Fix diffusion tests

src/ImageSharp/Dithering/ErrorDiffusion/ErrorDiffuser.cs

@@ -69,15 +69,15 @@ namespace SixLabors.ImageSharp.Dithering
 
         /// <inheritdoc />
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void Dither<TPixel>(ImageBase<TPixel> pixels, TPixel source, TPixel transformed, int x, int y, int width, int height)
+        public void Dither<TPixel>(ImageBase<TPixel> pixels, TPixel source, TPixel transformed, int x, int y, int minX, int minY, int maxX, int maxY)
             where TPixel : struct, IPixel<TPixel>
         {
-            this.Dither(pixels, source, transformed, x, y, width, height, true);
+            this.Dither(pixels, source, transformed, x, y, minX, minY, maxX, maxY, true);
         }
 
         /// <inheritdoc />
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public void Dither<TPixel>(ImageBase<TPixel> image, TPixel source, TPixel transformed, int x, int y, int width, int height, bool replacePixel)
+        public void Dither<TPixel>(ImageBase<TPixel> image, TPixel source, TPixel transformed, int x, int y, int minX, int minY, int maxX, int maxY, bool replacePixel)
             where TPixel : struct, IPixel<TPixel>
         {
             if (replacePixel)
@@ -93,7 +93,7 @@ namespace SixLabors.ImageSharp.Dithering
             for (int row = 0; row < this.matrixHeight; row++)
             {
                 int matrixY = y + row;
-                if (matrixY > 0 && matrixY < height)
+                if (matrixY > minY && matrixY < maxY)
                 {
                     Span<TPixel> rowSpan = image.GetRowSpan(matrixY);
 
@@ -101,7 +101,7 @@ namespace SixLabors.ImageSharp.Dithering
                     {
                         int matrixX = x + (col - this.startingOffset);
 
-                        if (matrixX > 0 && matrixX < width)
+                        if (matrixX > minX && matrixX < maxX)
                         {
                             float coefficient = this.matrix[row, col];
 

src/ImageSharp/Dithering/ErrorDiffusion/IErrorDiffuser.cs

@@ -18,10 +18,12 @@ namespace SixLabors.ImageSharp.Dithering
         /// <param name="transformed">The transformed pixel</param>
         /// <param name="x">The column index.</param>
         /// <param name="y">The row index.</param>
-        /// <param name="width">The image width.</param>
-        /// <param name="height">The image height.</param>
+        /// <param name="minX">The minimum column value.</param>
+        /// <param name="minY">The minimum row value.</param>
+        /// <param name="maxX">The maximum column value.</param>
+        /// <param name="maxY">The maximum row value.</param>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
-        void Dither<TPixel>(ImageBase<TPixel> image, TPixel source, TPixel transformed, int x, int y, int width, int height)
+        void Dither<TPixel>(ImageBase<TPixel> image, TPixel source, TPixel transformed, int x, int y, int minX, int minY, int maxX, int maxY)
             where TPixel : struct, IPixel<TPixel>;
 
         /// <summary>
@@ -32,14 +34,16 @@ namespace SixLabors.ImageSharp.Dithering
         /// <param name="transformed">The transformed pixel</param>
         /// <param name="x">The column index.</param>
         /// <param name="y">The row index.</param>
-        /// <param name="width">The image width.</param>
-        /// <param name="height">The image height.</param>
+        /// <param name="minX">The minimum column value.</param>
+        /// <param name="minY">The minimum row value.</param>
+        /// <param name="maxX">The maximum column value.</param>
+        /// <param name="maxY">The maximum row value.</param>
         /// <param name="replacePixel">
         /// Whether to replace the pixel at the given coordinates with the transformed value.
         /// Generally this would be true for standard two-color dithering but when used in conjunction with color quantization this should be false.
         /// </param>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
-        void Dither<TPixel>(ImageBase<TPixel> image, TPixel source, TPixel transformed, int x, int y, int width, int height, bool replacePixel)
+        void Dither<TPixel>(ImageBase<TPixel> image, TPixel source, TPixel transformed, int x, int y, int minX, int minY, int maxX, int maxY, bool replacePixel)
             where TPixel : struct, IPixel<TPixel>;
     }
 }

src/ImageSharp/Dithering/Ordered/IOrderedDither.cs

@@ -21,10 +21,8 @@ namespace SixLabors.ImageSharp.Dithering
         /// <param name="index">The component index to test the threshold against. Must range from 0 to 3.</param>
         /// <param name="x">The column index.</param>
         /// <param name="y">The row index.</param>
-        /// <param name="width">The image width.</param>
-        /// <param name="height">The image height.</param>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
-        void Dither<TPixel>(ImageBase<TPixel> image, TPixel source, TPixel upper, TPixel lower, byte[] bytes, int index, int x, int y, int width, int height)
+        void Dither<TPixel>(ImageBase<TPixel> image, TPixel source, TPixel upper, TPixel lower, byte[] bytes, int index, int x, int y)
             where TPixel : struct, IPixel<TPixel>;
     }
 }

src/ImageSharp/Dithering/Ordered/OrderedDither4x4.cs

@@ -26,7 +26,7 @@ namespace SixLabors.ImageSharp.Dithering.Ordered
         }
 
         /// <inheritdoc />
-        public void Dither<TPixel>(ImageBase<TPixel> image, TPixel source, TPixel upper, TPixel lower, byte[] bytes, int index, int x, int y, int width, int height)
+        public void Dither<TPixel>(ImageBase<TPixel> image, TPixel source, TPixel upper, TPixel lower, byte[] bytes, int index, int x, int y)
             where TPixel : struct, IPixel<TPixel>
         {
             // TODO: This doesn't really cut it for me.

src/ImageSharp/Processing/Processors/Binarization/ErrorDiffusionDitherProcessor.cs

@@ -61,39 +61,21 @@ namespace SixLabors.ImageSharp.Processing.Processors
         /// <inheritdoc/>
         protected override void OnApply(ImageBase<TPixel> source, Rectangle sourceRectangle)
         {
-            int startY = sourceRectangle.Y;
-            int endY = sourceRectangle.Bottom;
-            int startX = sourceRectangle.X;
-            int endX = sourceRectangle.Right;
+            var interest = Rectangle.Intersect(sourceRectangle, source.Bounds());
+            int startY = interest.Y;
+            int endY = interest.Bottom;
+            int startX = interest.X;
+            int endX = interest.Right;
 
-            // Align start/end positions.
-            int minX = Math.Max(0, startX);
-            int maxX = Math.Min(source.Width, endX);
-            int minY = Math.Max(0, startY);
-            int maxY = Math.Min(source.Height, endY);
-
-            // Reset offset if necessary.
-            if (minX > 0)
-            {
-                startX = 0;
-            }
-
-            if (minY > 0)
-            {
-                startY = 0;
-            }
-
-            for (int y = minY; y < maxY; y++)
+            for (int y = startY; y < endY; y++)
             {
-                int offsetY = y - startY;
-                Span<TPixel> row = source.GetRowSpan(offsetY);
+                Span<TPixel> row = source.GetRowSpan(y);
 
-                for (int x = minX; x < maxX; x++)
+                for (int x = startX; x < endX; x++)
                 {
-                    int offsetX = x - startX;
-                    TPixel sourceColor = row[offsetX];
+                    TPixel sourceColor = row[x];
                     TPixel transformedColor = sourceColor.ToVector4().X >= this.Threshold ? this.UpperColor : this.LowerColor;
-                    this.Diffuser.Dither(source, sourceColor, transformedColor, offsetX, offsetY, maxX, maxY);
+                    this.Diffuser.Dither(source, sourceColor, transformedColor, x, y, startX, startY, endX, endY);
                 }
             }
         }

src/ImageSharp/Processing/Processors/Binarization/OrderedDitherProcessor.cs

@@ -69,39 +69,21 @@ namespace SixLabors.ImageSharp.Processing.Processors
         /// <inheritdoc/>
         protected override void OnApply(ImageBase<TPixel> source, Rectangle sourceRectangle)
         {
-            int startY = sourceRectangle.Y;
-            int endY = sourceRectangle.Bottom;
-            int startX = sourceRectangle.X;
-            int endX = sourceRectangle.Right;
-
-            // Align start/end positions.
-            int minX = Math.Max(0, startX);
-            int maxX = Math.Min(source.Width, endX);
-            int minY = Math.Max(0, startY);
-            int maxY = Math.Min(source.Height, endY);
-
-            // Reset offset if necessary.
-            if (minX > 0)
-            {
-                startX = 0;
-            }
-
-            if (minY > 0)
-            {
-                startY = 0;
-            }
+            var interest = Rectangle.Intersect(sourceRectangle, source.Bounds());
+            int startY = interest.Y;
+            int endY = interest.Bottom;
+            int startX = interest.X;
+            int endX = interest.Right;
 
             byte[] bytes = new byte[4];
-            for (int y = minY; y < maxY; y++)
+            for (int y = startY; y < endY; y++)
             {
-                int offsetY = y - startY;
-                Span<TPixel> row = source.GetRowSpan(offsetY);
+                Span<TPixel> row = source.GetRowSpan(y);
 
-                for (int x = minX; x < maxX; x++)
+                for (int x = startX; x < endX; x++)
                 {
-                    int offsetX = x - startX;
-                    TPixel sourceColor = row[offsetX];
-                    this.Dither.Dither(source, sourceColor, this.UpperColor, this.LowerColor, bytes, this.Index, offsetX, offsetY, maxX, maxY);
+                    TPixel sourceColor = row[x];
+                    this.Dither.Dither(source, sourceColor, this.UpperColor, this.LowerColor, bytes, this.Index, x, y);
                 }
             }
         }

src/ImageSharp/Quantizers/OctreeQuantizer{TPixel}.cs

@@ -103,7 +103,7 @@ namespace SixLabors.ImageSharp.Quantizers
                     if (this.Dither)
                     {
                         // Apply the dithering matrix. We have to reapply the value now as the original has changed.
-                        this.DitherType.Dither(source, sourcePixel, transformedPixel, x, y, width, height, false);
+                        this.DitherType.Dither(source, sourcePixel, transformedPixel, x, y, 0, 0, width, height, false);
                     }
 
                     output[(y * source.Width) + x] = pixelValue;

src/ImageSharp/Quantizers/PaletteQuantizer{TPixel}.cs

@@ -99,7 +99,7 @@ namespace SixLabors.ImageSharp.Quantizers
                     if (this.Dither)
                     {
                         // Apply the dithering matrix. We have to reapply the value now as the original has changed.
-                        this.DitherType.Dither(source, sourcePixel, transformedPixel, x, y, width, height, false);
+                        this.DitherType.Dither(source, sourcePixel, transformedPixel, x, y, 0, 0, width, height, false);
                     }
 
                     output[(y * source.Width) + x] = pixelValue;

src/ImageSharp/Quantizers/WuQuantizer{TPixel}.cs

@@ -277,7 +277,7 @@ namespace SixLabors.ImageSharp.Quantizers
                     if (this.Dither)
                     {
                         // Apply the dithering matrix. We have to reapply the value now as the original has changed.
-                        this.DitherType.Dither(source, sourcePixel, transformedPixel, x, y, width, height, false);
+                        this.DitherType.Dither(source, sourcePixel, transformedPixel, x, y, 0, 0, width, height, false);
                     }
 
                     output[(y * source.Width) + x] = pixelValue;

tests/ImageSharp.Tests/Processing/Processors/Binarization/DitherTests.cs

@@ -111,8 +111,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Processors.Binarization
             }
         }
 
-        // TODO: Does not work because of a bug! Fix it!
-        [Theory(Skip = "TODO: Does not work because of a bug! Fix it!")]
+        [Theory]
         [WithFile(TestImages.Png.CalliphoraPartial, DefaultPixelType)]
         public void ApplyDiffusionFilterInBox<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : struct, IPixel<TPixel>