How to draw text in QQuickItem?



  • Hi,
    I want to implement my custom QQuickItem subclass and I want it to draw some text. I found out that there is a QQuickTextNode class, but it seems to be private. So my question is: how can I do text drawing with QQuickItem?

    Thanks in advance!



  • QML TextInput or QML Text Element can be used to draw text.



  • Thank you for the answer, but I need to draw text using C++, not QML.



  • Can't your custom QQuickItem not simply create one or more QML text elements for the text rendering?



  • Or perhaps you can just have a text property that the C++ updates, which is then bound to a qml based Text{} ?



  • Has anybody come up with a solution?



  • [quote author="tcmichals" date="1390932810"]Has anybody come up with a solution?[/quote]

    Why didn't you try the above solution mentioned by Andre or Thomas Sander.



  • I would recommend you to use QQuickPaintedItem class that extends QQuickItem. It has method "paint", where you have QPainter as a result you can draw any text with any font/geometry. If QQuickPaintedItem is not a case for you, that you can try to draw text in "updatePaintNode" method using QSG* classes, but definitely it's much harder than with QQuickPaintedItem



  • Another method to do this would be passing a QAbstractListModel including the Text to a QML ListView so you can have as many Text Elements as you want. Create a Text as a delegate for the ListView and pass your Text to the "text" property of the Text delegate. You can modify and even set all the other properties of your Texts by accessing the childrens of your ListView which can be done from Cpp. I haven't tested it and also i don't have a code for it but it theoretically should work.



  • I tried to use paint text with the QQuickPaintedItem paint() but sometimes it crash my application.

    Have you succeeded ?



  • I used QQuickPaintedItem but unfortunately the performance was quite poor. Fortunately there was a fairly easy solution which improved performance significantly. Call this in your QQuickPaintedItem constructor:

    setRenderTarget(QQuickPaintedItem::FramebufferObject);



  • Also, I've looked at the QML Text source code, and I'm afraid it is incredibly complicated to draw text the "right" QML way from C++.

    Hopefully they will provide a useful solution at some point as more people try to create custom QQuickItem's and realise they can't draw text...



  • @Alexey: Have you found a way to render text in the QQuickItem?



  • i also use QQuickPaintedItem, and when i am reimplement the updatePaintNode function, then i get no call for the paint function.

    Has anybody solved the problem how to render text in QQuickPaintedItem, or QQuickItem?

    I wish there is something like a public QSGTextNode...



  • if you use QQuickPaintedItem, you have to reimplement
    @
    virtual void paint(QPainter *painter) override;
    @

    This paint method will be called when you invoke update(); method



  • We don't want to use QQuickPaintedItem, We want to use QQuickItem



  • Thats the point, i have reimplemented paint, but i also have reimplemented updatePaintNode...
    Maybe i have forgotten something in my reimplementation of updatePaintNode?

    here is some code:

    @MyQuickPaintedItem::MyQuickPaintedItem(QQuickItem *parent)
    : QQuickPaintedItem(parent)
    , m_xAxisLineCount(500)
    {
    setFlag(ItemHasContents, true);

    setRenderTarget(QQuickPaintedItem::FramebufferObject);
    setPerformanceHint(QQuickPaintedItem::FastFBOResizing);
    setAntialiasing(true);
    //setOpaquePainting(true);
    setMipmap(true);
    update();
    

    }

    QSGNode *MyQuickPaintedItem::updatePaintNode(QSGNode *oldNode, UpdatePaintNodeData *data)
    {
    QSGGeometryNode *node = 0;
    QSGGeometry *geometry = 0;

    if (!oldNode) {
        node = new QSGGeometryNode;
    
        geometry = new QSGGeometry(QSGGeometry::defaultAttributes_Point2D(), m_xAxisLineCount * 2);
        geometry->setLineWidth(1);
        geometry->setDrawingMode(GL_LINES);
        node->setGeometry(geometry);
        node->setFlag(QSGNode::OwnsGeometry);
    
        QSGFlatColorMaterial *material = new QSGFlatColorMaterial;
        material->setColor(QColor(255, 0, 0));
        node->setMaterial(material);
        node->setFlag(QSGNode::OwnsMaterial);
    
    } else {
        node = static_cast<QSGGeometryNode *>(oldNode);
        geometry = node->geometry();
        geometry->allocate(m_xAxisLineCount * 2);
    }
    
    //qDebug("in updatePaintNode");
    
    QRectF bounds = boundingRect();
    QSGGeometry::Point2D *vertices = geometry->vertexDataAsPoint2D();
    
    
    int iPlus = 0;
    
    for (int i = 0; i <m_xAxisLineCount; ++i) {
        qreal t = i / qreal(m_xAxisLineCount - 1);
    
        vertices[iPlus].set(i, bounds.height() / 2.0);
    
        iPlus++;
    

    // QPointF pos_amplitude (t, 0.8 );

    // x = bounds.x() + pos_amplitude.x() * bounds.width();
    // y = bounds.y() + pos_amplitude.y() * bounds.height();
    int height = bounds.height();
    int amplitude = rand() % height;
    //int amplitude = height;

        vertices[iPlus].set(i, amplitude);
        iPlus++;
    }
    node->markDirty(QSGNode::DirtyGeometry);
    
    return node;
    

    }

    void MyQuickPaintedItem::paint(QPainter *painter)
    {
    // // Pen
    QColor randomColor(255,255,60);
    QPen myPenRandomColor(randomColor);

    QRectF bounds = contentsBoundingRect();
    
    // Font
    QFont font;
    font.setFamily("Arial");
    font.setPixelSize(20);
    painter->setFont(font);
    
    painter->setPen(myPenRandomColor);
    qDebug("in paint");
    
    
    painter->drawText(bounds,Qt::AlignCenter, "text");
    

    }@@@@@

    so if i take out the reimplementation of updatePaindNode, then the paint function is called...

    some Idea how to call booth functions? i want to render text with the QPainter, but draw lines with QSG classes...



  • [quote author="aabc" date="1410860899"]We don't want to use QQuickPaintedItem, We want to use QQuickItem[/quote]

    I know, i also want to use QQuickItem, but i think if it is possible, then only with QQuickPaintedItem, if you have an idea, how to render text with QQuickItem, then is perfect, do you have?

    greetings Tom



  • reading the qt 5.4 documentation, and maybe the "QOpenGLWidget":http://doc-snapshot.qt-project.org/qt5-5.4/qopenglwidget.html#details
    is a good way.
    i read, that it is possible to construct a QPainter to draw primitives and render text...

    "this":http://blog.qt.digia.com/blog/2014/09/10/qt-weekly-19-qopenglwidget/ is also a good article about the good old QGL classes, that i use in the moment... :-( because it is new for me, and unluckily it is old and deprecated...



  • I think i found a way... :-)

    here is a blog post how to render with QPainter in an QImage or FBO...
    "http://dangelog.wordpress.com/2013/02/10/using-fbos-instead-of-pbuffers-in-qt-5-2/":http://dangelog.wordpress.com/2013/02/10/using-fbos-instead-of-pbuffers-in-qt-5-2/

    With this you can make a FBO and render text with QPainter in it...

    Then you take the FBO or the QImage and create a QSGSimpleTextureNode
    "http://qt-project.org/doc/qt-5/qsgsimpletexturenode.html#setTexture":http://qt-project.org/doc/qt-5/qsgsimpletexturenode.html#setTexture

    with setTexture you can set the texture to it... and just append the QSGSimpleTextureNode as child to your other node, and thats it :-) i hope...

    I will try it on monday... and report if it works...



  • Hi, I'm having this problem also.

    I need to render a text on my custom geometry, I don't want to use QPainter because of the blurry text issue in iOS (using QQuickPaintedItem class).

    Please advise. TIA.



  • I need it too, because performance.
    I looked at Qt's source code (qquicktextnode.cpp) and I found following lines. Perhaps it helps someone...

    QSGGlyphNode *QQuickTextNode::addGlyphs(const QPointF &position, const QGlyphRun &glyphs, const QColor &color,
                                     QQuickText::TextStyle style, const QColor &styleColor,
                                     QSGNode *parentNode)
    {
        QSGRenderContext *sg = QQuickItemPrivate::get(m_ownerElement)->sceneGraphRenderContext();
        QRawFont font = glyphs.rawFont();
        bool preferNativeGlyphNode = m_useNativeRenderer;
        if (!preferNativeGlyphNode) {
            QRawFontPrivate *fontPriv = QRawFontPrivate::get(font);
            if (fontPriv->fontEngine->hasUnreliableGlyphOutline())
                preferNativeGlyphNode = true;
            else
                preferNativeGlyphNode = !QFontDatabase().isSmoothlyScalable(font.familyName(), font.styleName());
        }
    
        QSGGlyphNode *node = sg->sceneGraphContext()->createGlyphNode(sg, preferNativeGlyphNode);
    
        node->setOwnerElement(m_ownerElement);
        node->setGlyphs(position + QPointF(0, glyphs.rawFont().ascent()), glyphs);
        node->setStyle(style);
        node->setStyleColor(styleColor);
        node->setColor(color);
        node->update();
    
        /* We flag the geometry as static, but we never call markVertexDataDirty
           or markIndexDataDirty on them. This is because all text nodes are
           discarded when a change occurs. If we start appending/removing from
           existing geometry, then we also need to start marking the geometry as
           dirty.
         */
        node->geometry()->setIndexDataPattern(QSGGeometry::StaticPattern);
        node->geometry()->setVertexDataPattern(QSGGeometry::StaticPattern);
    
        if (parentNode == 0)
            parentNode = this;
        parentNode->appendChildNode(node);
    
        return node;
    }


  • I'm making a custom QQuickItem too. And it needs to accept a delegate that'll appear in the specific position.

    So, is it the right solution to expose a QRect property and do a QML wrapper that creates and positions that sub-item with a Loader?

    Or it's somehow possible to attach other items directly to one of QSGNode of a custom QQuickItem?



  • @Alexey the only way is to use QQuickText and use private classes


Log in to reply
 

Looks like your connection to Qt Forum was lost, please wait while we try to reconnect.