//Hint: Spherical waves

#include "TROOT.h"
#include "TCanvas.h"
#include "TColor.h"
#include "TArc.h"
#include "TGraph.h"
#include "TF2.h"
#include "TLine.h"
#include "TLatex.h"
#include "TMath.h"
#include "TStyle.h"
#include "Riostream.h"


TF2 * finter;
//____________________________________________________________________________________

Double_t interference( Double_t *x, Double_t *par) {
   Double_t x_p2 = x[0] * x[0];
   Double_t d_2 = 0.5 * par[2];
   Double_t ym_p2 = (x[1] - d_2) * (x[1] - d_2);
   Double_t yp_p2 = (x[1] + d_2) * (x[1] + d_2);
   Double_t  tpi_l = TMath::Pi() /  par[1];
   Double_t amplitude = par[0] * (cos(tpi_l  * sqrt(x_p2 + ym_p2)) 
                         + par[3] * cos(tpi_l  * sqrt(x_p2 + yp_p2)));
   return amplitude * amplitude;
}; 
//____________________________________________________________________________________

Double_t result( Double_t *x, Double_t *par) {
   Double_t xint[2];
 
   Double_t  maxintens = 0, xcur = 14;
   Double_t dlambda = 0.1 * par[1];
   for(Int_t i=0; i<10; i++){
      xint[0] = xcur;
      xint[1] = x[1];   
      Double_t  intens = interference(xint, par);
      if(intens > maxintens) maxintens = intens;
      xcur -= dlambda;
   }
   return maxintens;
}
//____________________________________________________________________________________

void waves( Double_t d = 3, Double_t lambda = 1, Double_t amp = 10)
{
//   extern void * interference;
   TCanvas *c1 = new TCanvas("waves", "A double slit experiment", 300,40, 1004, 759);
   c1->Range(0, -10,  30, 10);
   c1->SetFillColor(0);
   TPad *pad = new TPad("pr","pr",  0.5, 0 , 1., 1);
   pad->Range(0, -10,  15, 10);
   pad->Draw();

   const Int_t colNum = 30;
   Int_t palette[colNum];
   for (Int_t i=0;i<colNum;i++) {
      TColor *color = new TColor(301+i
      ,    pow(i/((colNum)*1.0),0.3)
      ,    pow(i/((colNum)*1.0),0.3)
      ,0.5*(i/((colNum)*1.0)),"");
      palette[i] = 301+i;
      if(color);
   }
   gStyle->SetPalette(colNum,palette);
   c1->cd();
   TF2 * f0 = new TF2("ray_source",interference, 0.02, 15, -8, 8, 4);

   f0->SetParameters(amp, lambda, 0, 0);
   f0->SetNpx(200);
   f0->SetNpy(200);
   f0->SetContour(colNum-2);
   f0->Draw("samecolz");

   TLatex title;
   title.DrawLatex(1.6, 8.5, "A double slit experiment");

   TGraph *graph = new TGraph(4);
   graph->SetFillColor(0);
   graph->SetFillStyle(1001);
   graph->SetLineWidth(0);
   graph->SetPoint(0, 0., 0.1);
   graph->SetPoint(1, 14.8, 8);
   graph->SetPoint(2, 0, 8);
   graph->SetPoint(3, 0, 0.1);
   graph->Draw("F");

   graph = new TGraph(4);
   graph->SetFillColor(0);
   graph->SetFillStyle(1001);
   graph->SetLineWidth(0);
   graph->SetPoint(0, 0, -0.1);
   graph->SetPoint(1, 14.8, -8);
   graph->SetPoint(2, 0, -8);
   graph->SetPoint(3, 0, -0.1);
   graph->Draw("F");

   TLine * line;
   line = new TLine(15,-10, 15, 0 - 0.5*d -0.2);
   line->SetLineWidth(10); line->Draw();
   line = new TLine(15, 0 - 0.5*d +0.2 ,15, 0 + 0.5*d -0.2);
   line->SetLineWidth(10); line->Draw();

   line = new TLine(15,0 + 0.5*d + 0.2,15, 10);
   line->SetLineWidth(10); line->Draw();

   pad ->cd();
   finter = new TF2("interference",interference, 0.01, 14, -10, 10, 4);

   finter->SetParameters(amp, lambda, d, 1);
   finter->SetNpx(200);
   finter->SetNpy(200);
   finter->SetContour(colNum-2);
   finter->Draw("samecolorz");
   
   TArc * arc;
   Float_t r = 0.5 * lambda, dr = lambda;
   for(Int_t i = 0; i < 26; i++){
      arc = new TArc(0, 0.5 * d, r);
      arc->Draw();
      arc->SetLineWidth(2);
      arc->SetLineColor(5);
      arc = new TArc(0, -0.5 * d, r);
      arc->SetLineWidth(2);
      arc->SetLineColor(5);
      arc->Draw();
      r += dr;
   }

   pad ->cd();
   TF2 * fresult = new TF2("result",result, 14, 15, -10, 10, 4);

   fresult->SetParameters(amp, lambda, d, 1);
   fresult->SetNpx(300);
   fresult->SetNpy(300);
   fresult->SetContour(colNum-2);
   fresult->Draw("samecolor");
   line = new TLine(13.8,-10, 14, 10);
   line->SetLineWidth(10); line->SetLineColor(0); line->Draw();
   c1->Modified(kTRUE);
   c1->Update();
   c1->SetEditable(kTRUE);
}