Function do_vis_physics_sim

physics/physics.cpp:2425–2545

----------------------------------------------------------------------------------------------------------- Simulate a physics object for this frame

//	-----------------------------------------------------------------------------------------------------------
// Simulate a physics object for this frame
void do_vis_physics_sim(vis_effect *vis) {
  if (Frametime <= 0.0f)
    return;

  vector total_force;
  vector old_pos = vis->pos;

#ifdef _DEBUG
  if (!Game_do_vis_sim) {
    return;
  }
#endif

  if (vis->flags & VF_DEAD) {
    return;
  }

  if (fabsf(vis->velocity.x) < 0.000001f && fabsf(vis->velocity.y) < 0.000001f && fabsf(vis->velocity.z) < 0.000001f &&
      !(vis->phys_flags & PF_GRAVITY)) {
    return;
  }

  // Determine velocity
  if (vis->phys_flags & PF_FIXED_VELOCITY) {
    vis->pos += vis->velocity * Frametime;
  } else {
    if (vis->mass > 0.0f && vis->drag > 0.0f) {
      // If the object is effected by gravity (normal, lighter than air, and anti-gravity)
      if (vis->phys_flags & PF_GRAVITY) {
        total_force.x = total_force.z = 0.0f;
        total_force.y = Gravity_strength * vis->mass;
      } else if (vis->phys_flags & PF_REVERSE_GRAVITY) {
        total_force.x = total_force.z = 0.0f;
        total_force.y = -Gravity_strength * vis->mass;
      } else {
        total_force.x = total_force.y = total_force.z = 0.0f;
      }

      // Note: The math here is done in 64bit floats because we will run into precision problems with 32bit
      const double forceOverDrag[3] = {total_force.x / vis->drag, total_force.y / vis->drag, total_force.z / vis->drag};
      const double frameTime = Frametime;
      const double massOverDrag = vis->mass / vis->drag;
      const double dragOverMass = vis->drag / vis->mass;
      const double expDoMFt = exp(-dragOverMass * frameTime);

      double visNewPos[3];
      visNewPos[0] = double(vis->pos.x) + forceOverDrag[0] * frameTime +
                     massOverDrag * (double(vis->velocity.x) - forceOverDrag[0]) * (1.0 - expDoMFt);
      visNewPos[1] = double(vis->pos.y) + forceOverDrag[1] * frameTime +
                     massOverDrag * (double(vis->velocity.y) - forceOverDrag[1]) * (1.0 - expDoMFt);
      visNewPos[2] = double(vis->pos.z) + forceOverDrag[2] * frameTime +
                     massOverDrag * (double(vis->velocity.z) - forceOverDrag[2]) * (1.0 - expDoMFt);

      double visNewVel[3];
      visNewVel[0] = (double(vis->velocity.x) - forceOverDrag[0]) * expDoMFt + forceOverDrag[0];
      visNewVel[1] = (double(vis->velocity.y) - forceOverDrag[1]) * expDoMFt + forceOverDrag[1];
      visNewVel[2] = (double(vis->velocity.z) - forceOverDrag[2]) * expDoMFt + forceOverDrag[2];