c# winforms窗体边框中带边框颜色的圆角边框

using System;
using System.Drawing;
using System.Windows.Forms;

public class CustomForm : Form
{
    private Color borderColor = Color.Red; // 设置边框颜色
    private int borderWidth = 2; // 设置边框宽度
    private int borderRadius = 10; // 设置圆角半径

    public CustomForm()
    {
        this.FormBorderStyle = FormBorderStyle.None; // 设置边框样式为None
        this.Load += CustomForm_Load;
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);

        Graphics g = e.Graphics;
        Pen borderPen = new Pen(borderColor, borderWidth);

        // 绘制圆角矩形边框
        g.DrawRoundedRectangle(borderPen, new Rectangle(borderWidth / 2, borderWidth / 2, this.Width - borderWidth, this.Height - borderWidth), borderRadius);
    }

    private void CustomForm_Load(object sender, EventArgs e)
    {
        this.Invalidate(); // 触发重绘操作
    }
}

public static class GraphicsExtensions
{
    public static void DrawRoundedRectangle(this Graphics graphics, Pen pen, Rectangle bounds, int cornerRadius)
    {
        int diameter = cornerRadius * 2;
        Size size = new Size(diameter, diameter);
        Rectangle arcBounds = new Rectangle(bounds.Location, size);
        graphics.DrawArc(pen, arcBounds, 180, 90);
        arcBounds.X = bounds.Right - diameter;
        graphics.DrawArc(pen, arcBounds, 270, 90);
        arcBounds.Y = bounds.Bottom - diameter;
        graphics.DrawArc(pen, arcBounds, 0, 90);
        arcBounds.X = bounds.Left;
        graphics.DrawArc(pen, arcBounds, 90, 90);
        graphics.DrawLine(pen, bounds.Left + cornerRadius, bounds.Top, bounds.Right - cornerRadius, bounds.Top);
        graphics.DrawLine(pen, bounds.Left + cornerRadius, bounds.Bottom, bounds.Right - cornerRadius, bounds.Bottom);
        graphics.DrawLine(pen, bounds.Left, bounds.Top + cornerRadius, bounds.Left, bounds.Bottom - cornerRadius);
        graphics.DrawLine(pen, bounds.Right, bounds.Top + cornerRadius, bounds.Right, bounds.Bottom - cornerRadius);
    }
}