Update equality check and add ests. Fix #1116

src/ImageSharp/Primitives/DenseMatrix{T}.cs

@@ -136,7 +136,7 @@ namespace SixLabors.ImageSharp
         /// </returns>
         [MethodImpl(InliningOptions.ShortMethod)]
 #pragma warning disable SA1008 // Opening parenthesis should be spaced correctly
-        public static implicit operator T[,] (in DenseMatrix<T> data)
+        public static implicit operator T[,](in DenseMatrix<T> data)
 #pragma warning restore SA1008 // Opening parenthesis should be spaced correctly
         {
             var result = new T[data.Rows, data.Columns];
@@ -153,6 +153,24 @@ namespace SixLabors.ImageSharp
             return result;
         }
 
+        /// <summary>
+        /// Compares the two <see cref="DenseMatrix{T}"/> instances to determine whether they are unequal.
+        /// </summary>
+        /// <param name="left">The first source instance.</param>
+        /// <param name="right">The second source instance.</param>
+        /// <returns>The <see cref="bool"/>.</returns>
+        public static bool operator ==(DenseMatrix<T> left, DenseMatrix<T> right)
+            => left.Equals(right);
+
+        /// <summary>
+        /// Compares the two <see cref="DenseMatrix{T}"/> instances to determine whether they are equal.
+        /// </summary>
+        /// <param name="left">The first source instance.</param>
+        /// <param name="right">The second source instance.</param>
+        /// <returns>The <see cref="bool"/>.</returns>
+        public static bool operator !=(DenseMatrix<T> left, DenseMatrix<T> right)
+            => !(left == right);
+
         /// <summary>
         /// Transposes the rows and columns of the dense matrix.
         /// </summary>
@@ -210,15 +228,32 @@ namespace SixLabors.ImageSharp
         }
 
         /// <inheritdoc/>
-        public override bool Equals(object obj) => obj is DenseMatrix<T> other && this.Equals(other);
+        public override bool Equals(object obj)
+            => obj is DenseMatrix<T> other && this.Equals(other);
 
         /// <inheritdoc/>
+        [MethodImpl(InliningOptions.ShortMethod)]
         public bool Equals(DenseMatrix<T> other) =>
             this.Columns == other.Columns
             && this.Rows == other.Rows
             && this.Span.SequenceEqual(other.Span);
 
         /// <inheritdoc/>
-        public override int GetHashCode() => this.Data.GetHashCode();
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public override int GetHashCode()
+        {
+            HashCode code = default;
+
+            code.Add(this.Columns);
+            code.Add(this.Rows);
+
+            Span<T> span = this.Span;
+            for (int i = 0; i < span.Length; i++)
+            {
+                code.Add(span[i]);
+            }
+
+            return code.ToHashCode();
+        }
     }
 }

src/ImageSharp/Processing/Processors/Dithering/ErrorDither.cs

@@ -14,7 +14,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     /// An error diffusion dithering implementation.
     /// <see href="http://www.efg2.com/Lab/Library/ImageProcessing/DHALF.TXT"/>
     /// </summary>
-    public readonly partial struct ErrorDither : IDither, IEquatable<ErrorDither>
+    public readonly partial struct ErrorDither : IDither, IEquatable<ErrorDither>, IEquatable<IDither>
     {
         private readonly int offset;
         private readonly DenseMatrix<float> matrix;
@@ -31,6 +31,60 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
             this.offset = offset;
         }
 
+        /// <summary>
+        /// Compares the two <see cref="ErrorDither"/> instances to determine whether they are equal.
+        /// </summary>
+        /// <param name="left">The first source instance.</param>
+        /// <param name="right">The second source instance.</param>
+        /// <returns>The <see cref="bool"/>.</returns>
+        public static bool operator ==(IDither left, ErrorDither right)
+            => right == left;
+
+        /// <summary>
+        /// Compares the two <see cref="ErrorDither"/> instances to determine whether they are unequal.
+        /// </summary>
+        /// <param name="left">The first source instance.</param>
+        /// <param name="right">The second source instance.</param>
+        /// <returns>The <see cref="bool"/>.</returns>
+        public static bool operator !=(IDither left, ErrorDither right)
+            => !(right == left);
+
+        /// <summary>
+        /// Compares the two <see cref="ErrorDither"/> instances to determine whether they are equal.
+        /// </summary>
+        /// <param name="left">The first source instance.</param>
+        /// <param name="right">The second source instance.</param>
+        /// <returns>The <see cref="bool"/>.</returns>
+        public static bool operator ==(ErrorDither left, IDither right)
+            => left.Equals(right);
+
+        /// <summary>
+        /// Compares the two <see cref="ErrorDither"/> instances to determine whether they are unequal.
+        /// </summary>
+        /// <param name="left">The first source instance.</param>
+        /// <param name="right">The second source instance.</param>
+        /// <returns>The <see cref="bool"/>.</returns>
+        public static bool operator !=(ErrorDither left, IDither right)
+            => !(left == right);
+
+        /// <summary>
+        /// Compares the two <see cref="ErrorDither"/> instances to determine whether they are equal.
+        /// </summary>
+        /// <param name="left">The first source instance.</param>
+        /// <param name="right">The second source instance.</param>
+        /// <returns>The <see cref="bool"/>.</returns>
+        public static bool operator ==(ErrorDither left, ErrorDither right)
+            => left.Equals(right);
+
+        /// <summary>
+        /// Compares the two <see cref="ErrorDither"/> instances to determine whether they are unequal.
+        /// </summary>
+        /// <param name="left">The first source instance.</param>
+        /// <param name="right">The second source instance.</param>
+        /// <returns>The <see cref="bool"/>.</returns>
+        public static bool operator !=(ErrorDither left, ErrorDither right)
+            => !(left == right);
+
         /// <inheritdoc/>
         [MethodImpl(InliningOptions.ShortMethod)]
         public void ApplyQuantizationDither<TFrameQuantizer, TPixel>(
@@ -155,6 +209,10 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
         public bool Equals(ErrorDither other)
             => this.offset == other.offset && this.matrix.Equals(other.matrix);
 
+        /// <inheritdoc/>
+        public bool Equals(IDither other)
+            => this.Equals((object)other);
+
         /// <inheritdoc/>
         public override int GetHashCode()
             => HashCode.Combine(this.offset, this.matrix);

src/ImageSharp/Processing/Processors/Dithering/OrderedDither.cs

@@ -13,7 +13,7 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
     /// <summary>
     /// An ordered dithering matrix with equal sides of arbitrary length
     /// </summary>
-    public readonly partial struct OrderedDither : IDither, IEquatable<OrderedDither>
+    public readonly partial struct OrderedDither : IDither, IEquatable<OrderedDither>, IEquatable<IDither>
     {
         private readonly DenseMatrix<float> thresholdMatrix;
         private readonly int modulusX;
@@ -47,6 +47,60 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
             this.thresholdMatrix = thresholdMatrix;
         }
 
+        /// <summary>
+        /// Compares the two <see cref="OrderedDither"/> instances to determine whether they are equal.
+        /// </summary>
+        /// <param name="left">The first source instance.</param>
+        /// <param name="right">The second source instance.</param>
+        /// <returns>The <see cref="bool"/>.</returns>
+        public static bool operator ==(IDither left, OrderedDither right)
+            => right == left;
+
+        /// <summary>
+        /// Compares the two <see cref="OrderedDither"/> instances to determine whether they are unequal.
+        /// </summary>
+        /// <param name="left">The first source instance.</param>
+        /// <param name="right">The second source instance.</param>
+        /// <returns>The <see cref="bool"/>.</returns>
+        public static bool operator !=(IDither left, OrderedDither right)
+            => !(right == left);
+
+        /// <summary>
+        /// Compares the two <see cref="OrderedDither"/> instances to determine whether they are equal.
+        /// </summary>
+        /// <param name="left">The first source instance.</param>
+        /// <param name="right">The second source instance.</param>
+        /// <returns>The <see cref="bool"/>.</returns>
+        public static bool operator ==(OrderedDither left, IDither right)
+            => left.Equals(right);
+
+        /// <summary>
+        /// Compares the two <see cref="OrderedDither"/> instances to determine whether they are unequal.
+        /// </summary>
+        /// <param name="left">The first source instance.</param>
+        /// <param name="right">The second source instance.</param>
+        /// <returns>The <see cref="bool"/>.</returns>
+        public static bool operator !=(OrderedDither left, IDither right)
+            => !(left == right);
+
+        /// <summary>
+        /// Compares the two <see cref="OrderedDither"/> instances to determine whether they are equal.
+        /// </summary>
+        /// <param name="left">The first source instance.</param>
+        /// <param name="right">The second source instance.</param>
+        /// <returns>The <see cref="bool"/>.</returns>
+        public static bool operator ==(OrderedDither left, OrderedDither right)
+            => left.Equals(right);
+
+        /// <summary>
+        /// Compares the two <see cref="OrderedDither"/> instances to determine whether they are unequal.
+        /// </summary>
+        /// <param name="left">The first source instance.</param>
+        /// <param name="right">The second source instance.</param>
+        /// <returns>The <see cref="bool"/>.</returns>
+        public static bool operator !=(OrderedDither left, OrderedDither right)
+            => !(left == right);
+
         /// <inheritdoc/>
         [MethodImpl(InliningOptions.ShortMethod)]
         public void ApplyQuantizationDither<TFrameQuantizer, TPixel>(
@@ -133,10 +187,16 @@ namespace SixLabors.ImageSharp.Processing.Processors.Dithering
             => obj is OrderedDither dither && this.Equals(dither);
 
         /// <inheritdoc/>
+        [MethodImpl(InliningOptions.ShortMethod)]
         public bool Equals(OrderedDither other)
             => this.thresholdMatrix.Equals(other.thresholdMatrix) && this.modulusX == other.modulusX && this.modulusY == other.modulusY;
 
         /// <inheritdoc/>
+        public bool Equals(IDither other)
+            => this.Equals((object)other);
+
+        /// <inheritdoc/>
+        [MethodImpl(InliningOptions.ShortMethod)]
         public override int GetHashCode()
             => HashCode.Combine(this.thresholdMatrix, this.modulusX, this.modulusY);
 

tests/ImageSharp.Tests/Primitives/DenseMatrixTests.cs

@@ -116,5 +116,25 @@ namespace SixLabors.ImageSharp.Tests.Primitives
             Assert.Equal(2, transposed[1, 0]);
             Assert.Equal(3, transposed[2, 0]);
         }
+
+        [Fact]
+        public void DenseMatrixEquality()
+        {
+            var dense = new DenseMatrix<int>(3, 1);
+            var dense2 = new DenseMatrix<int>(3, 1);
+            var dense3 = new DenseMatrix<int>(1, 3);
+
+            Assert.True(dense == dense2);
+            Assert.False(dense != dense2);
+            Assert.Equal(dense, dense2);
+            Assert.Equal(dense, (object)dense2);
+            Assert.Equal(dense.GetHashCode(), dense2.GetHashCode());
+
+            Assert.False(dense == dense3);
+            Assert.True(dense != dense3);
+            Assert.NotEqual(dense, dense3);
+            Assert.NotEqual(dense, (object)dense3);
+            Assert.NotEqual(dense.GetHashCode(), dense3.GetHashCode());
+        }
     }
 }

tests/ImageSharp.Tests/Processing/Dithering/DitherTest.cs

@@ -104,5 +104,71 @@ namespace SixLabors.ImageSharp.Tests.Processing.Binarization
             Assert.Equal(this.errorDiffuser, p.Dither);
             Assert.Equal(this.testPalette, p.Palette);
         }
+
+        [Fact]
+        public void ErrorDitherEquality()
+        {
+            IDither dither = KnownDitherings.FloydSteinberg;
+            ErrorDither dither2 = ErrorDither.FloydSteinberg;
+            ErrorDither dither3 = ErrorDither.FloydSteinberg;
+
+            Assert.True(dither == dither2);
+            Assert.True(dither2 == dither);
+            Assert.False(dither != dither2);
+            Assert.False(dither2 != dither);
+            Assert.Equal(dither, dither2);
+            Assert.Equal(dither, (object)dither2);
+            Assert.Equal(dither.GetHashCode(), dither2.GetHashCode());
+
+            dither = null;
+            Assert.False(dither == dither2);
+            Assert.False(dither2 == dither);
+            Assert.True(dither != dither2);
+            Assert.True(dither2 != dither);
+            Assert.NotEqual(dither, dither2);
+            Assert.NotEqual(dither, (object)dither2);
+            Assert.NotEqual(dither?.GetHashCode(), dither2.GetHashCode());
+
+            Assert.True(dither2 == dither3);
+            Assert.True(dither3 == dither2);
+            Assert.False(dither2 != dither3);
+            Assert.False(dither3 != dither2);
+            Assert.Equal(dither2, dither3);
+            Assert.Equal(dither2, (object)dither3);
+            Assert.Equal(dither2.GetHashCode(), dither3.GetHashCode());
+        }
+
+        [Fact]
+        public void OrderedDitherEquality()
+        {
+            IDither dither = KnownDitherings.Bayer2x2;
+            OrderedDither dither2 = OrderedDither.Bayer2x2;
+            OrderedDither dither3 = OrderedDither.Bayer2x2;
+
+            Assert.True(dither == dither2);
+            Assert.True(dither2 == dither);
+            Assert.False(dither != dither2);
+            Assert.False(dither2 != dither);
+            Assert.Equal(dither, dither2);
+            Assert.Equal(dither, (object)dither2);
+            Assert.Equal(dither.GetHashCode(), dither2.GetHashCode());
+
+            dither = null;
+            Assert.False(dither == dither2);
+            Assert.False(dither2 == dither);
+            Assert.True(dither != dither2);
+            Assert.True(dither2 != dither);
+            Assert.NotEqual(dither, dither2);
+            Assert.NotEqual(dither, (object)dither2);
+            Assert.NotEqual(dither?.GetHashCode(), dither2.GetHashCode());
+
+            Assert.True(dither2 == dither3);
+            Assert.True(dither3 == dither2);
+            Assert.False(dither2 != dither3);
+            Assert.False(dither3 != dither2);
+            Assert.Equal(dither2, dither3);
+            Assert.Equal(dither2, (object)dither3);
+            Assert.Equal(dither2.GetHashCode(), dither3.GetHashCode());
+        }
     }
 }