C# 更改椭圆中包含的高度级别

我用如下所示的代码绘制椭圆。如何使红色的高度在椭圆内可以改变，例如从0%-100%。如果0%，则表示红色高度级别为空。如果50%，则红色的高度级别为椭圆的一半。如果100%，则红色的高度级别为满。多谢各位

    private void panel1_Paint(object sender, PaintEventArgs e)
    {
        Rectangle r1= new Rectangle(10, 130, 60, 60);

        // Create solid brush.
        SolidBrush redBrush = new SolidBrush(Color.Red);

        // Create location and size of ellipse.
        float x = 20F;
        float y = 20F;
        float width = 80.0F;
        float height = 200.0F;

        // Fill ellipse on screen.
        e.Graphics.FillEllipse(redBrush, x, y, width, height);
    }

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请尝试以下代码：

void panel1_Paint(object sender, PaintEventArgs e)
    float percent = 0.75f;
    RectangleF bounds = new RectangleF(20, 20, 80, 200);
    FillEllipse(e.Graphics, bounds, percent);
}
static void FillEllipse(Graphics g, RectangleF bounds, float percent) {
    g.DrawEllipse(Pens.Red, bounds);
    g.SetClip(new RectangleF(
        bounds.X,
        bounds.Y + (1f - percent) * bounds.Height,
        bounds.Width,
        percent * bounds.Height));

    g.FillEllipse(Brushes.Red, bounds);
    g.ResetClip();
}