c# 鼠标框选 截屏

在C#中，可以使用以下代码实现鼠标框选截屏功能：

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

public static class ScreenShot
{
    public static void TakeScreenShot(Rectangle rect, string fileName)
    {
        // 创建一个与指定矩形大小相同的图像
        using (Bitmap bmp = new Bitmap(rect.Width, rect.Height))
        {
            // 将指定矩形区域的屏幕图像拷贝到位图中
            using (Graphics g = Graphics.FromImage(bmp))
            {
                g.CopyFromScreen(rect.Location, new Point(0, 0), rect.Size);
            }

            // 保存图像到文件
            bmp.Save(fileName, System.Drawing.Imaging.ImageFormat.Png);
        }
    }
}

public class ScreenShotForm : Form
{
    private Point _startPoint;
    private Rectangle _rect;
    private bool _isDrawing;

    public ScreenShotForm()
    {
        // 设置窗口样式
        FormBorderStyle = FormBorderStyle.None;
        WindowState = FormWindowState.Maximized;
        Cursor = Cursors.Cross;

        // 注册鼠标事件
        MouseDown += ScreenShotForm_MouseDown;
        MouseMove += ScreenShotForm_MouseMove;
        MouseUp += ScreenShotForm_MouseUp;
    }

    private void ScreenShotForm_MouseDown(object sender, MouseEventArgs e)
    {
        // 记录鼠标按下时的位置
        _startPoint = e.Location;
        _isDrawing = true;
    }

    private void ScreenShotForm_MouseMove(object sender, MouseEventArgs e)
    {
        if (_isDrawing)
        {
            // 计算框选矩形的位置和大小
            int x = Math.Min(_startPoint.X, e.X);
            int y = Math.Min(_startPoint.Y, e.Y);
            int width = Math.Abs(_startPoint.X - e.X);
            int height = Math.Abs(_startPoint.Y - e.Y);
            _rect = new Rectangle(x, y, width, height);

            // 重绘窗口
            Invalidate();
        }
    }

    private void ScreenShotForm_MouseUp(object sender, MouseEventArgs e)
    {
        if (_isDrawing)
        {
            // 停止框选并保存截图
            _isDrawing = false;
            ScreenShot.TakeScreenShot(_rect, "screenshot.png");

            // 关闭窗口
            Close();
        }
    }

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

        if (_isDrawing)
        {
            // 绘制框选矩形
            using (Pen pen = new Pen(Color.Red, 2))
            {
                e.Graphics.DrawRectangle(pen, _rect);
            }
        }
    }
}

使用时，可以创建一个 `ScreenShotForm` 实例，它会全屏显示并允许鼠标框选截图：

Application.Run(new ScreenShotForm());