Move re-usable orientation logic into OrientationHelper

src/ImageSharp.Web/FormattedImage.cs

@@ -15,15 +15,15 @@ namespace SixLabors.ImageSharp.Web
     /// <summary>
     /// A class encapsulating an image with a particular file encoding.
     /// </summary>
-    /// <seealso cref="IDisposable"/>
+    /// <seealso cref="IDisposable" />
     public sealed class FormattedImage : IDisposable
     {
         private readonly ImageFormatManager imageFormatsManager;
         private IImageFormat format;
         private IImageEncoder encoder;
 
         /// <summary>
-        /// Initializes a new instance of the <see cref="FormattedImage"/> class.
+        /// Initializes a new instance of the <see cref="FormattedImage" /> class.
         /// </summary>
         /// <param name="image">The image.</param>
         /// <param name="format">The format.</param>
@@ -70,7 +70,7 @@ public IImageEncoder Encoder
                     ThrowNull(nameof(value));
                 }
 
-                // The given type should match the format encoder.
+                // The given type should match the format encoder
                 IImageEncoder reference = this.imageFormatsManager.FindEncoder(this.Format);
                 if (reference.GetType() != value.GetType())
                 {
@@ -86,10 +86,11 @@ public IImageEncoder Encoder
         /// </summary>
         /// <param name="configuration">The configuration.</param>
         /// <param name="source">The source.</param>
-        /// <returns>The <see cref="FormattedImage"/>.</returns>
+        /// <returns>The <see cref="FormattedImage" />.</returns>
         public static FormattedImage Load(Configuration configuration, Stream source)
         {
             var image = ImageSharp.Image.Load<Rgba32>(configuration, source, out IImageFormat format);
+
             return new FormattedImage(image, format);
         }
 
@@ -98,10 +99,11 @@ public static FormattedImage Load(Configuration configuration, Stream source)
         /// </summary>
         /// <param name="configuration">The configuration.</param>
         /// <param name="source">The source.</param>
-        /// <returns>A <see cref="Task{FormattedImage}"/> representing the asynchronous operation.</returns>
+        /// <returns>A <see cref="Task{FormattedImage}" /> representing the asynchronous operation.</returns>
         public static async Task<FormattedImage> LoadAsync(Configuration configuration, Stream source)
         {
             (Image<Rgba32> image, IImageFormat format) = await ImageSharp.Image.LoadWithFormatAsync<Rgba32>(configuration, source);
+
             return new FormattedImage(image, format);
         }
 
@@ -115,32 +117,24 @@ public static async Task<FormattedImage> LoadAsync(Configuration configuration,
         /// Saves image to the specified destination stream.
         /// </summary>
         /// <param name="destination">The destination stream.</param>
-        /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+        /// <returns>A <see cref="Task" /> representing the asynchronous operation.</returns>
         public Task SaveAsync(Stream destination) => this.Image.SaveAsync(destination, this.encoder);
 
         /// <summary>
-        /// Gets the EXIF orientation metata for the <see cref="FormattedImage"/>.
+        /// Gets the EXIF orientation metata for the <see cref="FormattedImage" />.
         /// </summary>
-        /// <param name="value">
-        /// When this method returns, contains the value parsed from decoded EXIF metadata; otherwise,
-        /// the default value for the type of the <paramref name="value"/> parameter.
-        /// This parameter is passed uninitialized. Use <see cref="ExifOrientationMode"/> for comparison.
-        /// </param>
+        /// <param name="value">When this method returns, contains the value parsed from decoded EXIF metadata;
+        /// otherwise, the default value for the type of the <paramref name="value" /> parameter.
+        /// This parameter is passed uninitialized. Use <see cref="ExifOrientationMode" /> for comparison.</param>
         /// <returns>
-        /// <see langword="true"/> if the <see cref="FormattedImage"/> contains EXIF orientation metadata
-        /// for <see cref="ExifTag.Orientation"/>; otherwise, <see langword="false"/>.
+        /// <see langword="true" /> if the <see cref="FormattedImage" /> contains EXIF orientation metadata
+        /// for <see cref="ExifTag.Orientation" />; otherwise, <see langword="false" />.
         /// </returns>
         public bool TryGetExifOrientation(out ushort value)
         {
-            value = ExifOrientationMode.Unknown;
-            if (this.Image.Metadata.ExifProfile != null)
+            if (this.Image.Metadata.ExifProfile is ExifProfile exifProfile &&
+                exifProfile.GetValue(ExifTag.Orientation) is IExifValue<ushort> orientation)
             {
-                IExifValue<ushort> orientation = this.Image.Metadata.ExifProfile.GetValue(ExifTag.Orientation);
-                if (orientation is null)
-                {
-                    return false;
-                }
-
                 if (orientation.DataType == ExifDataType.Short)
                 {
                     value = orientation.Value;
@@ -153,12 +147,12 @@ public bool TryGetExifOrientation(out ushort value)
                 return true;
             }
 
+            value = ExifOrientationMode.Unknown;
             return false;
         }
 
         /// <summary>
-        /// Performs application-defined tasks associated with freeing, releasing, or resetting
-        /// unmanaged resources.
+        /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
         /// </summary>
         public void Dispose()
         {

src/ImageSharp.Web/OrientationHelper.cs

@@ -0,0 +1,209 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.Collections.Generic;
+using System.Globalization;
+using System.Numerics;
+using SixLabors.ImageSharp.Metadata.Profiles.Exif;
+using SixLabors.ImageSharp.Processing;
+using SixLabors.ImageSharp.Web.Commands;
+
+namespace SixLabors.ImageSharp.Web
+{
+    /// <summary>
+    /// Helper method for handling orientation parsing/transforms in processors.
+    /// </summary>
+    public static class OrientationHelper
+    {
+        /// <summary>
+        /// The command constant for the orientation handling mode.
+        /// </summary>
+        public const string Command = "orient";
+
+        /// <summary>
+        /// Gets the orientation.
+        /// </summary>
+        /// <param name="image">The image to process.</param>
+        /// <param name="commands">The ordered collection containing the processing commands.</param>
+        /// <param name="parser">The command parser use for parting commands.</param>
+        /// <param name="culture">The <see cref="CultureInfo" /> to use as the current parsing culture.</param>
+        /// <param name="orientation">The orientation.</param>
+        /// <returns>
+        /// The <see cref="bool"/> indicating whether orientation should be handled.
+        /// </returns>
+        public static bool GetOrientation(FormattedImage image, CommandCollection commands, CommandParser parser, CultureInfo culture, out ushort orientation)
+        {
+            // Browsers now implement 'image-orientation: from-image' by default.
+            // https://developer.mozilla.org/en-US/docs/web/css/image-orientation
+            // This makes orientation handling confusing for users who expect images to be resized in accordance
+            // to what they observe rather than pure (and correct) methods.
+            //
+            // To accomodate this we parse the dimensions to use based upon decoded EXIF orientation values.
+            // We default to 'true' for EXIF orientation handling. By passing 'false' it can be turned off.
+            if (commands.Contains(Command) && !parser.ParseValue<bool>(commands.GetValueOrDefault(Command), culture))
+            {
+                orientation = ExifOrientationMode.Unknown;
+                return false;
+            }
+
+            return image.TryGetExifOrientation(out orientation) && orientation != ExifOrientationMode.TopLeft;
+        }
+
+        /// <summary>
+        /// Transforms the specified value depending on the specified <paramref name="orientation" />.
+        /// </summary>
+        /// <param name="value">The value.</param>
+        /// <param name="orientation">The EXIF orientation.</param>
+        public static void Transform(ref ResizeOptions value, ushort orientation)
+        {
+            value.Size = Transform(value.Size, orientation);
+
+            if (value.CenterCoordinates.HasValue)
+            {
+                value.CenterCoordinates = Transform(value.CenterCoordinates.Value, orientation);
+            }
+
+            value.Position = Transform(value.Position, orientation);
+        }
+
+        /// <summary>
+        /// Transforms the specified value depending on the specified <paramref name="orientation" />.
+        /// </summary>
+        /// <param name="value">The value.</param>
+        /// <param name="orientation">The EXIF orientation.</param>
+        /// <returns>
+        /// The transformed value.
+        /// </returns>
+        public static Size Transform(Size value, ushort orientation)
+            => orientation switch
+            {
+                ExifOrientationMode.LeftTop or
+                ExifOrientationMode.RightTop or
+                ExifOrientationMode.RightBottom or
+                ExifOrientationMode.LeftBottom => new Size(value.Height, value.Width),
+                _ => value
+            };
+
+        /// <summary>
+        /// Transforms the specified value depending on the specified <paramref name="orientation" />.
+        /// </summary>
+        /// <param name="value">The value.</param>
+        /// <param name="orientation">The EXIF orientation.</param>
+        /// <returns>
+        /// The transformed value.
+        /// </returns>
+        public static PointF Transform(PointF value, ushort orientation)
+        {
+            AffineTransformBuilder builder = new();
+            Size sourceSize = new(1, 1);
+
+            // New XY is calculated based on flipping and rotating the input XY
+            switch (orientation)
+            {
+                case ExifOrientationMode.TopRight:
+                    builder.AppendTranslation(new PointF(sourceSize.Width - value.X, 0));
+                    break;
+                case ExifOrientationMode.BottomRight:
+                    builder.AppendRotationDegrees(180);
+                    builder.AppendTranslation(new PointF(0, -(sourceSize.Height - value.Y)));
+                    break;
+                case ExifOrientationMode.BottomLeft:
+                    builder.AppendRotationDegrees(180);
+                    builder.AppendTranslation(new PointF(sourceSize.Width - value.X, -(sourceSize.Height - value.Y)));
+                    break;
+                case ExifOrientationMode.LeftTop:
+                    builder.AppendRotationDegrees(90);
+                    builder.AppendTranslation(new PointF(sourceSize.Width - value.X, 0));
+                    break;
+                case ExifOrientationMode.RightTop:
+                    builder.AppendRotationDegrees(270);
+                    break;
+                case ExifOrientationMode.RightBottom:
+                    builder.AppendRotationDegrees(270);
+                    builder.AppendTranslation(new PointF(-(sourceSize.Width - value.X), -(sourceSize.Height - value.Y)));
+                    break;
+                case ExifOrientationMode.LeftBottom:
+                    builder.AppendRotationDegrees(90);
+                    builder.AppendTranslation(new PointF(-(sourceSize.Width - value.X), 0));
+                    break;
+                default:
+                    return value;
+            }
+
+            Matrix3x2 matrix = builder.BuildMatrix(sourceSize);
+
+            return Vector2.Transform(value, matrix);
+        }
+
+        /// <summary>
+        /// Transforms the specified value depending on the specified <paramref name="orientation" />.
+        /// </summary>
+        /// <param name="value">The value.</param>
+        /// <param name="orientation">The EXIF orientation.</param>
+        /// <returns>
+        /// The transformed value.
+        /// </returns>
+        public static AnchorPositionMode Transform(AnchorPositionMode value, ushort orientation)
+             => value switch
+             {
+                 AnchorPositionMode.Center => value,
+                 AnchorPositionMode.Top => orientation switch
+                 {
+                     ExifOrientationMode.BottomLeft or ExifOrientationMode.BottomRight => AnchorPositionMode.Bottom,
+                     ExifOrientationMode.LeftTop or ExifOrientationMode.RightTop => AnchorPositionMode.Left,
+                     ExifOrientationMode.LeftBottom or ExifOrientationMode.RightBottom => AnchorPositionMode.Right,
+                     _ => value,
+                 },
+                 AnchorPositionMode.Bottom => orientation switch
+                 {
+                     ExifOrientationMode.BottomLeft or ExifOrientationMode.BottomRight => AnchorPositionMode.Top,
+                     ExifOrientationMode.LeftTop or ExifOrientationMode.RightTop => AnchorPositionMode.Right,
+                     ExifOrientationMode.LeftBottom or ExifOrientationMode.RightBottom => AnchorPositionMode.Left,
+                     _ => value,
+                 },
+                 AnchorPositionMode.Left => orientation switch
+                 {
+                     ExifOrientationMode.TopRight or ExifOrientationMode.BottomRight => AnchorPositionMode.Right,
+                     ExifOrientationMode.LeftTop or ExifOrientationMode.LeftBottom => AnchorPositionMode.Top,
+                     ExifOrientationMode.RightTop or ExifOrientationMode.RightBottom => AnchorPositionMode.Bottom,
+                     _ => value,
+                 },
+                 AnchorPositionMode.Right => orientation switch
+                 {
+                     ExifOrientationMode.TopRight or ExifOrientationMode.BottomRight => AnchorPositionMode.Left,
+                     ExifOrientationMode.LeftTop or ExifOrientationMode.LeftBottom => AnchorPositionMode.Bottom,
+                     ExifOrientationMode.RightTop or ExifOrientationMode.RightBottom => AnchorPositionMode.Top,
+                     _ => value,
+                 },
+                 AnchorPositionMode.TopLeft => orientation switch
+                 {
+                     ExifOrientationMode.TopRight or ExifOrientationMode.LeftBottom => AnchorPositionMode.TopRight,
+                     ExifOrientationMode.BottomRight or ExifOrientationMode.RightTop => AnchorPositionMode.BottomLeft,
+                     ExifOrientationMode.BottomLeft or ExifOrientationMode.RightBottom => AnchorPositionMode.BottomRight,
+                     _ => value,
+                 },
+                 AnchorPositionMode.TopRight => orientation switch
+                 {
+                     ExifOrientationMode.TopRight or ExifOrientationMode.RightTop => AnchorPositionMode.TopLeft,
+                     ExifOrientationMode.BottomRight or ExifOrientationMode.LeftBottom => AnchorPositionMode.BottomRight,
+                     ExifOrientationMode.BottomLeft or ExifOrientationMode.LeftTop => AnchorPositionMode.BottomLeft,
+                     _ => value,
+                 },
+                 AnchorPositionMode.BottomRight => orientation switch
+                 {
+                     ExifOrientationMode.TopRight or ExifOrientationMode.LeftBottom => AnchorPositionMode.BottomLeft,
+                     ExifOrientationMode.BottomLeft or ExifOrientationMode.RightTop => AnchorPositionMode.TopRight,
+                     ExifOrientationMode.BottomRight or ExifOrientationMode.RightBottom => AnchorPositionMode.TopLeft,
+                     _ => value,
+                 },
+                 AnchorPositionMode.BottomLeft => orientation switch
+                 {
+                     ExifOrientationMode.TopRight or ExifOrientationMode.RightTop => AnchorPositionMode.BottomRight,
+                     ExifOrientationMode.BottomLeft or ExifOrientationMode.LeftBottom => AnchorPositionMode.TopLeft,
+                     ExifOrientationMode.BottomRight or ExifOrientationMode.LeftTop => AnchorPositionMode.TopRight,
+                     _ => value,
+                 },
+                 _ => value,
+             };
+    }
+}