Rotation around custom center point. Rename PrependCenteredRotationRadians back to PrependRotationRadians

src/ImageSharp/Processing/AffineTransformBuilder.cs

@@ -20,33 +20,55 @@ namespace SixLabors.ImageSharp.Processing
         /// Prepends a centered rotation matrix using the given rotation in radians.
         /// </summary>
         /// <param name="radians">The amount of rotation, in radians.</param>
+        /// <param name="centerPoint">The rotation center point</param>
         /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
-        public AffineTransformBuilder PrependCenteredRotationRadians(float radians)
+        public AffineTransformBuilder PrependRotationRadians(float radians, Vector2 centerPoint)
-            => this.Prepend(size => TransformUtils.CreateRotationMatrixRadians(radians, size));
+            => this.PrependMatrix(Matrix3x2.CreateRotation(radians, centerPoint));
 
         /// <summary>
         /// Appends a centered rotation matrix using the given rotation in radians.
         /// </summary>
         /// <param name="radians">The amount of rotation, in radians.</param>
+        /// <param name="centerPoint">The rotation center point</param>
+        /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
+        public AffineTransformBuilder AppendRotationRadians(float radians, Vector2 centerPoint)
+            => this.AppendMatrix(Matrix3x2.CreateRotation(radians, centerPoint));
+
+        /// <summary>
+        /// Prepends a rotation matrix using the given rotation angle in radians
+        /// and the image center point as rotation center.
+        /// </summary>
+        /// <param name="radians">The amount of rotation, in radians.</param>
+        /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
+        public AffineTransformBuilder PrependRotationRadians(float radians)
+            => this.Prepend(size => TransformUtils.CreateRotationMatrixRadians(radians, size));
+
+        /// <summary>
+        /// Appends a rotation matrix using the given rotation angle in radians
+        /// and the image center point as rotation center.
+        /// </summary>
+        /// <param name="radians">The amount of rotation, in radians.</param>
         /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
-        public AffineTransformBuilder AppendCenteredRotationRadians(float radians)
+        public AffineTransformBuilder AppendRotationRadians(float radians)
             => this.Append(size => TransformUtils.CreateRotationMatrixRadians(radians, size));
 
         /// <summary>
-        /// Prepends a centered rotation matrix using the given rotation in degrees.
+        /// Prepends a rotation matrix using the given rotation angle in degrees
+        /// and the image center point as rotation center.
         /// </summary>
         /// <param name="degrees">The amount of rotation, in degrees.</param>
         /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
-        public AffineTransformBuilder PrependCenteredRotationDegrees(float degrees)
+        public AffineTransformBuilder PrependRotationDegrees(float degrees)
-            => this.PrependCenteredRotationRadians(ImageMaths.DegreesToRadians(degrees));
+            => this.PrependRotationRadians(ImageMaths.DegreesToRadians(degrees));
 
         /// <summary>
-        /// Appends a centered rotation matrix using the given rotation in degrees.
+        /// Appends a rotation matrix using the given rotation angle in degrees
+        /// and the image center point as rotation center.
         /// </summary>
         /// <param name="degrees">The amount of rotation, in degrees.</param>
         /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
-        public AffineTransformBuilder AppendCenteredRotationDegrees(float degrees)
+        public AffineTransformBuilder AppendRotationDegrees(float degrees)
-            => this.AppendCenteredRotationRadians(ImageMaths.DegreesToRadians(degrees));
+            => this.AppendRotationRadians(ImageMaths.DegreesToRadians(degrees));
 
         /// <summary>
         /// Prepends a scale matrix from the given uniform scale.

src/ImageSharp/Processing/ProjectiveTransformBuilder.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using System.Collections.Generic;
 using System.Numerics;
 using SixLabors.ImageSharp.Processing.Processors.Transforms;
@@ -67,7 +68,7 @@ namespace SixLabors.ImageSharp.Processing
         /// </summary>
         /// <param name="radians">The amount of rotation, in radians.</param>
         /// <returns>The <see cref="ProjectiveTransformBuilder"/>.</returns>
-        public ProjectiveTransformBuilder PrependCenteredRotationRadians(float radians)
+        public ProjectiveTransformBuilder PrependRotationRadians(float radians)
         {
             var m = new Matrix4x4(TransformUtils.CreateRotationMatrixRadians(radians, this.Size));
             return this.PrependMatrix(m);
@@ -78,27 +79,51 @@ namespace SixLabors.ImageSharp.Processing
         /// </summary>
         /// <param name="radians">The amount of rotation, in radians.</param>
         /// <returns>The <see cref="ProjectiveTransformBuilder"/>.</returns>
-        public ProjectiveTransformBuilder AppendCenteredRotationRadians(float radians)
+        public ProjectiveTransformBuilder AppendRotationRadians(float radians)
         {
             var m = new Matrix4x4(TransformUtils.CreateRotationMatrixRadians(radians, this.Size));
             return this.AppendMatrix(m);
         }
 
+        /// <summary>
+        /// Appends a centered rotation matrix using the given rotation in radians.
+        /// </summary>
+        /// <param name="radians">The amount of rotation, in radians.</param>
+        /// <param name="centerPoint">The rotation center.</param>
+        /// <returns>The <see cref="ProjectiveTransformBuilder"/>.</returns>
+        internal ProjectiveTransformBuilder PrependRotationRadians(float radians, Vector2 centerPoint)
+        {
+            var m = Matrix4x4.CreateRotationZ(radians, new Vector3(centerPoint, 0));
+            return this.PrependMatrix(m);
+        }
+
+        /// <summary>
+        /// Appends a centered rotation matrix using the given rotation in radians.
+        /// </summary>
+        /// <param name="radians">The amount of rotation, in radians.</param>
+        /// <param name="centerPoint">The rotation center.</param>
+        /// <returns>The <see cref="ProjectiveTransformBuilder"/>.</returns>
+        internal ProjectiveTransformBuilder AppendRotationRadians(float radians, Vector2 centerPoint)
+        {
+            var m = Matrix4x4.CreateRotationZ(radians, new Vector3(centerPoint, 0));
+            return this.AppendMatrix(m);
+        }
+
         /// <summary>
         /// Prepends a centered rotation matrix using the given rotation in degrees.
         /// </summary>
         /// <param name="degrees">The amount of rotation, in degrees.</param>
         /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
         public ProjectiveTransformBuilder PrependCenteredRotationDegrees(float degrees)
-            => this.PrependCenteredRotationRadians(ImageMaths.DegreesToRadians(degrees));
+            => this.PrependRotationRadians(ImageMaths.DegreesToRadians(degrees));
 
         /// <summary>
         /// Appends a centered rotation matrix using the given rotation in degrees.
         /// </summary>
         /// <param name="degrees">The amount of rotation, in degrees.</param>
         /// <returns>The <see cref="AffineTransformBuilder"/>.</returns>
-        public ProjectiveTransformBuilder AppendCenteredRotationDegrees(float degrees)
+        public ProjectiveTransformBuilder AppendRotationDegrees(float degrees)
-            => this.AppendCenteredRotationRadians(ImageMaths.DegreesToRadians(degrees));
+            => this.AppendRotationRadians(ImageMaths.DegreesToRadians(degrees));
 
         /// <summary>
         /// Prepends a scale matrix from the given uniform scale.

tests/ImageSharp.Tests/Drawing/DrawImageTest.cs

@@ -74,7 +74,7 @@ namespace SixLabors.ImageSharp.Tests
             using (var blend = Image.Load<TPixel>(TestFile.Create(TestImages.Bmp.Car).Bytes))
             {
                 AffineTransformBuilder builder = new AffineTransformBuilder()
-                    .AppendCenteredRotationDegrees(45F)
+                    .AppendRotationDegrees(45F)
                     .AppendScale(new SizeF(.25F, .25F))
                     .AppendTranslation(new PointF(10, 10));
 

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

@@ -14,11 +14,15 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
     {
         protected override void AppendTranslation(AffineTransformBuilder builder, PointF translate) => builder.AppendTranslation(translate);
         protected override void AppendScale(AffineTransformBuilder builder, SizeF scale) => builder.AppendScale(scale);
-        protected override void AppendRotationRadians(AffineTransformBuilder builder, float radians) => builder.AppendCenteredRotationRadians(radians);
+        protected override void AppendRotationRadians(AffineTransformBuilder builder, float radians) => builder.AppendRotationRadians(radians);
+        protected override void AppendRotationRadians(AffineTransformBuilder builder, float radians, Vector2 center) =>
+            builder.AppendRotationRadians(radians, center);
 
         protected override void PrependTranslation(AffineTransformBuilder builder, PointF translate) => builder.PrependTranslation(translate);
         protected override void PrependScale(AffineTransformBuilder builder, SizeF scale) => builder.PrependScale(scale);
-        protected override void PrependRotationRadians(AffineTransformBuilder builder, float radians) => builder.PrependCenteredRotationRadians(radians);
+        protected override void PrependRotationRadians(AffineTransformBuilder builder, float radians) => builder.PrependRotationRadians(radians);
+        protected override void PrependRotationRadians(AffineTransformBuilder builder, float radians, Vector2 center) =>
+            builder.PrependRotationRadians(radians, center);
 
         protected override AffineTransformBuilder CreateBuilder(Rectangle rectangle) => new AffineTransformBuilder();
 

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

@@ -80,7 +80,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
             using (Image<TPixel> image = provider.GetImage())
             {
                 AffineTransformBuilder builder = new AffineTransformBuilder()
-                    .AppendCenteredRotationDegrees(30);
+                    .AppendRotationDegrees(30);
 
                 image.Mutate(c => c.Transform(builder, resampler));
                 image.DebugSave(provider, resamplerName);
@@ -102,7 +102,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
             {
                 image.DebugSave(provider, $"_original");
                 AffineTransformBuilder builder = new AffineTransformBuilder()
-                    .AppendCenteredRotationDegrees(angleDeg)
+                    .AppendRotationDegrees(angleDeg)
                     .AppendScale(new SizeF(sx, sy))
                     .AppendTranslation(new PointF(tx, ty));
 
@@ -124,7 +124,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
             using (Image<TPixel> image = provider.GetImage())
             {
                 AffineTransformBuilder builder = new AffineTransformBuilder()
-                    .AppendCenteredRotationDegrees(angleDeg)
+                    .AppendRotationDegrees(angleDeg)
                     .AppendScale(new SizeF(s, s));
 
                 image.Mutate(i => i.Transform(builder, KnownResamplers.Bicubic));
@@ -197,7 +197,7 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
             using (Image<TPixel> image = provider.GetImage())
             {
                 AffineTransformBuilder builder = new AffineTransformBuilder()
-                    .AppendCenteredRotationDegrees(50)
+                    .AppendRotationDegrees(50)
                     .AppendScale(new SizeF(.6F, .6F));
 
                 image.Mutate(i => i.Transform(builder, sampler));

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

@@ -39,11 +39,15 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
 
         protected override void AppendTranslation(ProjectiveTransformBuilder builder, PointF translate) => builder.AppendTranslation(translate);
         protected override void AppendScale(ProjectiveTransformBuilder builder, SizeF scale) => builder.AppendScale(scale);
-        protected override void AppendRotationRadians(ProjectiveTransformBuilder builder, float radians) => builder.AppendCenteredRotationRadians(radians);
+        protected override void AppendRotationRadians(ProjectiveTransformBuilder builder, float radians) => builder.AppendRotationRadians(radians);
+        protected override void AppendRotationRadians(ProjectiveTransformBuilder builder, float radians, Vector2 center) =>
+            builder.AppendRotationRadians(radians, center);
 
         protected override void PrependTranslation(ProjectiveTransformBuilder builder, PointF translate) => builder.PrependTranslation(translate);
         protected override void PrependScale(ProjectiveTransformBuilder builder, SizeF scale) => builder.PrependScale(scale);
-        protected override void PrependRotationRadians(ProjectiveTransformBuilder builder, float radians) => builder.PrependCenteredRotationRadians(radians);
+        protected override void PrependRotationRadians(ProjectiveTransformBuilder builder, float radians) => builder.PrependRotationRadians(radians);
+        protected override void PrependRotationRadians(ProjectiveTransformBuilder builder, float radians, Vector2 center) =>
+            builder.PrependRotationRadians(radians, center);
 
         protected override Vector2 Execute(
             ProjectiveTransformBuilder builder,

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

@@ -87,7 +87,12 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
         [InlineData(200, 100, 10, 42, 84)]
         [InlineData(200, 100, 100, 42, 84)]
         [InlineData(100, 200, -10, 42, 84)]
-        public void RotateDegrees_ShouldCreateCenteredMatrix(int width, int height, float deg, float x, float y)
+        public void AppendRotationDegrees_WithoutSpecificRotationCenter_RotationIsCenteredAroundImageCenter(
+            int width,
+            int height,
+            float deg,
+            float x,
+            float y)
         {
             var size = new Size(width, height);
             TBuilder builder = this.CreateBuilder(size);
@@ -97,13 +102,41 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
             // TODO: We should also test CreateRotationMatrixDegrees() (and all TransformUtils stuff!) for correctness
             Matrix3x2 matrix = TransformUtils.CreateRotationMatrixDegrees(deg, size);
 
-            var position = new Vector2(x,  y);
+            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, 30, 61, 42, 84)]
+        [InlineData(200, 100, 100, 30, 10, 20, 84)]
+        [InlineData(100, 200, -10, 30, 20, 11, 84)]
+        public void AppendRotationDegrees_WithRotationCenter(
+            int width,
+            int height,
+            float deg,
+            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.AppendRotationDegrees(builder, deg, centerPoint);
+
+            var matrix = Matrix3x2.CreateRotation(ImageMaths.DegreesToRadians(deg), 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);
+        }
+
         [Fact]
         public void AppendPrependOpposite()
         {
@@ -116,10 +149,12 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
             // Forwards
             this.AppendRotationRadians(b1, pi);
             this.AppendScale(b1, new SizeF(2, 0.5f));
+            this.AppendRotationRadians(b1, pi / 2, new Vector2(-0.5f, -0.1f));
             this.AppendTranslation(b1, new PointF(123, 321));
 
             // Backwards
             this.PrependTranslation(b2, new PointF(123, 321));
+            this.PrependRotationRadians(b2, pi / 2, new Vector2(-0.5f, -0.1f));
             this.PrependScale(b2, new SizeF(2, 0.5f));
             this.PrependRotationRadians(b2, pi);
 
@@ -152,14 +187,19 @@ namespace SixLabors.ImageSharp.Tests.Processing.Transforms
         protected abstract void AppendTranslation(TBuilder builder, PointF translate);
         protected abstract void AppendScale(TBuilder builder, SizeF scale);
         protected abstract void AppendRotationRadians(TBuilder builder, float radians);
+        protected abstract void AppendRotationRadians(TBuilder builder, float radians, Vector2 center);
 
         protected abstract void PrependTranslation(TBuilder builder, PointF translate);
         protected abstract void PrependScale(TBuilder builder, SizeF scale);
         protected abstract void PrependRotationRadians(TBuilder builder, float radians);
+        protected abstract void PrependRotationRadians(TBuilder b1, float v, Vector2 vector2);
 
         protected virtual void AppendRotationDegrees(TBuilder builder, float degrees) =>
             this.AppendRotationRadians(builder, ImageMaths.DegreesToRadians(degrees));
 
+        protected virtual void AppendRotationDegrees(TBuilder builder, float degrees, Vector2 center) =>
+            this.AppendRotationRadians(builder, ImageMaths.DegreesToRadians(degrees), center);
+
         protected abstract Vector2 Execute(TBuilder builder, Rectangle rectangle, Vector2 sourcePoint);
         
         private static float Sqrt(float a) => (float)Math.Sqrt(a);