refactor into using ImageSharp

.gitignore

@@ -1,2 +1,4 @@
 bin
 obj
+.vs
+*.png

LiloStitcher.cs

@@ -1,5 +1,8 @@
 using Microsoft.Extensions.Caching.Memory;
-using SkiaSharp;
+using SixLabors.ImageSharp;
+using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.ImageSharp.Processing;
+using SixLabors.ImageSharp.Formats.Png;
 
 namespace LiloStitcher;
 
@@ -10,7 +13,7 @@ public record GenerateRequest(
     double OutputScale
 );
 
-public record struct PlateCoordinate( int Row, int Col )
+public readonly record struct PlateCoordinate(int Row, int Col)
 {
     public static PlateCoordinate Parse(string token)
     {
@@ -19,24 +22,21 @@ public record struct PlateCoordinate( int Row, int Col )
 
         int row = 0;
         foreach (var c in rowPart)
-        {
             row = row * 26 + (c - 'A' + 1);
-        }
 
         int.TryParse(colPart, out int col);
-
         return new PlateCoordinate(row, col);
     }
 }
 
 public class TileCache(IMemoryCache cache)
 {
-    private const long TileBytes = 720L * 720 * 4;
+    private const long TileBytes = 720L * 720 * 3;
 
-    public SKBitmap? Get( string key ) => cache.TryGetValue( key, out SKBitmap? bmp ) ? bmp : null;
+    public Image<Rgba32>? Get(string key) => cache.TryGetValue(key, out Image<Rgba32>? img) ? img : null;
 
-    public void Set( string key, SKBitmap bmp ) =>
-        cache.Set( key, bmp, new MemoryCacheEntryOptions
+    public void Set(string key, Image<Rgba32> img) =>
+        cache.Set(key, img, new MemoryCacheEntryOptions
         {
             Size = TileBytes,
             SlidingExpiration = TimeSpan.FromMinutes(20)
@@ -45,18 +45,16 @@ public class TileCache( IMemoryCache cache )
 
 public class TileLoader(TileCache cache, string assetDir)
 {
-    public async Task<SKBitmap> LoadAsync( string name, CancellationToken ct )
+    public async Task<Image<Rgba32>> LoadAsync(string name, CancellationToken ct)
     {
-        if( cache.Get( name ) is { } hit ) return hit;
+        if (cache.Get(name) is { } hit)
+            return hit;
 
         var path = Path.Combine(assetDir, $"{name}.png");
-
-        var bytes = await File.ReadAllBytesAsync( path, ct ).ConfigureAwait( false );
-
-        using var data = SKData.CreateCopy( bytes );
-        var bmp = SKBitmap.Decode( data );
-        cache.Set( name, bmp );
-        return bmp;
+        await using var fs = File.OpenRead(path);
+        var image = await Image.LoadAsync<Rgba32>(fs, ct).ConfigureAwait(false);
+        cache.Set(name, image);
+        return image;
     }
 }
 
@@ -66,8 +64,8 @@ public class LiloStitcher( TileLoader loader )
 
     public async Task<byte[]> CreateImageAsync(GenerateRequest req, CancellationToken ct)
     {
-        var parts = req.CanvasRect.ToUpperInvariant().Split( ':', StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries );
-
+        var parts = req.CanvasRect.ToUpperInvariant()
+            .Split(':', StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries);
         var part1 = PlateCoordinate.Parse(parts[0]);
         var part2 = PlateCoordinate.Parse(parts[1]);
 
@@ -84,52 +82,61 @@ public class LiloStitcher( TileLoader loader )
             .ToArray();
 
         var bitmaps = await Task.WhenAll(names.Select(n => loader.LoadAsync(n, ct))).ConfigureAwait(false);
-
-        var fullInfo = new SKImageInfo( cols * TileSize, rows * TileSize );
-        using var surface = SKSurface.Create( fullInfo );
-        var canvas = surface.Canvas;
+        var stitched = new Image<Rgba32>(cols * TileSize, rows * TileSize);
 
         int idx = 0;
-        for( int row = 0; row < rows; row++ )
-            for( int column = 0; column < cols; column++, idx++ )
-                canvas.DrawBitmap( bitmaps[idx], column * TileSize, row * TileSize );
+        for (int r = 0; r < rows; r++)
+        {
+            for (int c = 0; c < cols; c++, idx++)
+            {
+                stitched.Mutate(ctx => ctx.DrawImage(bitmaps[idx], new Point(c * TileSize, r * TileSize), 1f));
+            }
+        }
 
-        using var full = new SKBitmap( fullInfo );
-        surface.ReadPixels( fullInfo, full.GetPixels(), full.RowBytes, 0, 0 );
+        Validate(req.CropOffset, 2, nameof(req.CropOffset), inclusiveUpper: true);
+        Validate(req.CropSize, 2, nameof(req.CropSize), inclusiveUpper: true);
 
-        ValidateFraction( req.CropOffset, 2, nameof( req.CropOffset ), inclusiveUpper: true );
-        ValidateFraction( req.CropSize, 2, nameof( req.CropSize ), inclusiveUpper: true );
+        int offsetX = (int)(req.CropOffset[0] * stitched.Width);
+        int offsetY = (int)(req.CropOffset[1] * stitched.Height);
+        int cropWidth = (int)(req.CropSize[0] * stitched.Width);
+        int cropHeight = (int)(req.CropSize[1] * stitched.Height);
 
-        int offsetX = (int)( req.CropOffset[0] * fullInfo.Width );
-        int offsetY = (int)( req.CropOffset[1] * fullInfo.Height );
-        int cropWidth = (int)( req.CropSize[0] * fullInfo.Width );
-        int cropHeight = (int)( req.CropSize[1] * fullInfo.Height );
+        if (offsetX + cropWidth > stitched.Width) cropWidth = stitched.Width - offsetX;
+        if (offsetY + cropHeight > stitched.Height) cropHeight = stitched.Height - offsetY;
 
-        if( offsetX + cropWidth > fullInfo.Width ) cropWidth = fullInfo.Width - offsetX;
-        if( offsetY + cropHeight > fullInfo.Height ) cropHeight = fullInfo.Height - offsetY;
+        var cropRect = new Rectangle(offsetX, offsetY, cropWidth, cropHeight);
 
-        var cropRect = new SKRectI( offsetX, offsetY, offsetX + cropWidth, offsetY + cropHeight );
-        using var crop = new SKBitmap( cropWidth, cropHeight );
-        full.ExtractSubset( crop, cropRect );
+        using var cropped = stitched.Clone(ctx => ctx.Crop(cropRect));
 
         double scale = Math.Clamp(req.OutputScale, 0.0, 1.0);
-        int truncatedWidth = Math.Max( 1, (int)Math.Round( cropWidth * scale ) );
-        int truncatedHeight = Math.Max( 1, (int)Math.Round( cropHeight * scale ) );
-
-        using var finalBmp = scale < 1.0
-            ? crop.Resize( new SKSizeI( truncatedWidth, truncatedHeight ), new SKSamplingOptions( SKFilterMode.Linear ) )
-            : crop;
-
-        using var image = SKImage.FromBitmap( finalBmp );
-        using var data = image.Encode( SKEncodedImageFormat.Png, 100 );
-        return data.ToArray();
-
-        static void ValidateFraction( double[] arr, int len, string name, bool inclusiveUpper )
+        Image<Rgba32> output;
+        if (scale < 1.0)
         {
+            int width = Math.Max(1, (int)Math.Truncate(cropWidth * scale));
+            int height = Math.Max(1, (int)Math.Truncate(cropHeight * scale));
+            output = cropped.Clone(ctx => ctx.Resize(width, height));
+        }
+        else
+        {
+            output = cropped.Clone();
+        }
+
+        using var memStream = new MemoryStream();
+        await output.SaveAsync(memStream, new PngEncoder
+        {
+        }, ct).ConfigureAwait(false);
+        return memStream.ToArray();
+
+        static void Validate(double[] arr, int len, string name, bool inclusiveUpper)
+        {
+            if (arr is null || arr.Length < len)
+                throw new ArgumentException($"{name} must have length {len}");
+            double upper = inclusiveUpper ? 1.0 : 1.0 - double.Epsilon;
             for (int i = 0; i < len; i++)
             {
-                double v = arr[i];
-                double upper = inclusiveUpper ? 1.0 : 1.0 - double.Epsilon;
+                var v = arr[i];
+                if (v < 0 || v > upper)
+                    throw new ArgumentOutOfRangeException($"{name}[{i}]= {v} outside [0,{upper}]");
             }
         }
 

Program.cs

@@ -1,4 +1,4 @@
-
+using System.Diagnostics;
 using Microsoft.Extensions.Caching.Memory;
 
 namespace LiloStitcher;
@@ -8,14 +8,18 @@ public static class Program
     {
         try
         {
-            var opt = new Options();
-            opt.CanvasRect = "A1:H12";
-            opt.CropOffset = [0.25, 0.25];
-            opt.CropSize = [0.75, 0.75];
-            opt.OutputScale = 0.5;
-            opt.OutputPath = "stitched.png";
+            Stopwatch sw = Stopwatch.StartNew();
+            var begin = sw.ElapsedMilliseconds;
+            var opt = new Options
+            {
+                CanvasRect = "A1:AE55",
+                CropOffset = [0.0, 0.0],
+                CropSize = [1.0, 1.0],
+                OutputScale = 1.0,
+                OutputPath = "stitched.png"
+            };
 
-            string tileFilePath = "../stitch-a-ton/tiles1705";
+            string tileFilePath = "../tiles1705"; // should later be directed to the read-only `ASSET_PATH_RO` environment variable
             string assetDir = Path.GetFullPath(Path.Combine(Directory.GetCurrentDirectory(), tileFilePath));
 
             using var memCache = new MemoryCache(new MemoryCacheOptions { SizeLimit = 256L * 1024 * 1024 });
@@ -31,10 +35,12 @@ public static class Program
             );
 
             Console.WriteLine("Stitching...");
-            var png = await stitcher.CreateImageAsync( req, CancellationToken.None );
+            var pngBytes = await stitcher.CreateImageAsync(req, CancellationToken.None);
 
-            File.WriteAllBytes( opt.OutputPath!, png );
-            Console.WriteLine( $"Done. Wrote {opt.OutputPath}  ({png.Length / 1024.0:F1} KB)" );
+            File.WriteAllBytes(opt.OutputPath!, pngBytes);
+            Console.WriteLine($"Done. Wrote {opt.OutputPath}  ({pngBytes.Length / 1024.0:F1} KB)");
+
+            Console.WriteLine(begin - sw.ElapsedMilliseconds);
             return 0;
         }
         catch (Exception ex)

lilo-stitcher-console.csproj

@@ -10,8 +10,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.Extensions.Caching.Memory" Version="9.0.7" />
-    <PackageReference Include="SkiaSharp" Version="3.119.0" />
-    <PackageReference Include="SkiaSharp.NativeAssets.Linux" Version="3.119.0" />
+    <PackageReference Include="SixLabors.ImageSharp" Version="3.1.10" />
   </ItemGroup>
 
 </Project>