Markers and their fast display on plot

[carhun]

Hello!

I want to know what I can do with next problem...

I have a lot of curves ( that are brushed/solid ) and I want to display values ( Y ) in some point pos.x() of the QwtPlot.
For displaying I am using QwtPlotMarker's.

But it is work to slowly display when I drag mouse and program need to recalculate and replot QwtPlot.

So can I do in this situation?
As I understand that problem is with function replot().... There is hard for program to do replot() with a lot of brushed/solid curves...
And as I understand without replot() I can't display QwtPlotMarker...

And another one question:
I can do that marker will show in brushed rectangle, but how i can do that marker will show in f.e. circle?

[Spitfire]

You could create transparent plot without axes, stack it on top of the current plot and attach all markers to this one.
reploting it will be much faster.

You also re-engineer plotting to re-plot only affected part of the plot, not whole plot.

You could create simple transparent overlay on which you would draw your markers (not qwtplotmarker) and interact with them.

Qwt could greatly benefit from layered approach.
Items that change more offten should be put in different (foreground) layer than those more static objects.
Reploting layer of markers would be much faster than reploting all markers and curves on the plot.

[Uwe]

Qwt could greatly benefit from layered approach.
Items that change more offten should be put in different (foreground) layer than those more static objects.

Qwt has this layered approach - the z value of the plot items. You can easily introcuce a cache for plot items below a certain z value by overloading QwtPlot::drawItems.

Uwe

[Spitfire]

That's what I meant.
I know about the z-value but there's no out-of-the-box way of doing it.
I'm not saying it can't be done, I'm just suggesting that it would be nice out-of-the-box feature

[carhun]

Qwt has this layered approach - the z value of the plot items. You can easily introcuce a cache for plot items below a certain z value by overloading QwtPlot::drawItems.

Uwe

Is it example of this?

[Uwe]

That's what I meant.
I know about the z-value but there's no out-of-the-box way of doing it.
I'm not saying it can't be done, I'm just suggesting that it would be nice out-of-the-box feature

I usually prefer to use overlay widgets, because with this technique Qt calculates optimized update regions, what results in a better performance - important for user interactions. On fast multicore systems this might be neglectable, but on many other systems it will be significant.

In SVN trunk you find a new class QwtPlotOverlay that was made for this use case. You also find a new example called itemeditor, that shows how to implement an editor that drags objects on the plot canvas.

Uwe