DrawLine using QPaintedItem is not proper

[Ajay Krishna]

Hi ,
I am trying to draw wave forms using QPaintedItem with drawLine .
When i try to draw continuous line with real time data i can see some pixels are getting missed .

With same data if i draw using charview (lineseries,valueAxis) drawing is perfect.

can somebody help what can be issue ? Should i set anything before drawing ?

I am using QPen to draw right now .

Thanks in advance .

[mrjj]

Hi
Its hard to guess at with no code but
maybe its due to double to int capping and not doing rounding.

Can you show your draw code ?

[Ajay Krishna]

void DrawGraph::updateGraph(qreal x, qreal y)
{
QPointF newpoint(xPlotPosition,yPlotPosition);
line = QLineF(lastPoint, newpoint);
lastPoint = newpoint;

rect.setRect(newpoint.x()-2,yGraphStartPixel,30,this->height());
update(rect);

}

void DrawGraph::paint(QPainter *painter)
{
this->drawGraph(painter);
}

void DrawGraph::drawGraph(QPainter *painter)
{
painter->setPen(QPen(Qt::green,2));

painter->drawLine(line); // QLineF line;

}

[mrjj]

Hi
Seems fine
what types are xPlotPosition,yPlotPosition ?

[Ajay Krishna]

xPlotPosition and yPlotPosition are qreal type

[mrjj]

@Ajay-Krishna

I would inspect newpoint.x() and see how much its truncated
comapred to the xPlotPosition

Also maybe turn on antialiasing for QPainter

but it really looks like it get truncated.