#include <cassert>
#include <cmath>
#include <algorithm>
//---------------------------------------------------------------------------
//From http://www.richelbilderbeek.nl/CppRgbGradient.htm
void RgbGradient(
  const double x, 
  unsigned char& r, 
  unsigned char& g, 
  unsigned char& b)
{
  r = GetRed(x);
  g = GetGreen(x);
  b = GetBlue(x);
}
//---------------------------------------------------------------------------
//From http://www.richelbilderbeek.nl/CppRgbGradient.htm
unsigned char GetRed(const double x)
{
  assert( x >= 0.0 && x < 1.0);
  const double f = std::max(0.0,
    (x < 0.5
    ?  std::cos(x * 1.5 * M_PI)
    : -std::sin(x * 1.5 * M_PI)
    ) );
  assert( f >= 0.0);
  assert( f <= 1.0);
  const double y = 255.0 * f;
  assert( static_cast<int>(y) < 256 );
  return static_cast<unsigned char>(y);
}
//---------------------------------------------------------------------------
//From http://www.richelbilderbeek.nl/CppRgbGradient.htm
unsigned char GetGreen(const double x)
{
  assert( x >= 0.0 && x < 1.0);

  const double f = std::max(0.0, std::sin( x * 1.5 * M_PI ) );
  assert( f >= 0.0);
  assert( f <= 1.0);
  const double y = 255.0 * f;
  assert( static_cast<int>(y) < 256 );
  return static_cast<unsigned char>(y);
}
//---------------------------------------------------------------------------
//From http://www.richelbilderbeek.nl/CppRgbGradient.htm
unsigned char GetBlue(const double x)
{
  assert( x >= 0.0 && x < 1.0);

  const double f = std::max(0.0, -std::cos( x * 1.5 * M_PI ) );

  assert( f >= 0.0);
  assert( f <= 1.0);
  const double y = 255.0 * f;
  assert( static_cast<int>(y) < 256 );
  return static_cast<unsigned char>(y);
}
//---------------------------------------------------------------------------