a few questions about using QwtMatrixRasterData (and other classes)

this component is very useful for my circle of tasks
but I need to change something and don't know how to do that exactly.

1. we have z-(color)-scale with gradient
Attachment 8795
I have 4 colors.
in my case it's very necessary to have only clear colors without smooth gradient between each color.
can I achieve it with this component? and how... may be try another alternative?


2. Also got it from example - possibility of hint
Attachment 8796

code:

Code:

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class MyZoomer: public QwtPlotZoomer {
 
public:
    MyZoomer( QwtPlotCanvas *canvas ):
        QwtPlotZoomer(canvas) {
        setTrackerMode(AlwaysOn);
    }
 
    virtual QwtText trackerTextF(const QPointF &pos) const {
        QColor bg(Qt::white);
        bg.setAlpha(200);
 
        QwtText text = QwtPlotZoomer::trackerTextF(pos);
        text.setBackgroundBrush(QBrush(bg));
        return text;
    }
};

---

hereby we have coordinates in the hint near cursor (x, y)
how to add here the third value of z axis?


3. How to disable zooming out below a certain value (for example when the pic fit to width)?
example:
here in the picture good variant
Attachment 8797

and here - not appropriate
Attachment 8798


thanks a lot!

Quote:

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I have 4 colors. in my case it's very necessary to have only clear colors without smooth gradient between each color.
can I achieve it with this component? and how... may be try another alternative?

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How to map values to colors is the job of the color map. You can write your own one, but I guess setting QwtLinearColorMap::FixedColors mode is all what needs to be done.

Quote:

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hereby we have coordinates in the hint near cursor (x, y)
how to add here the third value of z axis?

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pos is the position in plot coordinates. All you need to do is to ask the matrix raster data object for the z value at the position.

Quote:

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How to disable zooming out below a certain value (for example when the pic fit to width)?

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Depends on how you have implemented zooming.

F.e. QwtPlotZoomer never zooms out of the initial scale ranges, that have been set by the application. Here the answer would be simply: don't assign scale ranges you don't want to have.

Uwe

Quote:

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setting QwtLinearColorMap::FixedColors mode is all what needs to be done.

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oh, sorry, didn't noticed, right that's what I need!

the second: I got it (z value) through the value() method of QwtMatrixRasterData as you told me, thanks!

and the third:

class MyZoomer - that's all I have about implemented zooming.
and it seems I didn't assign scale ranges anywhere at all.
how can I do it?
is the method setZoomBase() helpful in this case?

Quote:

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Originally Posted by layer

and it seems I didn't assign scale ranges anywhere at all.
how can I do it?

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QwtPlot::setAxisScale().

Uwe

thank you Uwe!

:) all that I needed to do for the last question is write these few lines:

Code:

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QwtPlotMagnifier *magnifier = new QwtPlotMagnifier(canvas());
magnifier->setAxisEnabled(QwtPlot::xBottom, false);

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forbid zooming for x-axis, such pretty simple.
great Lib:)