first commit

Services/Utilities/ImageProcessor.cs

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+using SixLabors.ImageSharp;
+using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.ImageSharp.Processing;
+
+namespace StitcherApi.Services.Utilities;
+
+internal class ImageProcessor
+{
+    private readonly string _assetPath;
+    private const int TILE_SIZE = 720;
+
+    public ImageProcessor(string assetPath)
+    {
+        _assetPath = assetPath;
+    }
+
+    public async Task<byte[]> StitchAndCropAsync(StitchRequest stitchRequest)
+    {
+        using var finalImage = new Image<Rgba32>(stitchRequest.CropW, stitchRequest.CropH);
+
+        for (var r = stitchRequest.StartTileRow; r <= stitchRequest.EndTileRow; r++)
+        {
+            for (var c = stitchRequest.StartTileCol; c <= stitchRequest.EndTileCol; c++)
+            {
+                var tileFileName = TileHelper.GetTileFileName(r, c);
+                var tileFilePath = Path.Combine(_assetPath, tileFileName);
+
+                if (!File.Exists(tileFilePath))
+                {
+                    throw new FileNotFoundException($"Asset not found: {tileFileName}");
+                }
+
+                using var tileImage = await Image.LoadAsync(tileFilePath);
+
+                var tileOriginX = (c - stitchRequest.MinCol) * TILE_SIZE;
+                var tileOriginY = (r - stitchRequest.MinRow) * TILE_SIZE;
+
+                var srcX = Math.Max(0, stitchRequest.CropX - tileOriginX);
+                var srcY = Math.Max(0, stitchRequest.CropY - tileOriginY);
+                var destX = Math.Max(0, tileOriginX - stitchRequest.CropX);
+                var destY = Math.Max(0, tileOriginY - stitchRequest.CropY);
+
+                var overlapW = Math.Max(
+                    0,
+                    Math.Min(stitchRequest.CropX + stitchRequest.CropW, tileOriginX + TILE_SIZE)
+                        - Math.Max(stitchRequest.CropX, tileOriginX)
+                );
+                var overlapH = Math.Max(
+                    0,
+                    Math.Min(stitchRequest.CropY + stitchRequest.CropH, tileOriginY + TILE_SIZE)
+                        - Math.Max(stitchRequest.CropY, tileOriginY)
+                );
+
+                if (overlapW > 0 && overlapH > 0)
+                {
+                    var sourceRect = new Rectangle(srcX, srcY, overlapW, overlapH);
+                    finalImage.Mutate(ctx =>
+                        ctx.DrawImage(
+                            tileImage,
+                            new Point(destX, destY),
+                            sourceRect,
+                            new GraphicsOptions()
+                        )
+                    );
+                }
+            }
+        }
+
+        if (stitchRequest.OutputScale > 0 && stitchRequest.OutputScale < 1.0)
+        {
+            var newWidth = (int)(stitchRequest.CropW * stitchRequest.OutputScale);
+            var newHeight = (int)(stitchRequest.CropH * stitchRequest.OutputScale);
+            finalImage.Mutate(x => x.Resize(newWidth, newHeight, KnownResamplers.Bicubic));
+        }
+
+        using var memoryStream = new MemoryStream();
+        await finalImage.SaveAsPngAsync(memoryStream);
+        return memoryStream.ToArray();
+    }
+}
+
+internal record StitchRequest(
+    int MinRow,
+    int MinCol,
+    int StartTileRow,
+    int StartTileCol,
+    int EndTileRow,
+    int EndTileCol,
+    int CropX,
+    int CropY,
+    int CropW,
+    int CropH,
+    float OutputScale
+);