/// <summary>
/// Rescales a convex hull shape.
/// </summary>
/// <param name="shape">The shape.</param>
/// <param name="scaleFactor">The scaling factor.</param>
/// <returns>The new hull.</returns>
public static ConvexHullShape Rescale(this ConvexHullShape shape, Vector3 scaleFactor)
{
ReadOnlyList <Vector3> verts = shape.Vertices;
List <Vector3> newlist = new List <Vector3>(verts.Count);
foreach (Vector3 vert in verts)
{
newlist.Add(vert * scaleFactor);
}
double len = scaleFactor.Length();
RawList <int> triangles = CommonResources.GetIntList();
ConvexHullHelper.GetConvexHull(newlist, triangles);
InertiaHelper.ComputeShapeDistribution(newlist, triangles, out double volume, out Matrix3x3 volumeDistribution);
ConvexShapeDescription csd = new ConvexShapeDescription()
{
CollisionMargin = shape.CollisionMargin,
EntityShapeVolume = new BEPUphysics.CollisionShapes.EntityShapeVolumeDescription()
{
Volume = volume,
VolumeDistribution = volumeDistribution
},
MaximumRadius = shape.MaximumRadius * len,
MinimumRadius = shape.MinimumRadius * len
};
CommonResources.GiveBack(triangles);
return(new ConvexHullShape(newlist, csd));
}
/// <summary>
/// Recenters the triangle data and computes the volume distribution.
/// </summary>
/// <param name="data">Mesh data to analyze.</param>
/// <returns>Computed center, volume, and volume distribution.</returns>
private ShapeDistributionInformation ComputeVolumeDistribution(TransformableMeshData data)
{
//Compute the surface vertices of the shape.
ShapeDistributionInformation shapeInformation;
if (solidity == MobileMeshSolidity.Solid)
{
//The following inertia tensor calculation assumes a closed mesh.
var transformedVertices = CommonResources.GetVectorList();
if (transformedVertices.Capacity < data.vertices.Length)
{
transformedVertices.Capacity = data.vertices.Length;
}
transformedVertices.Count = data.vertices.Length;
for (int i = 0; i < data.vertices.Length; ++i)
{
data.GetVertexPosition(i, out transformedVertices.Elements[i]);
}
InertiaHelper.ComputeShapeDistribution(transformedVertices, data.indices, out shapeInformation.Center, out shapeInformation.Volume, out shapeInformation.VolumeDistribution);
CommonResources.GiveBack(transformedVertices);
if (shapeInformation.Volume > F64.C0)
{
return(shapeInformation);
}
throw new ArgumentException("A solid mesh must have volume.");
}
shapeInformation.Center = new Vector3();
shapeInformation.VolumeDistribution = new Matrix3x3();
Fix64 totalWeight = F64.C0;
for (int i = 0; i < data.indices.Length; i += 3)
{
//Compute the center contribution.
Vector3 vA, vB, vC;
data.GetTriangle(i, out vA, out vB, out vC);
Vector3 vAvB;
Vector3 vAvC;
Vector3.Subtract(ref vB, ref vA, out vAvB);
Vector3.Subtract(ref vC, ref vA, out vAvC);
Vector3 cross;
Vector3.Cross(ref vAvB, ref vAvC, out cross);
Fix64 weight = cross.Length();
totalWeight += weight;
Fix64 perVertexWeight = weight * F64.OneThird;
shapeInformation.Center += perVertexWeight * (vA + vB + vC);
//Compute the inertia contribution of this triangle.
//Approximate it using pointmasses positioned at the triangle vertices.
//(There exists a direct solution, but this approximation will do plenty fine.)
Matrix3x3 aContribution, bContribution, cContribution;
InertiaHelper.GetPointContribution(perVertexWeight, ref Toolbox.ZeroVector, ref vA, out aContribution);
InertiaHelper.GetPointContribution(perVertexWeight, ref Toolbox.ZeroVector, ref vB, out bContribution);
InertiaHelper.GetPointContribution(perVertexWeight, ref Toolbox.ZeroVector, ref vC, out cContribution);
Matrix3x3.Add(ref aContribution, ref shapeInformation.VolumeDistribution, out shapeInformation.VolumeDistribution);
Matrix3x3.Add(ref bContribution, ref shapeInformation.VolumeDistribution, out shapeInformation.VolumeDistribution);
Matrix3x3.Add(ref cContribution, ref shapeInformation.VolumeDistribution, out shapeInformation.VolumeDistribution);
}
shapeInformation.Center /= totalWeight;
//The extra factor of 2 is used because the cross product length was twice the actual area.
Matrix3x3.Multiply(ref shapeInformation.VolumeDistribution, F64.C1 / (F64.C2 * totalWeight), out shapeInformation.VolumeDistribution);
//Move the inertia tensor into position according to the center.
Matrix3x3 additionalInertia;
InertiaHelper.GetPointContribution(F64.C0p5, ref Toolbox.ZeroVector, ref shapeInformation.Center, out additionalInertia);
Matrix3x3.Subtract(ref shapeInformation.VolumeDistribution, ref additionalInertia, out shapeInformation.VolumeDistribution);
shapeInformation.Volume = F64.C0;
return(shapeInformation);
}