QQuickPaintedItem

narayanan.krish

Hello all !!!

I have a qml file on which I want to display the spectrum and the input for the player comes from qml.
I am trying to re-implement spectrum analyzer example (<Qt Dir>/examples/multimedia/spectrum) using
QQuickPaintedItem. I have re-implemented Paint instead of paintEvent and made following changes :

But bars are not changing. Can some one help me to fix this.

@
void SpectrographQML::paint(QPainter *painter)
{
//m_bars.resize(10);
const int numBars = 10;
painter->fillRect(contentsBoundingRect(), Qt::black);

QColor barColor(51, 204, 102);
QColor clipColor(255, 255, 0);

// Draw the outline
const QColor gridColor = barColor.darker();
QPen gridPen(gridColor);
painter->setPen(gridPen);
 painter->drawLine(contentsBoundingRect().topLeft(), contentsBoundingRect().topRight());
 painter->drawLine(contentsBoundingRect().topRight(), contentsBoundingRect().bottomRight());
 painter->drawLine(contentsBoundingRect().bottomRight(), contentsBoundingRect().bottomLeft());
 painter->drawLine(contentsBoundingRect().bottomLeft(), contentsBoundingRect().topLeft());

QVector<qreal> dashes;
dashes << 2 << 2;
gridPen.setDashPattern(dashes);
painter->setPen(gridPen);

// Draw vertical lines between bars
if (numBars) {
    const int numHorizontalSections = 10;
    QLine line1(contentsBoundingRect().toAlignedRect().topLeft(), contentsBoundingRect().toAlignedRect().bottomLeft());
    for (int i=1; i<numHorizontalSections; ++i) {
        line1.translate(contentsBoundingRect().width()/numBars, 0);
        painter->drawLine(line1);
    }
}

// Draw horizontal lines
const int numVerticalSections = 10;
QLineF line(contentsBoundingRect().topLeft(), contentsBoundingRect().topRight());
for (int i=1; i<numVerticalSections; ++i) {
    line.translate(0, contentsBoundingRect().height()/numBars);
    painter->drawLine(line);
}
    // Calculate width of bars and gaps
    const int widgetWidth = boundingRect().width();
    const int barPlusGapWidth = widgetWidth / numBars;
    const int barWidth = 0.8 * barPlusGapWidth;
    const int gapWidth = barPlusGapWidth - barWidth;
    const int paddingWidth = widgetWidth - numBars * (barWidth + gapWidth);
    const int leftPaddingWidth = (paddingWidth + gapWidth) / 2;
    const int barHeight = boundingRect().height() - 2 * gapWidth;

    for (int i=0; i<numBars; ++i) {
        qreal value = m_bars[i].value; // value is always zero, not updating ...
        Q_ASSERT(value >= 0.0 && value <= 1.0);
        QRectF bar = contentsBoundingRect();
        bar.setLeft(boundingRect().left() + leftPaddingWidth + (i * (gapWidth + barWidth)));
        bar.setWidth(barWidth);
        bar.setTop(boundingRect().top() + gapWidth + (1.0 - value) * barHeight);
        bar.setBottom(boundingRect().bottom() - gapWidth);

        QColor color = barColor;
        if (m_bars[i].clipped)
            color = clipColor;
       painter->fillRect(bar, color);
    }

}
@

Thanks & Regards,
Narayanan K

p3c0

Hi,

paint() needs to called when ever your data changes unlike paintevent().
Use a QTimer to update it and make sure the data is changing or else it will just paint the same thing.