public SphericalRoundBullet(XY offset0, float z0, float r, XY v, XY o0)
        {
            __v      = v;
            __angle0 = Mathf.Atan2(z0, offset0.X);
            var axisOffset = XY.Project(offset0, v.Rotated90CW());

            __offset    = o0 + axisOffset;
            __r         = Mathf.Sqrt(r * r - axisOffset.SqrLength);
            BorderColor = Color.Red;
            MainColor   = Color.Red;
            R           = 5;
        }