CPidController.h

//
// Class to represent a PID Controller. 
//
// To use, first set the P, I, and D coefficients with SetCoefficients(), 
// then begin recording error values with Record(). Use GetOutput()
// to calculate the current output of the controller.
//

#ifndef CPIDCONTOLLER_H
#define CPIDCONTOLLER_H

#define NUM_ERROR_SLOTS 10

class CPidController
{
public:
    CPidController()                        { SetCoefficients(0.0f, 0.0f, 0.0f); Clear(); }
    ~CPidController()                       { }

    void    SetCoefficients(float p_coefficient, float i_coefficient, float d_coefficient) { m_P_Coefficient = p_coefficient; m_I_Coefficient = i_coefficient; m_D_Coefficient = d_coefficient; }

    void    Record(float error, float timestep);

    void    Clear();
    bool    IsFull()                        { return (m_NumErrorsRecorded == NUM_ERROR_SLOTS); }

    float   GetError();
    float   GetErrorIntegral();
    float   GetErrorDerivative();

    float   GetOutput();

    void    DumpState();

private:
    float   CalculateIntegralDirectly();

    float   m_P_Coefficient;                // Our current P coefficient
    float   m_I_Coefficient;                // Our current I coefficient
    float   m_D_Coefficient;                // Our current D coefficient

    float   m_Error[NUM_ERROR_SLOTS];       // The last NUM_ERROR_SLOTS error terms that have been recorded
    float   m_Timestep[NUM_ERROR_SLOTS];    // The last NUM_ERROR_SLOTS timesteps that have been recorded

    int     m_CurrentIndex;                 // Index into m_Error[] anmd m_Timestep[] of the last recorded error
    int     m_PreviousIndex;                // Index into m_Error[] anmd m_Timestep[] of the next-to-last recorded error
    int     m_NumErrorsRecorded;            // Number of error values that have been recorded so far. Between 0 and NUM_ERROR_SLOTS.

    float   m_CurrentIntegral;              // The current value of our integral term
};

#endif