APNG support

src/ImageSharp/Compression/Zlib/ZlibInflateStream.cs

@@ -123,12 +123,12 @@ public override int ReadByte()
     /// <inheritdoc/>
     public override int Read(byte[] buffer, int offset, int count)
     {
-        if (this.currentDataRemaining == 0)
+        if (this.currentDataRemaining is 0)
         {
             // Last buffer was read in its entirety, let's make sure we don't actually have more in additional IDAT chunks.
             this.currentDataRemaining = this.getData();
 
-            if (this.currentDataRemaining == 0)
+            if (this.currentDataRemaining is 0)
             {
                 return 0;
             }
@@ -142,11 +142,11 @@ public override int Read(byte[] buffer, int offset, int count)
         // Keep reading data until we've reached the end of the stream or filled the buffer.
         int bytesRead = 0;
         offset += totalBytesRead;
-        while (this.currentDataRemaining == 0 && totalBytesRead < count)
+        while (this.currentDataRemaining is 0 && totalBytesRead < count)
         {
             this.currentDataRemaining = this.getData();
 
-            if (this.currentDataRemaining == 0)
+            if (this.currentDataRemaining is 0)
             {
                 return totalBytesRead;
             }

src/ImageSharp/Configuration.cs

@@ -43,7 +43,7 @@ public Configuration()
     /// Initializes a new instance of the <see cref="Configuration" /> class.
     /// </summary>
     /// <param name="configurationModules">A collection of configuration modules to register.</param>
-    public Configuration(params IImageFormatConfigurationModule[] configurationModules)
+    public Configuration(params IImageFormatConfigurationModule[]? configurationModules)
     {
         if (configurationModules != null)
         {

src/ImageSharp/Formats/Png/APngBlendOperation.cs

@@ -0,0 +1,20 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Png;
+
+/// <summary>
+/// Specifies whether the frame is to be alpha blended into the current output buffer content, or whether it should completely replace its region in the output buffer.
+/// </summary>
+public enum APngBlendOperation
+{
+    /// <summary>
+    /// All color components of the frame, including alpha, overwrite the current contents of the frame's output buffer region.
+    /// </summary>
+    Source,
+
+    /// <summary>
+    /// The frame should be composited onto the output buffer based on its alpha, using a simple OVER operation as described in the "Alpha Channel Processing" section of the PNG specification [PNG-1.2]. Note that the second variation of the sample code is applicable.
+    /// </summary>
+    Over
+}

src/ImageSharp/Formats/Png/APngDisposeOperation.cs

@@ -0,0 +1,25 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats.Png;
+
+/// <summary>
+/// Specifies how the output buffer should be changed at the end of the delay (before rendering the next frame).
+/// </summary>
+public enum APngDisposeOperation
+{
+    /// <summary>
+    /// No disposal is done on this frame before rendering the next; the contents of the output buffer are left as is.
+    /// </summary>
+    None,
+
+    /// <summary>
+    /// The frame's region of the output buffer is to be cleared to fully transparent black before rendering the next frame.
+    /// </summary>
+    Background,
+
+    /// <summary>
+    /// The frame's region of the output buffer is to be reverted to the previous contents before rendering the next frame.
+    /// </summary>
+    Previous
+}

src/ImageSharp/Formats/Png/APngFrameMetadata.cs

@@ -0,0 +1,94 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using SixLabors.ImageSharp.Formats.Png.Chunks;
+
+namespace SixLabors.ImageSharp.Formats.Png;
+
+/// <summary>
+/// Provides APng specific metadata information for the image frame.
+/// </summary>
+public class APngFrameMetadata : IDeepCloneable
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="APngFrameMetadata"/> class.
+    /// </summary>
+    public APngFrameMetadata()
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="APngFrameMetadata"/> class.
+    /// </summary>
+    /// <param name="other">The metadata to create an instance from.</param>
+    private APngFrameMetadata(APngFrameMetadata other)
+    {
+        this.Width = other.Width;
+        this.Height = other.Height;
+        this.XOffset = other.XOffset;
+        this.YOffset = other.YOffset;
+        this.DelayNumber = other.DelayNumber;
+        this.DelayDenominator = other.DelayDenominator;
+        this.DisposeOperation = other.DisposeOperation;
+        this.BlendOperation = other.BlendOperation;
+    }
+
+    /// <summary>
+    /// Gets or sets the width of the following frame
+    /// </summary>
+    public int Width { get; set; }
+
+    /// <summary>
+    /// Gets or sets the height of the following frame
+    /// </summary>
+    public int Height { get; set; }
+
+    /// <summary>
+    /// Gets or sets the X position at which to render the following frame
+    /// </summary>
+    public int XOffset { get; set; }
+
+    /// <summary>
+    /// Gets or sets the Y position at which to render the following frame
+    /// </summary>
+    public int YOffset { get; set; }
+
+    /// <summary>
+    /// Gets or sets the frame delay fraction numerator
+    /// </summary>
+    public short DelayNumber { get; set; }
+
+    /// <summary>
+    /// Gets or sets the frame delay fraction denominator
+    /// </summary>
+    public short DelayDenominator { get; set; }
+
+    /// <summary>
+    /// Gets or sets the type of frame area disposal to be done after rendering this frame
+    /// </summary>
+    public APngDisposeOperation DisposeOperation { get; set; }
+
+    /// <summary>
+    /// Gets or sets the type of frame area rendering for this frame
+    /// </summary>
+    public APngBlendOperation BlendOperation { get; set; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="APngFrameMetadata"/> class.
+    /// </summary>
+    /// <param name="frameControl">The chunk to create an instance from.</param>
+    internal void FromChunk(APngFrameControl frameControl)
+    {
+        this.Width = frameControl.Width;
+        this.Height = frameControl.Height;
+        this.XOffset = frameControl.XOffset;
+        this.YOffset = frameControl.YOffset;
+        this.DelayNumber = frameControl.DelayNumber;
+        this.DelayDenominator = frameControl.DelayDenominator;
+        this.DisposeOperation = frameControl.DisposeOperation;
+        this.BlendOperation = frameControl.BlendOperation;
+    }
+
+    /// <inheritdoc/>
+    public IDeepCloneable DeepClone() => new APngFrameMetadata(this);
+}

src/ImageSharp/Formats/Png/Chunks/APngAnimationControl.cs

@@ -0,0 +1,43 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Buffers.Binary;
+
+namespace SixLabors.ImageSharp.Formats.Png.Chunks;
+
+internal record APngAnimationControl(
+    int NumberFrames,
+    int NumberPlays)
+{
+    public const int Size = 8;
+
+    /// <summary>
+    /// Gets the number of frames
+    /// </summary>
+    public int NumberFrames { get; } = NumberFrames;
+
+    /// <summary>
+    /// Gets the number of times to loop this APNG.  0 indicates infinite looping.
+    /// </summary>
+    public int NumberPlays { get; } = NumberPlays;
+
+    /// <summary>
+    /// Writes the acTL to the given buffer.
+    /// </summary>
+    /// <param name="buffer">The buffer to write to.</param>
+    public void WriteTo(Span<byte> buffer)
+    {
+        BinaryPrimitives.WriteInt32BigEndian(buffer[..4], this.NumberFrames);
+        BinaryPrimitives.WriteInt32BigEndian(buffer[4..8], this.NumberPlays);
+    }
+
+    /// <summary>
+    /// Parses the APngAnimationControl from the given data buffer.
+    /// </summary>
+    /// <param name="data">The data to parse.</param>
+    /// <returns>The parsed acTL.</returns>
+    public static APngAnimationControl Parse(ReadOnlySpan<byte> data)
+        => new(
+            NumberFrames: BinaryPrimitives.ReadInt32BigEndian(data[..4]),
+            NumberPlays: BinaryPrimitives.ReadInt32BigEndian(data[4..8]));
+}

src/ImageSharp/Formats/Png/Chunks/APngFrameControl.cs

@@ -0,0 +1,172 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Buffers.Binary;
+
+namespace SixLabors.ImageSharp.Formats.Png.Chunks;
+
+internal readonly struct APngFrameControl
+{
+    public const int Size = 26;
+
+    public APngFrameControl(
+        int sequenceNumber,
+        int width,
+        int height,
+        int xOffset,
+        int yOffset,
+        short delayNumber,
+        short delayDenominator,
+        APngDisposeOperation disposeOperation,
+        APngBlendOperation blendOperation)
+    {
+        this.SequenceNumber = sequenceNumber;
+        this.Width = width;
+        this.Height = height;
+        this.XOffset = xOffset;
+        this.YOffset = yOffset;
+        this.DelayNumber = delayNumber;
+        this.DelayDenominator = delayDenominator;
+        this.DisposeOperation = disposeOperation;
+        this.BlendOperation = blendOperation;
+    }
+
+    /// <summary>
+    /// Gets the sequence number of the animation chunk, starting from 0
+    /// </summary>
+    public int SequenceNumber { get; }
+
+    /// <summary>
+    /// Gets the width of the following frame
+    /// </summary>
+    public int Width { get; }
+
+    /// <summary>
+    /// Gets the height of the following frame
+    /// </summary>
+    public int Height { get; }
+
+    /// <summary>
+    /// Gets the X position at which to render the following frame
+    /// </summary>
+    public int XOffset { get; }
+
+    /// <summary>
+    /// Gets the Y position at which to render the following frame
+    /// </summary>
+    public int YOffset { get; }
+
+    /// <summary>
+    /// Gets the frame delay fraction numerator
+    /// </summary>
+    public short DelayNumber { get; }
+
+    /// <summary>
+    /// Gets the frame delay fraction denominator
+    /// </summary>
+    public short DelayDenominator { get; }
+
+    /// <summary>
+    /// Gets the type of frame area disposal to be done after rendering this frame
+    /// </summary>
+    public APngDisposeOperation DisposeOperation { get; }
+
+    /// <summary>
+    /// Gets the type of frame area rendering for this frame
+    /// </summary>
+    public APngBlendOperation BlendOperation { get; }
+
+    /// <summary>
+    /// Validates the APng fcTL.
+    /// </summary>
+    /// <exception cref="NotSupportedException">
+    /// Thrown if the image does pass validation.
+    /// </exception>
+    public void Validate(PngHeader hdr)
+    {
+        if (this.XOffset < 0)
+        {
+            throw new NotSupportedException($"Invalid XOffset. Expected >= 0. Was '{this.XOffset}'.");
+        }
+
+        if (this.YOffset < 0)
+        {
+            throw new NotSupportedException($"Invalid YOffset. Expected >= 0. Was '{this.YOffset}'.");
+        }
+
+        if (this.Width <= 0)
+        {
+            throw new NotSupportedException($"Invalid Width. Expected > 0. Was '{this.Width}'.");
+        }
+
+        if (this.Height <= 0)
+        {
+            throw new NotSupportedException($"Invalid Height. Expected > 0. Was '{this.Height}'.");
+        }
+
+        if (this.XOffset + this.Width > hdr.Width)
+        {
+            throw new NotSupportedException($"Invalid XOffset or Width. The sum > PngHeader.Width. Was '{this.XOffset + this.Width}'.");
+        }
+
+        if (this.YOffset + this.Height > hdr.Height)
+        {
+            throw new NotSupportedException($"Invalid YOffset or Height. The sum > PngHeader.Height. Was '{this.YOffset + this.Height}'.");
+        }
+    }
+
+    /// <summary>
+    /// Parses the APngFrameControl from the given metadata.
+    /// </summary>
+    /// <param name="frameMetadata">The metadata to parse.</param>
+    /// <param name="sequenceNumber">Sequence number.</param>
+    public static APngFrameControl FromMetadata(APngFrameMetadata frameMetadata, int sequenceNumber)
+    {
+        APngFrameControl fcTL = new(
+            sequenceNumber,
+            frameMetadata.Width,
+            frameMetadata.Height,
+            frameMetadata.XOffset,
+            frameMetadata.YOffset,
+            frameMetadata.DelayNumber,
+            frameMetadata.DelayDenominator,
+            frameMetadata.DisposeOperation,
+            frameMetadata.BlendOperation);
+        return fcTL;
+    }
+
+    /// <summary>
+    /// Writes the fcTL to the given buffer.
+    /// </summary>
+    /// <param name="buffer">The buffer to write to.</param>
+    public void WriteTo(Span<byte> buffer)
+    {
+        BinaryPrimitives.WriteInt32BigEndian(buffer[..4], this.SequenceNumber);
+        BinaryPrimitives.WriteInt32BigEndian(buffer[4..8], this.Width);
+        BinaryPrimitives.WriteInt32BigEndian(buffer[8..12], this.Height);
+        BinaryPrimitives.WriteInt32BigEndian(buffer[12..16], this.XOffset);
+        BinaryPrimitives.WriteInt32BigEndian(buffer[16..20], this.YOffset);
+        BinaryPrimitives.WriteInt16BigEndian(buffer[20..22], this.DelayNumber);
+        BinaryPrimitives.WriteInt16BigEndian(buffer[22..24], this.DelayDenominator);
+
+        buffer[24] = (byte)this.DisposeOperation;
+        buffer[25] = (byte)this.BlendOperation;
+    }
+
+    /// <summary>
+    /// Parses the APngFrameControl from the given data buffer.
+    /// </summary>
+    /// <param name="data">The data to parse.</param>
+    /// <returns>The parsed fcTL.</returns>
+    public static APngFrameControl Parse(ReadOnlySpan<byte> data)
+        => new(
+            sequenceNumber: BinaryPrimitives.ReadInt32BigEndian(data[..4]),
+            width: BinaryPrimitives.ReadInt32BigEndian(data[4..8]),
+            height: BinaryPrimitives.ReadInt32BigEndian(data[8..12]),
+            xOffset: BinaryPrimitives.ReadInt32BigEndian(data[12..16]),
+            yOffset: BinaryPrimitives.ReadInt32BigEndian(data[16..20]),
+            delayNumber: BinaryPrimitives.ReadInt16BigEndian(data[20..22]),
+            delayDenominator: BinaryPrimitives.ReadInt16BigEndian(data[22..24]),
+            disposeOperation: (APngDisposeOperation)data[24],
+            blendOperation: (APngBlendOperation)data[25]);
+}