Complete Webp and add tests

Author: JimBobSquarePants

src/ImageSharp/Formats/Gif/GifEncoderCore.cs

@@ -190,19 +190,20 @@ private static GifMetadata GetGifMetadata<TPixel>(Image<TPixel> image)
             return GifMetadata.FromAnimatedMetadata(ani);
         }
 
+        // Return explicit new instance so we do not mutate the original metadata.
         return new();
     }
 
     private static GifFrameMetadata? GetGifFrameMetadata<TPixel>(ImageFrame<TPixel> frame, int transparencyIndex)
         where TPixel : unmanaged, IPixel<TPixel>
     {
-        if (frame.Metadata.TryGetGifFrameMetadata(out GifFrameMetadata? gif))
+        if (frame.Metadata.TryGetGifMetadata(out GifFrameMetadata? gif))
         {
             return gif;
         }
 
         GifFrameMetadata? metadata = null;
-        if (frame.Metadata.TryGetPngFrameMetadata(out PngFrameMetadata? png))
+        if (frame.Metadata.TryGetPngMetadata(out PngFrameMetadata? png))
         {
             AnimatedImageFrameMetadata ani = png.ToAnimatedImageFrameMetadata();
             metadata = GifFrameMetadata.FromAnimatedMetadata(ani);
@@ -342,7 +343,20 @@ private void EncodeAdditionalFrame<TPixel>(
             }
         }
 
-        this.DeDuplicatePixels(previousFrame, currentFrame, encodingFrame, replacement);
+        // We can't deduplicate here as we need the background pixels to be present in the buffer.
+        if (metadata?.DisposalMethod == GifDisposalMethod.RestoreToBackground)
+        {
+            for (int y = 0; y < currentFrame.PixelBuffer.Height; y++)
+            {
+                Span<TPixel> sourceRow = currentFrame.PixelBuffer.DangerousGetRowSpan(y);
+                Span<TPixel> destinationRow = encodingFrame.PixelBuffer.DangerousGetRowSpan(y);
+                sourceRow.CopyTo(destinationRow);
+            }
+        }
+        else
+        {
+            this.DeDuplicatePixels(previousFrame, currentFrame, encodingFrame, replacement);
+        }
 
         IndexedImageFrame<TPixel> quantized;
         if (useLocal)

src/ImageSharp/Formats/Gif/MetadataExtensions.cs

@@ -56,16 +56,25 @@ public static GifFrameMetadata GetGifMetadata(this ImageFrameMetadata source)
     /// <returns>
     /// <see langword="true"/> if the gif frame metadata exists; otherwise, <see langword="false"/>.
     /// </returns>
-    public static bool TryGetGifFrameMetadata(this ImageFrameMetadata source, [NotNullWhen(true)] out GifFrameMetadata? metadata)
+    public static bool TryGetGifMetadata(this ImageFrameMetadata source, [NotNullWhen(true)] out GifFrameMetadata? metadata)
         => source.TryGetFormatMetadata(GifFormat.Instance, out metadata);
 
     internal static AnimatedImageMetadata ToAnimatedImageMetadata(this GifMetadata source)
-        => new()
+    {
+        Color background = Color.Transparent;
+        if (source.GlobalColorTable != null)
+        {
+            background = source.GlobalColorTable.Value.Span[source.BackgroundColorIndex];
+        }
+
+        return new()
         {
             ColorTable = source.GlobalColorTable,
             ColorTableMode = source.ColorTableMode == GifColorTableMode.Global ? FrameColorTableMode.Global : FrameColorTableMode.Local,
             RepeatCount = source.RepeatCount,
+            BackgroundColor = background,
         };
+    }
 
     internal static AnimatedImageFrameMetadata ToAnimatedImageFrameMetadata(this GifFrameMetadata source)
         => new()

src/ImageSharp/Formats/Png/MetadataExtensions.cs

@@ -36,7 +36,7 @@ public static bool TryGetPngMetadata(this ImageMetadata source, [NotNullWhen(tru
     /// </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);
+    public static PngFrameMetadata GetPngMetadata(this ImageFrameMetadata source) => source.GetFormatMetadata(PngFormat.Instance);
 
     /// <summary>
     /// Gets the png format specific metadata for the image frame.
@@ -46,7 +46,7 @@ public static bool TryGetPngMetadata(this ImageMetadata source, [NotNullWhen(tru
     /// <returns>
     /// <see langword="true"/> if the png frame metadata exists; otherwise, <see langword="false"/>.
     /// </returns>
-    public static bool TryGetPngFrameMetadata(this ImageFrameMetadata source, [NotNullWhen(true)] out PngFrameMetadata? metadata)
+    public static bool TryGetPngMetadata(this ImageFrameMetadata source, [NotNullWhen(true)] out PngFrameMetadata? metadata)
         => source.TryGetFormatMetadata(PngFormat.Instance, out metadata);
 
     internal static AnimatedImageMetadata ToAnimatedImageMetadata(this PngMetadata source)
@@ -58,17 +58,25 @@ internal static AnimatedImageMetadata ToAnimatedImageMetadata(this PngMetadata s
         };
 
     internal static AnimatedImageFrameMetadata ToAnimatedImageFrameMetadata(this PngFrameMetadata source)
-        => new()
+    {
+        double delay = source.FrameDelay.ToDouble();
+        if (double.IsNaN(delay))
+        {
+            delay = 0;
+        }
+
+        return new()
         {
             ColorTableMode = FrameColorTableMode.Global,
-            Duration = TimeSpan.FromMilliseconds(source.FrameDelay.ToDouble() * 1000),
+            Duration = TimeSpan.FromMilliseconds(delay * 1000),
             DisposalMode = GetMode(source.DisposalMethod),
             BlendMode = source.BlendMethod == PngBlendMethod.Source ? FrameBlendMode.Source : FrameBlendMode.Over,
         };
+    }
 
     private static FrameDisposalMode GetMode(PngDisposalMethod method) => method switch
     {
-        PngDisposalMethod.None => FrameDisposalMode.DoNotDispose,
+        PngDisposalMethod.DoNotDispose => FrameDisposalMode.DoNotDispose,
         PngDisposalMethod.RestoreToBackground => FrameDisposalMode.RestoreToBackground,
         PngDisposalMethod.RestoreToPrevious => FrameDisposalMode.RestoreToPrevious,
         _ => FrameDisposalMode.Unspecified,

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -581,7 +581,7 @@ private void InitializeImage<TPixel>(ImageMetadata metadata, FrameControl frameC
             this.header.Height,
             metadata);
 
-        PngFrameMetadata frameMetadata = image.Frames.RootFrame.Metadata.GetPngFrameMetadata();
+        PngFrameMetadata frameMetadata = image.Frames.RootFrame.Metadata.GetPngMetadata();
         frameMetadata.FromChunk(in frameControl);
 
         this.bytesPerPixel = this.CalculateBytesPerPixel();
@@ -630,7 +630,7 @@ private void InitializeFrame<TPixel>(
             pixelRegion.Clear();
         }
 
-        PngFrameMetadata frameMetadata = frame.Metadata.GetPngFrameMetadata();
+        PngFrameMetadata frameMetadata = frame.Metadata.GetPngMetadata();
         frameMetadata.FromChunk(currentFrameControl);
 
         this.previousScanline?.Dispose();

src/ImageSharp/Formats/Png/PngDisposalMethod.cs

@@ -11,7 +11,7 @@ public enum PngDisposalMethod
     /// <summary>
     /// No disposal is done on this frame before rendering the next; the contents of the output buffer are left as is.
     /// </summary>
-    None,
+    DoNotDispose,
 
     /// <summary>
     /// The frame's region of the output buffer is to be cleared to fully transparent black before rendering the next frame.

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -7,8 +7,10 @@
 using System.Runtime.InteropServices;
 using SixLabors.ImageSharp.Common.Helpers;
 using SixLabors.ImageSharp.Compression.Zlib;
+using SixLabors.ImageSharp.Formats.Gif;
 using SixLabors.ImageSharp.Formats.Png.Chunks;
 using SixLabors.ImageSharp.Formats.Png.Filters;
+using SixLabors.ImageSharp.Formats.Webp;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
@@ -137,7 +139,7 @@ public PngEncoderCore(Configuration configuration, PngEncoder encoder)
     /// <param name="stream">The <see cref="Stream"/> to encode the image data to.</param>
     /// <param name="cancellationToken">The token to request cancellation.</param>
     public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken cancellationToken)
-            where TPixel : unmanaged, IPixel<TPixel>
+        where TPixel : unmanaged, IPixel<TPixel>
     {
         Guard.NotNull(image, nameof(image));
         Guard.NotNull(stream, nameof(stream));
@@ -146,7 +148,7 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream, CancellationToken
         this.height = image.Height;
 
         ImageMetadata metadata = image.Metadata;
-        PngMetadata pngMetadata = metadata.GetFormatMetadata(PngFormat.Instance);
+        PngMetadata pngMetadata = GetPngMetadata(image);
         this.SanitizeAndSetEncoderOptions<TPixel>(this.encoder, pngMetadata, out this.use16Bit, out this.bytesPerPixel);
 
         stream.Write(PngConstants.HeaderBytes);
@@ -234,6 +236,54 @@ public void Dispose()
         this.currentScanline?.Dispose();
     }
 
+    private static PngMetadata GetPngMetadata<TPixel>(Image<TPixel> image)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        if (image.Metadata.TryGetPngMetadata(out PngMetadata? png))
+        {
+            return png;
+        }
+
+        if (image.Metadata.TryGetGifMetadata(out GifMetadata? gif))
+        {
+            AnimatedImageMetadata ani = gif.ToAnimatedImageMetadata();
+            return PngMetadata.FromAnimatedMetadata(ani);
+        }
+
+        if (image.Metadata.TryGetWebpMetadata(out WebpMetadata? webp))
+        {
+            AnimatedImageMetadata ani = webp.ToAnimatedImageMetadata();
+            return PngMetadata.FromAnimatedMetadata(ani);
+        }
+
+        // Return explicit new instance so we do not mutate the original metadata.
+        return new();
+    }
+
+    private static PngFrameMetadata GetPngFrameMetadata<TPixel>(ImageFrame<TPixel> frame)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        if (frame.Metadata.TryGetPngMetadata(out PngFrameMetadata? png))
+        {
+            return png;
+        }
+
+        if (frame.Metadata.TryGetGifMetadata(out GifFrameMetadata? gif))
+        {
+            AnimatedImageFrameMetadata ani = gif.ToAnimatedImageFrameMetadata();
+            return PngFrameMetadata.FromAnimatedMetadata(ani);
+        }
+
+        if (frame.Metadata.TryGetWebpFrameMetadata(out WebpFrameMetadata? webp))
+        {
+            AnimatedImageFrameMetadata ani = webp.ToAnimatedImageFrameMetadata();
+            return PngFrameMetadata.FromAnimatedMetadata(ani);
+        }
+
+        // Return explicit new instance so we do not mutate the original metadata.
+        return new();
+    }
+
     /// <summary>
     /// Convert transparent pixels, to transparent black pixels, which can yield to better compression in some cases.
     /// </summary>
@@ -985,9 +1035,10 @@ private void WriteTransparencyChunk(Stream stream, PngMetadata pngMetadata)
     /// <param name="stream">The <see cref="Stream"/> containing image data.</param>
     /// <param name="imageFrame">The image frame.</param>
     /// <param name="sequenceNumber">The frame sequence number.</param>
-    private FrameControl WriteFrameControlChunk(Stream stream, ImageFrame imageFrame, uint sequenceNumber)
+    private FrameControl WriteFrameControlChunk<TPixel>(Stream stream, ImageFrame<TPixel> imageFrame, uint sequenceNumber)
+        where TPixel : unmanaged, IPixel<TPixel>
     {
-        PngFrameMetadata frameMetadata = imageFrame.Metadata.GetPngFrameMetadata();
+        PngFrameMetadata frameMetadata = GetPngFrameMetadata(imageFrame);
 
         // TODO: If we can clip the indexed frame for transparent bounds we can set properties here.
         FrameControl fcTL = new(

src/ImageSharp/Formats/Png/PngFrameMetadata.cs

@@ -34,7 +34,7 @@ private PngFrameMetadata(PngFrameMetadata other)
     /// wait before continuing with the processing of the Data Stream.
     /// The clock starts ticking immediately after the graphic is rendered.
     /// </summary>
-    public Rational FrameDelay { get; set; }
+    public Rational FrameDelay { get; set; } = new(0);
 
     /// <summary>
     /// Gets or sets the type of frame area disposal to be done after rendering this frame
@@ -59,4 +59,20 @@ internal void FromChunk(in FrameControl frameControl)
 
     /// <inheritdoc/>
     public IDeepCloneable DeepClone() => new PngFrameMetadata(this);
+
+    internal static PngFrameMetadata FromAnimatedMetadata(AnimatedImageFrameMetadata metadata)
+        => new()
+        {
+            FrameDelay = new(metadata.Duration.TotalMilliseconds / 1000),
+            DisposalMethod = GetMode(metadata.DisposalMode),
+            BlendMethod = metadata.BlendMode == FrameBlendMode.Source ? PngBlendMethod.Source : PngBlendMethod.Over,
+        };
+
+    private static PngDisposalMethod GetMode(FrameDisposalMode mode) => mode switch
+    {
+        FrameDisposalMode.RestoreToBackground => PngDisposalMethod.RestoreToBackground,
+        FrameDisposalMode.RestoreToPrevious => PngDisposalMethod.RestoreToPrevious,
+        FrameDisposalMode.DoNotDispose => PngDisposalMethod.DoNotDispose,
+        _ => PngDisposalMethod.DoNotDispose,
+    };
 }

src/ImageSharp/Formats/Png/PngMetadata.cs

@@ -85,4 +85,37 @@ private PngMetadata(PngMetadata other)
 
     /// <inheritdoc/>
     public IDeepCloneable DeepClone() => new PngMetadata(this);
+
+    internal static PngMetadata FromAnimatedMetadata(AnimatedImageMetadata metadata)
+    {
+        // Should the conversion be from a format that uses a 24bit palette entries (gif)
+        // we need to clone and adjust the color table to allow for transparency.
+        ReadOnlyMemory<Color>? colorTable = metadata.ColorTable;
+        if (metadata.ColorTable.HasValue)
+        {
+            Color[] clone = metadata.ColorTable.Value.ToArray();
+            for (int i = 0; i < clone.Length; i++)
+            {
+                ref Color c = ref clone[i];
+                if (c == metadata.BackgroundColor)
+                {
+                    // Png treats background as fully empty
+                    c = default;
+                    break;
+                }
+            }
+
+            colorTable = clone;
+        }
+
+        return new()
+        {
+            ColorType = colorTable.HasValue ? PngColorType.Palette : null,
+            BitDepth = colorTable.HasValue
+                        ? (PngBitDepth)Numerics.Clamp(ColorNumerics.GetBitsNeededForColorDepth(colorTable.Value.Length), 1, 8)
+                        : null,
+            ColorTable = colorTable,
+            RepeatCount = metadata.RepeatCount,
+        };
+    }
 }

src/ImageSharp/Formats/Webp/Chunks/WebpFrameData.cs

@@ -33,7 +33,7 @@ public WebpFrameData(uint dataSize, uint x, uint y, uint width, uint height, uin
             height,
             duration,
             (flags & 2) == 0 ? WebpBlendingMethod.Over : WebpBlendingMethod.Source,
-            (flags & 1) == 1 ? WebpDisposalMethod.RestoreToBackground : WebpDisposalMethod.None)
+            (flags & 1) == 1 ? WebpDisposalMethod.RestoreToBackground : WebpDisposalMethod.DoNotDispose)
     {
     }
 

src/ImageSharp/Formats/Webp/Lossless/Vp8LEncoder.cs

@@ -259,7 +259,7 @@ public void EncodeHeader<TPixel>(Image<TPixel> image, Stream stream, bool hasAni
 
         if (hasAnimation)
         {
-            WebpMetadata webpMetadata = metadata.GetWebpMetadata();
+            WebpMetadata webpMetadata = WebpCommonUtils.GetWebpMetadata(image);
             BitWriterBase.WriteAnimationParameter(stream, webpMetadata.BackgroundColor, webpMetadata.RepeatCount);
         }
     }
@@ -307,7 +307,7 @@ public void Encode<TPixel>(ImageFrame<TPixel> frame, Stream stream, bool hasAnim
 
         if (hasAnimation)
         {
-            WebpFrameMetadata frameMetadata = frame.Metadata.GetWebpMetadata();
+            WebpFrameMetadata frameMetadata = WebpCommonUtils.GetWebpFrameMetadata(frame);
 
             // TODO: If we can clip the indexed frame for transparent bounds we can set properties here.
             prevPosition = new WebpFrameData(