void annotation3d()
{
   auto c = new TCanvas("c", "c", 600, 600);
   c->SetTheta(30);
   c->SetPhi(50);
   gStyle->SetOptStat(0);
   gStyle->SetHistTopMargin(0);
   gStyle->SetOptTitle(kFALSE);

   // Define and draw a surface
   auto f = new TF2("f", "[0]*cos(x)*cos(y)", -1, 1, -1, 1);
   f->SetParameter(0, 1);
   double s = 1. / f->Integral(-1, 1, -1, 1);
   f->SetParameter(0, s);
   f->SetNpx(50);
   f->SetNpy(50);

   f->GetXaxis()->SetTitle("x");
   f->GetXaxis()->SetTitleOffset(1.4);
   f->GetXaxis()->SetTitleSize(0.04);
   f->GetXaxis()->CenterTitle();
   f->GetXaxis()->SetNdivisions(505);
   f->GetXaxis()->SetTitleOffset(1.3);
   f->GetXaxis()->SetLabelSize(0.03);
   f->GetXaxis()->ChangeLabelByValue(-0.5, -1, -1, -1, kRed, -1, "X_{0}");

   f->GetYaxis()->SetTitle("y");
   f->GetYaxis()->CenterTitle();
   f->GetYaxis()->SetTitleOffset(1.4);
   f->GetYaxis()->SetTitleSize(0.04);
   f->GetYaxis()->SetTitleOffset(1.3);
   f->GetYaxis()->SetNdivisions(505);
   f->GetYaxis()->SetLabelSize(0.03);

   f->GetZaxis()->SetTitle("dP/dx");
   f->GetZaxis()->CenterTitle();
   f->GetZaxis()->SetTitleOffset(1.3);
   f->GetZaxis()->SetNdivisions(505);
   f->GetZaxis()->SetTitleSize(0.04);
   f->GetZaxis()->SetLabelSize(0.03);

   f->SetLineWidth(1);
   f->SetLineColorAlpha(kAzure - 2, 0.3);

   c->Add(f, "surf1 fb");

   // Lines for 3D annotation
   double x[11] = {-0.500, -0.5, -0.5, -0.5, -0.5, -0.5, -0.5, -0.5, -0.5, -0.5, -0.500};
   double y[11] = {-0.985, -0.8, -0.6, -0.4, -0.2, 0.0, 0.2, 0.4, 0.6, 0.8, 0.985};
   double z[11];
   for (int i = 0; i < 11; ++i)
      z[i] = s * cos(x[i]) * cos(y[i]);
   auto g2 = new TPolyLine3D(11, x, y, z);

   double xx[2] = {-0.5, -0.5};
   double yy[2] = {-0.985, -0.985};
   double zz[2] = {0.11, s * cos(-0.5) * cos(-0.985)};
   auto l2 = new TPolyLine3D(2, xx, yy, zz);

   g2->SetLineColor(kRed);
   g2->SetLineWidth(3);
   c->Add(g2);

   l2->SetLineColor(kRed);
   l2->SetLineStyle(kDashed);
   l2->SetLineWidth(1);
   c->Add(l2);

   // Draw text Annotations
   auto txt = new TAnnotation(-0.45, -0.2, 0.33, "f(y,x_{0})");
   txt->SetTextFont(42);
   txt->SetTextColor(kRed);
   c->Add(txt);

   auto txt1 = new TAnnotation(0.5, 0.5, 0.3, "f(x,y)");
   txt1->SetTextColor(kBlue);
   txt1->SetTextFont(42);
   c->Add(txt1);
}