项目 4 任务 2 网络摄像机：PictureBox、Image / Bitmap、照片列表

- 摄像头：自绘东围墙场景（Camera/scene.svg），按云台位置切成 640×480 帧（build-frames.ts）；
  Pan 每次转一格，红外对射被遮挡时画面出现翻墙的人；类名、委托、事件参数与教材 dll 一致，
  ImageRead 每 250 ms 在后台线程触发
- Image / Bitmap 保存真实图片数据：Save、FromFile、FromStream，文件夹不存在时报 GDI+ 一般性错误；
  图片每张只发给浏览器一次（按内容哈希缓存）
- 程序所在目录（AppDomain.CurrentDomain.BaseDirectory，编译检查单独放行）和当前目录指向可写的 bin/Debug，
  沙箱里在沙箱的临时目录
- PictureBox（SizeMode、BorderStyle）；设计器工具箱加"图片框"；运行区显示程序保存的图片，点开看大图；
  实训台摄像头图标显示开启状态
- 评分规则加图片框显示图片、摄像头开关与转向、保存图片三种检查；示例 p4-t2-网络摄像机
- 测试：摄像头端到端、图片读写与程序目录、AppDomain 编译检查、评分出错情况

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

runtime/Sim.WinForms/Drawing/Image.cs

@@ -0,0 +1,105 @@
+using System.ComponentModel;
+using System.Drawing.Imaging;
+using System.IO;
+using System.Runtime.InteropServices;
+using System.Security.Cryptography;
+using Sim.Host;
+
+namespace System.Drawing;
+
+/// <summary>
+/// 图片。System.Drawing 在 Linux 上不受支持，这里只保存图片文件的原始数据（JPEG、PNG、GIF、BMP）和尺寸：
+/// 能显示在 PictureBox 上、保存成文件、从文件或流读回，不能逐像素绘制。
+/// </summary>
+public abstract class Image : IDisposable, ICloneable
+{
+    private string? _simKey;
+
+    private protected Image(byte[] data)
+    {
+        Data = data;
+        (RawFormat, Width, Height) = ReadHeader(data) ?? throw new ArgumentException("参数无效：不是 JPEG、PNG、GIF 或 BMP 格式的图片。");
+    }
+
+    internal byte[] Data { get; }
+
+    public int Width { get; }
+    public int Height { get; }
+    public Size Size => new(Width, Height);
+    public ImageFormat RawFormat { get; }
+    public object? Tag { get; set; }
+
+    /// <summary>平台内部使用：图片内容的哈希，浏览器按它缓存图片，同一张图只传一次</summary>
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    public string SimKey => _simKey ??= Convert.ToHexString(SHA1.HashData(Data)).ToLowerInvariant();
+
+    internal string MimeType => RawFormat.MimeType;
+
+    public static Image FromFile(string filename) => new Bitmap(filename);
+
+    public static Image FromStream(Stream stream) => new Bitmap(stream);
+
+    public void Save(string filename) => Save(filename, RawFormat);
+
+    /// <summary>按原格式写出图片数据（不做格式转换）。目录不存在时和 GDI+ 一样报"一般性错误"</summary>
+    public void Save(string filename, ImageFormat format)
+    {
+        try
+        {
+            File.WriteAllBytes(filename, Data);
+        }
+        catch (DirectoryNotFoundException)
+        {
+            throw new ExternalException("GDI+ 中发生一般性错误。（保存图片的文件夹不存在，先用 Directory.CreateDirectory 创建）");
+        }
+        SimHost.ImageSaved(Path.GetFullPath(filename), this);
+    }
+
+    public void Save(Stream stream, ImageFormat format) => stream.Write(Data, 0, Data.Length);
+
+    public object Clone() => new Bitmap(this);
+
+    public void Dispose() => GC.SuppressFinalize(this);
+
+    private static (ImageFormat, int, int)? ReadHeader(byte[] d)
+    {
+        if (d.Length >= 24 && d[0] == 0x89 && d[1] == 'P' && d[2] == 'N' && d[3] == 'G')
+            return (ImageFormat.Png, BigEndian(d, 16), BigEndian(d, 20));
+        if (d.Length >= 10 && d[0] == 'G' && d[1] == 'I' && d[2] == 'F')
+            return (ImageFormat.Gif, d[6] | d[7] << 8, d[8] | d[9] << 8);
+        if (d.Length >= 26 && d[0] == 'B' && d[1] == 'M')
+            return (ImageFormat.Bmp, BitConverter.ToInt32(d, 18), Math.Abs(BitConverter.ToInt32(d, 22)));
+        if (d.Length >= 4 && d[0] == 0xFF && d[1] == 0xD8)
+        {
+            // 依次跳过各段，找到记录尺寸的 SOF 段
+            var i = 2;
+            while (i + 9 < d.Length && d[i] == 0xFF)
+            {
+                var marker = d[i + 1];
+                var length = d[i + 2] << 8 | d[i + 3];
+                if (marker is >= 0xC0 and <= 0xCF and not 0xC4 and not 0xC8 and not 0xCC)
+                    return (ImageFormat.Jpeg, d[i + 7] << 8 | d[i + 8], d[i + 5] << 8 | d[i + 6]);
+                i += 2 + length;
+            }
+        }
+        return null;
+    }
+
+    private static int BigEndian(byte[] d, int offset) => d[offset] << 24 | d[offset + 1] << 16 | d[offset + 2] << 8 | d[offset + 3];
+}
+
+public sealed class Bitmap : Image
+{
+    public Bitmap(string filename) : base(File.ReadAllBytes(filename)) { }
+
+    public Bitmap(Stream stream) : base(ReadAll(stream)) { }
+
+    public Bitmap(Image original) : base(original.Data) { }
+
+    private static byte[] ReadAll(Stream stream)
+    {
+        using var buffer = new MemoryStream();
+        stream.CopyTo(buffer);
+        return buffer.ToArray();
+    }
+}

runtime/Sim.WinForms/Drawing/ImageFormat.cs

@@ -0,0 +1,23 @@
+namespace System.Drawing.Imaging;
+
+/// <summary>图片格式。Image.Save 时只用来对应文件类型，不做格式转换</summary>
+public sealed class ImageFormat
+{
+    private readonly string _name;
+
+    private ImageFormat(string name, string mimeType)
+    {
+        _name = name;
+        MimeType = mimeType;
+    }
+
+    internal string MimeType { get; }
+
+    public static ImageFormat Jpeg { get; } = new("Jpeg", "image/jpeg");
+    public static ImageFormat Png { get; } = new("Png", "image/png");
+    public static ImageFormat Gif { get; } = new("Gif", "image/gif");
+    public static ImageFormat Bmp { get; } = new("Bmp", "image/bmp");
+    public static ImageFormat Icon { get; } = new("Icon", "image/x-icon");
+
+    public override string ToString() => _name;
+}

runtime/Sim.WinForms/Forms/PictureBox.cs

@@ -0,0 +1,84 @@
+using System.ComponentModel;
+using System.Drawing;
+using System.Text.Json.Nodes;
+using Sim.Host;
+
+namespace System.Windows.Forms;
+
+public enum PictureBoxSizeMode { Normal, StretchImage, AutoSize, CenterImage, Zoom }
+
+/// <summary>图片框（教材项目 4 显示摄像头画面）</summary>
+public class PictureBox : Control, ISupportInitialize
+{
+    private Image? _image;
+    private PictureBoxSizeMode _sizeMode;
+    private BorderStyle _borderStyle;
+
+    protected override Size DefaultSize => new(100, 50);
+
+    /// <summary>
+    /// 要显示的图片。不检查调用线程：教材在摄像头回调（后台线程）里直接给 Image 赋值，
+    /// 真实 WinForms 的 PictureBox 也不会因此报错。
+    /// </summary>
+    public Image? Image
+    {
+        get => _image;
+        set
+        {
+            LegacyThreads.CheckPoint();
+            if (ReferenceEquals(_image, value)) return;
+            _image = value;
+            NotifyChanged(nameof(Image), value);
+            if (_sizeMode == PictureBoxSizeMode.AutoSize) FitToImage();
+        }
+    }
+
+    public PictureBoxSizeMode SizeMode
+    {
+        get => _sizeMode;
+        set
+        {
+            if (SetProp(ref _sizeMode, value, nameof(SizeMode)) && value == PictureBoxSizeMode.AutoSize) FitToImage();
+        }
+    }
+
+    public BorderStyle BorderStyle
+    {
+        get => _borderStyle;
+        set => SetProp(ref _borderStyle, value, nameof(BorderStyle));
+    }
+
+    public string? ImageLocation { get; set; }
+    public Image? ErrorImage { get; set; }
+    public Image? InitialImage { get; set; }
+    public bool WaitOnLoad { get; set; }
+
+    /// <summary>从文件加载图片（只支持本地文件）</summary>
+    public void Load(string url)
+    {
+        ImageLocation = url;
+        Image = Image.FromFile(url);
+    }
+
+    public void Load()
+    {
+        if (!string.IsNullOrEmpty(ImageLocation)) Load(ImageLocation);
+    }
+
+    // Designer.cs 里 VS 生成 ((ISupportInitialize)pictureBox1).BeginInit() / EndInit()
+    public void BeginInit() { }
+    public void EndInit() { }
+
+    private void FitToImage()
+    {
+        if (_image != null) Size = _image.Size;
+    }
+
+    protected override void WriteProps(JsonObject props)
+    {
+        base.WriteProps(props);
+        props["Image"] = PropValue.From(_image);
+        props["SizeMode"] = _sizeMode.ToString();
+        props["BorderStyle"] = _borderStyle.ToString();
+    }
+}

runtime/Sim.WinForms/Host/PropValue.cs

@@ -31,6 +31,7 @@ public static class PropValue
             ["underline"] = f.Underline,
             ["strikeout"] = f.Strikeout,
         },
+        Image image => new JsonObject { ["key"] = SimHost.ImageKey(image), ["width"] = image.Width, ["height"] = image.Height },
         Padding p => new JsonObject { ["left"] = p.Left, ["top"] = p.Top, ["right"] = p.Right, ["bottom"] = p.Bottom },
         IEnumerable list => ListOf(list),
         _ => JsonValueOf(value.ToString() ?? ""),

runtime/Sim.WinForms/Host/SimHost.cs

@@ -75,6 +75,42 @@ public static class SimHost
         _output.WriteLine(new JsonObject { ["type"] = "patch", ["changes"] = changes }.ToJsonString(JsonOptions));
     }
 
+    // ---------- 图片 ----------
+
+    private static readonly HashSet<string> SentImages = new();
+
+    /// <summary>
+    /// 学生程序的"程序所在目录"（AppDomain.CurrentDomain.BaseDirectory），可写，程序结束后清掉。
+    /// 运行器启动时设定；保存的图片按相对这里的路径显示在网页的照片列表里。
+    /// </summary>
+    public static string AppBaseDirectory { get; set; } = AppContext.BaseDirectory;
+
+    /// <summary>图片在浏览器端的编号；第一次用到时先把图片数据发过去，浏览器缓存后同一张图不再重发</summary>
+    public static string ImageKey(System.Drawing.Image image)
+    {
+        var key = image.SimKey;
+        bool isNew;
+        lock (SentImages) isNew = SentImages.Add(key);
+        if (isNew)
+        {
+            Send(new JsonObject
+            {
+                ["type"] = "image",
+                ["key"] = key,
+                ["mime"] = image.MimeType,
+                ["data"] = Convert.ToBase64String(image.Data),
+            });
+        }
+        return key;
+    }
+
+    /// <summary>学生程序用 Image.Save 保存了图片：网页的照片列表里显示出来</summary>
+    public static void ImageSaved(string fullPath, System.Drawing.Image image)
+    {
+        var path = fullPath.StartsWith(AppBaseDirectory, StringComparison.Ordinal) ? fullPath[AppBaseDirectory.Length..] : fullPath;
+        Send(new JsonObject { ["type"] = "imageSaved", ["path"] = path, ["image"] = ImageKey(image) });
+    }
+
     public static void SendConsole(string text) => Send(new JsonObject { ["type"] = "console", ["text"] = text });
 
     public static void SendDevice(string device, string action, object? data)