[Interest] Plotting 2d line with color depending on value (like colormap)

[Massimiliano Maini]

Thx Jason, this looks exactly what I need.

But I guess adding this to QCustomPlot library is beyond what I could do.
I'm left with asking for it to be implemented by the author.

Cheers !

On Thu, 21 Jun 2018 at 17:11, Jason H <jhihn at gmx.com> wrote:

> You'll have to write code, but it's not that hard.
>
> Pens don't know about where they are on the painted surface.
> Painters do know where they are drawing, and they use the pen, so the code
> using the painter has to do it.
>
> QPainter painter
>
> double range = max-min;
>
> for (const auto &segment :segments) {
> double y_hue=(((segment.y1+segment.y2)/2) - min) / range;
> QColor color= QColor::fromHSFV( y_hue,1,1);
> painter.setPen(color);
> painter.drawLine(segment.x1, segment.y1, segment.x2, segment.2);
> }
>
> or somehing like that.
>
>
> *Sent:* Thursday, June 21, 2018 at 10:20 AM
> *From:* "Massimiliano Maini" <maxmaini at gmail.com>
> *To:* jhihn at gmx.com
> *Cc:* interest at qt-project.org
> *Subject:* Re: [Interest] Plotting 2d line with color depending on value
> (like colormap)
> Thanks Uwe and Jason.
>
> At the moment I'm using a 3rd party library (http://www.qcustomplot.com/):
> very handy but doesn't seem to support what I need.
> I was wondering if I the feature could be easily added as it is easily
> doable in Qt (as in "there's a special QPen to do this") or not.
> Looks like the answer is NO.
>
> Regards,
>
> On Thu, 21 Jun 2018 at 15:42, Jason H <jhihn at gmx.com> wrote:
>
>> It's a simple mapping of y value to "H" in a HSV space over the
>> normalized range of values.
>>
>> To do it in a bitmap is easy, to do it as a line like you 'd want on a
>> vector plot, i'd take the y midpoint value of the segment and use that for
>> the pen color for the whole line, choosing a sensible number of points.
>>
>>
>>
>>
>>
>> *Sent:* Thursday, June 21, 2018 at 5:51 AM
>> *From:* "Massimiliano Maini" <maxmaini at gmail.com>
>> *To:* interest at qt-project.org
>> *Subject:* [Interest] Plotting 2d line with color depending on value
>> (like colormap)
>> Hi all,
>>
>> I'd need to do something like this: https://imgur.com/MLAEuad
>>
>> I have a set of (x,y,z) data points and want to plot them on a usual 2d
>> plot ( x and y values), but with the line color depending on the z values
>> (colormap).
>>
>> How can this be achieved in Qt ?
>>
>> Max.
>>
>>
>> _______________________________________________ Interest mailing list
>> Interest at qt-project.org
>> http://lists.qt-project.org/mailman/listinfo/interest
>>
>
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