How to draw polyline using vector computed from another class

[PXMYH]

Hi,

I am having trouble draw a polyline from a vector of QPointF which is calculated in another class "getAvgHighTempVec".

Here is my code:

// main.cpp
    size_t qpoint_size = c.getAvgHighTempVec().size();
    QVector<QPointF> points(qpoint_size);
 
    for(size_t i=0; i < qpoint_size; i++){
       points[i].setX(i);
       points[i].setY(c.getAvgHighTempVec().at(i));
     }
 
    weatherStationGUI.draw(points);

// main.cpp
    size_t qpoint_size = c.getAvgHighTempVec().size();
    QVector<QPointF> points(qpoint_size);

    for(size_t i=0; i < qpoint_size; i++){
       points[i].setX(i);
       points[i].setY(c.getAvgHighTempVec().at(i));
     }

    weatherStationGUI.draw(points);

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//weatherstationgui.h
namespace Ui {
class weatherstationgui;
}
class weatherstationgui : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit weatherstationgui(QWidget *parent = 0);
    ~weatherstationgui();
 
    void draw( QVector<QPointF>  dataIn);
 
private:
    Ui::weatherstationgui *ui;
 
    QVector<QPointF>  wellData;
 
protected:
    // paint method
    void paintEvent(QPaintEvent *event);
};

//weatherstationgui.h
namespace Ui {
class weatherstationgui;
}
class weatherstationgui : public QMainWindow
{
    Q_OBJECT

public:
    explicit weatherstationgui(QWidget *parent = 0);
    ~weatherstationgui();

    void draw( QVector<QPointF>  dataIn);

private:
    Ui::weatherstationgui *ui;

    QVector<QPointF>  wellData;

protected:
    // paint method
    void paintEvent(QPaintEvent *event);
};

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//weatherstationgui.cpp
void weatherstationgui::draw(QVector<QPointF>  dataIn){
   wellData = dataIn;
   update();
}
 
void weatherstationgui::paintEvent(QPaintEvent *event){
 
    // create a painter
    QPainter painter(this);
 
    painter.drawPolyline(wellData.data(), static_cast<int>(wellData.size()));
}

//weatherstationgui.cpp
void weatherstationgui::draw(QVector<QPointF>  dataIn){
   wellData = dataIn;
   update();
}

void weatherstationgui::paintEvent(QPaintEvent *event){

    // create a painter
    QPainter painter(this);

    painter.drawPolyline(wellData.data(), static_cast<int>(wellData.size()));
}

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In the debugger I can see 'wellData' indeed has the correct QPointF points values, but it just doesn't draw on the main window.

Is there anything wrong with my code?

Thanks

[ChrisW67]

What are typical values in the points array? As you have presented it these values will be treated as equivalent to pixel coordinates.

[PXMYH]

yes, you are absolutely right. The values stored in the vector points are the coordinates. It looks like { (1.6, 0) , (2.3, 1) ...} in debugger.

[ChrisW67]

Your points are being drawn in a few pixels in the top left of the window. You need to scale the values yourself or use a transform on the painter to do it for you.
See Coordinate transforms

[PXMYH]

Thank you Chris! its been there all the time but I chose to ignore it