Problems with QwtPlotRenderer from Qwt 6

[mariposa]

I also have problems regarding the mapping of the elements when using custom PlotItems:

In my application I visualize found peaks by labels which are painted on the top part of the plot canvas. Therefore I created a class that inherits QwtPlotItem and I implemented the draw() function accordingly. On screen everything works fine and I like the result very much:

screenshot.jpg

Then I export the plot as graphics file using the following code:

QwtPlotRenderer renderer;
renderer.renderDocument(par->spectrum_plot, fileName, QSizeF(200, 150), 150);

QwtPlotRenderer renderer;
renderer.renderDocument(par->spectrum_plot, fileName, QSizeF(200, 150), 150);

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And that is the result:

exported.jpg

As you can see, the labels are aligned as if the plot still had screen resolution. The higher resolution of the output image is not taken into account. That's why the labels are displaced.

The problem with the much too small axis persists as well.

Does anyone have an idea how to solve this?

Many thanks in advance

[Uwe]

In my application I visualize found peaks by labels which are painted on the top part of the plot canvas. Therefore I created a class that inherits QwtPlotItem and I implemented the draw() function accordingly

Guess the implementation of your QwtPlotItem doesn't work together with painter transformations, that are enabled when painting to a paint device with a different resolution than the screen resolution.

But without knowing your code it is impossible to say more,

Uwe

[mariposa]

I can't paste the whole code for the peak labels since it is quite long. If anyone is interested nonetheless:
https://cutenmr.svn.sourceforge.net/.../peaklabel.cpp

I will instead paste snippets of a minimal example I created. I already expected that it is caused by my (wrong) implementation.

My minimal example is a straight red line that is painted from the top of the canvas to the 0 position of my y-axis. The x-position is "3" in the unit of the x-axis. This is a screenshot of the (expected) result:

screen2.jpg

I mainly used the code from the cpupiemarker example for implementing my QwtPlotItem:

First, I get the QwtScaleMap from my PlotWidget (which is part of a parameters object that I can easily pass to other objects):

QwtScaleMap xMap = par->spectrum_plot->canvasMap(QwtPlot::xBottom);
QwtScaleMap yMap = par->spectrum_plot->canvasMap(QwtPlot::yLeft);

QwtScaleMap xMap = par->spectrum_plot->canvasMap(QwtPlot::xBottom);
QwtScaleMap yMap = par->spectrum_plot->canvasMap(QwtPlot::yLeft);

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Then the code for drawing the line:

p->save();
p->setPen(QColor(Qt::red));
p->drawLine(QPointF(xMap.transform(3), 0), QPointF(xMap.transform(3), yMap.transform(0)));
p->restore();

p->save();
p->setPen(QColor(Qt::red));
p->drawLine(QPointF(xMap.transform(3), 0), QPointF(xMap.transform(3), yMap.transform(0)));
p->restore();

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And that's all you can find in my draw() function. Everything else is identical to the cpupiemarker example.

I attach the QwtPlotItem using this code:

peakLabel* pL = new peakLabel(par);
pL->attach(par->spectrum_plot);

peakLabel* pL = new peakLabel(par);
pL->attach(par->spectrum_plot);

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And the (unexpected) result of the exported image is:

export2.jpg

If you need other parts of the code to evaluate what my mistake is, just ask.

Many thanks

[Uwe]

First, I get the QwtScaleMap from my PlotWidget (which is part of a parameters object that I can easily pass to other objects):

Wrong maps - as long as you don't want to paint to the plot canvas widget. Instead you have to use the maps, that are passed as parameters f.e. to QwtPlotItem::draw().

Uwe

[mariposa]

Wrong maps - as long as you don't want to paint to the plot canvas widget. Instead you have to use the maps, that are passed as parameters f.e. to QwtPlotItem::draw().

Yes, that caused the problem of the displacement
I can't believe I missed something that obvious. Thank you very much

But the problem with the small axes and labels when using high resolutions persists.