text: /*
   * vol.h - Volume rendering definitions etc.
   *
   *  $Id: extvol.h,v 1.12 2011/02/05 08:10:11 johns Exp $
   */
  
  typedef struct {
    RT_OBJECT_HEAD
    vector min;       /**< minimum box vertex coordinate                */
    vector max;       /**< maximum box vertex coordinate                */
    flt ambient;      /**< ambient lighting coefficient                 */
    flt diffuse;      /**< diffuse lighting coefficient                 */
    flt opacity;      /**< surface transmission factor                  */
    int samples;      /**< number of samples to take through volume     */
    flt (* evaluator)(flt, flt, flt); /**< user-defined sample fctn ptr */
  } extvol;
  
  extvol * newextvol(void * voidtex, vector min, vector max, 
                     int samples, flt (* evaluator)(flt, flt, flt));
  color ext_volume_texture(const vector *, const texture *, ray *);
  
  
  