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Animated webp encoder #2569

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Nov 6, 2023
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124 changes: 124 additions & 0 deletions src/ImageSharp/Common/Helpers/RiffHelper.cs
Original file line number Diff line number Diff line change
@@ -0,0 +1,124 @@
// Copyright (c) Six Labors.
// Licensed under the Six Labors Split License.

using System.Buffers.Binary;
using System.Text;

namespace SixLabors.ImageSharp.Common.Helpers;

internal static class RiffHelper
{
/// <summary>
/// The header bytes identifying RIFF file.
/// </summary>
private const uint RiffFourCc = 0x52_49_46_46;

public static void WriteRiffFile(Stream stream, string formType, Action<Stream> func) =>
WriteChunk(stream, RiffFourCc, s =>
{
s.Write(Encoding.ASCII.GetBytes(formType));
func(s);
});

public static void WriteChunk(Stream stream, uint fourCc, Action<Stream> func)
{
Span<byte> buffer = stackalloc byte[4];

// write the fourCC
BinaryPrimitives.WriteUInt32BigEndian(buffer, fourCc);
stream.Write(buffer);

long sizePosition = stream.Position;
stream.Position += 4;

func(stream);

long position = stream.Position;

uint dataSize = (uint)(position - sizePosition - 4);

// padding
if (dataSize % 2 == 1)
{
stream.WriteByte(0);
position++;
}

BinaryPrimitives.WriteUInt32LittleEndian(buffer, dataSize);
stream.Position = sizePosition;
stream.Write(buffer);
stream.Position = position;
}

public static void WriteChunk(Stream stream, uint fourCc, ReadOnlySpan<byte> data)
{
Span<byte> buffer = stackalloc byte[4];

// write the fourCC
BinaryPrimitives.WriteUInt32BigEndian(buffer, fourCc);
stream.Write(buffer);
uint size = (uint)data.Length;
BinaryPrimitives.WriteUInt32LittleEndian(buffer, size);
stream.Write(buffer);
stream.Write(data);

// padding
if (size % 2 is 1)
{
stream.WriteByte(0);
}
}

public static unsafe void WriteChunk<TStruct>(Stream stream, uint fourCc, in TStruct chunk)
where TStruct : unmanaged
{
fixed (TStruct* ptr = &chunk)
{
WriteChunk(stream, fourCc, new Span<byte>(ptr, sizeof(TStruct)));
}
}

public static long BeginWriteChunk(Stream stream, uint fourCc)
{
Span<byte> buffer = stackalloc byte[4];

// write the fourCC
BinaryPrimitives.WriteUInt32BigEndian(buffer, fourCc);
stream.Write(buffer);

long sizePosition = stream.Position;
stream.Position += 4;

return sizePosition;
}

public static void EndWriteChunk(Stream stream, long sizePosition)
{
Span<byte> buffer = stackalloc byte[4];

long position = stream.Position;

uint dataSize = (uint)(position - sizePosition - 4);

// padding
if (dataSize % 2 is 1)
{
stream.WriteByte(0);
position++;
}

BinaryPrimitives.WriteUInt32LittleEndian(buffer, dataSize);
stream.Position = sizePosition;
stream.Write(buffer);
stream.Position = position;
}

public static long BeginWriteRiffFile(Stream stream, string formType)
{
long sizePosition = BeginWriteChunk(stream, RiffFourCc);
stream.Write(Encoding.ASCII.GetBytes(formType));
return sizePosition;
}

public static void EndWriteRiffFile(Stream stream, long sizePosition) => EndWriteChunk(stream, sizePosition);
}
2 changes: 1 addition & 1 deletion src/ImageSharp/Formats/Webp/AlphaDecoder.cs
Original file line number Diff line number Diff line change
Expand Up @@ -59,7 +59,7 @@ public AlphaDecoder(int width, int height, IMemoryOwner<byte> data, byte alphaCh

if (this.Compressed)
{
Vp8LBitReader bitReader = new(data);
Vp8LBitReader bitReader = new Vp8LBitReader(data);
this.LosslessDecoder = new WebpLosslessDecoder(bitReader, memoryAllocator, configuration);
this.LosslessDecoder.DecodeImageStream(this.Vp8LDec, width, height, true);

Expand Down
40 changes: 20 additions & 20 deletions src/ImageSharp/Formats/Webp/AlphaEncoder.cs
Original file line number Diff line number Diff line change
Expand Up @@ -19,25 +19,25 @@ internal static class AlphaEncoder
/// Data is either compressed as lossless webp image or uncompressed.
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
/// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
/// <param name="frame">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
/// <param name="configuration">The global configuration.</param>
/// <param name="memoryAllocator">The memory manager.</param>
/// <param name="skipMetadata">Whether to skip metadata encoding.</param>
/// <param name="compress">Indicates, if the data should be compressed with the lossless webp compression.</param>
/// <param name="size">The size in bytes of the alpha data.</param>
/// <returns>The encoded alpha data.</returns>
public static IMemoryOwner<byte> EncodeAlpha<TPixel>(
Image<TPixel> image,
ImageFrame<TPixel> frame,
Configuration configuration,
MemoryAllocator memoryAllocator,
bool skipMetadata,
bool compress,
out int size)
where TPixel : unmanaged, IPixel<TPixel>
{
int width = image.Width;
int height = image.Height;
IMemoryOwner<byte> alphaData = ExtractAlphaChannel(image, configuration, memoryAllocator);
int width = frame.Width;
int height = frame.Height;
IMemoryOwner<byte> alphaData = ExtractAlphaChannel(frame, configuration, memoryAllocator);

if (compress)
{
Expand All @@ -58,9 +58,9 @@ public static IMemoryOwner<byte> EncodeAlpha<TPixel>(
// The transparency information will be stored in the green channel of the ARGB quadruplet.
// The green channel is allowed extra transformation steps in the specification -- unlike the other channels,
// that can improve compression.
using Image<Rgba32> alphaAsImage = DispatchAlphaToGreen(image, alphaData.GetSpan());
using ImageFrame<Rgba32> alphaAsFrame = DispatchAlphaToGreen(frame, alphaData.GetSpan());

size = lossLessEncoder.EncodeAlphaImageData(alphaAsImage, alphaData);
size = lossLessEncoder.EncodeAlphaImageData(alphaAsFrame, alphaData);

return alphaData;
}
Expand All @@ -73,19 +73,19 @@ public static IMemoryOwner<byte> EncodeAlpha<TPixel>(
/// Store the transparency in the green channel.
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
/// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
/// <param name="frame">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
/// <param name="alphaData">A byte sequence of length width * height, containing all the 8-bit transparency values in scan order.</param>
/// <returns>The transparency image.</returns>
private static Image<Rgba32> DispatchAlphaToGreen<TPixel>(Image<TPixel> image, Span<byte> alphaData)
/// <returns>The transparency frame.</returns>
private static ImageFrame<Rgba32> DispatchAlphaToGreen<TPixel>(ImageFrame<TPixel> frame, Span<byte> alphaData)
where TPixel : unmanaged, IPixel<TPixel>
{
int width = image.Width;
int height = image.Height;
Image<Rgba32> alphaAsImage = new(width, height);
int width = frame.Width;
int height = frame.Height;
ImageFrame<Rgba32> alphaAsFrame = new ImageFrame<Rgba32>(Configuration.Default, width, height);

for (int y = 0; y < height; y++)
{
Memory<Rgba32> rowBuffer = alphaAsImage.DangerousGetPixelRowMemory(y);
Memory<Rgba32> rowBuffer = alphaAsFrame.DangerousGetPixelRowMemory(y);
Span<Rgba32> pixelRow = rowBuffer.Span;
Span<byte> alphaRow = alphaData.Slice(y * width, width);
for (int x = 0; x < width; x++)
Expand All @@ -95,23 +95,23 @@ private static Image<Rgba32> DispatchAlphaToGreen<TPixel>(Image<TPixel> image, S
}
}

return alphaAsImage;
return alphaAsFrame;
}

/// <summary>
/// Extract the alpha data of the image.
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
/// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
/// <param name="frame">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
/// <param name="configuration">The global configuration.</param>
/// <param name="memoryAllocator">The memory manager.</param>
/// <returns>A byte sequence of length width * height, containing all the 8-bit transparency values in scan order.</returns>
private static IMemoryOwner<byte> ExtractAlphaChannel<TPixel>(Image<TPixel> image, Configuration configuration, MemoryAllocator memoryAllocator)
private static IMemoryOwner<byte> ExtractAlphaChannel<TPixel>(ImageFrame<TPixel> frame, Configuration configuration, MemoryAllocator memoryAllocator)
where TPixel : unmanaged, IPixel<TPixel>
{
Buffer2D<TPixel> imageBuffer = image.Frames.RootFrame.PixelBuffer;
int height = image.Height;
int width = image.Width;
Buffer2D<TPixel> imageBuffer = frame.PixelBuffer;
int height = frame.Height;
int width = frame.Width;
IMemoryOwner<byte> alphaDataBuffer = memoryAllocator.Allocate<byte>(width * height);
Span<byte> alphaData = alphaDataBuffer.GetSpan();

Expand Down
48 changes: 0 additions & 48 deletions src/ImageSharp/Formats/Webp/AnimationFrameData.cs

This file was deleted.

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