NullSensor.h

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/**<!-------------------------------------------------------------------->
   @class  NullSensor
   @author Travis Fischer (fisch0920@gmail.com)
   @author Matthew Jacobs (jacobs.mh@gmail.com)
   @date   Fall 2008
   
   @brief
      Null sensor which doesn't emit any importance
   <!-------------------------------------------------------------------->**/

#ifndef NULL_SENSOR_H_
#define NULL_SENSOR_H_

#include <materials/Sensor.h>

class NullSensor : public Sensor {
   public:
      ///@name Constructors
      //@{-----------------------------------------------------------------
      
      inline   NullSensor(SurfacePoint &pt, Material *parent = NULL)
         : Sensor(pt, parent)
      { }
      
      virtual ~NullSensor() 
      { }
      
      
      //@}-----------------------------------------------------------------
      ///@name Initialization
      //@{-----------------------------------------------------------------
      
      /**
       * @brief
       *    Performs any initialization that may be necessary before beginning 
       * to use this sensor
       */
      virtual void init();
      
      
      //@}-----------------------------------------------------------------
      ///@name Main usage interface
      //@{-----------------------------------------------------------------
      
      /**
       * @returns true iff this sensor emits importance (is a valid sensor)
       * 
       * @note if 'isSensor' returns false, 'getWe' and 'getImportance' must 
       *    return SpectralSampleSet::black
       */
      virtual bool isSensor();
      
      /**
       * @returns the spectral importance emitted along the given vector
       */
      virtual SpectralSampleSet getWe(const Vector3 &wo);
      
      /**
       * @returns the spectral importance of this sensor, representing the 
       *    total radiant energy emitted from surfaces associated with this 
       *    sensor; TODO: what units?
       * 
       * @note total We emitted by integrating 'getWe' over the the sphere of 
       *    exitant directions should equal the importance of this sensor
       */
      virtual SpectralSampleSet getImportance();
      
      
      //@}-----------------------------------------------------------------
      ///@name Sampling interface
      //@{-----------------------------------------------------------------
      
      /**
       * @brief
       *    Samples an exitent vector according to the underlying distribution 
       * of emitted importance at the surface point
       * 
       * @returns the sampled vector
       */
      virtual Event sample();
      
      /**
       * @returns the probability density of having sampled the given out 
       *    out vector 'event' with respect to whatever underlying sampling 
       *    strategy is being used to sample this sensor
       */
      virtual real_t getPdf(const Event &event);
      
      /**
       * @brief
       *    Mimics the behavior of a BSDF by separating emittance, We(x,wo), 
       * into two parts: We(x,wo,0) and We(x,wo,1).
       *    We(x,wo,0) is independent of 'wo' and represents the total 
       * importance emitted at point x.
       *    We(x,wo,1) represents We(x,w) / We(x,wo,0), or in words, the 
       * directional distribution of importance emitted at x, corresponding to 
       * the fraction of importance emitted in direction 'wo' with respect to the
       * total importance emitted at point x.
       * 
       * @returns the directional distribution of importance emitted in 
       *    direction 'wo'
       * @note all implementations should disregard 'wo', as it has no physical
       *    interpretation in the context of a sensor
       * @note for details, see Eric Veach's thesis, section 8.3.2
       */
      virtual SpectralSampleSet getBSDF(const Vector3 &wi, const Vector3 &wo);
      
      
      //@}-----------------------------------------------------------------
};

#endif // NULL_SENSOR_H_