How to redraw preserving axis settings

Newbie
,
1

Hello,
I am implementing a javascript dashboard which every second loads a .ROOT file and draws it in a div:

let isFirstDraw = true;
async function update(){
    let file = await JSROOT.openFile(`dashboard/resources/${relPath}`);
    let obj = await file.readObject("c");

    if (isFirstDraw) {
      await JSROOT.draw("drawing", obj);
    } else {
      await JSROOT.redraw("drawing", obj);
    }

    isFirstDraw = false;
}

I want the redrawing to persist information such as whether the axes are in log scale, how do I do so?

As part of my tests I tried using draw(dom, obj, "logy"), which correctly sets the y axis to log scale, however using redraw(dom, obj, "logy") resets the axis to linear scale. Is this meant to be the case? In general, how do I get settings for the current canvas (obj is a TCanvas) and then update them? For example, I was able to get the logy from:

const canvas = await draw(dom, obj)
const logY = canvas.getObject().fLogy;

but am not sure as to how I’d then update another canvas with this. For example, this is an idea I had, which didn’t work.

Object.assign(canvas.getObject(), {fLogy: logY})

For further information, this is the code that creates the plot:

npoints = data["num_entries"]

graph = ROOT.TGraph(npoints)

for i in range(npoints):
    t = data["timestamps"][i].timestamp()
    y = data["values"][i]
    graph.SetPoint(i, t, y)


c = ROOT.TCanvas("c", "Canvas", 800, 600)

graph.Draw("AP")

xaxis = graph.GetXaxis()
xaxis.SetTimeDisplay(1)
xaxis.SetTimeFormat("%Y-%m-%d %H:%M:%S")
xaxis.SetLabelSize(0.03)

c.Modified()
c.Update()

c.SaveAs(f'{output_file}')

Thanks in advance.

ROOT Version: 6.32.08
Platform: macosxarm64
Compiler: Apple clang 16.0.0

2

Hi @frezzonico

Welcome to the ROOT forum and thanks for your question.

I’m adding @linev in the loop

3

Hi,

If you are using TCanvas for drawing, log scale will be applied from the new instance of TCanvas in JSROOT.redraw call. It is possible to copy log scale attributes before calling redraw like:

const canv_painter = await draw(dom, obj);

...

new_obj.fLogy = canv_painter.getObject().fLogy;
await redraw(dom, new_object);

But you also can try to draw/redraw TGraph object. In such case TCanvas will be created and preserved by JSROOT - including log scale settings.

Regards,
Sergey