gistfile1.cpp

class Fault: public TerrainFn {
  protected:
    const float4 center;
    const float4 plane;
    const float4 displacement;
    const float amplitude;
    
  public:
    Fault(fn_handle _input, float4 c, float4 p, float amp):
        TerrainFn{std::move(_input)},
        center{c},
        plane{vnormalized3(p)},
        displacement{vnormalized3(vcross3(y_cross3(p), p))*amp},
        amplitude(amp)
    {}
    
    virtual auto operator()(float4 pt) -> VolumeVal
    {
        auto dir = pt - center;
        float t = vdot3(dir, plane);
        float lowd = 2.0f/(1.0f + std::fabs(t/amplitude));
        float highd = 1.0f/(1.0f + sqr(t/amplitude));
        
        if(t < 0.0f) {
            // Do lower half of fault + spillover
            VolumeVal low = (*input)(pt - displacement*lowd);
            if(low.type != kAirVolume)
                return low;
            else // spillover
                return (*input)(pt + displacement*highd + float4{0.0f, sqr(t/amplitude)*4.0f, 0.0f});
        }
        else {
            // do upper half of fault
            return (*input)(pt + displacement*highd);
        }
    }
};