How to draw text in QQuickItem?

Timmmm

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);

Timmmm

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...

Mephisto

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

Mephisto

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...

maksim1979

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

aabc

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

Mephisto

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...

Mephisto

[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

Mephisto

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...

Mephisto

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...

literA2

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.

seyed

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;
}

devel

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?

vladstelmahovsky

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