Help: How to add QwtPlotMarker at a FIX position?

[jwieland]

Hi,

I have a plot (derived from the bode example) that can plot multiple curves. I am trying to put legends on either upper left or upper right corner of the canvas to show the name and color of each curve using QwtPlotMarker. Once I added the legends, I want them to stay exactly at the same location but couldn't make it work. Every time user zoom in/out, the legends position changes (sometime out of display), Or every time user append a new curve, the scale changes and the legend position also change

Is there anyway to make the legends appear at a fixed place on the canvas? Is QwtPlotMarker the right way to use (I want a color line with text next to it to show the name of the curve and the color of the curve)?

Thank so much for all your help.

[FelixB]

there is a simple solution: use the other axes for the markers! Your zoomer zooms QwtPlot::xBottom/QwtPlot::yLeft. QwtPlot::xTop/QwtPlot::yRight remain unchanged. Now you set a simple scale fot xTop/yRight and set the values for your markers depending on these scales.

hope this helps
Felix

[jwieland]

Thanks, Felix, for you response. Unfortunately I use both Y-axes for my plot (to plot main curves and their corresponding integrals). Your input is highly appreciated though.

Any other?

[jwieland]

Anybody, please?

[FelixB]

ok, next idea: you have to work with canvas pixel.

first, you have to find the pixel position where your legend should appear (remember: in pexels, (0/0) is top-left)
second, translate this position into axis values using qwtplot::transform or qwtplot::invtransform (sorry, I'm always confused which one translates in which direction...)
third, do second step after each zoom (the zoomer emits a "zoomed(...)"-signal which you can connect to a custom slot)

have fun
Felix

[Uwe]

Check the CpuPieMarker from the cpuplot example. Instead of the pie draw your legend.

Uwe