C#でGIMPのパス機能ぽいものを試作する。

namespace Maru1;

using System.Drawing.Drawing2D;
using System.Collections.Generic;
using System.Linq;

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

        // コントロールの生成
        var panel1 = new Panel {
            Dock = DockStyle.Fill,
            AutoScroll = true,
        };
        Controls.Add(panel1);
        var picbox1 = new PictureBox {
            SizeMode = PictureBoxSizeMode.AutoSize,
            Image = new Bitmap(1024, 1024),
        };
        panel1.Controls.Add(picbox1);

        // パス
        LinkedList<GraphicsPath> marus = new();
        GraphicsPath lines = new();

        // ペン
        var pen1 = new Pen(Brushes.Black, 1);

        // ポイントの削除及び移動
        LinkedListNode<GraphicsPath>? targetPoint = null;
        PointF? removePoint = null;

        // マウスダウン
        picbox1.MouseDown += (s, e) => {
            
            LinkedListNode<GraphicsPath>? p = marus.First;
            while(p != null) {
                var tmp = p.Value;
                if (tmp.IsVisible(e.Location)) {
                    targetPoint = p;
                }
                p = p.Next;
            }
            if (targetPoint != null) {
                // 〇を削除
                removePoint = e.Location;
                return;
            } else {
                // 〇を追加
                var path = new GraphicsPath();
                path.AddEllipse(e.X-5, e.Y-5, 10, 10);
                var n = new LinkedListNode<GraphicsPath>(path);
                marus.AddLast(n);
            }
            picbox1.Invalidate();
        };
        // マウスアップ
        picbox1.MouseUp += (s, e) => {
            if (targetPoint != null) {
                if (removePoint == e.Location) {
                    // 〇を削除
                    marus.Remove(targetPoint);
                    targetPoint.Value.Dispose();
                }
                targetPoint = null;
                picbox1.Invalidate();
            }
        };
        // マウス移動
        picbox1.MouseMove += (s, e) => {
            if (targetPoint != null) {
                // 〇を移動
                targetPoint.Value.Dispose();
                targetPoint.Value = new GraphicsPath();
                targetPoint.Value.AddEllipse(e.X-5, e.Y-5, 10, 10);
                picbox1.Invalidate();
            }
        };
        // ペイント
        picbox1.Paint += (s, e) => {
            // 背景色でクリア
            e.Graphics.Clear(picbox1.BackColor);
            

            List<PointF> points = new();
            LinkedListNode<GraphicsPath>? p = marus.First;
            while(p != null) {
                var path = p.Value;

                e.Graphics.DrawPath(pen1, path);
                PointF pf = new(path.PathPoints[0].X-5, path.PathPoints[0].Y);
                points.Add(pf);

                p = p.Next;
            }
            if (points.Any()) {
                lines.Dispose();
                lines = new GraphicsPath();
                lines.AddLines(points.ToArray());
                e.Graphics.DrawPath(pen1, lines);
            };
        };
    }
}