/// <inheritdoc/>
public override void Apply(RigidBody body)
{
if (body == null)
{
throw new ArgumentNullException("body", "Rigid body in area of effect must not be null.");
}
// Get BuoyancyData. If necessary create new data.
BuoyancyData data = body.BuoyancyData;
if (data == null)
{
Prepare(body);
data = body.BuoyancyData;
}
// Compute size of volume that is in the water and the center of the submerged volume.
Vector3 centerOfSubmergedVolume;
float submergedVolume = GetSubmergedVolume(body.Scale, body.Pose, data.Mesh, out centerOfSubmergedVolume);
if (submergedVolume > 0)
{
// The up force.
Vector3 buoyancyForce = (Density * submergedVolume * Gravity) * Surface.Normal;
// The total volume of the body.
float totalVolume = data.Volume * body.Scale.X * body.Scale.Y * body.Scale.Z;
// The fraction of the total mass that is under the water (assuming constant density).
float submergedMass = body.MassFrame.Mass * submergedVolume / totalVolume;
// Compute linear drag.
Vector3 centerLinearVelocity = body.GetVelocityOfWorldPoint(centerOfSubmergedVolume);
Vector3 dragForce = (submergedMass * LinearDrag) * (Velocity - centerLinearVelocity);
// Apply up force and linear drag force.
Vector3 totalForce = buoyancyForce + dragForce;
AddForce(body, totalForce, centerOfSubmergedVolume);
// Apply torque for angular drag.
// body.Length is proportional to the unscaled shape. Apply scaling to get a new
// proportional value for the scaled shape.
float length = data.Length * 1.0f / 3.0f * (body.Scale.X + body.Scale.Y + body.Scale.Z);
float lengthSquared = length * length;
Vector3 dragTorque = (-submergedMass * AngularDrag * lengthSquared) * body.AngularVelocity;
AddTorque(body, dragTorque);
}
}
/// <summary>
/// Prepares the specified rigid body for the buoyancy effect.
/// </summary>
/// <param name="body">The rigid body.</param>
/// <remarks>
/// <para>
/// This method is automatically called for each body that touches the water. It computes
/// additional information per rigid body that is needed for the buoyancy effect.
/// </para>
/// <para>
/// To prepare the rigid bodies ahead of time, this method can be called manually - but this
/// is not required. It is sufficient to call this method once per rigid body, then the body
/// is prepared for all buoyancy effect instances.
/// </para>
/// </remarks>
/// <exception cref="ArgumentNullException">
/// <paramref name="body"/> is <see langword="null"/>.
/// </exception>
public static void Prepare(RigidBody body)
{
// Must be called once per shape not really per body - but we keep this info internal in
// case we make changes in the future, like per-body buoyancy settings.
if (body == null)
{
throw new ArgumentNullException("body");
}
Shape shape = body.Shape;
// Try to use existing data for the same shape.
var simulation = body.Simulation;
if (simulation != null)
{
int numberOfRigidBodies = simulation.RigidBodies.Count;
for (int i = 0; i < numberOfRigidBodies; i++)
{
var otherBody = simulation.RigidBodies[i];
if (otherBody.Shape == shape && otherBody.BuoyancyData != null)
{
body.BuoyancyData = otherBody.BuoyancyData;
return;
}
}
}
BuoyancyData data = new BuoyancyData();
data.Mesh = shape.GetMesh(0.01f, 4);
data.Volume = data.Mesh.GetVolume();
data.Length = shape.GetAabb(Pose.Identity).Extent.LargestComponent;
body.BuoyancyData = data;
}