buildray

/************* Begin of buildray Function ****************************/
/***********************************************************************/
/*                                                                     */
/* FUNCTION: buildray                                                */
/* DESCRIPTION: builds ray through ith,jth pixel in world coords       */
/* INPUT:  i,j - row, and column                                       */
/* OUTPUT: ray - RAY                                                   */
/***********************************************************************/

void buildray(float du, float dv, vector3f *i,vector3f *j, ray3f *ray)
{
	vector3f  eye, uvn, trans;
	matrix3f ctm;

  	uvn.x = winwidth - camera.e.u;                      /* build i,j th ray */
  	uvn.y = winheight - camera.e.v;
  	uvn.z  = -camera.e.n;
                                       /* compute row delta and column delta */
  	i->x = i->z = 0.0f; i->y = dv;
  	j->x = du; j->y = j->z = 0.0f;


	// get view translation factor
	trans.x = mvm[0][3]; trans.y = mvm[1][3]; trans.z = 0.0f;

	// set start position, eye represents camera eye in world cooords translated by vrp
	eye = mat3fxvec3f(vwm, camera.e);
	eye = vec3fadd(eye, camera.r);

  	ray->orig.x = eye.x - trans.x;
  	ray->orig.y = eye.y - trans.y;
  	ray->orig.z = eye.z - trans.z;

	// transpose to get inverse rotation
	for (int i=0; i<3; i++)
		for (int j=0; j<3; j++)
			ctm[i][j] = mvm[j][i];
	// rotate ray origin by inverse current modelview
	ray->orig = mat3fxvec3f(ctm, ray->orig);

	// concatenate with view to world transform matrix to transform ray with a single matrix multiply
  	mat3fxmat3f(ctm, vwm);
    // compute direction vector 
  	ray->dir = mat3fxvec3f(ctm, ray->dir);

    // compute i,j increment values 
  	*i = mat3fxvec3f(ctm,*i);
  	*j = mat3fxvec3f(ctm,*j);
}

/************* End of buildray  Function*******************************/