problem with Qpainter being too slow (Maemo5)

[asdf]

Hi,

I have this problem with QPainter. I'm making widget that has many lines and dots. Problem is that it's realy slow.

I trying to make scrollable widget that's in QScrollArea. Here is a example picture how it looks on Maemo5:



In mainwindow.cpp I have scrollArea and I put my widget in to it by:

PainterWidget *mypainterWidget = new PainterWidget(ui->scrollArea);
ui->verticalLayout->addWidget(mypainterWidget);

PainterWidget *mypainterWidget = new PainterWidget(ui->scrollArea);
ui->verticalLayout->addWidget(mypainterWidget);

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In PainterWidget I have paintEvent like this:

void PainterWidget::paintEvent(QPaintEvent *)
{
 
    QPainter painter2(this);
    painter2.setRenderHint(QPainter::Antialiasing, true);
    painter2.setPen(QPen(Qt::white, 1, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
    QPainter painter3(this);
    painter3.setRenderHint(QPainter::Antialiasing, true);
    painter3.setPen(QPen(QColor(198,0,0,255), 1, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
 
    QPainterPath path;
 
    for(int i=0 ; i<30;i++){
 
        if(i>0){
            path.moveTo(col[i-1]+5, row[i-1]+5);
            path.cubicTo(col[i-1]+5, row[i-1]+5, ((col[i-1]+col[i])/2), ((row[i-1]+row[i])/2), col[i], row[i]+5);
 
            painter3.drawPath(path);
 
        }
 
    }
 
 
    for(int i=0 ; i<30;i++){  
 
        painter.drawEllipse(col[i], row[i], 10, 10);
 
    }
 
}

void PainterWidget::paintEvent(QPaintEvent *)
{

    QPainter painter2(this);
    painter2.setRenderHint(QPainter::Antialiasing, true);
    painter2.setPen(QPen(Qt::white, 1, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
    QPainter painter3(this);
    painter3.setRenderHint(QPainter::Antialiasing, true);
    painter3.setPen(QPen(QColor(198,0,0,255), 1, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));

    QPainterPath path;

    for(int i=0 ; i<30;i++){

        if(i>0){
            path.moveTo(col[i-1]+5, row[i-1]+5);
            path.cubicTo(col[i-1]+5, row[i-1]+5, ((col[i-1]+col[i])/2), ((row[i-1]+row[i])/2), col[i], row[i]+5);

            painter3.drawPath(path);

        }

    }


    for(int i=0 ; i<30;i++){  

        painter.drawEllipse(col[i], row[i], 10, 10);

    }

}

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It's highly possible that I'm just doin something wrong here. Can someone help me with these information.

How can I make this to work faster?

[asdf]

Should I use some other kind of method?

Is it possible to draw image with QPainter and then set it into ScrollArea?

I have realy tried to make this work for a couple of days now but nothing works well..

[Talei]

Probably this is not the best advice, and I don't know if it will speed things up (never programmed to Maemo5), but try to draw into QImage and then display that QImage.

[asdf]

Finally I found a solution.

painter2.setRenderHint(QPainter::Antialiasing, true); is too heavy to use. Now it woks fine.