public void FVector3AndTheta(FVector3 v, Fix64 theta)
{
// initializes a quaternion based on a 3d direction vector and angle
// note the direction vector must be a unit vector
// and the angle is in rads
Fix64 theta_div_2 = theta * Fix64.Half; // compute theta/2
// compute the quaterion, note this is from chapter 4
// pre-compute to save time
Fix64 sinf_theta = Fix64.Sin(theta_div_2);
x = sinf_theta * v.x;
y = sinf_theta * v.y;
z = sinf_theta * v.z;
w = Fix64.Cos(theta_div_2);
}
// //
// // 摘要:
// // Creates a rotation which rotates from fromDirection to toDirection.
// //
// // 参数:
// // fromDirection:
// //
// // toDirection:
// public void SetFromToRotation(Vector3 fromDirection, Vector3 toDirection);
// //
// // 摘要:
// // Creates a rotation with the specified forward and upwards directions.
// //
// // 参数:
// // view:
// // The direction to look in.
// //
// // up:
// // The vector that defines in which direction up is.
// public void SetLookRotation(Vector3 view, [DefaultValue("Vector3.up")] Vector3 up);
// //
// // 摘要:
// // Creates a rotation with the specified forward and upwards directions.
// //
// // 参数:
// // view:
// // The direction to look in.
// //
// // up:
// // The vector that defines in which direction up is.
// [ExcludeFromDocs]
// public void SetLookRotation(Vector3 view);
public void ToAngleAxis(out Fix64 angle, out FVector3 axis)
{
// this function converts a unit quaternion into a unit direction
// vector and rotation angle about that vector
// extract theta
angle = Fix64.Acos(w);
// pre-compute to save time
Fix64 sinf_theta_inv = Fix64.One / Fix64.Sin(angle);
// now the vector
axis.x = x * sinf_theta_inv;
axis.y = y * sinf_theta_inv;
axis.z = z * sinf_theta_inv;
// multiply by 2
angle *= Fix64.Two;
}