//======================================================================
// surfacePoint.cc:	Demonstrates two bugs with VecGeom USolids
//
// Simple program to exercise G4VSolid::GetPointOnSurface() for a
// cylinder.  With standard Geant4, each run will have a different set
// of random values, and the cylinder will have its top and bottom
// faces populated uniformly.  With USolids (VecGeom), every run will
// be identical (use of std::rand() instead of Geant4 random engine),
// and the cylinder will have points concentrated at the center of
// each face (incorrect radial coordinate selection).
//
// 20220302  Michael Kelsey (TAMU) <kelsey@slac.stanford.edu>
//======================================================================

#include "globals.hh"
#include "G4PhysicalConstants.hh"
#include "Randomize.hh"
#include "G4Tubs.hh"
#include "G4ThreeVector.hh"
#include <stdlib.h>
#include <time.h>


int main(int argc, char* argv[]) {
  // Get number of points from command line, or display usage
  if (argc < 2 || G4String(argv[1]) == "-h") {
    G4cout << "Usage: " << argv[0] << " <npoints>" << G4endl;
    return 0;
  }

  G4int npoints = atoi(argv[1]);

  // Initialize Geant4 random engine with unique seeds every time
  CLHEP::HepRandom::setTheSeed(time(NULL));

  // Generate points on surface of cylinder
  G4VSolid* cyl = new G4Tubs("Cylinder", 0., 1., 1., 0., twopi);

  G4cout << npoints << " surface points on " << cyl->GetName()
	 << " (" << cyl->GetEntityType() << ")" << G4endl;

  G4ThreeVector pt; 
  for (G4int i=0; i<npoints; i++) {
    pt = cyl->GetPointOnSurface();
    G4cout << pt[0] << " " << pt[1] << " " << pt[2] << G4endl;
  }
}