triangles.C

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/// \file
/// \ingroup tutorial_graphics
/// \notebook
/// Create small triangles at random positions on the canvas.
/// Assign a unique ID to each triangle, and give each one a random color from the color palette.
///
/// ~~~{.cpp}
/// root > .x triangles.C
/// ~~~
///
/// When a triangle is clicked, a message displaying its unique number and color will be printed.
///
/// \macro_image
/// \macro_code
///
/// \author Rene Brun
 
void triangles(int ntriangles=50)
{
   auto c1 = new TCanvas("c1","triangles",10,10,700,700);
   gStyle->SetPalette(kCMYK);
   TRandom r;
   double dx = 0.2; double dy = 0.2;
   int ncolors = TColor::GetNumberOfColors();
   double x[4],y[4];
   for (int i=0;i<ntriangles;i++) {
      x[0] = r.Uniform(.05,.95); y[0] = r.Uniform(.05,.95);
      x[1] = x[0] + dx*r.Rndm(); y[1] = y[0] + dy*r.Rndm();
      x[2] = x[1] - dx*r.Rndm(); y[2] = y[1] - dy*r.Rndm();
      x[3] = x[0];               y[3] = y[0];
      auto pl = new TPolyLine(4,x,y);
      pl->SetUniqueID(i);
      int ci = ncolors*r.Rndm();
      TColor *c = gROOT->GetColor(TColor::GetColorPalette(ci));
      c->SetAlpha(r.Rndm());
      pl->SetFillColor(c->GetNumber());
      pl->Draw("f");
   }
   c1->AddExec("ex","TriangleClicked()");
}
 
void TriangleClicked()
{
   //this action function is called whenever you move the mouse
   //it just prints the id of the picked triangle
   //you can add graphics actions instead
   int event = gPad->GetEvent();
   if (event != 11) return; //may be comment this line
   TObject *select = gPad->GetSelected();
   if (!select) return;
   if (select->InheritsFrom(TPolyLine::Class())) {
      TPolyLine *pl = (TPolyLine*)select;
      printf("You have clicked triangle %d, color=%d\n",
              pl->GetUniqueID(),pl->GetFillColor());
   }
}