How to change tooltip when using THttpServer

[zsh0327]

When I use THttpServer to show our histogram, I want to reverse the yaxis. But I still hope that the data can be reversed at the same time. How should we do?

My code is here:

void ReverseXAxis(TH1 *h)
{
   // Remove the current axis
   h->GetXaxis()->SetLabelOffset(999);
   h->GetXaxis()->SetTickLength(0);
 
   // Redraw the new axis
   gPad->Update();
   TGaxis *newaxis = new TGaxis(gPad->GetUxmax(),
                                gPad->GetUymin(),
                                gPad->GetUxmin(),
                                gPad->GetUymin(),
                                h->GetXaxis()->GetXmin(),
                                h->GetXaxis()->GetXmax(),
                                510,"-");
   newaxis->SetLabelOffset(-0.03);
   newaxis->Draw();
}
 
void ReverseYAxis(TH1 *h)
{
   // Remove the current axis
   h->GetYaxis()->SetLabelOffset(999);
   h->GetYaxis()->SetTickLength(0);
 
   // Redraw the new axis
   gPad->Update();
   TGaxis *newaxis = new TGaxis(gPad->GetUxmin(),
                                gPad->GetUymax(),
                                gPad->GetUxmin()-0.001,
                                gPad->GetUymin(),
                                h->GetYaxis()->GetXmin(),
                                h->GetYaxis()->GetXmax(),
                                510,"+");
   newaxis->SetLabelOffset(-0.03);
   newaxis->Draw();
}
int main()
{
    gStyle->SetOptStat(0);

    TH2F *hpxpy  = new TH2F("hpxpy","py vs px",40,-4,4,40,-4,4);
    TCanvas *c1 = new TCanvas("c1");

    THttpServer *serv = new THttpServer("http:6666");
    serv->Register("/", c1);
    serv->SetItemField("/","_monitoring","1000");
    while(1)
    {
        gSystem->ProcessEvents();
        // gettimeofday(&current_time, NULL);
        
        {  
            c1->cd(1);
            hpxpy->Reset();
            Float_t px, py;
            TRandom r;
            for (Int_t i = 0; i < 25000; i++) {
                r.Rannor(px,py);
                hpxpy->Fill(px,py);
            }
            hpxpy->Draw("colz");
            ReverseXAxis(hpxpy);
            ReverseYAxis(hpxpy);
        }
        
    }
    return 0;
}

ROOT Version: 6.24/06
Platform: Centos7.9
Compiler: gcc8

---

[linev]

Hi,

You do not need to use TGaxis for display of reversed axes.
JSROOT which is used for drawing of histograms by THttpServer, just natively supports
reverse axis by “rx_ry” draw option:

JSROOT examples

Tooltips will work properly then.

Regards,
Sergey

[linev]

Also it is not necessary to call hpxpy->Draw("colz"); in the loop.
Once histogram drawn on the canvas - it can be used by THttpServer.
And one just need to fill that histogram.

[zsh0327]

Thank you. I got it.
I hava another question. If I want to show the histogram in Gray Scale Imag when using TH2F. How should I do?
Such as the following picture in python.

[linev]

Hi,

You can select palete code for color drawing in the options like “col_pal52”. Code for grey color palete is 52.

Of course, you can combine all options together: “col_rx_ry_pal52”

Regards,
Sergey

[linev]

Here is list of colors palette implemented in the ROOT:

https://root.cern/doc/master/classTColor.html#C05

[zsh0327]

Thank you very much. I got it.