C#のWinFormsでScrollBar付PictureBoxをUserControlで作成してみた。

using System.Diagnostics;

class CustomControl : UserControl
{
    HScrollBar _hScrollBar;
    VScrollBar _vScrollBar;
    PictureBox _pictureBox;
    public CustomControl()
    {
        _hScrollBar = new()
        {
            Dock = DockStyle.Bottom,
        };
        _vScrollBar = new()
        {
            Dock = DockStyle.Right,
        };
        _pictureBox = new()
        {
            Dock = DockStyle.Fill,
        };
        this.Controls.Add(this._hScrollBar);
        this.Controls.Add(this._vScrollBar);
        this.Controls.Add(this._pictureBox);

        this._vScrollBar.Scroll += VScrollBar_Scroll;
        this._hScrollBar.Scroll += HScrollBar_Scroll;
        this._pictureBox.Paint += PictureBox_Paint;
        this.Resize += CustomControl_Resize;
    }
    Bitmap? _bitmap = null;
    public Bitmap? Bitmap
    {
        get { return _bitmap; }
        set
        {
            if (value == _bitmap) return;

            _bitmap?.Dispose();
            _bitmap = value;
            ShowBitmap();
        }
    }
    void ResetScrollBar()
    {
        if (Bitmap is null) return;

        _hScrollBar.Minimum = 0;
        _hScrollBar.Maximum = 0;

        int width = _pictureBox.Width - _hScrollBar.Height;
        int height = _pictureBox.Height - _vScrollBar.Width;
        if(Bitmap.Width - width > 0)
        {
            float ratio = (float)width / (float)Bitmap.Width; 
            int largeChange = (int)((float)width * ratio);
            _hScrollBar.LargeChange = largeChange;
            _hScrollBar.Maximum = Bitmap.Width - width + largeChange;
            _hScrollBar.Visible = true;
        }
        else
        {
            _hScrollBar.Visible = false;
        }

        _vScrollBar.Minimum = 0;
        _vScrollBar.Maximum = 0;

        if(Bitmap.Height - height > 0)
        {
            float ratio = (float)height / (float)Bitmap.Height; 
            int largeChange = (int)((float)height * ratio);
            _vScrollBar.LargeChange = largeChange;
            _vScrollBar.Maximum = Bitmap.Height - height + largeChange;
            _vScrollBar.Visible = true;
        }
        else
        {
            _vScrollBar.Visible = false;
        }

    }
    void ShowBitmap()
    {
        if (Bitmap is null) return;

        ResetScrollBar();
        _pictureBox.Invalidate();
    }
    void PictureBox_Paint(Object? s, PaintEventArgs e)
    {
        if (Bitmap is null) return;

        RectangleF rectf = new (
            _hScrollBar.Value, _vScrollBar.Value,
            _pictureBox.ClientSize.Width, _pictureBox.ClientSize.Height);
        
        e.Graphics.DrawImage(Bitmap, 0, 0, rectf, GraphicsUnit.Pixel);
    }
    void VScrollBar_Scroll(Object? s, ScrollEventArgs e)
    {
        _pictureBox.Invalidate();
    }
    void HScrollBar_Scroll(Object? s, ScrollEventArgs e)
    {
        _pictureBox.Invalidate();
    }
    void CustomControl_Resize(Object? s, EventArgs e)
    {
        if (Bitmap is null) return;

        if (_pictureBox.Width == 0) return;

        ResetScrollBar();
        _pictureBox.Invalidate();
    }
}

namespace UserControl01;

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

        CustomControl obj = new ()
        {
            Parent = this,
            Dock = DockStyle.Fill,
        };
        Bitmap bmp = new (@"H:\csharp\dotnet8\winforms\UserControl01\202406041040.png");
        obj.Bitmap = bmp;
    }
}