C#のWinFomrsで画像の矩形選択機能を試作する。

using System.Drawing.Drawing2D;

namespace PictureBox04;

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        this.Size = new Size(256, 256);

        var bmp = new Bitmap(512, 512);
        using(var g = Graphics.FromImage(bmp))
        {
            g.Clear(Color.Blue);
            var rect = new Rectangle(64, 64, 128, 128);
            var rect2 = new Rectangle(64+128, 64+128, 128, 128);
            g.FillPie(Brushes.White, rect, 0f, 360f);
            g.FillRectangle(Brushes.White, rect2);
        }

        var panel1 = new Panel()
        {
            AutoScroll = true,
            Dock = DockStyle.Fill,
            Parent = this,
        };

        var picbox1 = new PictureBox()
        {
            SizeMode = PictureBoxSizeMode.AutoSize,
            Image = bmp,
            Parent = panel1,
        };
        
        int x1 = -1;
        int y1 = -1;
        int x2 = -1;
        int y2 = -1;
        bool mouseMoving = false;
        Pen pen1 = new Pen(Brushes.Black, 3.0f);
        GraphicsPath path1 = new();
        // ピクチャボックス上のマウスダウンイベント
        picbox1.MouseDown += (s, e) =>
        {
            x1 = e.Location.X;
            y1 = e.Location.Y;
            x2 = -1;
            y2 = -1;
            mouseMoving = true;
        };
        // ピクチャボックス上のマウスの移動イベント
        picbox1.MouseMove += (s, e) =>
        {
            if (mouseMoving == true)
            {
                int x = e.Location.X;
                int y = e.Location.Y;
                var rect = new Rectangle(x1, y1, x-x1, y-y1);
                path1?.Dispose();
                path1 = new GraphicsPath();
                path1.AddRectangle(rect);
                picbox1.Invalidate();
            }
        };
        // ピクチャボックス再描画
        picbox1.Paint += (s, e) =>
        {
            if (mouseMoving)
                e.Graphics.DrawPath(pen1, path1);
        };
        // ピクチャボックス上のマウスアップ
        picbox1.MouseUp += (s, e) =>
        {
            x2 = e.Location.X;
            y2 = e.Location.Y;
            mouseMoving = false;
        };

    }
}