A question about coordinate transform

[lazy_learner]

I reimplement the mousePressEvent and use QwtPlot::invTransform to transform the coordinate.But it don't work as I expected.


void plot :: mousePressEvent(QMouseEvent *e)
{
if(e->button() == Qt::LeftButton)
{
QPointF temp = e->posF();
QMessageBox::information(this,tr("information!"),tr("the original x posation is %1 and y posation is %2").arg(temp.x()).arg(temp.y()),QMessageBox::Ok|QMes sageBox::Default,QMessageBox::NoButton,QMessageBox ::NoButton);
//picker->invTransform()
temp.setX(this->invTransform(QwtPlot::xBottom,temp.x()));
temp.setY(this->invTransform(QwtPlot::yLeft,temp.y()));

QMessageBox::information(this,tr("information!"),tr("changed x posation is %1 and y posation is %2").arg(temp.x()).arg(temp.y()),QMessageBox::Ok|QMes sageBox::Default,QMessageBox::NoButton,QMessageBox ::NoButton);

}

}


well , it look just like 90569057

but the real coordinate in the axis is is not x=688.05 and y=553.371

[lazy_learner]

Can anyone help me ?

[lanz]

Your code seems correct to me.
How do you know that x=688.05 and y=553.371 isn't correct values?
Post a screenshot maybe where it is clearly visible, it may give a pointer.
Also it helps if you attach minimal compilable project.

[lazy_learner]

because the value on the QwtPlotpicker donesn't is not 688.05 553.371... wait a moment , I 'll post a screenshot...

Added after 1 41 minutes:

906590669066

[Uwe]

Wrong widget: canvas != plot.

You have to install an event filter for the canvas - or with Qwt 6.1 you can overload the mouse event handler of it. If you want to keep your code you have to translate the coordinates of the mouse click into coordinates that are relative to the canvas - f.e. with mapToGlobal() and mapFromGlobal() - or simply by subtracting the position of the canvas.

Uwe

[lazy_learner]

yes ,you're right. In the first version of my program. I solved this problem by subtract a certain value , but I don't know why and how it happen.Er.. But how can I know the position of the canvas ?

[Uwe]

Use QWidget::pos() or QWidget::geometry() - the canvas is a child of the plot widget.

Uwe

[lazy_learner]

thank you~you're very helpful~