/// <summary>
/// Computes the inertia tensor of a rigid body using box inertia definition
/// </summary>
public static void ComputeIntertiaTensor(MyRigidBody rbo)
{
MyCommonDebugUtils.AssertDebug(rbo != null);
MyCommonDebugUtils.AssertDebug(rbo.GetRBElementList().Count > 0);
MyCommonDebugUtils.AssertDebug(rbo.GetMass() > 0);
float mass = rbo.GetMass();
BoundingBox box;
box.Min = new Vector3(FLT_MAX);
box.Max = new Vector3(FLT_MIN);
BoundingBox aabb;
Matrix infTensor = new Matrix();
infTensor.M11 = FLT_MAX;
infTensor.M22 = FLT_MAX;
infTensor.M33 = FLT_MAX;
infTensor.M44 = 1.0f;
if (rbo.IsStatic())
{
rbo.InertiaTensor = infTensor;
return;
}
if (rbo.GetRBElementList().Count > 1)
{
for (int e = 0; e < rbo.GetRBElementList().Count; e++)
{
MyRBElement el = rbo.GetRBElementList()[e];
switch (el.GetElementType())
{
case MyRBElementType.ET_TRIANGLEMESH:
{
rbo.InertiaTensor = infTensor;
return;
}
break;
case MyRBElementType.ET_VOXEL:
{
rbo.InertiaTensor = infTensor;
return;
}
break;
default:
{
aabb = el.GetWorldSpaceAABB();
box = BoundingBox.CreateMerged(box, aabb);
}
break;
}
}
Vector3 size = box.Max - box.Min;
infTensor.M11 = mass * (size.Y * size.Y + size.Z * size.Z) / 12.0f;
infTensor.M22 = mass * (size.X * size.X + size.Z * size.Z) / 12.0f;
infTensor.M33 = mass * (size.X * size.X + size.Y * size.Y) / 12.0f;
infTensor.M44 = 1.0f;
rbo.InertiaTensor = infTensor;
rbo.InvertInertiaTensor = Matrix.Invert(infTensor);
return;
}
MyRBElement elem = rbo.GetRBElementList()[0];
switch (elem.GetElementType())
{
case MyRBElementType.ET_TRIANGLEMESH:
{
rbo.InertiaTensor = infTensor;
infTensor.M11 = 0.0f;
infTensor.M22 = 0.0f;
infTensor.M33 = 0.0f;
infTensor.M44 = 0.0f;
rbo.InvertInertiaTensor = infTensor;
return;
}
break;
case MyRBElementType.ET_VOXEL:
{
rbo.InertiaTensor = infTensor;
infTensor.M11 = 0.0f;
infTensor.M22 = 0.0f;
infTensor.M33 = 0.0f;
infTensor.M44 = 0.0f;
rbo.InvertInertiaTensor = infTensor;
return;
}
case MyRBElementType.ET_SPHERE:
{
float radius = ((MyRBSphereElement)elem).Radius;
infTensor.M11 = 2.0f / 5.0f * mass * radius * radius;
infTensor.M22 = 2.0f / 5.0f * mass * radius * radius;
infTensor.M33 = 2.0f / 5.0f * mass * radius * radius;
infTensor.M44 = 1.0f;
rbo.InertiaTensor = infTensor;
//rbo.InvertInertiaTensor = Matrix.Invert(infTensor);
return;
}
break;
case MyRBElementType.ET_BOX:
{
//Vector3 size = ((MyRBBoxElement)elem).Size;
//infTensor.M11 = mass * (size.Y * size.Y + size.Z * size.Z) / 12.0f;
//infTensor.M22 = mass * (size.X * size.X + size.Z * size.Z) / 12.0f;
//infTensor.M33 = mass * (size.X * size.X + size.Y * size.Y) / 12.0f;
//infTensor.M44 = 1.0f;
//rbo.InertiaTensor = infTensor;
//rbo.InvertInertiaTensor = Matrix.Invert(infTensor);
// HACK: After speaking with PetrM, computing changed like box is sphere
float radius = ((MyRBBoxElement)elem).Size.Length() / 2;
infTensor.M11 = 2.0f / 5.0f * mass * radius * radius;
infTensor.M22 = 2.0f / 5.0f * mass * radius * radius;
infTensor.M33 = 2.0f / 5.0f * mass * radius * radius;
infTensor.M44 = 1.0f;
rbo.InertiaTensor = infTensor;
//rbo.InvertInertiaTensor = Matrix.Invert(infTensor);
return;
}
break;
default:
MyCommonDebugUtils.AssertDebug(false);
break;
}
}
