From 204f94e84bc01975c191ce0ed3611e69c1d9425f Mon Sep 17 00:00:00 2001
From: Brian Popow <popow@gmx.de>
Date: Fri, 18 Feb 2022 14:43:10 +0100
Subject: [PATCH] Add tiff decoder option to only decode first frame

---
 src/ImageSharp/Formats/Gif/GifDecoder.cs           |  1 -
 src/ImageSharp/Formats/Tiff/ITiffDecoderOptions.cs |  7 +++++++
 src/ImageSharp/Formats/Tiff/TiffDecoder.cs         |  6 ++++++
 src/ImageSharp/Formats/Tiff/TiffDecoderCore.cs     | 14 ++++++++++++--
 4 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/src/ImageSharp/Formats/Gif/GifDecoder.cs b/src/ImageSharp/Formats/Gif/GifDecoder.cs
index 196d77ad77..c31a2c1c94 100644
--- a/src/ImageSharp/Formats/Gif/GifDecoder.cs
+++ b/src/ImageSharp/Formats/Gif/GifDecoder.cs
@@ -5,7 +5,6 @@ using System.IO;
 using System.Threading;
 using System.Threading.Tasks;
 using SixLabors.ImageSharp.IO;
-using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
 
diff --git a/src/ImageSharp/Formats/Tiff/ITiffDecoderOptions.cs b/src/ImageSharp/Formats/Tiff/ITiffDecoderOptions.cs
index 5372384397..d6d1bb8a4c 100644
--- a/src/ImageSharp/Formats/Tiff/ITiffDecoderOptions.cs
+++ b/src/ImageSharp/Formats/Tiff/ITiffDecoderOptions.cs
@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using SixLabors.ImageSharp.Metadata;
+
 namespace SixLabors.ImageSharp.Formats.Tiff
 {
     /// <summary>
@@ -12,5 +14,10 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         /// Gets a value indicating whether the metadata should be ignored when the image is being decoded.
         /// </summary>
         bool IgnoreMetadata { get; }
+
+        /// <summary>
+        /// Gets the decoding mode for multi-frame images.
+        /// </summary>
+        FrameDecodingMode DecodingMode { get; }
     }
 }
diff --git a/src/ImageSharp/Formats/Tiff/TiffDecoder.cs b/src/ImageSharp/Formats/Tiff/TiffDecoder.cs
index 9d52e34dfe..b4d7520199 100644
--- a/src/ImageSharp/Formats/Tiff/TiffDecoder.cs
+++ b/src/ImageSharp/Formats/Tiff/TiffDecoder.cs
@@ -4,6 +4,7 @@
 using System.IO;
 using System.Threading;
 using System.Threading.Tasks;
+using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Tiff
@@ -18,6 +19,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         /// </summary>
         public bool IgnoreMetadata { get; set; }
 
+        /// <summary>
+        /// Gets or sets the decoding mode for multi-frame images.
+        /// </summary>
+        public FrameDecodingMode DecodingMode { get; set; }
+
         /// <inheritdoc/>
         public Image<TPixel> Decode<TPixel>(Configuration configuration, Stream stream)
             where TPixel : unmanaged, IPixel<TPixel>
diff --git a/src/ImageSharp/Formats/Tiff/TiffDecoderCore.cs b/src/ImageSharp/Formats/Tiff/TiffDecoderCore.cs
index 05c5358f59..cd06282f18 100644
--- a/src/ImageSharp/Formats/Tiff/TiffDecoderCore.cs
+++ b/src/ImageSharp/Formats/Tiff/TiffDecoderCore.cs
@@ -13,7 +13,6 @@ using SixLabors.ImageSharp.IO;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
-using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Tiff
@@ -33,6 +32,11 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         /// </summary>
         private readonly bool ignoreMetadata;
 
+        /// <summary>
+        /// Gets the decoding mode for multi-frame images
+        /// </summary>
+        private FrameDecodingMode decodingMode;
+
         /// <summary>
         /// The stream to decode from.
         /// </summary>
@@ -59,6 +63,7 @@ namespace SixLabors.ImageSharp.Formats.Tiff
 
             this.Configuration = configuration ?? Configuration.Default;
             this.ignoreMetadata = options.IgnoreMetadata;
+            this.decodingMode = options.DecodingMode;
             this.memoryAllocator = this.Configuration.MemoryAllocator;
         }
 
@@ -160,11 +165,16 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                 cancellationToken.ThrowIfCancellationRequested();
                 ImageFrame<TPixel> frame = this.DecodeFrame<TPixel>(ifd, cancellationToken);
                 frames.Add(frame);
+
+                if (this.decodingMode is FrameDecodingMode.First)
+                {
+                    break;
+                }
             }
 
             ImageMetadata metadata = TiffDecoderMetadataCreator.Create(frames, this.ignoreMetadata, reader.ByteOrder, reader.IsBigTiff);
 
-            // TODO: Tiff frames can have different sizes
+            // TODO: Tiff frames can have different sizes.
             ImageFrame<TPixel> root = frames[0];
             this.Dimensions = root.Size();
             foreach (ImageFrame<TPixel> frame in frames)