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// calculate the length of the hypotenuse of a right-angle triangle
float hypot( in float x, in float y )
{
  // (sqrt( x * x + y * y )) might over- or underflow
  // see http://en.wikipedia.org/wiki/Hypot for details
  x = abs( x );
  y = abs( y );
  float t = min( x, y );
  x = max( x, y );
  t = t/x;
  return( x * sqrt( 1.0 + ( t * t ) ) );
}

float gradientGetPosition( in int gradientMode, in vec2 xy )
{
  // clamp to [0,1]
  vec2 tex = xy - floor( xy );

  switch( gradientMode )
  {
    case gradient_linear :
      return( tex.x );
    case gradient_squared :
      return( tex.x * tex.x );
    case gradient_box :
      // gradient is based on the distance from the center
      return( max( abs( tex.x - 0.5 ), abs( tex.y - 0.5 ) ) );
    case gradient_diagonal :
      // gradient is based on the distance from the diagonal
      return( sqrt(2.0) * abs( tex.x - tex.y ) );
    case gradient_90_degree :
      // Need to check
      return( 0.0 );
    case gradient_symmetric_90_degree :
       // Need to check
      return( 0.0 );
    case gradient_radial :
      // Distance from center
      return( 2.0 * hypot( tex.x - 0.5, tex.y - 0.5 ) );
    case gradient_360_degree :
      // fall through need to check
    default :
      return( 0.0 );
  }
}