Qwt : QwtPlotZoomer with Qt 6.0.1, fixed grid

[lionel.s]

Hello,

I try to have a zoom function which doesn't change the grid display. Major ticks have to stay on the same position. If I use QwtPlotZoomer with function zoom(QRect) the display of the grid is different.
So I have reimplement the QwtPlotZoomer::zoom(QRect) function and add this code :

float spaceX = (float)pRect.width()/5;
    float spaceY = (float)pRect.height()/10;
 
    QList<double> majorTicksX;
    QList<double> majorTicksY;
    for(int i=0; i<11; i++)
    {
        if(i<6)
            majorTicksX.append(pRect.x() + spaceX*i);
 
        majorTicksY.append(pRect.y() + spaceY*i);
    }
 
    QwtScaleDiv divX;
    divX.setInterval(double(pRect.x()), double(pRect.x() + spaceX*5));
    divX.setTicks(QwtScaleDiv::MajorTick, majorTicksX);
    QwtScaleDiv divY;
    divY.setInterval(double(pRect.y()), double(pRect.y() + spaceY*10));
    divY.setTicks(QwtScaleDiv::MajorTick, majorTicksY);
 
    plot()->setAxisScaleDiv(QwtPlot::xBottom, divX);
    plot()->setAxisScaleDiv(QwtPlot::yLeft, divY);
 
    static_cast<YourScaleDraw*>(plot()->axisScaleDraw(QwtPlot::xBottom))->min = pRect.x();
    static_cast<YourScaleDraw*>(plot()->axisScaleDraw(QwtPlot::xBottom))->max = pRect.x()+ spaceX*5;
 
    plot()->replot();

float spaceX = (float)pRect.width()/5;
    float spaceY = (float)pRect.height()/10;

    QList<double> majorTicksX;
    QList<double> majorTicksY;
    for(int i=0; i<11; i++)
    {
        if(i<6)
            majorTicksX.append(pRect.x() + spaceX*i);

        majorTicksY.append(pRect.y() + spaceY*i);
    }

    QwtScaleDiv divX;
    divX.setInterval(double(pRect.x()), double(pRect.x() + spaceX*5));
    divX.setTicks(QwtScaleDiv::MajorTick, majorTicksX);
    QwtScaleDiv divY;
    divY.setInterval(double(pRect.y()), double(pRect.y() + spaceY*10));
    divY.setTicks(QwtScaleDiv::MajorTick, majorTicksY);

    plot()->setAxisScaleDiv(QwtPlot::xBottom, divX);
    plot()->setAxisScaleDiv(QwtPlot::yLeft, divY);

    static_cast<YourScaleDraw*>(plot()->axisScaleDraw(QwtPlot::xBottom))->min = pRect.x();
    static_cast<YourScaleDraw*>(plot()->axisScaleDraw(QwtPlot::xBottom))->max = pRect.x()+ spaceX*5;

    plot()->replot();

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Class YourScaleDraw

class YourScaleDraw: public QwtScaleDraw
{
public:
    virtual QwtText label( double v ) const
    {
        if(alignment() == LeftScale)
        {
            return QwtScaleDraw::label( int( v ) );
        }
        else if(alignment() == BottomScale)
        {
            return QwtScaleDraw::label(v);
        }
    }
 
    virtual void drawLabel(QPainter* painter, double value) const
    {
        if(value == min && alignment() == BottomScale)
        {
            QRect boundingRect = boundingLabelRect(painter->font(), value);
            boundingRect.setX(boundingRect.x() + boundingRect.width()/2);
            boundingRect.setWidth(boundingRect.width()*2);
            painter->fillRect(boundingRect, QColor(Qt::darkRed));
            painter->drawText(boundingRect, Qt::AlignLeft, label(value).text());
        }
        else if(value == max && alignment() == BottomScale)
        {
            QRect boundingRect = boundingLabelRect(painter->font(), value);
            boundingRect.setX(boundingRect.x() - boundingRect.width()/2);
            boundingRect.setWidth(boundingRect.width() - boundingRect.width()/2);
            painter->fillRect(boundingRect, QColor(Qt::darkRed));
            painter->drawText(boundingRect, Qt::AlignLeft, label(value).text());
        }
        else
        {
            QRect boundingRect = boundingLabelRect(painter->font(), value);
            painter->fillRect(boundingRect, QColor(Qt::darkRed));
            painter->drawText(boundingRect, Qt::AlignLeft, label(value).text());
        }
    }
 
    double min, max;
};

class YourScaleDraw: public QwtScaleDraw
{
public:
    virtual QwtText label( double v ) const
    {
        if(alignment() == LeftScale)
        {
            return QwtScaleDraw::label( int( v ) );
        }
        else if(alignment() == BottomScale)
        {
            return QwtScaleDraw::label(v);
        }
    }

    virtual void drawLabel(QPainter* painter, double value) const
    {
        if(value == min && alignment() == BottomScale)
        {
            QRect boundingRect = boundingLabelRect(painter->font(), value);
            boundingRect.setX(boundingRect.x() + boundingRect.width()/2);
            boundingRect.setWidth(boundingRect.width()*2);
            painter->fillRect(boundingRect, QColor(Qt::darkRed));
            painter->drawText(boundingRect, Qt::AlignLeft, label(value).text());
        }
        else if(value == max && alignment() == BottomScale)
        {
            QRect boundingRect = boundingLabelRect(painter->font(), value);
            boundingRect.setX(boundingRect.x() - boundingRect.width()/2);
            boundingRect.setWidth(boundingRect.width() - boundingRect.width()/2);
            painter->fillRect(boundingRect, QColor(Qt::darkRed));
            painter->drawText(boundingRect, Qt::AlignLeft, label(value).text());
        }
        else
        {
            QRect boundingRect = boundingLabelRect(painter->font(), value);
            painter->fillRect(boundingRect, QColor(Qt::darkRed));
            painter->drawText(boundingRect, Qt::AlignLeft, label(value).text());
        }
    }

    double min, max;
};

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But this is not working with Qwt 6.0.1 but it is working with Qwt 6.1.0.

What can I do to make it work with Qwt 6.0.1.

Thanks
Lionel

[Uwe]

What about disabling QwtPlotItem::ScaleInterest for your grid item - at least once you have your initial setup ?

Uwe

[lionel.s]

It is an Histogram and I'm drawning data with a reimpl of drawColumn from QwtPlotHistogram.

I'm trying to zoom -> change the x and y axis so the grid doesn't change. I always need 5 major ticks on the bottom axis and 10 on the left axis. But they should not move. Only the value of each ticks may change. Well it works with the Qwt 6.1.0 but the customer don't want to use another version than the 6.0.1. I don't use QwtPlotItem.

Is it possible with Qwt 6.0.1 to have a fixe grid ?

[Uwe]

Instead of overloading QwtPlotZoomer::zoom() better overload QwtLinearScaleEngine::divideScale() - this is the right place for your first code snippet !
The motivation behind the second seems to be to right/left align the min/max tick label, to avoid the extra space at the borders ?

Which of your code snippets doesn't work with Qwt 6.0 ?

Uwe