Initial commit

Infra/Buffers/ArrayOwner.cs

@@ -0,0 +1,29 @@
+using System.Buffers;
+
+namespace StitchATon2.Infra.Buffers;
+
+public class ArrayOwner<T> : IBuffer<T> where T : unmanaged 
+{
+    private readonly ArrayPool<T> _owner;
+    private readonly T[] _buffer;
+
+    public ArrayOwner(ArrayPool<T> owner, int size)
+    {
+        _owner = owner;
+        _buffer = owner.Rent(size);
+    }
+    
+    ~ArrayOwner() => Dispose();
+    
+    public void Dispose()
+    {
+        _owner.Return(_buffer);
+        GC.SuppressFinalize(this);
+    }
+
+    public ref T this[int index] => ref _buffer[index];
+
+    public Span<T> Span => _buffer;
+
+    public T[] Array => _buffer;
+}

Infra/Buffers/IBuffer.cs

@@ -0,0 +1,8 @@
+namespace StitchATon2.Infra.Buffers;
+
+public interface IBuffer<T> : IDisposable where T : unmanaged
+{
+    ref T this[int index] { get; }
+        
+    Span<T> Span { get; }
+}

Infra/Buffers/MemoryAllocator.cs

@@ -0,0 +1,15 @@
+using System.Buffers;
+
+namespace StitchATon2.Infra.Buffers;
+
+public static class MemoryAllocator
+{
+    public static IBuffer<T> Allocate<T>(int count) where T : unmanaged
+        => new UnmanagedMemory<T>(count);
+    
+    public static IMemoryOwner<T> AllocateManaged<T>(int count)
+        => MemoryPool<T>.Shared.Rent(count);
+    
+    public static ArrayOwner<T> AllocateArray<T>(int count) where T : unmanaged
+        => new(ArrayPool<T>.Shared, count);
+}

Infra/Buffers/UnmanagedMemory.cs

@@ -0,0 +1,28 @@
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace StitchATon2.Infra.Buffers;
+
+internal sealed unsafe class UnmanagedMemory<T> : IBuffer<T> where T : unmanaged
+{
+    private readonly void* _pointer;
+    private readonly int _count;
+
+    public ref T this[int index] => ref Unsafe.AsRef<T>((T*)_pointer + index); // *((T*)_pointer + index);
+
+    public Span<T> Span => new(_pointer, _count);
+
+    public UnmanagedMemory(int count)
+    {
+        _pointer = NativeMemory.Alloc((nuint)count, (nuint)Unsafe.SizeOf<T>());
+        _count = count;
+    }
+    
+    ~UnmanagedMemory() => Dispose();
+
+    public void Dispose()
+    {
+        NativeMemory.Free(_pointer);
+        GC.SuppressFinalize(this);
+    }
+}

Infra/Encoders/Crc32.cs

@@ -0,0 +1,33 @@
+namespace StitchATon2.Infra.Encoders;
+
+public static class Crc32
+{
+    private static readonly Lazy<uint[]> LazyTable = new(GenerateTable);
+    private static uint[] Table => LazyTable.Value;
+
+    public static uint Compute(Span<byte> buffer, uint initial = 0xFFFFFFFF)
+    {
+        uint crc = initial;
+        foreach (var b in buffer)
+        {
+            crc = Table[(crc ^ b) & 0xFF] ^ (crc >> 8);
+        }
+        return ~crc;
+    }
+
+    private static uint[] GenerateTable()
+    {
+        const uint poly = 0xEDB88320;
+        var table = new uint[256];
+        for (uint i = 0; i < 256; i++)
+        {
+            uint c = i;
+            for (int j = 0; j < 8; j++)
+            {
+                c = (c & 1) != 0 ? (poly ^ (c >> 1)) : (c >> 1);
+            }
+            table[i] = c;
+        }
+        return table;
+    }
+}

Infra/Encoders/PngStreamEncoder.cs

@@ -0,0 +1,143 @@
+using System.Buffers.Binary;
+using System.IO.Compression;
+
+namespace StitchATon2.Infra.Encoders;
+
+public class PngStreamEncoder : IDisposable, IAsyncDisposable
+{
+    private const int BufferSize = 8 * 1024;
+    private const int FlushThreshold = 1024;
+    
+    private readonly Stream _stream;
+    private readonly MemoryStream _memoryStream;
+    private readonly int _width;
+    private readonly int _height;
+
+    private readonly ZLibStream _zlibStream;
+    private bool _disposed;
+    private bool _shouldFlush;
+    
+    public PngStreamEncoder(Stream writableStream, int width, int height)
+    {
+        _stream = writableStream;
+        _width = width;
+        _height = height;
+        _memoryStream = new MemoryStream(BufferSize * 2);
+        _zlibStream = new ZLibStream(_memoryStream, CompressionLevel.Optimal, leaveOpen: true);
+        _memoryStream.SetLength(8);
+        _memoryStream.Position = 8;
+    }
+
+    ~PngStreamEncoder() => Dispose();
+
+    public async Task WriteHeader()
+    {
+        byte[] headerBytes = [
+            0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, // PNG Signature
+            0x00, 0x00, 0x00, 0x0D, // Length
+            
+            // IHDR chunk
+            0x49, 0x48, 0x44, 0x52, // IHDR
+            0x00, 0x00, 0x00, 0x00, // Reserve to write Width
+            0x00, 0x00, 0x00, 0x00, // Reserve to write Height
+            0x08, // Bit depth
+            0x02, // Color type
+            0x00, // Compression method
+            0x00, // Filter method
+            0x00, // Interlace method
+            0x00, 0x00, 0x00, 0x00, // Reserve to write CRC-32
+        ];
+        
+        BinaryPrimitives.WriteInt32BigEndian(headerBytes.AsSpan(16), _width);
+        BinaryPrimitives.WriteInt32BigEndian(headerBytes.AsSpan(20), _height);
+        var crc = Crc32.Compute(headerBytes.AsSpan(12, 17));
+        
+        BinaryPrimitives.WriteUInt32BigEndian(headerBytes.AsSpan(29), crc);
+        
+        await _stream.WriteAsync(headerBytes);
+    }
+
+    public async Task WriteData(Memory<byte> data)
+    {
+        _zlibStream.Write([0]);
+        
+        var dataSlice = data;
+        while (dataSlice.Length > FlushThreshold)
+        {
+            await _zlibStream.WriteAsync(dataSlice[..FlushThreshold]);
+            await _zlibStream.FlushAsync();
+            dataSlice = dataSlice[FlushThreshold..];
+            if(_memoryStream.Length >= BufferSize)
+                await Flush();
+        }
+        
+        if (dataSlice.Length > 0)
+        {
+            await _zlibStream.WriteAsync(dataSlice);
+            await _zlibStream.FlushAsync();
+            _shouldFlush = true;
+        }
+    }
+
+    private async Task Flush()
+    {
+        await _zlibStream.FlushAsync();
+        var dataSize = (int)(_memoryStream.Length - 8);
+
+        _memoryStream.Write("\0\0\0\0"u8);
+
+        _memoryStream.Position = 4;
+        _memoryStream.Write("IDAT"u8);
+
+        var buffer = _memoryStream.GetBuffer();
+        BinaryPrimitives.WriteInt32BigEndian(buffer, dataSize);
+
+        // write Crc
+        var crc = Crc32.Compute(buffer.AsSpan(4, dataSize + 4));
+        BinaryPrimitives.WriteUInt32BigEndian(buffer.AsSpan(dataSize + 8), crc);
+            
+        await _stream.WriteAsync(buffer.AsMemory(0, dataSize + 12));
+        _memoryStream.SetLength(8);
+        _memoryStream.Position = 8;
+        _shouldFlush = false;
+    }
+
+    public async ValueTask WriteEndOfFile()
+    {
+        if(_shouldFlush)
+            await Flush();
+        
+        var endChunk = new byte[] {
+            0x00, 0x00, 0x00, 0x00, // Length
+            0x49, 0x45, 0x4E, 0x44, // IEND
+            0xAE, 0x42, 0x60, 0x82, // Crc
+        };
+        
+        await _stream.WriteAsync(endChunk);
+        await DisposeAsync();
+    }
+
+    public void Dispose()
+    {
+        if (!_disposed)
+        {
+            _zlibStream.Dispose();
+            _memoryStream.Dispose();
+            _disposed = true;
+        }
+        
+        GC.SuppressFinalize(this);
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        if (!_disposed)
+        {
+            await _zlibStream.DisposeAsync();
+            await _memoryStream.DisposeAsync();
+            _disposed = true;
+        }
+        
+        GC.SuppressFinalize(this);
+    }
+}

Infra/ImageIntegral.cs

@@ -0,0 +1,387 @@
+using System.Buffers;
+using System.IO.MemoryMappedFiles;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using SixLabors.ImageSharp.Formats;
+using SixLabors.ImageSharp.Formats.Png;
+using SixLabors.ImageSharp.PixelFormats;
+using StitchATon2.Infra.Buffers;
+
+namespace StitchATon2.Infra;
+
+public class ImageIntegral : IDisposable
+{
+    private const int MaxProcessingQueue = 4;
+
+    private readonly string _imagePath;
+    private readonly string _outputDirectory;
+    private readonly int _width;
+    private readonly int _height;
+
+    private IMemoryOwner<ManualResetEventSlim>? _rowLocks;
+    private MemoryMappedFile? _memoryMappedFile;
+    private readonly object _lock = new();
+
+    private readonly ManualResetEventSlim _queueLock = new(true);
+    private readonly ManualResetEventSlim _initializationLock = new(false);
+
+    private volatile int _processedRows;
+    private volatile int _queueCounter;
+
+    public ImageIntegral(string imagePath, string outputDirectory, int width, int height)
+    {
+        _imagePath = imagePath;
+        _outputDirectory = outputDirectory;
+        _width = width;
+        _height = height;
+    }
+    
+    ~ImageIntegral() => Dispose();
+
+    public void Acquire(int row, Int32Pixel[] buffer, CancellationToken cancellationToken = default)
+    {
+        Acquire(row, cancellationToken);
+        ReadRow(row, buffer);
+    }
+
+    public void Acquire(int row, Span<Int32Pixel> buffer, CancellationToken cancellationToken = default)
+    {
+        Acquire(row, cancellationToken);
+        ReadRow(row, buffer);
+    }
+
+    private void Acquire(int row, CancellationToken cancellationToken)
+    {
+        if (_memoryMappedFile is null)
+        {
+            lock (_lock)
+            {
+                if (_memoryMappedFile is null)
+                {
+                    Task.Factory.StartNew(() => Initialize(cancellationToken), cancellationToken);
+                    _initializationLock.Wait(cancellationToken);
+                    _initializationLock.Dispose();
+                }
+            }
+        }
+
+        _rowLocks?.Memory.Span[row].Wait(cancellationToken);
+    }
+
+    private void Initialize(CancellationToken cancellationToken)
+    {
+        var fileName = Path.GetFileNameWithoutExtension(_imagePath);
+        var path = Path.Combine(_outputDirectory, $"{fileName}.mmf");
+
+        var backedFileStream = InitializeBackedFile(path, out var header);
+        _processedRows = header.ProcessedRows;
+
+        if (header.ProcessedRows >= _height)
+        {
+            // When statement above is true
+            // then it is guaranteed that backed file is valid and fully processed
+            _memoryMappedFile = MemoryMappedFile.CreateFromFile(path, FileMode.Open);
+            _initializationLock.Set();
+            return;
+        }
+        
+        var taskQueue = backedFileStream == null
+            ? Task.CompletedTask
+            : AllocateBackedFile(backedFileStream, header);
+
+        taskQueue = taskQueue.ContinueWith(
+            _ =>
+            {
+                _memoryMappedFile = MemoryMappedFile.CreateFromFile(path, FileMode.Open);
+                _initializationLock.Set();
+            },
+            cancellationToken);
+
+        // initialize resource gating, all rows is expected to be locked
+        // if the backed file require to allocate, it should be safe to do this
+        // asynchronously
+        var rowLocks = MemoryAllocator.AllocateManaged<ManualResetEventSlim>(_height);
+        var rowLocksSpan = rowLocks.Memory.Span;
+        for (int i = 0; i < _height; i++)
+        {
+            var isOpen = i < header.ProcessedRows;
+            rowLocksSpan[i] = new ManualResetEventSlim(isOpen);
+        }
+
+        _rowLocks = rowLocks;
+        ProcessIntegral(taskQueue, cancellationToken);
+    }
+
+    private void ProcessIntegral(Task taskQueue, CancellationToken cancellationToken)
+    {
+        PngDecoderOptions decoderOptions = new()
+        {
+            PngCrcChunkHandling = PngCrcChunkHandling.IgnoreAll,
+            GeneralOptions = new DecoderOptions
+            {
+                MaxFrames = 1,
+                SkipMetadata = true,
+            }
+        };
+        
+        using var fileStream = File.OpenRead(_imagePath);
+        using var image = PngDecoder.Instance.Decode<Rgb24>(decoderOptions, fileStream);
+        var imageBuffer = image.Frames.RootFrame.PixelBuffer;
+        
+        var accumulator = Int32Pixel.Zero;
+        var buffer = MemoryAllocator.AllocateArray<Int32Pixel>(_width);
+        var processedRows = _processedRows;
+        Interlocked.Exchange(ref _queueCounter, 0);
+        
+        // First row
+        if (processedRows == 0)
+        {
+            var sourceRow = imageBuffer.DangerousGetRowSpan(0);
+            for (var x = 0; x < sourceRow.Length; x++)
+            {
+                accumulator.Accumulate(sourceRow[x]);
+                buffer[x] = accumulator;
+            }
+            
+            taskQueue = QueueWriterTask(taskQueue, 0, buffer.Clone(_width), cancellationToken);
+            processedRows++;
+        }
+        else
+        {
+            ReadRow(processedRows - 1, buffer);
+        }
+        
+        if(cancellationToken.IsCancellationRequested)
+            return;
+
+        var prevBuffer = buffer;
+        buffer = MemoryAllocator.AllocateArray<Int32Pixel>(_width);
+        
+        for (int y = processedRows; y < image.Height; y++)
+        {
+            var sourceRow = imageBuffer.DangerousGetRowSpan(y);
+            accumulator = (Int32Pixel)sourceRow[0];
+            buffer[0] = accumulator + prevBuffer[0];
+
+            // Process all other columns
+            for (var x = 1; x < sourceRow.Length; x++)
+            {
+                accumulator.Accumulate(sourceRow[x]);
+                buffer[x] = accumulator + prevBuffer[x];
+            }
+
+            if (_queueCounter >= MaxProcessingQueue)
+            {
+                _queueLock.Reset();
+                _queueLock.Wait(cancellationToken);
+            }
+
+            if(cancellationToken.IsCancellationRequested)
+                break;
+
+            var writeBuffer = prevBuffer;
+            Array.Copy(buffer.Array, writeBuffer.Array, image.Width);
+            taskQueue = QueueWriterTask(taskQueue, y, writeBuffer, cancellationToken);
+            prevBuffer = buffer;
+            buffer = MemoryAllocator.AllocateArray<Int32Pixel>(_width);
+        }
+
+        buffer.Dispose();
+        if(cancellationToken.IsCancellationRequested)
+            return;
+
+        taskQueue = taskQueue.ContinueWith(task =>
+        {
+            if (task.IsCompletedSuccessfully)
+            {
+                DisposeRowLocks();
+                _queueLock.Dispose();
+            }
+        }, cancellationToken);
+
+        taskQueue.Wait(cancellationToken);
+    }
+
+    private Task QueueWriterTask(
+        Task taskQueue,
+        int row,
+        ArrayOwner<Int32Pixel> writeBuffer,
+        CancellationToken cancellationToken)
+    {
+        Interlocked.Increment(ref _queueCounter);
+        cancellationToken.Register(writeBuffer.Dispose);
+        return taskQueue.ContinueWith(_ =>
+        {
+            using (var view = AcquireView(row, MemoryMappedFileAccess.Write))
+                view.WriteArray(0, writeBuffer.Array, 0, _width);
+                
+            writeBuffer.Dispose();
+            _rowLocks!.Memory.Span[row].Set();
+            Interlocked.Increment(ref _processedRows);
+
+            using (var view = AcquireHeaderView(MemoryMappedFileAccess.Write))
+                view.Write(16, _processedRows);
+                
+            Interlocked.Decrement(ref _queueCounter);
+            _queueLock.Set();
+        }, cancellationToken);
+    }
+
+    private MemoryMappedViewAccessor AcquireHeaderView(MemoryMappedFileAccess access)
+        => _memoryMappedFile!.CreateViewAccessor(0, Header.Size, access);
+
+    private MemoryMappedViewAccessor AcquireView(int row, MemoryMappedFileAccess access)
+    {
+        var size = _width * Int32Pixel.Size;
+        var offset = row * size + Header.Size;
+        return _memoryMappedFile!.CreateViewAccessor(offset, size, access);
+    }
+
+    private void ReadRow(int row, Int32Pixel[] readBuffer)
+    {
+        using var view = AcquireView(row, MemoryMappedFileAccess.Read);
+        view.ReadArray(0, readBuffer, 0, _width);
+    }
+
+    private void ReadRow(int row, Span<Int32Pixel> buffer)
+    {
+        using var view = AcquireView(row, MemoryMappedFileAccess.Read);
+        view.DangerousReadSpan(0, buffer, 0, _width);
+    }
+
+    private void ReadRow(int row, IBuffer<Int32Pixel> buffer)
+    {
+        using var view = AcquireView(row, MemoryMappedFileAccess.Read);
+        view.DangerousReadSpan(0, buffer.Span, 0, _width);
+    }
+
+    private FileStream? InitializeBackedFile(string path, out Header header)
+    {
+        var expectedHeader = Header.CreateInitial(_width, _height);
+        
+        // Expectation when file exists:
+        // - throws IOException when it's being processed, handle it if possible
+        // - returns null if file is valid
+        // - delete the existing file if it's not valid (modified from external)
+        FileStream fs;
+        if (File.Exists(path))
+        {
+            fs = File.OpenRead(path);
+            if (fs.Length < expectedHeader.Length + Header.Size)
+            {
+                fs.Dispose();
+                File.Delete(path);
+            }
+            
+            Span<byte> headerBytes = stackalloc byte[Header.Size];
+            fs.ReadExactly(headerBytes);
+            
+            header = MemoryMarshal.Cast<byte, Header>(headerBytes)[0];
+            var isValid = expectedHeader.Identifier == header.Identifier
+                          && expectedHeader.Width == header.Width
+                          && expectedHeader.Height == header.Height
+                          && expectedHeader.Length == header.Length;
+            
+            fs.Dispose();
+            Console.WriteLine($"Image integral file found: {path}");
+            
+            if (!isValid) File.Delete(path);
+            else return null;
+        }
+        
+        // Expected process:
+        // - Initialize file creation
+        // - Write the header
+        // - Allocate initial content by Header.Length
+        // - Action above should be done asynchronously and return the task handle.
+        var fsOptions = new FileStreamOptions
+        {
+            Access = FileAccess.Write,
+            Share = FileShare.None,
+            Mode = FileMode.CreateNew,
+            PreallocationSize = Header.Size,
+        };
+        
+        Console.WriteLine($"Create image integral file: {path}");
+        
+        Directory.CreateDirectory(_outputDirectory);
+        fs = File.Open(path, fsOptions);
+        fs.Write(MemoryMarshal.AsBytes([expectedHeader]));
+        header = expectedHeader;
+        return fs;
+    }
+
+    private static async Task AllocateBackedFile(FileStream fileStream, Header header)
+    {
+        // The input filestream is expected to be empty with
+        // initial cursor at the beginning of the file and the content
+        // is pre-allocated for at least Header.Length bytes
+        // No other process should be accessed the file while being
+        // allocated.
+        // Allocated bytes is not necessary to be zeroed.
+
+        // const int writeBufferSize = 4 * 1024;
+        // using var writeBuffer = MemoryPool<byte>.Shared.Rent(writeBufferSize);
+        //
+        // var written = 0;
+        // while (written + writeBufferSize < header.Length)
+        // {
+        //     await fileStream.WriteAsync(writeBuffer.Memory, cancellationToken);
+        //     written += writeBufferSize;
+        // }
+        //
+        // if (written < header.Length)
+        // {
+        //     await fileStream.WriteAsync(writeBuffer.Memory[..(header.Length - written)], cancellationToken);
+        // }
+        
+        fileStream.SetLength(header.Length + Header.Size);
+        
+        await fileStream.DisposeAsync();
+    }
+
+    [StructLayout(LayoutKind.Sequential)]
+    private struct Header
+    {
+        private const int Signature = 0x47544e49; // INTG
+
+        public static int Size => Unsafe.SizeOf<Header>();
+        
+        public uint Identifier;
+        public int Width;
+        public int Height;
+        public int Length;
+        public int ProcessedRows;
+
+        public static Header CreateInitial(int width, int height) => new()
+        {
+            Identifier = Signature,
+            Width = width,
+            Height = height,
+            Length = width * height * Int32Pixel.Size,
+            ProcessedRows = 0,
+        };
+    }
+
+    private void DisposeRowLocks()
+    {
+        if (_rowLocks is { } locks)
+        {
+            _rowLocks = null;
+            var lockSpan = locks.Memory.Span;
+            for(int i = 0; i < _height; i++)
+                lockSpan[i].Dispose();
+
+            locks.Dispose();
+        }
+    }
+
+    public void Dispose()
+    {
+        DisposeRowLocks();
+        _memoryMappedFile?.Dispose();
+        _queueLock.Dispose();
+        _initializationLock.Dispose();
+        GC.SuppressFinalize(this);
+    }
+}

Infra/Int32Pixel.cs

@@ -0,0 +1,82 @@
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace StitchATon2.Infra;
+
+[StructLayout(LayoutKind.Sequential)]
+public record struct Int32Pixel
+{
+    public static int Size
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => Unsafe.SizeOf<Int32Pixel>();
+    }
+
+    public static Int32Pixel Zero
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => new();
+    }
+    
+    public int R;
+    public int G;
+    public int B;
+
+    public Int32Pixel(int r, int g, int b)
+    {
+        R = r;
+        G = g;
+        B = b;
+    }
+
+    public void Accumulate(Int32Pixel pixel)
+    {
+        R += pixel.R;
+        G += pixel.G;
+        B += pixel.B;
+    }
+
+    public void Accumulate(Rgb24 pixel)
+    {
+        R += pixel.R;
+        G += pixel.G;
+        B += pixel.B;
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static Int32Pixel operator +(Int32Pixel a, Int32Pixel b)
+    {
+        return new Int32Pixel(a.R + b.R, a.G + b.G, a.B + b.B);
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static Int32Pixel operator +(Int32Pixel a, int b)
+    {
+        return new Int32Pixel(a.R + b, a.G + b, a.B + b);
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static Int32Pixel operator -(Int32Pixel a, Int32Pixel b)
+    {
+        return new Int32Pixel(a.R - b.R, a.G - b.G, a.B - b.B);
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static Int32Pixel operator /(Int32Pixel a, int b)
+    {
+        return new Int32Pixel(a.R / b, a.G / b, a.B / b);
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static explicit operator Int32Pixel(Rgb24 pixel)
+    {
+        return new  Int32Pixel(pixel.R, pixel.G, pixel.B);
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static explicit operator Rgb24(Int32Pixel pixel)
+    {
+        return new  Rgb24((byte)pixel.R, (byte)pixel.G, (byte)pixel.B);
+    }
+}

Infra/StitchATon2.Infra.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net8.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+        <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <PackageReference Include="SixLabors.ImageSharp" Version="3.1.10" />
+    </ItemGroup>
+
+</Project>

Infra/Synchronization/TaskHelper.cs

@@ -0,0 +1,12 @@
+namespace StitchATon2.Infra.Synchronization;
+
+public static class TaskHelper
+{
+    public static TaskFactory CreateTaskFactory()
+    {
+        return new TaskFactory(
+            TaskCreationOptions.AttachedToParent,
+            TaskContinuationOptions.ExecuteSynchronously
+            );
+    }
+}

Infra/Utils.cs

@@ -0,0 +1,56 @@
+using System.IO.MemoryMappedFiles;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using StitchATon2.Infra.Buffers;
+
+namespace StitchATon2.Infra;
+
+public static class Utils
+{
+    [UnsafeAccessor(UnsafeAccessorKind.Field, Name = "_buffer")]
+    private static extern ref SafeBuffer GetSafeBuffer(this UnmanagedMemoryAccessor view);
+
+    [UnsafeAccessor(UnsafeAccessorKind.Field, Name = "_offset")]
+    private static extern ref long GetOffset(this UnmanagedMemoryAccessor view);
+
+    private static unsafe uint AlignedSizeOf<T>() where T : unmanaged
+    {
+        uint size = (uint)sizeof(T);
+        return size is 1 or 2 ? size : (uint)((size + 3) & (~3));
+    }
+
+    public static void DangerousReadSpan<T>(this UnmanagedMemoryAccessor view, long position, Span<T> span, int offset, int count)
+        where T : unmanaged
+    {
+        uint sizeOfT = AlignedSizeOf<T>();
+        int n = count;
+        long spaceLeft = view.Capacity - position;
+        if (spaceLeft < 0)
+        {
+            n = 0;
+        }
+        else
+        {
+            ulong spaceNeeded = (ulong)(sizeOfT * count);
+            if ((ulong)spaceLeft < spaceNeeded)
+            {
+                n = (int)(spaceLeft / sizeOfT);
+            }
+        }
+
+        var byteOffset = (ulong)(view.GetOffset() + position);
+        view.GetSafeBuffer().ReadSpan(byteOffset, span.Slice(offset, n));
+    }
+
+    public static ArrayOwner<T> Clone<T>(this ArrayOwner<T> arrayOwner, int length) where T : unmanaged
+    {
+        var newArrayOwner = MemoryAllocator.AllocateArray<T>(length);
+        Array.Copy(arrayOwner.Array, 0, newArrayOwner.Array, 0, length);
+        return newArrayOwner;
+    }
+
+    public static void CopyTo<T>(this ArrayOwner<T> arrayOwner, ArrayOwner<T> target, int length) where T : unmanaged
+    {
+        Array.Copy(arrayOwner.Array, 0, target.Array, 0, length);
+    }
+}