c# 实现框选截图功能

以下是 C# 实现框选截图功能的代码示例：

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

public class ScreenCapture : Form
{
    private Point start;
    private Rectangle rect;

    public ScreenCapture()
    {
        this.DoubleBuffered = true;
        this.FormBorderStyle = FormBorderStyle.None;
        this.WindowState = FormWindowState.Maximized;
        this.Cursor = Cursors.Cross;
        this.MouseDown += ScreenCapture_MouseDown;
        this.MouseMove += ScreenCapture_MouseMove;
        this.MouseUp += ScreenCapture_MouseUp;
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);
        using (Pen pen = new Pen(Color.Red, 2))
        {
            e.Graphics.DrawRectangle(pen, rect);
        }
    }

    private void ScreenCapture_MouseDown(object sender, MouseEventArgs e)
    {
        start = new Point(e.X, e.Y);
        rect = new Rectangle(start, Size.Empty);
    }

    private void ScreenCapture_MouseMove(object sender, MouseEventArgs e)
    {
        if (e.Button == MouseButtons.Left)
        {
            Point current = new Point(e.X, e.Y);
            rect.Location = new Point(
                Math.Min(start.X, current.X),
                Math.Min(start.Y, current.Y));
            rect.Size = new Size(
                Math.Abs(start.X - current.X),
                Math.Abs(start.Y - current.Y));
            Invalidate();
        }
    }

    private void ScreenCapture_MouseUp(object sender, MouseEventArgs e)
    {
        if (rect.Width > 0 && rect.Height > 0)
        {
            using (Bitmap bitmap = new Bitmap(rect.Width, rect.Height))
            {
                using (Graphics graphics = Graphics.FromImage(bitmap))
                {
                    graphics.CopyFromScreen(rect.Location, Point.Empty, rect.Size);
                }
                Clipboard.SetImage(bitmap);
                MessageBox.Show("截图已复制到剪贴板。");
            }
        }
        Close();
    }

    public static void Main()
    {
        Application.Run(new ScreenCapture());
    }
}

这个程序创建了一个全屏的窗体，并在窗体上绘制了一个红色的矩形，用于框选截图。当用户按下鼠标左键并拖动时，矩形会跟随鼠标移动。当用户释放鼠标左键时，程序会将框选区域的屏幕截图复制到剪贴板，并关闭窗体。