winform GDI+ 画扇形 想消除一部分 怎么做

[絔颵柒]

如何消除黑框里的部分 只剩下圆环的那部分
代码如下

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Drawing.Drawing2D;
using System.IO;

namespace _64格子
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            this.DoubleBuffered = true;//开启双缓冲，减少闪烁
        }
        public int k;
        public int j;
        int r;
        public int l;
        Bitmap bmp;
        Graphics g;
        private void Form1_Load(object sender, EventArgs e)
        {
            k = -750;
            j = -375;
            r = 1500;
            //timer1.Start();
            l = 0;
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            
            bmp = new Bitmap(this.Width,this.Height);          
            Pen pen = new Pen(Color.Red, 1);
            g = Graphics.FromImage(bmp);
            g.SmoothingMode = SmoothingMode.AntiAlias;
            g.DrawPie(pen, k, j, r, r, -15, 30);
            g.DrawPie(pen, k, j, r, r, 0, 30);
            for (double n = 500; n <= r; n += 62.5)
            {
                g.DrawPie(pen, -(int)n/2+l, (int)(j + (r - n) / 2), (int)n, (int)n, -30, 60);
            }
             e.Graphics.DrawImage(bmp, new Point(0, 0));           
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            if (k <= 1500)
            {
                k += 50;
                l += 50;
                Refresh();
                g.Dispose();
                bmp.Dispose();
            }
            else
            { return; }
        }
    }
}

[crystal_lz]

[crystal_lz]

g.Clip 限制 gdi绘制的作用范围