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/Formats/Png/Chunks/AnimationControl.cs

@@ -0,0 +1,47 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Buffers.Binary;
+
+namespace SixLabors.ImageSharp.Formats.Png.Chunks;
+
+internal readonly struct AnimationControl
+{
+    public const int Size = 8;
+
+    public AnimationControl(int numberFrames, int numberPlays)
+    {
+        this.NumberFrames = numberFrames;
+        this.NumberPlays = numberPlays;
+    }
+
+    /// <summary>
+    /// Gets the number of frames
+    /// </summary>
+    public int NumberFrames { get; }
+
+    /// <summary>
+    /// Gets the number of times to loop this APNG.  0 indicates infinite looping.
+    /// </summary>
+    public int NumberPlays { get; }
+
+    /// <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 AnimationControl Parse(ReadOnlySpan<byte> data)
+        => new(
+            numberFrames: BinaryPrimitives.ReadInt32BigEndian(data[..4]),
+            numberPlays: BinaryPrimitives.ReadInt32BigEndian(data[4..8]));
+}

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

@@ -0,0 +1,160 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+using System.Buffers.Binary;
+
+namespace SixLabors.ImageSharp.Formats.Png.Chunks;
+
+internal readonly struct FrameControl
+{
+    public const int Size = 26;
+
+    public FrameControl(uint width, uint height)
+        : this(0, width, height, 0, 0, 0, 0, default, default)
+    {
+    }
+
+    public FrameControl(
+        uint sequenceNumber,
+        uint width,
+        uint height,
+        uint xOffset,
+        uint yOffset,
+        ushort delayNumerator,
+        ushort delayDenominator,
+        PngDisposalMethod disposeOperation,
+        PngBlendMethod blendOperation)
+    {
+        this.SequenceNumber = sequenceNumber;
+        this.Width = width;
+        this.Height = height;
+        this.XOffset = xOffset;
+        this.YOffset = yOffset;
+        this.DelayNumerator = delayNumerator;
+        this.DelayDenominator = delayDenominator;
+        this.DisposeOperation = disposeOperation;
+        this.BlendOperation = blendOperation;
+    }
+
+    /// <summary>
+    /// Gets the sequence number of the animation chunk, starting from 0
+    /// </summary>
+    public uint SequenceNumber { get; }
+
+    /// <summary>
+    /// Gets the width of the following frame
+    /// </summary>
+    public uint Width { get; }
+
+    /// <summary>
+    /// Gets the height of the following frame
+    /// </summary>
+    public uint Height { get; }
+
+    /// <summary>
+    /// Gets the X position at which to render the following frame
+    /// </summary>
+    public uint XOffset { get; }
+
+    /// <summary>
+    /// Gets the Y position at which to render the following frame
+    /// </summary>
+    public uint YOffset { get; }
+
+    /// <summary>
+    /// Gets the X limit at which to render the following frame
+    /// </summary>
+    public uint XMax => this.XOffset + this.Width;
+
+    /// <summary>
+    /// Gets the Y limit at which to render the following frame
+    /// </summary>
+    public uint YMax => this.YOffset + this.Height;
+
+    /// <summary>
+    /// Gets the frame delay fraction numerator
+    /// </summary>
+    public ushort DelayNumerator { get; }
+
+    /// <summary>
+    /// Gets the frame delay fraction denominator
+    /// </summary>
+    public ushort DelayDenominator { get; }
+
+    /// <summary>
+    /// Gets the type of frame area disposal to be done after rendering this frame
+    /// </summary>
+    public PngDisposalMethod DisposeOperation { get; }
+
+    /// <summary>
+    /// Gets the type of frame area rendering for this frame
+    /// </summary>
+    public PngBlendMethod BlendOperation { get; }
+
+    public Rectangle Bounds => new((int)this.XOffset, (int)this.YOffset, (int)this.Width, (int)this.Height);
+
+    /// <summary>
+    /// Validates the APng fcTL.
+    /// </summary>
+    /// <param name="header">The header.</param>
+    /// <exception cref="NotSupportedException">
+    /// Thrown if the image does pass validation.
+    /// </exception>
+    public void Validate(PngHeader header)
+    {
+        if (this.Width == 0)
+        {
+            PngThrowHelper.ThrowInvalidParameter(this.Width, "Expected > 0");
+        }
+
+        if (this.Height == 0)
+        {
+            PngThrowHelper.ThrowInvalidParameter(this.Height, "Expected > 0");
+        }
+
+        if (this.XMax > header.Width)
+        {
+            PngThrowHelper.ThrowInvalidParameter(this.XOffset, this.Width, $"The x-offset plus width > {nameof(PngHeader)}.{nameof(PngHeader.Width)}");
+        }
+
+        if (this.YMax > header.Height)
+        {
+            PngThrowHelper.ThrowInvalidParameter(this.YOffset, this.Height, $"The y-offset plus height > {nameof(PngHeader)}.{nameof(PngHeader.Height)}");
+        }
+    }
+
+    /// <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.WriteUInt32BigEndian(buffer[..4], this.SequenceNumber);
+        BinaryPrimitives.WriteUInt32BigEndian(buffer[4..8], this.Width);
+        BinaryPrimitives.WriteUInt32BigEndian(buffer[8..12], this.Height);
+        BinaryPrimitives.WriteUInt32BigEndian(buffer[12..16], this.XOffset);
+        BinaryPrimitives.WriteUInt32BigEndian(buffer[16..20], this.YOffset);
+        BinaryPrimitives.WriteUInt16BigEndian(buffer[20..22], this.DelayNumerator);
+        BinaryPrimitives.WriteUInt16BigEndian(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 FrameControl Parse(ReadOnlySpan<byte> data)
+        => new(
+            sequenceNumber: BinaryPrimitives.ReadUInt32BigEndian(data[..4]),
+            width: BinaryPrimitives.ReadUInt32BigEndian(data[4..8]),
+            height: BinaryPrimitives.ReadUInt32BigEndian(data[8..12]),
+            xOffset: BinaryPrimitives.ReadUInt32BigEndian(data[12..16]),
+            yOffset: BinaryPrimitives.ReadUInt32BigEndian(data[16..20]),
+            delayNumerator: BinaryPrimitives.ReadUInt16BigEndian(data[20..22]),
+            delayDenominator: BinaryPrimitives.ReadUInt16BigEndian(data[22..24]),
+            disposeOperation: (PngDisposalMethod)data[24],
+            blendOperation: (PngBlendMethod)data[25]);
+}

src/ImageSharp/Formats/Png/PngHeader.cs → src/ImageSharp/Formats/Png/Chunks/PngHeader.cs

@@ -4,7 +4,7 @@
 
 using System.Buffers.Binary;
 
-namespace SixLabors.ImageSharp.Formats.Png;
+namespace SixLabors.ImageSharp.Formats.Png.Chunks;
 
 /// <summary>
 /// Represents the png header chunk.

src/ImageSharp/Formats/Png/Chunks/PhysicalChunkData.cs → src/ImageSharp/Formats/Png/Chunks/PngPhysical.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
 using System.Buffers.Binary;
@@ -10,11 +10,11 @@ namespace SixLabors.ImageSharp.Formats.Png.Chunks;
 /// <summary>
 /// The pHYs chunk specifies the intended pixel size or aspect ratio for display of the image.
 /// </summary>
-internal readonly struct PhysicalChunkData
+internal readonly struct PngPhysical
 {
     public const int Size = 9;
 
-    public PhysicalChunkData(uint x, uint y, byte unitSpecifier)
+    public PngPhysical(uint x, uint y, byte unitSpecifier)
     {
         this.XAxisPixelsPerUnit = x;
         this.YAxisPixelsPerUnit = y;
@@ -44,13 +44,13 @@ public PhysicalChunkData(uint x, uint y, byte unitSpecifier)
     /// </summary>
     /// <param name="data">The data buffer.</param>
     /// <returns>The parsed PhysicalChunkData.</returns>
-    public static PhysicalChunkData Parse(ReadOnlySpan<byte> data)
+    public static PngPhysical Parse(ReadOnlySpan<byte> data)
     {
         uint hResolution = BinaryPrimitives.ReadUInt32BigEndian(data[..4]);
         uint vResolution = BinaryPrimitives.ReadUInt32BigEndian(data.Slice(4, 4));
         byte unit = data[8];
 
-        return new PhysicalChunkData(hResolution, vResolution, unit);
+        return new PngPhysical(hResolution, vResolution, unit);
     }
 
     /// <summary>
@@ -59,7 +59,7 @@ public static PhysicalChunkData Parse(ReadOnlySpan<byte> data)
     /// </summary>
     /// <param name="meta">The metadata.</param>
     /// <returns>The constructed PngPhysicalChunkData instance.</returns>
-    public static PhysicalChunkData FromMetadata(ImageMetadata meta)
+    public static PngPhysical FromMetadata(ImageMetadata meta)
     {
         byte unitSpecifier = 0;
         uint x;
@@ -92,7 +92,7 @@ public static PhysicalChunkData FromMetadata(ImageMetadata meta)
                 break;
         }
 
-        return new PhysicalChunkData(x, y, unitSpecifier);
+        return new PngPhysical(x, y, unitSpecifier);
     }
 
     /// <summary>

src/ImageSharp/Formats/Png/PngTextData.cs → src/ImageSharp/Formats/Png/Chunks/PngTextData.cs

@@ -1,7 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
-namespace SixLabors.ImageSharp.Formats.Png;
+namespace SixLabors.ImageSharp.Formats.Png.Chunks;
 
 /// <summary>
 /// Stores text data contained in the iTXt, tEXt, and zTXt chunks.

src/ImageSharp/Formats/Png/MetadataExtensions.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Diagnostics.CodeAnalysis;
 using SixLabors.ImageSharp.Formats.Png;
 using SixLabors.ImageSharp.Metadata;
 
@@ -14,7 +15,22 @@ public static partial class MetadataExtensions
     /// <summary>
     /// Gets the png format specific metadata for the image.
     /// </summary>
-    /// <param name="metadata">The metadata this method extends.</param>
+    /// <param name="source">The metadata this method extends.</param>
     /// <returns>The <see cref="PngMetadata"/>.</returns>
-    public static PngMetadata GetPngMetadata(this ImageMetadata metadata) => metadata.GetFormatMetadata(PngFormat.Instance);
+    public static PngMetadata GetPngMetadata(this ImageMetadata source) => source.GetFormatMetadata(PngFormat.Instance);
+
+    /// <summary>
+    /// Gets the aPng format specific metadata for the image frame.
+    /// </summary>
+    /// <param name="source">The metadata this method extends.</param>
+    /// <returns>The <see cref="PngFrameMetadata"/>.</returns>
+    public static PngFrameMetadata GetPngFrameMetadata(this ImageFrameMetadata source) => source.GetFormatMetadata(PngFormat.Instance);
+
+    /// <summary>
+    /// Gets the aPng format specific metadata for the image frame.
+    /// </summary>
+    /// <param name="source">The metadata this method extends.</param>
+    /// <param name="metadata">The metadata.</param>
+    /// <returns>The <see cref="PngFrameMetadata"/>.</returns>
+    public static bool TryGetPngFrameMetadata(this ImageFrameMetadata source, [NotNullWhen(true)] out PngFrameMetadata? metadata) => source.TryGetFormatMetadata(PngFormat.Instance, out metadata);
 }

src/ImageSharp/Formats/Png/PngBlendMethod.cs

@@ -0,0 +1,22 @@
+// 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 PngBlendMethod
+{
+    /// <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].
+    /// </summary>
+    Over
+}

src/ImageSharp/Formats/Png/PngChunk.cs

@@ -42,7 +42,8 @@ public PngChunk(int length, PngChunkType type, IMemoryOwner<byte> data = null)
     /// Gets a value indicating whether the given chunk is critical to decoding
     /// </summary>
     public bool IsCritical =>
-        this.Type == PngChunkType.Header ||
-        this.Type == PngChunkType.Palette ||
-        this.Type == PngChunkType.Data;
+        this.Type is PngChunkType.Header or
+        PngChunkType.Palette or
+        PngChunkType.Data or
+        PngChunkType.FrameData;
 }