hist016_TH1_different_scales_canvas.C

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/// \file
/// \ingroup tutorial_hist
/// \notebook
/// \preview Example of a canvas showing two histograms with different scales.
/// The second histogram is drawn in a transparent pad
///
/// \macro_image
/// \macro_code
///
/// \date November 2022
/// \author Rene Brun
 
void hist016_TH1_different_scales_canvas()
{
   TCanvas *c1 = new TCanvas("c1", "transparent pad", 200, 10, 700, 500);
   TPad *pad1 = new TPad("pad1", "", 0, 0, 1, 1);
   TPad *pad2 = new TPad("pad2", "", 0, 0, 1, 1);
   pad2->SetFillStyle(4000); // will be transparent
   pad1->Draw();
   pad1->cd();
 
   TH1F *h1 = new TH1F("h1", "h1", 100, -3, 3);
   TH1F *h2 = new TH1F("h2", "h2", 100, -3, 3);
   TRandom r;
   for (Int_t i = 0; i < 100000; i++) {
      Double_t x1 = r.Gaus(-1, 0.5);
      Double_t x2 = r.Gaus(1, 1.5);
      if (i < 1000)
         h1->Fill(x1);
      h2->Fill(x2);
   }
   h1->Draw();
   pad1->Update(); // this will force the generation of the "stats" box
   TPaveStats *ps1 = (TPaveStats *)h1->GetListOfFunctions()->FindObject("stats");
   ps1->SetX1NDC(0.4);
   ps1->SetX2NDC(0.6);
   pad1->Modified();
   c1->cd();
 
   // compute the pad range with suitable margins
   Double_t ymin = 0;
   Double_t ymax = 2000;
   Double_t dy = (ymax - ymin) / 0.8; // 10 per cent margins top and bottom
   Double_t xmin = -3;
   Double_t xmax = 3;
   Double_t dx = (xmax - xmin) / 0.8; // 10 per cent margins left and right
   pad2->Range(xmin - 0.1 * dx, ymin - 0.1 * dy, xmax + 0.1 * dx, ymax + 0.1 * dy);
   pad2->Draw();
   pad2->cd();
   h2->SetLineColor(kRed);
   h2->Draw("][sames");
   pad2->Update();
   TPaveStats *ps2 = (TPaveStats *)h2->GetListOfFunctions()->FindObject("stats");
   ps2->SetX1NDC(0.65);
   ps2->SetX2NDC(0.85);
   ps2->SetTextColor(kRed);
 
   // draw axis on the right side of the pad
   TGaxis *axis = new TGaxis(xmax, ymin, xmax, ymax, ymin, ymax, 50510, "+L");
   axis->SetLabelColor(kRed);
   axis->Draw();
}