## Code Excerpt for Texture Model Turbulence

    Scalar Persistence; // in [0 .. 1] stepsize 0.05
    Scalar Stretch;     // in [0 .. 1] stepsize 0.1
    Scalar Frequency;   // in [0 .. 1] stepsize 0.1

    void TextureTurbulence::setupParameter(const std::vector<Scalar> &parameter){

      persistence_= 0.5 + Persistence*2.5;
      stretch_= Stretch;
      frequency_=  Frequency*10;

    }

    Scalar TextureTurbulence::evaluate(const Scalar &x, const Scalar &y){

        return turbulence((1-stretch_)*x*frequency_, y*frequency_, persistence_);

    }