mandelbrot.C

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/// \file
/// \ingroup tutorial_graphics
/// \notebook -js
/// \preview Using TExec to handle keyboard events and TComplex to draw the Mandelbrot set.
///
/// Pressing the keys 'z' and 'u' will zoom and unzoom the picture
/// near the mouse location, 'r' will reset to the default view.
///
/// Try it (in compiled mode!) with:   `root mandelbrot.C+`
///
/// \macro_image (tcanvas_js)
///
/// ### Details
///
///    when a mouse event occurs the myexec() function is called (by
///    using AddExec). Depending on the pressed key, the mygenerate()
///    function is called, with the proper arguments. Note the
///    last_x and last_y variables that are used in myexec() to store
///    the last pointer coordinates (px is not a pointer position in
///    kKeyPress events).
///
/// \macro_code
///
/// \author Luigi Bardelli <bardelli@fi.infn.it>
 
#include <TStyle.h>
#include <TROOT.h>
#include <TH2.h>
#include <TComplex.h>
#include <TVirtualPad.h>
#include <TCanvas.h>
 
TH2F *last_histo = nullptr;
 
void mygenerate(double factor, double cen_x, double cen_y)
{
   printf("Regenerating...\n");
   // resize histo:
   if (factor > 0) {
      double dx = last_histo->GetXaxis()->GetXmax() - last_histo->GetXaxis()->GetXmin();
      double dy = last_histo->GetYaxis()->GetXmax() - last_histo->GetYaxis()->GetXmin();
      last_histo->SetBins(last_histo->GetNbinsX(), cen_x - factor * dx / 2, cen_x + factor * dx / 2,
                          last_histo->GetNbinsY(), cen_y - factor * dy / 2, cen_y + factor * dy / 2);
      last_histo->Reset();
   } else {
      if (last_histo)
         delete last_histo;
      // allocate first view...
      last_histo = new TH2F("h2", "Mandelbrot [move mouse and  press z to zoom, u to unzoom, r to reset]", 200, -2, 2,
                            200, -2, 2);
      last_histo->SetStats(false);
   }
   const int max_iter = 50;
   for (int bx = 1; bx <= last_histo->GetNbinsX(); bx++)
      for (int by = 1; by <= last_histo->GetNbinsY(); by++) {
         double x = last_histo->GetXaxis()->GetBinCenter(bx);
         double y = last_histo->GetYaxis()->GetBinCenter(by);
         TComplex point(x, y);
         TComplex z = point;
         int iter = 0;
         while (z.Rho() < 2) {
            z = z * z + point;
            last_histo->Fill(x, y);
            iter++;
            if (iter > max_iter)
               break;
         }
      }
   last_histo->SetContour(99);
   last_histo->Draw("colz");
   gPad->Modified();
   gPad->Update();
   printf("Done.\n");
}
 
void myexec()
{
   // get event information
   int event = gPad->GetEvent();
   int px = gPad->GetEventX();
   int py = gPad->GetEventY();
 
   // some magic to get the coordinates...
   double xd = gPad->AbsPixeltoX(px);
   double yd = gPad->AbsPixeltoY(py);
   float x = gPad->PadtoX(xd);
   float y = gPad->PadtoY(yd);
 
   static float last_x;
   static float last_y;
 
   if (event != kKeyPress) {
      last_x = x;
      last_y = y;
      return;
   }
 
   const double Z = 2.;
   switch (px) {
   case 'z': // ZOOM
      mygenerate(1. / Z, last_x, last_y);
      break;
   case 'u': // UNZOOM
      mygenerate(Z, last_x, last_y);
      break;
   case 'r': // RESET
      mygenerate(-1, last_x, last_y);
      break;
   };
}
 
void mandelbrot()
{
   // cosmetics...
   gStyle->SetPadGridX(kTRUE);
   gStyle->SetPadGridY(kTRUE);
   new TCanvas("canvas", "View Mandelbrot set");
   // this generates and draws the first view...
   mygenerate(-1, 0, 0);
 
   // add exec
   gPad->AddExec("myexec", "myexec()");
}