[hist] Allow to customize pads layout for THStack and TMultiGraph

[rlalik]

When using PADS drawing option, now one can add number specyfiing number of columns for new pads layout. Rows will be calculated autmatically.

Some examples:

auto make_hist(const char * name, const char * title, const char * f, int n_data) -> TH1I* {
    const int grad = 4;

    auto h = new TH1I(name, title, 20, -5, 5);

    for (int i = 0; i < n_data; ++i) {
        h->FillRandom(f, n_data);
    }
    h->SetLineColor(1);

    return h;
}

void demo() {
    gStyle->SetPalette(kRainBow);

    auto h1 = make_hist("Grupa 1", "Grupa 1;Punkty;Liczba", "gaus", 190);
    auto h3 = make_hist("Grupa 3", "Grupa 3;Punkty;Liczba", "gaus", 200);
    auto h4 = make_hist("Grupa 4", "Grupa 4;Punkty;Liczba", "gaus", 170);

    auto hs = new THStack();

    hs->Add(h1, "");
    hs->Add(h3, "");
    hs->Add(h4, "");

    auto can = new TCanvas("can", "can", 800, 400);
    can->Divide(2, 1);

    can->cd(1);
    hs->Draw("pfc");

    can->cd(2);
    hs->Draw("PADS3");
}

When changing the last but one line to:

hs->Draw("PADS1");

and backward comaptibility:

hs->Draw("PADS");
// or
hs->Draw("PADS2");

Same for graphs:

{
   auto mg  = new TMultiGraph();

   auto gr1 = new TGraph(); gr1->SetMarkerStyle(20);
   auto gr2 = new TGraph(); gr2->SetMarkerStyle(21);
   auto gr3 = new TGraph(); gr3->SetMarkerStyle(23);
   auto gr4 = new TGraph(); gr4->SetMarkerStyle(24);

   Double_t dx = 6.28/100;
   Double_t x  = -3.14;

   for (int i=0; i<=100; i++) {
      x = x+dx;
      gr1->SetPoint(i,x,2.*TMath::Sin(x));
      gr2->SetPoint(i,x,TMath::Cos(x));
      gr3->SetPoint(i,x,TMath::Cos(x*x));
      gr4->SetPoint(i,x,TMath::Cos(x*x*x));
   }

   mg->Add(gr4,"PL");
   mg->Add(gr3,"PL");
   mg->Add(gr2,"*L");
   mg->Add(gr1,"PL");

   mg->Draw("A pmc plc pads3");
}

This does not work with --web=on (Web Canvas) but I am not good enough in JS to fix that. But PADS seems to not work nicely with the web interface anyway. Perhaps it could be fixed - PADS in general and PADSn for this PR. @linev could you help with that?

Checklist:

• tested changes locally
• updated the docs (if necessary)

This PR fixes #

[ferdymercury]

a bit related: #20770

[hageboeck]

Hello @rlalik,

that's a great initiative, thank you!

I added a few comments below, please let me know what you think.

Finally, because now we are touching it, would you agree that a short paragraph about the PADS drawing option would make sense for TMultiGraph? One could add it maybe to the TMultiGraph documentation. What do you think?

[rlalik]

Finally, because now we are touching it, would you agree that a short paragraph about the PADS drawing option would make sense for TMultiGraph? One could add it maybe to the TMultiGraph documentation. What do you think?

I added short documentation to TMultiGraph.

[hageboeck]

Thanks a lot! The update of the documentation is amazing. Let's build and see what the CI says!

Update: I think we can ignore the clang-format failure. Trying to format the doxygen comments does more harm than good, I believe.