linearCylinderVortexForce.cxx

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/**
 * PANDA 3D SOFTWARE
 * Copyright (c) Carnegie Mellon University.  All rights reserved.
 *
 * All use of this software is subject to the terms of the revised BSD
 * license.  You should have received a copy of this license along
 * with this source code in a file named "LICENSE."
 *
 * @file linearCylinderVortexForce.cxx
 * @author charles
 * @date 2000-07-24
 */

#include "config_physics.h"
#include "linearCylinderVortexForce.h"
#include "nearly_zero.h"
#include "cmath.h"

TypeHandle LinearCylinderVortexForce::_type_handle;

/**
 * Simple Constructor
 */
LinearCylinderVortexForce::
LinearCylinderVortexForce(PN_stdfloat radius, PN_stdfloat length, PN_stdfloat coef,
                    PN_stdfloat a, bool md) :
  LinearForce(a, md),
  _radius(radius), _length(length), _coef(coef) {
}

/**
 * copy Constructor
 */
LinearCylinderVortexForce::
LinearCylinderVortexForce(const LinearCylinderVortexForce &copy) :
  LinearForce(copy) {
  _radius = copy._radius;
  _length = copy._length;
  _coef = copy._coef;
}

/**
 * Destructor
 */
LinearCylinderVortexForce::
~LinearCylinderVortexForce() {
}

/**
 * child copier
 */
LinearForce *LinearCylinderVortexForce::
make_copy() {
  return new LinearCylinderVortexForce(*this);
}

/**
 * returns the centripetal force vector for the passed-in object
 */
LVector3 LinearCylinderVortexForce::
get_child_vector(const PhysicsObject *po) {
  // get the force-space transform- this MUST be the relative matrix from the
  // point's local coordinate system to the attached node's local system.
  // LMatrix4 force_space_xform = LMatrix4::ident_mat();
  LVector3 force_vec(0.0f, 0.0f, 0.0f);

  // project the point into force_space
  LPoint3 point = po->get_position();

  // clip along length
  if (point[2] < 0.0f || point[2] > _length)
    return force_vec;

  // clip to radius
  PN_stdfloat x_squared = point[0] * point[0];
  PN_stdfloat y_squared = point[1] * point[1];
  PN_stdfloat dist_squared = x_squared + y_squared;
  PN_stdfloat radius_squared = _radius * _radius;

  // squared space increases monotonically wrt linear space, so there's no
  // need to sqrt to check insideoutside this disc.
  if (dist_squared > radius_squared)
    return force_vec;

  if IS_NEARLY_ZERO(dist_squared)
    return force_vec;

  PN_stdfloat r = csqrt(dist_squared);

  if IS_NEARLY_ZERO(r)
    return force_vec;

  LVector3 tangential = point;
  tangential[2] = 0.0f;
  tangential.normalize();
  tangential = tangential.cross(LVector3(0,0,1));

  LVector3 centripetal = -point;
  centripetal[2] = 0.0f;
  centripetal.normalize();

  LVector3 combined = tangential + centripetal;
  combined.normalize();

  // a = v^2  r centripetal = centripetal * _coef *
  // (tangential.length_squared() (r + get_nearly_zero_value(r)));

  centripetal = combined * _coef * po->get_velocity().length();

  // centripetal = combined * _coef * (po->get_velocity().length() (r +
  // get_nearly_zero_value(r)));

  return centripetal;
}

/**
 * Write a string representation of this instance to <out>.
 */
void LinearCylinderVortexForce::
output(std::ostream &out) const {
  #ifndef NDEBUG //[
  out<<"LinearCylinderVortexForce";
  #endif //] NDEBUG
}

/**
 * Write a string representation of this instance to <out>.
 */
void LinearCylinderVortexForce::
write(std::ostream &out, int indent) const {
  #ifndef NDEBUG //[
  out.width(indent); out<<""; out<<"LinearCylinderVortexForce:\n";
  LinearForce::write(out, indent+2);
  #endif //] NDEBUG
}