cast<QQuickTextNode *>(node);
    if (!n)
        n = new QQuickTextNode(this);
    n->removeAllChildNodes();
    n->addTextLayout(QPointF(5, 5), m_layout);
    return n;
}

*.qml

TextItem{
    text: "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vestibulum volutpat libero elit, eu egestas lacus lacinia nec. Curabitur tempus lectus est, eget blandit arcu lacinia non. Curabitur vestibulum dictum diam ut hendrerit. Sed vitae ultricies libero. Morbi non libero risus. Aenean vel volutpat ipsum, scelerisque lacinia dui. Donec molestie vitae dolor vitae porttitor. Phasellus et facilisis elit. Sed metus lacus, commodo non interdum eu, viverra eu justo. Praesent a blandit nisi, ac porta magna. Aenean a lectus vel tortor ullamcorper ornare id non quam. Suspendisse potenti. Nunc hendrerit, eros nec vestibulum egestas, dolor orci malesuada est, sit amet tristique ipsum sem in mauris. Nullam lorem lacus, laoreet non venenatis sit amet, consequat dictum ligula. Quisque bibendum tellus egestas ex ullamcorper dapibus."
    anchors.fill: parent
}

Output:

The complete example you find here.