#include "TROOT.h"
#include "TStyle.h"
#include "TCanvas.h"
#include "TView.h"
#include "TPolyLine3D.h"
#include "TLatex.h"

void rec_solid_angle(){
  gROOT->SetStyle("Plain");
  gStyle->SetTextFont(132);
  TCanvas *c1 = new TCanvas("c1","c1",400,400);
  c1->SetTheta(17.);
  c1->SetPhi(35.);
  TView *view = TView::CreateView(1);
  Double_t view_size = 0.7;
  view->SetRange(view_size*0.7,-view_size*1.0,-view_size*0.9,
		 view_size*2.7, view_size*1.0, view_size*1.1);

  const Int_t nPolyLine3D = 20;
  TPolyLine3D *guide[nPolyLine3D];
  for (Int_t i = 0; i<nPolyLine3D; i++){
    guide[i]=new TPolyLine3D();
  }

  Double_t pi = acos(-1.);
  Int_t    n = 30;
  Double_t r,theta,phi;
  Double_t theta0 = pi/5.;
  Double_t phi0   = pi/7.;
  Double_t x0 =  2.*tan(theta0/2.);
  Double_t y0 =  2.*tan(phi0/2.);

  r = 1.0;
  for (Int_t i=0;i<=n;i++) {
    theta = -i*theta0/2.0/n;
    phi   = i*phi0/2.0/n;
    guide[7]->SetNextPoint(r*cos(theta),r*sin(theta),0);
    guide[8]->SetNextPoint(r*cos(phi),0,r*sin(phi));
  }

  guide[1]->SetNextPoint(2,x0,y0);
  guide[1]->SetNextPoint(2,x0,-y0);
  guide[1]->SetNextPoint(2,-x0,-y0);
  guide[1]->SetNextPoint(2,-x0,y0);
  guide[1]->SetNextPoint(2,x0,y0);
  guide[2]->SetNextPoint(2,0,0);
  guide[2]->SetNextPoint(0,0,0);

  guide[5]->SetNextPoint(0,0,0);
  guide[5]->SetNextPoint(2,-x0,0);
  guide[5]->SetNextPoint(2,x0,0);
  guide[5]->SetNextPoint(0,0,0);
  guide[6]->SetNextPoint(0,0,0);
  guide[6]->SetNextPoint(2,0,-y0);
  guide[6]->SetNextPoint(2,0,y0);
  guide[6]->SetNextPoint(0,0,0);
  guide[5]->SetLineStyle(2);
  guide[6]->SetLineStyle(2);

  Double_t virlen = 0.15*x0;
  guide[9]->SetNextPoint(2,virlen,0);
  guide[9]->SetNextPoint(2-virlen,virlen,0);
  guide[9]->SetNextPoint(2-virlen,0,0);
  guide[9]->SetNextPoint(2-virlen,0,-virlen);
  guide[9]->SetNextPoint(2,0,-virlen);

  for (Int_t i = 0; i<nPolyLine3D; i++){
    guide[i]->Draw();
  }

  TLatex Tl;
  Tl.DrawLatex(-0.02,-0.12,"#it{#alpha}");
  Tl.DrawLatex(-0.12,-0.02,"#it{#beta}");
  Tl.DrawLatex(-0.87,-0.30,"O");
  Tl.DrawLatex(0.57,0.06,"C");
}