/******************************************************************/
/* BRDF.h                                                         */
/* -----------------------                                        */
/*                                                                */
/* A base class for BRDFs.  A BRDF encapsulates data about a      */
/*    a material's reflectance so that a single BRDFMaterial      */
/*    class can be used to render a variety of material types.    */
/*                                                                */
/* Chris Wyman (4/9/2006)                                         */
/******************************************************************/

#ifndef BRDF_H
#define BRDF_H

#include "DataTypes/Color.h"
#include "DataTypes/Vector.h"
#include "Utils/TextParsing.h"
#include "Utils/Random.h"
#include "Core/Ray.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

class Scene;

class BRDF {
public:
	BRDF() {}
	BRDF( FILE *f, Scene *s ) 
	     { printf("Virtual constructor BRDF( FILE *f ) called.  This is not implemented!\n"); }

	// This function returns the BRDF given the directions to the viewer and to the light.  The ray structure
	//    can be used to get information about the hitpoint, and perhaps other relevent information, e.g. the
	//    surface parameterization
	virtual Color  SampleBRDF( const Ray &r, const Vector &toViewer, const Vector &incidentLight ) const = 0;

	// This function returns a random vector sampled (somehow) over the hemisphere
	virtual Vector RandomlySelectOutgoingVector( Random *rng, const Vector &normVec ) const = 0;

	// Given the random vector from above, return the probability of selecting this vector.
	//    NOTE: One could consider incorporating this function with RandomlySelectOutgoingVector, by
	//          returning the probability in an additional parameter.  That is a little less clean,
	//          but it probably eliminates duplicate computations that would be needed for the 
	//          GetProbabilityOfSampling method with more complex sampling schemes.
	virtual float  GetProbabilityOfSampling( const Vector &normVec, const Vector &sampleVec ) const = 0;

};




#endif