✨ Converter from TIFF to plain image

src/Texim/Formats/Tiff2PlainFullImage.cs

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+namespace Texim.Formats;
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Texim.Colors;
+using Texim.Images;
+using Texim.Pixels;
+using Yarhl.FileFormat;
+
+public class Tiff2PlainFullImage : IConverter<TiffImage, FullImage>
+{
+    public FullImage Convert(TiffImage source)
+    {
+        ArgumentNullException.ThrowIfNull(source);
+
+        var image = new FullImage(source.CanvasWidth, source.CanvasHeight);
+        foreach (TiffPage page in source.Pages.Reverse()) {
+            DrawLayer(page, image);
+        }
+
+        return image;
+    }
+
+    private static void DrawLayer(TiffPage page, FullImage image)
+    {
+        for (int x = 0; x < page.Width; x++) {
+            for (int y = 0; y < page.Height; y++) {
+                Rgb pixel = GetColor(page, x, y);
+                if (pixel.Alpha == 0) {
+                    continue; // don't overwrite other layers.
+                }
+
+                int imageIdx = ((page.Y + y) * image.Width) + page.X + x;
+                image.Pixels[imageIdx] = pixel;
+            }
+        }
+    }
+
+    private static Rgb GetColor(TiffPage page, int x, int y)
+    {
+        int idx = (y * page.Width) + x;
+        if (page.IsIndexed) {
+            IndexedPixel pixel = page.IndexedPixels[idx];
+            return new Rgb(page.ColorMap[pixel.Index], pixel.Alpha);
+        }
+
+        return page.RgbPixels[idx];
+    }
+}