Add Skew methods and tests.

src/ImageSharp/Processing/AffineTransformBuilder.cs

@@ -145,6 +145,35 @@ namespace SixLabors.ImageSharp.Processing
         public AffineTransformBuilder PrependSkewDegrees(float degreesX, float degreesY)
             => this.Prepend(size => TransformUtils.CreateSkewMatrixDegrees(degreesX, degreesY, size));
 
+        /// <summary>
+        /// Prepends a centered skew matrix from the give angles in radians.
+        /// </summary>
+        /// <param name="radiansX">The X angle, in radians.</param>
+        /// <param name="radiansY">The Y angle, in radians.</param>
+        /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
+        public AffineTransformBuilder PrependSkewRadians(float radiansX, float radiansY)
+            => this.Prepend(size => TransformUtils.CreateSkewMatrixRadians(radiansX, radiansY, size));
+
+        /// <summary>
+        /// Prepends a skew matrix using the given angles in degrees at the given origin.
+        /// </summary>
+        /// <param name="degreesX">The X angle, in degrees.</param>
+        /// <param name="degreesY">The Y angle, in degrees.</param>
+        /// <param name="origin">The skew origin point.</param>
+        /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
+        public AffineTransformBuilder PrependSkewDegrees(float degreesX, float degreesY, Vector2 origin)
+            => this.PrependSkewRadians(GeometryUtilities.DegreeToRadian(degreesX), GeometryUtilities.DegreeToRadian(degreesY), origin);
+
+        /// <summary>
+        /// Prepends a skew matrix using the given angles in radians at the given origin.
+        /// </summary>
+        /// <param name="radiansX">The X angle, in radians.</param>
+        /// <param name="radiansY">The Y angle, in radians.</param>
+        /// <param name="origin">The skew origin point.</param>
+        /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
+        public AffineTransformBuilder PrependSkewRadians(float radiansX, float radiansY, Vector2 origin)
+            => this.PrependMatrix(Matrix3x2.CreateSkew(radiansX, radiansY, origin));
+
         /// <summary>
         /// Appends a centered skew matrix from the give angles in degrees.
         /// </summary>
@@ -154,6 +183,35 @@ namespace SixLabors.ImageSharp.Processing
         public AffineTransformBuilder AppendSkewDegrees(float degreesX, float degreesY)
             => this.Append(size => TransformUtils.CreateSkewMatrixDegrees(degreesX, degreesY, size));
 
+        /// <summary>
+        /// Appends a centered skew matrix from the give angles in radians.
+        /// </summary>
+        /// <param name="radiansX">The X angle, in radians.</param>
+        /// <param name="radiansY">The Y angle, in radians.</param>
+        /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
+        public AffineTransformBuilder AppendSkewRadians(float radiansX, float radiansY)
+            => this.Append(size => TransformUtils.CreateSkewMatrixRadians(radiansX, radiansY, size));
+
+        /// <summary>
+        /// Appends a skew matrix using the given angles in degrees at the given origin.
+        /// </summary>
+        /// <param name="degreesX">The X angle, in degrees.</param>
+        /// <param name="degreesY">The Y angle, in degrees.</param>
+        /// <param name="origin">The skew origin point.</param>
+        /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
+        public AffineTransformBuilder AppendSkewDegrees(float degreesX, float degreesY, Vector2 origin)
+            => this.AppendSkewRadians(GeometryUtilities.DegreeToRadian(degreesX), GeometryUtilities.DegreeToRadian(degreesY), origin);
+
+        /// <summary>
+        /// Appends a skew matrix using the given angles in radians at the given origin.
+        /// </summary>
+        /// <param name="radiansX">The X angle, in radians.</param>
+        /// <param name="radiansY">The Y angle, in radians.</param>
+        /// <param name="origin">The skew origin point.</param>
+        /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
+        public AffineTransformBuilder AppendSkewRadians(float radiansX, float radiansY, Vector2 origin)
+            => this.AppendMatrix(Matrix3x2.CreateSkew(radiansX, radiansY, origin));
+
         /// <summary>
         /// Prepends a translation matrix from the given vector.
         /// </summary>

src/ImageSharp/Processing/Processors/Transforms/TransformUtils.cs

@@ -46,6 +46,18 @@ namespace SixLabors.ImageSharp.Processing.Processors.Transforms
                 new Rectangle(Point.Empty, size),
                 Matrix3x2Extensions.CreateSkewDegrees(degreesX, degreesY, PointF.Empty));
 
+        /// <summary>
+        /// Creates a centered skew matrix from the give angles in radians and the source size.
+        /// </summary>
+        /// <param name="radiansX">The X angle, in radians.</param>
+        /// <param name="radiansY">The Y angle, in radians.</param>
+        /// <param name="size">The source image size.</param>
+        /// <returns>The <see cref="Matrix3x2"/>.</returns>
+        public static Matrix3x2 CreateSkewMatrixRadians(float radiansX, float radiansY, Size size)
+            => CreateCenteredTransformMatrix(
+                new Rectangle(Point.Empty, size),
+                Matrix3x2Extensions.CreateSkew(radiansX, radiansY, PointF.Empty));
+
         /// <summary>
         /// Gets the centered transform matrix based upon the source and destination rectangles.
         /// </summary>

src/ImageSharp/Processing/ProjectiveTransformBuilder.cs

@@ -152,6 +152,82 @@ namespace SixLabors.ImageSharp.Processing
         public ProjectiveTransformBuilder AppendScale(Vector2 scales)
             => this.AppendMatrix(Matrix4x4.CreateScale(new Vector3(scales, 1F)));
 
+        /// <summary>
+        /// Prepends a centered skew matrix from the give angles in degrees.
+        /// </summary>
+        /// <param name="degreesX">The X angle, in degrees.</param>
+        /// <param name="degreesY">The Y angle, in degrees.</param>
+        /// <returns>The <see cref="ProjectiveTransformBuilder"/>.</returns>
+        internal ProjectiveTransformBuilder PrependSkewDegrees(float degreesX, float degreesY)
+            => this.PrependSkewRadians(GeometryUtilities.DegreeToRadian(degreesX), GeometryUtilities.DegreeToRadian(degreesY));
+
+        /// <summary>
+        /// Prepends a centered skew matrix from the give angles in radians.
+        /// </summary>
+        /// <param name="radiansX">The X angle, in radians.</param>
+        /// <param name="radiansY">The Y angle, in radians.</param>
+        /// <returns>The <see cref="ProjectiveTransformBuilder"/>.</returns>
+        public ProjectiveTransformBuilder PrependSkewRadians(float radiansX, float radiansY)
+            => this.Prepend(size => new Matrix4x4(TransformUtils.CreateSkewMatrixRadians(radiansX, radiansY, size)));
+
+        /// <summary>
+        /// Prepends a skew matrix using the given angles in degrees at the given origin.
+        /// </summary>
+        /// <param name="degreesX">The X angle, in degrees.</param>
+        /// <param name="degreesY">The Y angle, in degrees.</param>
+        /// <param name="origin">The skew origin point.</param>
+        /// <returns>The <see cref="ProjectiveTransformBuilder"/>.</returns>
+        public ProjectiveTransformBuilder PrependSkewDegrees(float degreesX, float degreesY, Vector2 origin)
+            => this.PrependSkewRadians(GeometryUtilities.DegreeToRadian(degreesX), GeometryUtilities.DegreeToRadian(degreesY), origin);
+
+        /// <summary>
+        /// Prepends a skew matrix using the given angles in radians at the given origin.
+        /// </summary>
+        /// <param name="radiansX">The X angle, in radians.</param>
+        /// <param name="radiansY">The Y angle, in radians.</param>
+        /// <param name="origin">The skew origin point.</param>
+        /// <returns>The <see cref="ProjectiveTransformBuilder"/>.</returns>
+        public ProjectiveTransformBuilder PrependSkewRadians(float radiansX, float radiansY, Vector2 origin)
+            => this.PrependMatrix(new Matrix4x4(Matrix3x2.CreateSkew(radiansX, radiansY, origin)));
+
+        /// <summary>
+        /// Appends a centered skew matrix from the give angles in degrees.
+        /// </summary>
+        /// <param name="degreesX">The X angle, in degrees.</param>
+        /// <param name="degreesY">The Y angle, in degrees.</param>
+        /// <returns>The <see cref="ProjectiveTransformBuilder"/>.</returns>
+        internal ProjectiveTransformBuilder AppendSkewDegrees(float degreesX, float degreesY)
+            => this.AppendSkewRadians(GeometryUtilities.DegreeToRadian(degreesX), GeometryUtilities.DegreeToRadian(degreesY));
+
+        /// <summary>
+        /// Appends a centered skew matrix from the give angles in radians.
+        /// </summary>
+        /// <param name="radiansX">The X angle, in radians.</param>
+        /// <param name="radiansY">The Y angle, in radians.</param>
+        /// <returns>The <see cref="ProjectiveTransformBuilder"/>.</returns>
+        public ProjectiveTransformBuilder AppendSkewRadians(float radiansX, float radiansY)
+            => this.Append(size => new Matrix4x4(TransformUtils.CreateSkewMatrixRadians(radiansX, radiansY, size)));
+
+        /// <summary>
+        /// Appends a skew matrix using the given angles in degrees at the given origin.
+        /// </summary>
+        /// <param name="degreesX">The X angle, in degrees.</param>
+        /// <param name="degreesY">The Y angle, in degrees.</param>
+        /// <param name="origin">The skew origin point.</param>
+        /// <returns>The <see cref="ProjectiveTransformBuilder"/>.</returns>
+        public ProjectiveTransformBuilder AppendSkewDegrees(float degreesX, float degreesY, Vector2 origin)
+            => this.AppendSkewRadians(GeometryUtilities.DegreeToRadian(degreesX), GeometryUtilities.DegreeToRadian(degreesY), origin);
+
+        /// <summary>
+        /// Appends a skew matrix using the given angles in radians at the given origin.
+        /// </summary>
+        /// <param name="radiansX">The X angle, in radians.</param>
+        /// <param name="radiansY">The Y angle, in radians.</param>
+        /// <param name="origin">The skew origin point.</param>
+        /// <returns>The <see cref="ProjectiveTransformBuilder"/>.</returns>
+        public ProjectiveTransformBuilder AppendSkewRadians(float radiansX, float radiansY, Vector2 origin)
+            => this.AppendMatrix(new Matrix4x4(Matrix3x2.CreateSkew(radiansX, radiansY, origin)));
+
         /// <summary>
         /// Prepends a translation matrix from the given vector.
         /// </summary>

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

@@ -9,28 +9,55 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
 {
     public class AffineTransformBuilderTests : TransformBuilderTestBase<AffineTransformBuilder>
     {
-        protected override void AppendTranslation(AffineTransformBuilder builder, PointF translate) => builder.AppendTranslation(translate);
+        protected override AffineTransformBuilder CreateBuilder(Rectangle rectangle) => new AffineTransformBuilder();
 
-        protected override void AppendScale(AffineTransformBuilder builder, SizeF scale) => builder.AppendScale(scale);
+        protected override void AppendRotationDegrees(AffineTransformBuilder builder, float degrees)
+            => builder.AppendRotationDegrees(degrees);
 
-        protected override void AppendRotationRadians(AffineTransformBuilder builder, float radians) => builder.AppendRotationRadians(radians);
+        protected override void AppendRotationDegrees(AffineTransformBuilder builder, float degrees, Vector2 origin)
+            => builder.AppendRotationDegrees(degrees, origin);
 
-        protected override void AppendRotationRadians(AffineTransformBuilder builder, float radians, Vector2 origin) => builder.AppendRotationRadians(radians, origin);
+        protected override void AppendRotationRadians(AffineTransformBuilder builder, float radians)
+            => builder.AppendRotationRadians(radians);
 
-        protected override void AppendRotationDegrees(AffineTransformBuilder builder, float degrees) => builder.AppendRotationDegrees(degrees);
+        protected override void AppendRotationRadians(AffineTransformBuilder builder, float radians, Vector2 origin)
+            => builder.AppendRotationRadians(radians, origin);
 
-        protected override void AppendRotationDegrees(AffineTransformBuilder builder, float degrees, Vector2 origin) => builder.AppendRotationDegrees(degrees, origin);
+        protected override void AppendScale(AffineTransformBuilder builder, SizeF scale)
+            => builder.AppendScale(scale);
 
-        protected override void PrependTranslation(AffineTransformBuilder builder, PointF translate) => builder.PrependTranslation(translate);
+        protected override void AppendSkewDegrees(AffineTransformBuilder builder, float degreesX, float degreesY)
+            => builder.AppendSkewDegrees(degreesX, degreesY);
 
-        protected override void PrependScale(AffineTransformBuilder builder, SizeF scale) => builder.PrependScale(scale);
+        protected override void AppendSkewDegrees(AffineTransformBuilder builder, float degreesX, float degreesY, Vector2 origin)
+            => builder.AppendSkewDegrees(degreesX, degreesY, origin);
 
-        protected override void PrependRotationRadians(AffineTransformBuilder builder, float radians) => builder.PrependRotationRadians(radians);
+        protected override void AppendSkewRadians(AffineTransformBuilder builder, float radiansX, float radiansY)
+            => builder.AppendSkewRadians(radiansX, radiansY);
 
-        protected override void PrependRotationRadians(AffineTransformBuilder builder, float radians, Vector2 origin) =>
-            builder.PrependRotationRadians(radians, origin);
+        protected override void AppendSkewRadians(AffineTransformBuilder builder, float radiansX, float radiansY, Vector2 origin)
+            => builder.AppendSkewRadians(radiansX, radiansY, origin);
 
-        protected override AffineTransformBuilder CreateBuilder(Rectangle rectangle) => new AffineTransformBuilder();
+        protected override void AppendTranslation(AffineTransformBuilder builder, PointF translate)
+            => builder.AppendTranslation(translate);
+
+        protected override void PrependRotationRadians(AffineTransformBuilder builder, float radians)
+            => builder.PrependRotationRadians(radians);
+
+        protected override void PrependRotationRadians(AffineTransformBuilder builder, float radians, Vector2 origin)
+            => builder.PrependRotationRadians(radians, origin);
+
+        protected override void PrependScale(AffineTransformBuilder builder, SizeF scale)
+            => builder.PrependScale(scale);
+
+        protected override void PrependSkewRadians(AffineTransformBuilder builder, float radiansX, float radiansY)
+            => builder.PrependSkewRadians(radiansX, radiansY);
+
+        protected override void PrependSkewRadians(AffineTransformBuilder builder, float radiansX, float radiansY, Vector2 origin)
+            => builder.PrependSkewRadians(radiansX, radiansY, origin);
+
+        protected override void PrependTranslation(AffineTransformBuilder builder, PointF translate)
+            => builder.PrependTranslation(translate);
 
         protected override Vector2 Execute(
             AffineTransformBuilder builder,

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

@@ -11,24 +11,42 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
     {
         protected override ProjectiveTransformBuilder CreateBuilder(Rectangle rectangle) => new ProjectiveTransformBuilder();
 
-        protected override void AppendTranslation(ProjectiveTransformBuilder builder, PointF translate) => builder.AppendTranslation(translate);
+        protected override void AppendRotationDegrees(ProjectiveTransformBuilder builder, float degrees) => builder.AppendRotationDegrees(degrees);
 
-        protected override void AppendScale(ProjectiveTransformBuilder builder, SizeF scale) => builder.AppendScale(scale);
+        protected override void AppendRotationDegrees(ProjectiveTransformBuilder builder, float degrees, Vector2 origin) => builder.AppendRotationDegrees(degrees, origin);
 
         protected override void AppendRotationRadians(ProjectiveTransformBuilder builder, float radians) => builder.AppendRotationRadians(radians);
 
         protected override void AppendRotationRadians(ProjectiveTransformBuilder builder, float radians, Vector2 origin) => builder.AppendRotationRadians(radians, origin);
 
-        protected override void AppendRotationDegrees(ProjectiveTransformBuilder builder, float degrees) => builder.AppendRotationDegrees(degrees);
+        protected override void AppendScale(ProjectiveTransformBuilder builder, SizeF scale) => builder.AppendScale(scale);
 
-        protected override void AppendRotationDegrees(ProjectiveTransformBuilder builder, float degrees, Vector2 origin) => builder.AppendRotationDegrees(degrees, origin);
+        protected override void AppendSkewDegrees(ProjectiveTransformBuilder builder, float degreesX, float degreesY)
+    => builder.AppendSkewDegrees(degreesX, degreesY);
 
-        protected override void PrependTranslation(ProjectiveTransformBuilder builder, PointF translate) => builder.PrependTranslation(translate);
+        protected override void AppendSkewDegrees(ProjectiveTransformBuilder builder, float degreesX, float degreesY, Vector2 origin)
+            => builder.AppendSkewDegrees(degreesX, degreesY, origin);
 
-        protected override void PrependScale(ProjectiveTransformBuilder builder, SizeF scale) => builder.PrependScale(scale);
+        protected override void AppendSkewRadians(ProjectiveTransformBuilder builder, float radiansX, float radiansY)
+            => builder.AppendSkewRadians(radiansX, radiansY);
+
+        protected override void AppendSkewRadians(ProjectiveTransformBuilder builder, float radiansX, float radiansY, Vector2 origin)
+            => builder.AppendSkewRadians(radiansX, radiansY, origin);
+
+        protected override void AppendTranslation(ProjectiveTransformBuilder builder, PointF translate) => builder.AppendTranslation(translate);
 
         protected override void PrependRotationRadians(ProjectiveTransformBuilder builder, float radians) => builder.PrependRotationRadians(radians);
 
+        protected override void PrependScale(ProjectiveTransformBuilder builder, SizeF scale) => builder.PrependScale(scale);
+
+        protected override void PrependSkewRadians(ProjectiveTransformBuilder builder, float radiansX, float radiansY)
+            => builder.PrependSkewRadians(radiansX, radiansY);
+
+        protected override void PrependSkewRadians(ProjectiveTransformBuilder builder, float radiansX, float radiansY, Vector2 origin)
+            => builder.PrependSkewRadians(radiansX, radiansY, origin);
+
+        protected override void PrependTranslation(ProjectiveTransformBuilder builder, PointF translate) => builder.PrependTranslation(translate);
+
         protected override void PrependRotationRadians(ProjectiveTransformBuilder builder, float radians, Vector2 origin) =>
             builder.PrependRotationRadians(radians, origin);
 

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

@@ -86,17 +86,17 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
         public void AppendRotationDegrees_WithoutSpecificRotationCenter_RotationIsCenteredAroundImageCenter(
             int width,
             int height,
-            float deg,
+            float degrees,
             float x,
             float y)
         {
             var size = new Size(width, height);
             TBuilder builder = this.CreateBuilder(size);
 
-            this.AppendRotationDegrees(builder, deg);
+            this.AppendRotationDegrees(builder, degrees);
 
             // TODO: We should also test CreateRotationMatrixDegrees() (and all TransformUtils stuff!) for correctness
-            Matrix3x2 matrix = TransformUtils.CreateRotationMatrixDegrees(deg, size);
+            Matrix3x2 matrix = TransformUtils.CreateRotationMatrixDegrees(degrees, size);
 
             var position = new Vector2(x, y);
             var expected = Vector2.Transform(position, matrix);
@@ -112,7 +112,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
         public void AppendRotationDegrees_WithRotationCenter(
             int width,
             int height,
-            float deg,
+            float degrees,
             float cx,
             float cy,
             float x,
@@ -122,9 +122,63 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
             TBuilder builder = this.CreateBuilder(size);
 
             var centerPoint = new Vector2(cx, cy);
-            this.AppendRotationDegrees(builder, deg, centerPoint);
+            this.AppendRotationDegrees(builder, degrees, centerPoint);
 
-            var matrix = Matrix3x2.CreateRotation(GeometryUtilities.DegreeToRadian(deg), centerPoint);
+            var matrix = Matrix3x2.CreateRotation(GeometryUtilities.DegreeToRadian(degrees), centerPoint);
+
+            var position = new Vector2(x, y);
+            var expected = Vector2.Transform(position, matrix);
+            Vector2 actual = this.Execute(builder, new Rectangle(Point.Empty, size), position);
+
+            Assert.Equal(actual, expected, Comparer);
+        }
+
+        [Theory]
+        [InlineData(200, 100, 10, 10, 42, 84)]
+        [InlineData(200, 100, 100, 100, 42, 84)]
+        [InlineData(100, 200, -10, -10, 42, 84)]
+        public void AppendSkewDegrees_WithoutSpecificSkewCenter_SkewIsCenteredAroundImageCenter(
+            int width,
+            int height,
+            float degreesX,
+            float degreesY,
+            float x,
+            float y)
+        {
+            var size = new Size(width, height);
+            TBuilder builder = this.CreateBuilder(size);
+
+            this.AppendSkewDegrees(builder, degreesX, degreesY);
+
+            Matrix3x2 matrix = TransformUtils.CreateSkewMatrixDegrees(degreesX, degreesY, size);
+
+            var position = new Vector2(x, y);
+            var expected = Vector2.Transform(position, matrix);
+            Vector2 actual = this.Execute(builder, new Rectangle(Point.Empty, size), position);
+            Assert.Equal(actual, expected, Comparer);
+        }
+
+        [Theory]
+        [InlineData(200, 100, 10, 10, 30, 61, 42, 84)]
+        [InlineData(200, 100, 100, 100, 30, 10, 20, 84)]
+        [InlineData(100, 200, -10, -10, 30, 20, 11, 84)]
+        public void AppendSkewDegrees_WithSkewCenter(
+            int width,
+            int height,
+            float degreesX,
+            float degreesY,
+            float cx,
+            float cy,
+            float x,
+            float y)
+        {
+            var size = new Size(width, height);
+            TBuilder builder = this.CreateBuilder(size);
+
+            var centerPoint = new Vector2(cx, cy);
+            this.AppendSkewDegrees(builder, degreesX, degreesY, centerPoint);
+
+            var matrix = Matrix3x2.CreateSkew(GeometryUtilities.DegreeToRadian(degreesX), GeometryUtilities.DegreeToRadian(degreesY), centerPoint);
 
             var position = new Vector2(x, y);
             var expected = Vector2.Transform(position, matrix);
@@ -144,14 +198,18 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
 
             // Forwards
             this.AppendRotationRadians(b1, pi);
+            this.AppendSkewRadians(b1, pi, pi);
             this.AppendScale(b1, new SizeF(2, 0.5f));
             this.AppendRotationRadians(b1, pi / 2, new Vector2(-0.5f, -0.1f));
+            this.AppendSkewRadians(b1, pi, pi / 2, new Vector2(-0.5f, -0.1f));
             this.AppendTranslation(b1, new PointF(123, 321));
 
             // Backwards
             this.PrependTranslation(b2, new PointF(123, 321));
+            this.PrependSkewRadians(b2, pi, pi / 2, new Vector2(-0.5f, -0.1f));
             this.PrependRotationRadians(b2, pi / 2, new Vector2(-0.5f, -0.1f));
             this.PrependScale(b2, new SizeF(2, 0.5f));
+            this.PrependSkewRadians(b2, pi, pi);
             this.PrependRotationRadians(b2, pi);
 
             Vector2 p1 = this.Execute(b1, rectangle, new Vector2(32, 65));
@@ -180,25 +238,37 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
 
         protected abstract TBuilder CreateBuilder(Rectangle rectangle);
 
-        protected abstract void AppendTranslation(TBuilder builder, PointF translate);
+        protected abstract void AppendRotationDegrees(TBuilder builder, float degrees);
 
-        protected abstract void AppendScale(TBuilder builder, SizeF scale);
+        protected abstract void AppendRotationDegrees(TBuilder builder, float degrees, Vector2 origin);
 
         protected abstract void AppendRotationRadians(TBuilder builder, float radians);
 
         protected abstract void AppendRotationRadians(TBuilder builder, float radians, Vector2 origin);
 
-        protected abstract void PrependTranslation(TBuilder builder, PointF translate);
+        protected abstract void AppendScale(TBuilder builder, SizeF scale);
 
-        protected abstract void PrependScale(TBuilder builder, SizeF scale);
+        protected abstract void AppendSkewDegrees(TBuilder builder, float degreesX, float degreesY);
+
+        protected abstract void AppendSkewDegrees(TBuilder builder, float degreesX, float degreesY, Vector2 origin);
+
+        protected abstract void AppendSkewRadians(TBuilder builder, float radiansX, float radiansY);
+
+        protected abstract void AppendSkewRadians(TBuilder builder, float radiansX, float radiansY, Vector2 origin);
+
+        protected abstract void AppendTranslation(TBuilder builder, PointF translate);
 
         protected abstract void PrependRotationRadians(TBuilder builder, float radians);
 
         protected abstract void PrependRotationRadians(TBuilder builder, float radians, Vector2 origin);
 
-        protected abstract void AppendRotationDegrees(TBuilder builder, float degrees);
+        protected abstract void PrependScale(TBuilder builder, SizeF scale);
 
-        protected abstract void AppendRotationDegrees(TBuilder builder, float degrees, Vector2 origin);
+        protected abstract void PrependSkewRadians(TBuilder builder, float radiansX, float radiansY);
+
+        protected abstract void PrependSkewRadians(TBuilder builder, float radiansX, float radiansY, Vector2 origin);
+
+        protected abstract void PrependTranslation(TBuilder builder, PointF translate);
 
         protected abstract Vector2 Execute(TBuilder builder, Rectangle rectangle, Vector2 sourcePoint);
     }