include/crbn/sampler/mapping.hpp

#ifndef __mapping_hpp__
#define __mapping_hpp__

#include <math.h>

//
// A Low Distortion Map Between Disk and Square
// Peter Shirley / Kenneth Chiu (1997)
static
void MapSquareToDisk(const float& su, const float& sv,
                           float& du,       float &dv) {
  float r, theta;
  
  if((su == 0.0f) && (sv == 0.0f)) {
    du = dv = 0.0;
    return;
  } 

  if(su >= -sv){
    if(su > sv) {
      // First region of the disk
      r = su;
      theta = (sv > 0.0)?(sv / r):(8.0 + (sv / r));
    }
    else {
      // Second region
      r = sv;
      theta = 2.0 - (su / r);
    }
  }
  else {
    if(su <= sv) {
      // Third region
      r = -su;
      theta = 4.0 - (sv / r);
    }
    else {
      // Fourth region
      r = -sv;
      theta = 6.0 + (su / r);
    }
  }
  theta *= M_PI / 4.0f;

  du = r * cos(theta);
  dv = r * sin(theta);
}

#endif

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