setFromAxisAngle method
Implementation
Quaternion setFromAxisAngle(Vector3 axis, double angle) {
// http://www.euclideanspace.com/maths/geometry/rotations/conversions/angleToQuaternion/index.htm
// assumes axis is normalized
final halfAngle = angle / 2, s = math.sin(halfAngle);
_x = axis.x * s;
_y = axis.y * s;
_z = axis.z * s;
_w = math.cos(halfAngle);
onChangeCallback();
return this;
}