void grad2()
{
   //Gradient fill with transparency and "SAME" option.
   //This macro works ONLY on MacOS X with --enable-cocoa.
   
   TCanvas *cnv = new TCanvas("cnv", "gradient_test", 100, 100, 800, 600);
   //After canvas was created, gVirtualX should be non-null.
   if (gVirtualX && !gVirtualX->InheritsFrom("TGCocoa")) {
      std::cout<<"This macro works only on MacOS X with --enable-cocoa\n";
      delete cnv;
      return;
   }

   TH1F * hist = new TH1F("a", "b", 10, -2., 3.);
   TH1F * hist2 = new TH1F("c", "d", 10, -3., 3.);
   hist->FillRandom("landau", 100000);
   hist2->FillRandom("gaus", 100000);

   const Double_t locations[] = {0., 1.};
   new TColor(1001, 1., 0., 0., "red", 0.5);
   const Color_t idx1[] = {kOrange, 1001};
   //Gradient from ROOT's kOrange and my own semi-transparent red color.
   new TColorGradient(1002, TColorGradient::kGDVertical, 2, locations, idx1);
   hist->SetFillColor(1002);
   
   new TColor(1003, 0., 1., 0., "green", 0.5);
   const Color_t idx2[] = {kBlue, 1003};
   //Gradient from ROOT's kBlue and my own semi-transparent green color.
   new TColorGradient(1004, TColorGradient::kGDVertical, 2, locations, idx2);
   hist2->SetFillColor(1004);
   
   hist2->Draw();
   hist->Draw("SAME");
}