implement APNG encoder

Author: Poker-sang

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/Chunks/APngFrameControl.cs

@@ -115,6 +115,26 @@ public void Validate(PngHeader hdr)
         }
     }
 
+    /// <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>
@@ -126,8 +146,8 @@ public void WriteTo(Span<byte> buffer)
         BinaryPrimitives.WriteInt32BigEndian(buffer[8..12], this.Height);
         BinaryPrimitives.WriteInt32BigEndian(buffer[12..16], this.XOffset);
         BinaryPrimitives.WriteInt32BigEndian(buffer[16..20], this.YOffset);
-        BinaryPrimitives.WriteInt32BigEndian(buffer[20..22], this.DelayNumber);
-        BinaryPrimitives.WriteInt32BigEndian(buffer[12..24], this.DelayDenominator);
+        BinaryPrimitives.WriteInt16BigEndian(buffer[20..22], this.DelayNumber);
+        BinaryPrimitives.WriteInt16BigEndian(buffer[22..24], this.DelayDenominator);
 
         buffer[24] = (byte)this.DisposeOperation;
         buffer[25] = (byte)this.BlendOperation;

src/ImageSharp/Formats/Png/PngChunkType.cs

@@ -10,149 +10,149 @@ internal enum PngChunkType : uint
 {
     /// <summary>
     /// </summary>
-    /// <remarks>acTL</remarks>
+    /// <remarks>acTL (Single)</remarks>
     AnimationControl = 0x6163544cU,
 
     /// <summary>
     /// </summary>
-    /// <remarks>fcTL</remarks>
+    /// <remarks>fcTL (Multiple)</remarks>
     FrameControl = 0x6663544cU,
 
     /// <summary>
     /// </summary>
-    /// <remarks>fdAT</remarks>
+    /// <remarks>fdAT (Multiple)</remarks>
     FrameData = 0x66644154U,
 
     /// <summary>
     /// The IDAT chunk contains the actual image data. The image can contains more
     /// than one chunk of this type. All chunks together are the whole image.
     /// </summary>
-    /// <remarks>IDAT</remarks>
+    /// <remarks>IDAT (Multiple)</remarks>
     Data = 0x49444154U,
 
     /// <summary>
     /// This chunk must appear last. It marks the end of the PNG data stream.
     /// The chunk's data field is empty.
     /// </summary>
-    /// <remarks>IEND</remarks>
+    /// <remarks>IEND (Single)</remarks>
     End = 0x49454E44U,
 
     /// <summary>
     /// The first chunk in a png file. Can only exists once. Contains
     /// common information like the width and the height of the image or
     /// the used compression method.
     /// </summary>
-    /// <remarks>IHDR</remarks>
+    /// <remarks>IHDR (Single)</remarks>
     Header = 0x49484452U,
 
     /// <summary>
     /// The PLTE chunk contains from 1 to 256 palette entries, each a three byte
     /// series in the RGB format.
     /// </summary>
-    /// <remarks>PLTE</remarks>
+    /// <remarks>PLTE (Single)</remarks>
     Palette = 0x504C5445U,
 
     /// <summary>
     /// The eXIf data chunk which contains the Exif profile.
     /// </summary>
-    /// <remarks>eXIF</remarks>
+    /// <remarks>eXIF (Single)</remarks>
     Exif = 0x65584966U,
 
     /// <summary>
     /// This chunk specifies the relationship between the image samples and the desired
     /// display output intensity.
     /// </summary>
-    /// <remarks>gAMA</remarks>
+    /// <remarks>gAMA (Single)</remarks>
     Gamma = 0x67414D41U,
 
     /// <summary>
     /// This chunk specifies the intended pixel size or aspect ratio for display of the image.
     /// </summary>
-    /// <remarks>pHYs</remarks>
+    /// <remarks>pHYs (Single)</remarks>
     Physical = 0x70485973U,
 
     /// <summary>
     /// Textual information that the encoder wishes to record with the image can be stored in
     /// tEXt chunks. Each tEXt chunk contains a keyword and a text string.
     /// </summary>
-    /// <remarks>tEXT</remarks>
+    /// <remarks>tEXT (Multiple)</remarks>
     Text = 0x74455874U,
 
     /// <summary>
     /// Textual information that the encoder wishes to record with the image. The zTXt and tEXt chunks are semantically equivalent,
     /// but the zTXt chunk is recommended for storing large blocks of text. Each zTXt chunk contains a (uncompressed) keyword and
     /// a compressed text string.
     /// </summary>
-    /// <remarks>zTXt</remarks>
+    /// <remarks>zTXt (Multiple)</remarks>
     CompressedText = 0x7A545874U,
 
     /// <summary>
     /// This chunk contains International textual data. It contains a keyword, an optional language tag, an optional translated keyword
     /// and the actual text string, which can be compressed or uncompressed.
     /// </summary>
-    /// <remarks>iTXt</remarks>
+    /// <remarks>iTXt (Multiple)</remarks>
     InternationalText = 0x69545874U,
 
     /// <summary>
     /// This chunk specifies that the image uses simple transparency:
     /// either alpha values associated with palette entries (for indexed-color images)
     /// or a single transparent color (for grayscale and true color images).
     /// </summary>
-    /// <remarks>tRNS</remarks>
+    /// <remarks>tRNS (Single)</remarks>
     Transparency = 0x74524E53U,
 
     /// <summary>
     /// This chunk gives the time of the last image modification (not the time of initial image creation).
     /// </summary>
-    /// <remarks>tIME</remarks>
+    /// <remarks>tIME (Single)</remarks>
     Time = 0x74494d45,
 
     /// <summary>
     /// This chunk specifies a default background colour to present the image against.
     /// If there is any other preferred background, either user-specified or part of a larger page (as in a browser),
     /// the bKGD chunk should be ignored.
     /// </summary>
-    /// <remarks>bKGD</remarks>
+    /// <remarks>bKGD (Single)</remarks>
     Background = 0x624b4744,
 
     /// <summary>
     /// This chunk contains a embedded color profile. If the iCCP chunk is present,
     /// the image samples conform to the colour space represented by the embedded ICC profile as defined by the International Color Consortium.
     /// </summary>
-    /// <remarks>iCCP</remarks>
+    /// <remarks>iCCP (Single)</remarks>
     EmbeddedColorProfile = 0x69434350,
 
     /// <summary>
     /// This chunk defines the original number of significant bits (which can be less than or equal to the sample depth).
     /// This allows PNG decoders to recover the original data losslessly even if the data had a sample depth not directly supported by PNG.
     /// </summary>
-    /// <remarks>sBIT</remarks>
+    /// <remarks>sBIT (Single)</remarks>
     SignificantBits = 0x73424954,
 
     /// <summary>
     /// If the this chunk is present, the image samples conform to the sRGB colour space [IEC 61966-2-1] and should be displayed
     /// using the specified rendering intent defined by the International Color Consortium.
     /// </summary>
-    /// <remarks>sRGB</remarks>
+    /// <remarks>sRGB (Single)</remarks>
     StandardRgbColourSpace = 0x73524742,
 
     /// <summary>
     /// This chunk gives the approximate usage frequency of each colour in the palette.
     /// </summary>
-    /// <remarks>hIST</remarks>
+    /// <remarks>hIST (Single)</remarks>
     Histogram = 0x68495354,
 
     /// <summary>
     /// This chunk contains the suggested palette.
     /// </summary>
-    /// <remarks>sPLT</remarks>
+    /// <remarks>sPLT (Single)</remarks>
     SuggestedPalette = 0x73504c54,
 
     /// <summary>
     /// This chunk may be used to specify the 1931 CIE x,y chromaticities of the red,
     /// green, and blue display primaries used in the image, and the referenced white point.
     /// </summary>
-    /// <remarks>cHRM</remarks>
+    /// <remarks>cHRM (Single)</remarks>
     Chroma = 0x6348524d,
 
     /// <summary>

src/ImageSharp/Formats/Png/PngEncoder.cs

@@ -1,6 +1,5 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
-#nullable disable
 
 using SixLabors.ImageSharp.Advanced;
 
@@ -18,7 +17,12 @@ public PngEncoder() =>
 
         // We set the quantizer to null here to allow the underlying encoder to create a
         // quantizer with options appropriate to the encoding bit depth.
-        this.Quantizer = null;
+        this.Quantizer = null!;
+
+    /// <summary>
+    /// Gets whether the file is a simple PNG.
+    /// </summary>
+    public bool? IsSimplePng { get; init; }
 
     /// <summary>
     /// Gets the number of bits per sample or per palette index (not per pixel).