Stub out options types.

src/ImageSharp/Formats/Bmp/BmpDecoder2.cs

@@ -0,0 +1,30 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.IO;
+using System.Threading;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Formats.Bmp
+{
+    /// <summary>
+    /// Image decoder for generating an image out of a Windows bitmap stream.
+    /// </summary>
+    public class BmpDecoder2 : ImageDecoder<BmpDecoderOptions>
+    {
+        /// <inheritdoc/>
+        public override Image<TPixel> DecodeSpecialized<TPixel>(BmpDecoderOptions options, Stream stream, CancellationToken cancellationToken)
+        {
+            throw new NotImplementedException();
+        }
+
+        /// <inheritdoc/>
+        public override Image DecodeSpecialized(BmpDecoderOptions options, Stream stream, CancellationToken cancellationToken)
+            => this.DecodeSpecialized<Rgba32>(options, stream, cancellationToken);
+
+        /// <inheritdoc/>
+        public override IImageInfo IdentifySpecialized(BmpDecoderOptions options, Stream stream, CancellationToken cancellationToken)
+            => throw new NotImplementedException();
+    }
+}

src/ImageSharp/Formats/Bmp/BmpDecoderOptions.cs

@@ -0,0 +1,20 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.Bmp
+{
+    /// <summary>
+    /// Image decoder options for decoding Windows bitmap streams.
+    /// </summary>
+    public sealed class BmpDecoderOptions : ISpecializedDecoderOptions
+    {
+        /// <inheritdoc/>
+        public DecoderOptions GeneralOptions { get; set; } = new();
+
+        /// <summary>
+        /// Gets the value indicating how to deal with skipped pixels,
+        /// which can occur during decoding run length encoded bitmaps.
+        /// </summary>
+        public RleSkippedPixelHandling RleSkippedPixelHandling { get; }
+    }
+}

src/ImageSharp/Formats/DecoderOptions.cs

@@ -0,0 +1,33 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats
+{
+    /// <summary>
+    /// Provides general configuration options for decoding image formats.
+    /// </summary>
+    public sealed class DecoderOptions
+    {
+        /// <summary>
+        /// Gets or sets a custom Configuration instance to be used by the image processing pipeline.
+        /// </summary>
+        public Configuration Configuration { get; set; } = Configuration.Default;
+
+        /// <summary>
+        /// Gets or sets the target size to decode the image into.
+        /// </summary>
+        public Size? TargetSize { get; set; } = null;
+
+        /// <summary>
+        /// Gets or sets a value indicating whether to ignore encoded metadata when decoding.
+        /// </summary>
+        public bool SkipMetadata { get; set; } = false;
+
+        /// <summary>
+        /// Gets or sets the number of image frames to decode.
+        /// Leave <see langword="null"/> to decode all frames.
+        /// </summary>
+        // supported decoders may handle this internally but we will fallback to removeing additional frames after decode.
+        public int? MaxFrames { get; set; } = null;
+    }
+}

src/ImageSharp/Formats/IImageDecoder2.cs

@@ -0,0 +1,37 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.IO;
+using System.Threading;
+using SixLabors.ImageSharp.PixelFormats;
+
+namespace SixLabors.ImageSharp.Formats
+{
+    /// <summary>
+    /// Encapsulates properties and methods required for decoding an image from a stream.
+    /// </summary>
+    public interface IImageDecoder2
+    {
+        /// <summary>
+        /// Decodes the image from the specified stream to an <see cref="Image{TPixel}"/> of a specific pixel type.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel format.</typeparam>
+        /// <param name="options">The general decoder options.</param>
+        /// <param name="stream">The <see cref="Stream"/> containing image data.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests.</param>
+        /// <returns>The <see cref="Image{TPixel}"/>.</returns>
+        /// <exception cref="ImageFormatException">Thrown if the encoded image contains errors.</exception>
+        Image<TPixel> Decode<TPixel>(DecoderOptions options, Stream stream, CancellationToken cancellationToken)
+            where TPixel : unmanaged, IPixel<TPixel>;
+
+        /// <summary>
+        /// Decodes the image from the specified stream to an <see cref="Image"/>.
+        /// </summary>
+        /// <param name="options">The general decoder options.</param>
+        /// <param name="stream">The <see cref="Stream"/> containing image data.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests.</param>
+        /// <returns>The <see cref="Image"/>.</returns>
+        /// <exception cref="ImageFormatException">Thrown if the encoded image contains errors.</exception>
+        Image Decode(DecoderOptions options, Stream stream, CancellationToken cancellationToken);
+    }
+}

src/ImageSharp/Formats/IImageInfoDetector2.cs

@@ -0,0 +1,24 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.IO;
+using System.Threading;
+
+namespace SixLabors.ImageSharp.Formats
+{
+    /// <summary>
+    /// Encapsulates methods used for detecting the raw image information without fully decoding it.
+    /// </summary>
+    public interface IImageInfoDetector2
+    {
+        /// <summary>
+        /// Reads the raw image information from the specified stream.
+        /// </summary>
+        /// <param name="options">The general decoder options.</param>
+        /// <param name="stream">The <see cref="Stream"/> containing image data.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests.</param>
+        /// <returns>The <see cref="IImageInfo"/> object.</returns>
+        /// <exception cref="ImageFormatException">Thrown if the encoded image contains errors.</exception>
+        IImageInfo Identify(DecoderOptions options, Stream stream, CancellationToken cancellationToken);
+    }
+}

src/ImageSharp/Formats/ISpecializedDecoderOptions.cs

@@ -0,0 +1,16 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats
+{
+    /// <summary>
+    /// Provides specialized configuration options for decoding image formats.
+    /// </summary>
+    public interface ISpecializedDecoderOptions
+    {
+        /// <summary>
+        /// Gets or sets the general decoder options.
+        /// </summary>
+        DecoderOptions GeneralOptions { get; set; }
+    }
+}

src/ImageSharp/Formats/ImageDecoder{T}.cs

@@ -0,0 +1,119 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System.IO;
+using System.Threading;
+using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.ImageSharp.Processing;
+
+namespace SixLabors.ImageSharp.Formats
+{
+    /// <summary>
+    /// The base class for all image decoders.
+    /// </summary>
+    /// <typeparam name="T">The type of specialized decoder options.</typeparam>
+    public abstract class ImageDecoder<T> : IImageInfoDetector2, IImageDecoder2
+        where T : ISpecializedDecoderOptions, new()
+    {
+        /// <inheritdoc/>
+        public IImageInfo Identify(DecoderOptions options, Stream stream, CancellationToken cancellationToken)
+        {
+            T specializedOptions = new() { GeneralOptions = options };
+            return this.IdentifySpecialized(specializedOptions, stream, cancellationToken);
+        }
+
+        /// <inheritdoc/>
+        public Image<TPixel> Decode<TPixel>(DecoderOptions options, Stream stream, CancellationToken cancellationToken)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            T specializedOptions = new() { GeneralOptions = options };
+            Image<TPixel> image = this.DecodeSpecialized<TPixel>(specializedOptions, stream, cancellationToken);
+
+            Resize(options, image);
+
+            return image;
+        }
+
+        /// <inheritdoc/>
+        public Image Decode(DecoderOptions options, Stream stream, CancellationToken cancellationToken)
+        {
+            T specializedOptions = new() { GeneralOptions = options };
+            Image image = this.DecodeSpecialized(specializedOptions, stream, cancellationToken);
+
+            Resize(options, image);
+
+            return image;
+        }
+
+        /// <summary>
+        /// Reads the raw image information from the specified stream.
+        /// </summary>
+        /// <param name="options">The specialized decoder options.</param>
+        /// <param name="stream">The <see cref="Stream"/> containing image data.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests.</param>
+        /// <returns>The <see cref="IImageInfo"/> object.</returns>
+        /// <exception cref="ImageFormatException">Thrown if the encoded image contains errors.</exception>
+        public abstract IImageInfo IdentifySpecialized(T options, Stream stream, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// Decodes the image from the specified stream to an <see cref="Image{TPixel}"/> of a specific pixel type.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel format.</typeparam>
+        /// <param name="options">The specialized decoder options.</param>
+        /// <param name="stream">The <see cref="Stream"/> containing image data.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests.</param>
+        /// <returns>The <see cref="Image{TPixel}"/>.</returns>
+        /// <exception cref="ImageFormatException">Thrown if the encoded image contains errors.</exception>
+        public abstract Image<TPixel> DecodeSpecialized<TPixel>(T options, Stream stream, CancellationToken cancellationToken)
+            where TPixel : unmanaged, IPixel<TPixel>;
+
+        /// <summary>
+        /// Decodes the image from the specified stream to an <see cref="Image"/> of a specific pixel type.
+        /// </summary>
+        /// <param name="options">The specialized decoder options.</param>
+        /// <param name="stream">The <see cref="Stream"/> containing image data.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests.</param>
+        /// <returns>The <see cref="Image{TPixel}"/>.</returns>
+        /// <exception cref="ImageFormatException">Thrown if the encoded image contains errors.</exception>
+        public abstract Image DecodeSpecialized(T options, Stream stream, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// Performs a resize operation against the decoded image. If the target size is not set, or the image size
+        /// already matches the target size, the image is untouched.
+        /// </summary>
+        /// <param name="options">The decoder options.</param>
+        /// <param name="image">The decoded image.</param>
+        protected static void Resize(DecoderOptions options, Image image)
+        {
+            if (ShouldResize(options, image))
+            {
+                ResizeOptions resizeOptions = new()
+                {
+                    Size = options.TargetSize.Value,
+                    Sampler = KnownResamplers.Box,
+                    Mode = ResizeMode.Max
+                };
+
+                image.Mutate(x => x.Resize(resizeOptions));
+            }
+        }
+
+        /// <summary>
+        /// Determines whether the decoded image should be resized.
+        /// </summary>
+        /// <param name="options">The decoder options.</param>
+        /// <param name="image">The decoded image.</param>
+        /// <returns><see langword="true"/> if the image should be resized, otherwise; <see langword="false"/>.</returns>
+        private static bool ShouldResize(DecoderOptions options, Image image)
+        {
+            if (options.TargetSize is null)
+            {
+                return false;
+            }
+
+            Size targetSize = options.TargetSize.Value;
+            Size currentSize = image.Size();
+            return currentSize.Width != targetSize.Width && currentSize.Height != targetSize.Height;
+        }
+    }
+}