SVGRadialGradientBrush.CrossPoint C# (CSharp) Method

    private Vector2 CrossPoint(float x, float y)
    {
        Vector2 _point = new Vector2(0f, 0f);

        float dx = _fx - x;
        float dy = _fy - y;

        if(dx == 0) {
          _point.x = _fx;
          _point.y = (_fy > y) ? (_fy - _r) : (_fy + _r);
        } else {
          float a, b;
          a = dy / dx;
          b = _fy - a * _fx;

          double ta, tb, tc;

          ta = 1 + a * a;
          tb = 2 * (a * (b - _cy) - _cx);
          tc = (_cx * _cx) + (b - _cy) * (b - _cy) - (_r * _r);

          float delta = (float)((tb * tb) - 4 * ta * tc);

          delta = (float)Math.Sqrt(delta);
          float x1 = (float)((-tb + delta) / (2 * ta));
          float y1 = (float)(a * x1 + b);
          float x2 = (float)((-tb - delta) / (2 * ta));
          float y2 = (float)(a * x2 + b);

          Vector2 vt1 = new Vector2(x1 - _fx, y1 - _fy);
          Vector2 vt2 = new Vector2(x - _fx, y - _fy);

          if(((vt1.x * vt2.x) >= 0) && ((vt1.y * vt2.y) >= 0)) {
        _point.x = x1;
        _point.y = y1;
          } else {
        _point.x = x2;
        _point.y = y2;
          }
        }
        return _point;
    }