/// 視線方向を向く（upベクトルがY軸プラス方向に固定版）
static public void LookTrgVec(ref Matrix4 mtx, Vector3 lookVec)
{
Vector3 upVec = new Vector3(0.0f, 1.0f, 0.0f);
if (lookVec.X == 0.0f && lookVec.Z == 0.0f)
{
lookVec.Z = 1.0f;
}
// Z軸のセット
lookVec = lookVec.Normalize();
mtx.M31 = lookVec.X;
mtx.M32 = lookVec.Y;
mtx.M33 = lookVec.Z;
mtx.M34 = 0;
// X軸のセット
Vector3 calVecX = Common.VectorUtil.Cross2(upVec, lookVec);
calVecX = calVecX.Normalize();
mtx.M11 = calVecX.X;
mtx.M12 = calVecX.Y;
mtx.M13 = calVecX.Z;
mtx.M14 = 0;
// Y軸のセット
Vector3 calVecY = VectorUtil.Cross2(lookVec, calVecX);
calVecY = calVecY.Normalize();
mtx.M21 = calVecY.X;
mtx.M22 = calVecY.Y;
mtx.M23 = calVecY.Z;
mtx.M24 = 0;
}