#include "meshvolume.h"

inline void CrossProduct(const float *a,const float *b,float *cross)
{
	cross[0] = a[1]*b[2] - a[2]*b[1];
	cross[1] = a[2]*b[0] - a[0]*b[2];
	cross[2] = a[0]*b[1] - a[1]*b[0];
}

inline float DotProduct(const float *a,const float *b)
{
	return a[0] * b[0] + a[1] * b[1] + a[2] * b[2];
}

inline float tetVolume(const float *p0,const float *p1,const float *p2,const float *p3)
{
	float a[3];
	float b[3];
	float c[3];

  a[0] = p1[0] - p0[0];
  a[1] = p1[1] - p0[1];
  a[2] = p1[2] - p0[2];

	b[0] = p2[0] - p0[0];
	b[1] = p2[1] - p0[1];
	b[2] = p2[2] - p0[2];

  c[0] = p3[0] - p0[0];
  c[1] = p3[1] - p0[1];
  c[2] = p3[2] - p0[2];

  float cross[3];

  CrossProduct( b, c, cross );

	float volume = DotProduct( a, cross );

  if ( volume < 0 )
   return -volume;

  return volume;
}

inline float det(const float *p0,const float *p1,const float *p2,const float *p3)
{
  return  p1[0]*p2[1]*p3[2] + p2[0]*p3[1]*p1[2] + p3[0]*p1[1]*p2[2] -p1[0]*p3[1]*p2[2] - p2[0]*p1[1]*p3[2] - p3[0]*p2[1]*p1[2];
}

float computeMeshVolume(const float *vertices,unsigned int tcount,unsigned int *indices)
{
	float volume = 0;

	const float *p0 = vertices;
	for (unsigned int i=0; i<tcount; i++,indices+=3)
	{

		const float *p1 = &vertices[ indices[0]*3 ];
		const float *p2 = &vertices[ indices[1]*3 ];
		const float *p3 = &vertices[ indices[2]*3 ];

		volume+=tetVolume(p0,p1,p2,p3); // compute the volume of the tetrahdren relative to the root vertice
	}

  return volume * (1.0f / 6.0f );
}