/// <summary>
/// Reads the gif comments.
/// </summary>
private void ReadComments()
{
int length;
var stringBuilder = new StringBuilder();
while ((length = this.stream.ReadByte()) != 0)
{
if (length > GifConstants.MaxCommentSubBlockLength)
{
GifThrowHelper.ThrowInvalidImageContentException($"Gif comment length '{length}' exceeds max '{GifConstants.MaxCommentSubBlockLength}' of a comment data block");
}
if (this.IgnoreMetadata)
{
this.stream.Seek(length, SeekOrigin.Current);
continue;
}
using (IManagedByteBuffer commentsBuffer = this.MemoryAllocator.AllocateManagedByteBuffer(length))
{
this.stream.Read(commentsBuffer.Array, 0, length);
string commentPart = GifConstants.Encoding.GetString(commentsBuffer.Array, 0, length);
stringBuilder.Append(commentPart);
}
}
if (stringBuilder.Length > 0)
{
this.gifMetadata.Comments.Add(stringBuilder.ToString());
}
}
/// <summary>
/// Reads the image descriptor.
/// </summary>
private void ReadImageDescriptor()
{
this.stream.Read(this.buffer, 0, 9);
this.imageDescriptor = GifImageDescriptor.Parse(this.buffer);
if (this.imageDescriptor.Height == 0 || this.imageDescriptor.Width == 0)
{
GifThrowHelper.ThrowInvalidImageContentException("Width or height should not be 0");
}
}
/// <summary>
/// Decodes and decompresses all pixel indices from the stream.
/// </summary>
/// <param name="minCodeSize">Minimum code size of the data.</param>
/// <param name="pixels">The pixel array to decode to.</param>
public void DecodePixels(int minCodeSize, Buffer2D <byte> pixels)
{
// Calculate the clear code. The value of the clear code is 2 ^ minCodeSize
int clearCode = 1 << minCodeSize;
// It is possible to specify a larger LZW minimum code size than the palette length in bits
// which may leave a gap in the codes where no colors are assigned.
// http://www.matthewflickinger.com/lab/whatsinagif/lzw_image_data.asp#lzw_compression
if (minCodeSize < 2 || clearCode > MaxStackSize)
{
// Don't attempt to decode the frame indices.
// Theoretically we could determine a min code size from the length of the provided
// color palette but we won't bother since the image is most likely corrupted.
GifThrowHelper.ThrowInvalidImageContentException("Gif Image does not contain a valid LZW minimum code.");
}
// The resulting index table length.
int width = pixels.Width;
int height = pixels.Height;
int length = width * height;
int codeSize = minCodeSize + 1;
// Calculate the end code
int endCode = clearCode + 1;
// Calculate the available code.
int availableCode = clearCode + 2;
// Jillzhangs Code see: http://giflib.codeplex.com/
// Adapted from John Cristy's ImageMagick.
int code;
int oldCode = NullCode;
int codeMask = (1 << codeSize) - 1;
int bits = 0;
int top = 0;
int count = 0;
int bi = 0;
int xyz = 0;
int data = 0;
int first = 0;
ref int prefixRef = ref MemoryMarshal.GetReference(this.prefix.GetSpan());
/// <inheritdoc/>
public Image <TPixel> Decode <TPixel>(Configuration configuration, Stream stream)
where TPixel : unmanaged, IPixel <TPixel>
{
var decoder = new GifDecoderCore(configuration, this);
try
{
return(decoder.Decode <TPixel>(stream));
}
catch (InvalidMemoryOperationException ex)
{
Size dims = decoder.Dimensions;
GifThrowHelper.ThrowInvalidImageContentException($"Can not decode image. Failed to allocate buffers for possibly degenerate dimensions: {dims.Width}x{dims.Height}.", ex);
// Not reachable, as the previous statement will throw a exception.
return(null);
}
}