问为什么用Pen::DashPattern集绘制椭圆不能产生预期的结果？

EN

void EllipseDisplayControl::OnPaint(PaintEventArgs^ e)
{
    Graphics^ gfx = e->Graphics;
    gfx->SmoothingMode = Drawing2D::SmoothingMode::AntiAlias;

    int width = 100;
    int height = 10;

    for( int i = 0; i < 15; i ++ )
    {
        Drawing::Pen^ myPen = (Drawing::Pen^) Drawing::Pens::RoyalBlue->Clone(); //use the standard blue as a start point
        myPen->Color = Drawing::Color::FromArgb(64, 32, 111, 144);
        myPen->Width = 3;
        myPen->DashStyle = Drawing::Drawing2D::DashStyle::Solid;
        gfx->DrawEllipse(myPen, 0, 50+i*20, width, height); // Draw the blue ring

        float ellipseCircumference = Math::PI * Math::Sqrt(2* (Math::Pow(0.5*width,2) + Math::Pow(0.5*height,2)));
        array<Single>^ pattern = {4, ellipseCircumference};

        Drawing::Pen^ myPen2 = (Drawing::Pen^) Drawing::Pens::White->Clone(); //use the standard blue as a start point
        myPen2->DashPattern = pattern;
        myPen2->DashOffset = i*10;
        gfx->DrawEllipse(myPen2, 0, 50+i*20, width, height); // Draw the rotating white dot
    }
}