public void _UpdateCenterArmPos()
{
if( _isDirtyCenterArmPos ) {
_isDirtyCenterArmPos = false;
var nearArmPos = this.shoulderPos;
if( nearArmPos == null ) {
nearArmPos = this.armPos;
}
if( nearArmPos != null ) {
_centerArmPos = (nearArmPos[0] + nearArmPos[1]) * 0.5f;
}
}
}