Cleanup and add dedicated transform builder tests

src/ImageSharp/Processing/AffineTransformBuilder.cs

@@ -20,7 +20,13 @@ namespace SixLabors.ImageSharp.Processing
         /// Initializes a new instance of the <see cref="AffineTransformBuilder"/> class.
         /// </summary>
         /// <param name="sourceSize">The source image size.</param>
-        public AffineTransformBuilder(Size sourceSize) => this.Size = sourceSize;
+        public AffineTransformBuilder(Size sourceSize)
+        {
+            Guard.MustBeGreaterThan(sourceSize.Width, 0, nameof(sourceSize));
+            Guard.MustBeGreaterThan(sourceSize.Height, 0, nameof(sourceSize));
+
+            this.Size = sourceSize;
+        }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="AffineTransformBuilder"/> class.
@@ -41,10 +47,7 @@ namespace SixLabors.ImageSharp.Processing
         /// <param name="degrees">The amount of rotation, in degrees.</param>
         /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
         public AffineTransformBuilder PrependRotateMatrixDegrees(float degrees)
-        {
+            => this.PrependMatrix(TransformUtils.CreateRotationMatrixDegrees(degrees, this.Size));
-            this.PrependMatrix(TransformUtils.CreateRotationMatrixDegrees(degrees, this.Size));
-            return this;
-        }
 
         /// <summary>
         /// Appends a centered rotation matrix using the given rotation in degrees.
@@ -52,10 +55,7 @@ namespace SixLabors.ImageSharp.Processing
         /// <param name="degrees">The amount of rotation, in degrees.</param>
         /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
         public AffineTransformBuilder AppendRotateMatrixDegrees(float degrees)
-        {
+            => this.AppendMatrix(TransformUtils.CreateRotationMatrixDegrees(degrees, this.Size));
-            this.AppendMatrix(TransformUtils.CreateRotationMatrixDegrees(degrees, this.Size));
-            return this;
-        }
 
         /// <summary>
         /// Prepends a scale matrix from the given vector scale.
@@ -63,10 +63,7 @@ namespace SixLabors.ImageSharp.Processing
         /// <param name="scales">The horizontal and vertical scale.</param>
         /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
         public AffineTransformBuilder PrependScaleMatrix(SizeF scales)
-        {
+            => this.PrependMatrix(Matrix3x2Extensions.CreateScale(scales));
-            this.PrependMatrix(Matrix3x2Extensions.CreateScale(scales));
-            return this;
-        }
 
         /// <summary>
         /// Appends a scale matrix from the given vector scale.
@@ -74,10 +71,7 @@ namespace SixLabors.ImageSharp.Processing
         /// <param name="scales">The horizontal and vertical scale.</param>
         /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
         public AffineTransformBuilder AppendScaleMatrix(SizeF scales)
-        {
+            => this.AppendMatrix(Matrix3x2Extensions.CreateScale(scales));
-            this.AppendMatrix(Matrix3x2Extensions.CreateScale(scales));
-            return this;
-        }
 
         /// <summary>
         /// Prepends a centered skew matrix from the give angles in degrees.
@@ -86,10 +80,7 @@ namespace SixLabors.ImageSharp.Processing
         /// <param name="degreesY">The Y angle, in degrees.</param>
         /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
         public AffineTransformBuilder PrependSkewMatrixDegrees(float degreesX, float degreesY)
-        {
+            => this.PrependMatrix(TransformUtils.CreateSkewMatrixDegrees(degreesX, degreesY, this.Size));
-            this.PrependMatrix(TransformUtils.CreateSkewMatrixDegrees(degreesX, degreesY, this.Size));
-            return this;
-        }
 
         /// <summary>
         /// Appends a centered skew matrix from the give angles in degrees.
@@ -98,10 +89,7 @@ namespace SixLabors.ImageSharp.Processing
         /// <param name="degreesY">The Y angle, in degrees.</param>
         /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
         public AffineTransformBuilder AppendSkewMatrixDegrees(float degreesX, float degreesY)
-        {
+            => this.AppendMatrix(TransformUtils.CreateSkewMatrixDegrees(degreesX, degreesY, this.Size));
-            this.AppendMatrix(TransformUtils.CreateSkewMatrixDegrees(degreesX, degreesY, this.Size));
-            return this;
-        }
 
         /// <summary>
         /// Prepends a translation matrix from the given vector.
@@ -109,10 +97,7 @@ namespace SixLabors.ImageSharp.Processing
         /// <param name="position">The translation position.</param>
         /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
         public AffineTransformBuilder PrependTranslationMatrix(PointF position)
-        {
+            => this.PrependMatrix(Matrix3x2Extensions.CreateTranslation(position));
-            this.PrependMatrix(Matrix3x2Extensions.CreateTranslation(position));
-            return this;
-        }
 
         /// <summary>
         /// Appends a translation matrix from the given vector.
@@ -120,10 +105,7 @@ namespace SixLabors.ImageSharp.Processing
         /// <param name="position">The translation position.</param>
         /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
         public AffineTransformBuilder AppendTranslationMatrix(PointF position)
-        {
+            => this.AppendMatrix(Matrix3x2Extensions.CreateTranslation(position));
-            this.AppendMatrix(Matrix3x2Extensions.CreateTranslation(position));
-            return this;
-        }
 
         /// <summary>
         /// Prepends a raw matrix.

src/ImageSharp/Processing/ProjectiveTransformBuilder.cs

@@ -20,7 +20,13 @@ namespace SixLabors.ImageSharp.Processing
         /// Initializes a new instance of the <see cref="ProjectiveTransformBuilder"/> class.
         /// </summary>
         /// <param name="sourceSize">The source image size.</param>
-        public ProjectiveTransformBuilder(Size sourceSize) => this.Size = sourceSize;
+        public ProjectiveTransformBuilder(Size sourceSize)
+        {
+            Guard.MustBeGreaterThan(sourceSize.Width, 0, nameof(sourceSize));
+            Guard.MustBeGreaterThan(sourceSize.Height, 0, nameof(sourceSize));
+
+            this.Size = sourceSize;
+        }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ProjectiveTransformBuilder"/> class.
@@ -43,10 +49,7 @@ namespace SixLabors.ImageSharp.Processing
         /// <param name="fraction">The amount to taper.</param>
         /// <returns>The <see cref="ProjectiveTransformBuilder"/>.</returns>
         public ProjectiveTransformBuilder PrependTaperMatrix(TaperSide side, TaperCorner corner, float fraction)
-        {
+            => this.PrependMatrix(TransformUtils.CreateTaperMatrix(this.Size, side, corner, fraction));
-            this.PrependMatrix(TransformUtils.CreateTaperMatrix(this.Size, side, corner, fraction));
-            return this;
-        }
 
         /// <summary>
         /// Appends a matrix that performs a tapering projective transform.
@@ -56,10 +59,7 @@ namespace SixLabors.ImageSharp.Processing
         /// <param name="fraction">The amount to taper.</param>
         /// <returns>The <see cref="ProjectiveTransformBuilder"/>.</returns>
         public ProjectiveTransformBuilder AppendTaperMatrix(TaperSide side, TaperCorner corner, float fraction)
-        {
+            => this.AppendMatrix(TransformUtils.CreateTaperMatrix(this.Size, side, corner, fraction));
-            this.AppendMatrix(TransformUtils.CreateTaperMatrix(this.Size, side, corner, fraction));
-            return this;
-        }
 
         /// <summary>
         /// Prepends a raw matrix.

tests/ImageSharp.Tests/Processing/Transforms/AffineTransformBuilderTests.cs

@@ -0,0 +1,79 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Numerics;
+using SixLabors.ImageSharp.Processing;
+using SixLabors.Primitives;
+using Xunit;
+
+namespace SixLabors.ImageSharp.Tests.Processing.Transforms
+{
+    public class AffineTransformBuilderTests
+    {
+        [Fact]
+        public void ConstructorAssignsProperties()
+        {
+            var s = new Size(1, 1);
+            var builder = new AffineTransformBuilder(new Rectangle(Point.Empty, s));
+            Assert.Equal(s, builder.Size);
+        }
+
+        [Fact]
+        public void ConstructorThrowsInvalid()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() =>
+            {
+                var s = new Size(0, 1);
+                var builder = new AffineTransformBuilder(new Rectangle(Point.Empty, s));
+            });
+
+            Assert.Throws<ArgumentOutOfRangeException>(() =>
+            {
+                var s = new Size(1, 0);
+                var builder = new AffineTransformBuilder(new Rectangle(Point.Empty, s));
+            });
+        }
+
+        [Fact]
+        public void AppendPrependOpposite()
+        {
+            var rectangle = new Rectangle(-1, -1, 3, 3);
+            var b1 = new AffineTransformBuilder(rectangle);
+            var b2 = new AffineTransformBuilder(rectangle);
+
+            const float pi = (float)Math.PI;
+
+            // Forwards
+            b1.AppendRotateMatrixDegrees(pi)
+              .AppendSkewMatrixDegrees(pi, pi)
+              .AppendScaleMatrix(new SizeF(pi, pi))
+              .AppendTranslationMatrix(new PointF(pi, pi));
+
+            // Backwards
+            b2.PrependTranslationMatrix(new PointF(pi, pi))
+              .PrependScaleMatrix(new SizeF(pi, pi))
+              .PrependSkewMatrixDegrees(pi, pi)
+              .PrependRotateMatrixDegrees(pi);
+
+            Assert.Equal(b1.BuildMatrix(), b2.BuildMatrix());
+        }
+
+        [Fact]
+        public void BuilderCanClear()
+        {
+            var rectangle = new Rectangle(0, 0, 3, 3);
+            var builder = new AffineTransformBuilder(rectangle);
+            Matrix3x2 matrix = Matrix3x2.Identity;
+            matrix.M31 = (float)Math.PI;
+
+            Assert.Equal(Matrix3x2.Identity, builder.BuildMatrix());
+
+            builder.AppendMatrix(matrix);
+            Assert.NotEqual(Matrix3x2.Identity, builder.BuildMatrix());
+
+            builder.Clear();
+            Assert.Equal(Matrix3x2.Identity, builder.BuildMatrix());
+        }
+    }
+}

tests/ImageSharp.Tests/Processing/Transforms/ProjectiveTransformBuilderTests.cs

@@ -0,0 +1,78 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Numerics;
+using SixLabors.ImageSharp.Processing;
+using SixLabors.Primitives;
+using Xunit;
+
+namespace SixLabors.ImageSharp.Tests.Processing.Transforms
+{
+    public class ProjectiveTransformBuilderTests
+    {
+        [Fact]
+        public void ConstructorAssignsProperties()
+        {
+            var s = new Size(1, 1);
+            var builder = new ProjectiveTransformBuilder(new Rectangle(Point.Empty, s));
+            Assert.Equal(s, builder.Size);
+        }
+
+        [Fact]
+        public void ConstructorThrowsInvalid()
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() =>
+            {
+                var s = new Size(0, 1);
+                var builder = new ProjectiveTransformBuilder(new Rectangle(Point.Empty, s));
+            });
+
+            Assert.Throws<ArgumentOutOfRangeException>(() =>
+            {
+                var s = new Size(1, 0);
+                var builder = new ProjectiveTransformBuilder(new Rectangle(Point.Empty, s));
+            });
+        }
+
+        [Fact]
+        public void AppendPrependOpposite()
+        {
+            var rectangle = new Rectangle(-1, -1, 3, 3);
+            var b1 = new ProjectiveTransformBuilder(rectangle);
+            var b2 = new ProjectiveTransformBuilder(rectangle);
+
+            const float pi = (float)Math.PI;
+
+            Matrix4x4 m4 = Matrix4x4.Identity;
+            m4.M31 = pi;
+
+            // Forwards
+            b1.AppendMatrix(m4)
+              .AppendTaperMatrix(TaperSide.Left, TaperCorner.LeftOrTop, pi);
+
+            // Backwards
+            b2.PrependTaperMatrix(TaperSide.Left, TaperCorner.LeftOrTop, pi)
+              .PrependMatrix(m4);
+
+            Assert.Equal(b1.BuildMatrix(), b2.BuildMatrix());
+        }
+
+        [Fact]
+        public void BuilderCanClear()
+        {
+            var rectangle = new Rectangle(0, 0, 3, 3);
+            var builder = new ProjectiveTransformBuilder(rectangle);
+            Matrix4x4 matrix = Matrix4x4.Identity;
+            matrix.M31 = (float)Math.PI;
+
+            Assert.Equal(Matrix4x4.Identity, builder.BuildMatrix());
+
+            builder.AppendMatrix(matrix);
+            Assert.NotEqual(Matrix4x4.Identity, builder.BuildMatrix());
+
+            builder.Clear();
+            Assert.Equal(Matrix4x4.Identity, builder.BuildMatrix());
+        }
+    }
+}