void apply() const;
void update_data();
float *append();
float *operator[](unsigned i) { return &data[0]+i*stride; }
const float *operator[](unsigned i) const { return &data[0]+i*stride; }
private:
void apply() const;
void update_data();
float *append();
float *operator[](unsigned i) { return &data[0]+i*stride; }
const float *operator[](unsigned i) const { return &data[0]+i*stride; }
private: