public static Png Open(Stream stream, PngOpenerSettings settings)
{
if (stream == null)
{
throw new ArgumentNullException(nameof(stream));
}
if (!stream.CanRead)
{
throw new ArgumentException($"The provided stream of type {stream.GetType().FullName} was not readable.");
}
var validHeader = HasValidHeader(stream);
if (!validHeader.IsValid)
{
throw new ArgumentException($"The provided stream did not start with the PNG header. Got {validHeader}.");
}
var crc = new byte[4];
var imageHeader = ReadImageHeader(stream, crc);
var hasEncounteredImageEnd = false;
Palette palette = null;
using (var output = new MemoryStream())
{
using (var memoryStream = new MemoryStream())
{
while (TryReadChunkHeader(stream, out var header))
{
if (hasEncounteredImageEnd)
{
if (settings?.DisallowTrailingData == true)
{
throw new InvalidOperationException($"Found another chunk {header} after already reading the IEND chunk.");
}
break;
}
var bytes = new byte[header.Length];
var read = stream.Read(bytes, 0, bytes.Length);
if (read != bytes.Length)
{
throw new InvalidOperationException($"Did not read {header.Length} bytes for the {header} header, only found: {read}.");
}
if (header.IsCritical)
{
switch (header.Name)
{
case "PLTE":
if (header.Length % 3 != 0)
{
throw new InvalidOperationException($"Palette data must be multiple of 3, got {header.Length}.");
}
// Ignore palette data unless the header.ColorType indicates that the image is paletted.
if (imageHeader.ColorType.HasFlag(ColorType.PaletteUsed))
{
palette = new Palette(bytes);
}
break;
case "IDAT":
memoryStream.Write(bytes, 0, bytes.Length);
break;
case "IEND":
hasEncounteredImageEnd = true;
break;
default:
throw new NotSupportedException($"Encountered critical header {header} which was not recognised.");
}
}
else
{
switch (header.Name)
{
case "tRNS":
// Add transparency to palette, if the PLTE chunk has been read.
if (palette != null)
{
palette.SetAlphaValues(bytes);
}
break;
}
}
read = stream.Read(crc, 0, crc.Length);
if (read != 4)
{
throw new InvalidOperationException($"Did not read 4 bytes for the CRC, only found: {read}.");
}
var result = (int)Crc32.Calculate(Encoding.ASCII.GetBytes(header.Name), bytes);
var crcActual = (crc[0] << 24) + (crc[1] << 16) + (crc[2] << 8) + crc[3];
if (result != crcActual)
{
throw new InvalidOperationException($"CRC calculated {result} did not match file {crcActual} for chunk: {header.Name}.");
}
settings?.ChunkVisitor?.Visit(stream, imageHeader, header, bytes, crc);
}
memoryStream.Flush();
memoryStream.Seek(2, SeekOrigin.Begin);
using (var deflateStream = new DeflateStream(memoryStream, CompressionMode.Decompress))
{
deflateStream.CopyTo(output);
deflateStream.Close();
}
}
var bytesOut = output.ToArray();
var(bytesPerPixel, samplesPerPixel) = Decoder.GetBytesAndSamplesPerPixel(imageHeader);
bytesOut = Decoder.Decode(bytesOut, imageHeader, bytesPerPixel, samplesPerPixel);
return(new Png(imageHeader, new RawPngData(bytesOut, bytesPerPixel, palette, imageHeader), palette?.HasAlphaValues ?? false));
}
}
/// <summary>
/// Create a new <see cref="RawPngData"/>.
/// </summary>
/// <param name="data">The decoded pixel data as bytes.</param>
/// <param name="bytesPerPixel">The number of bytes in each pixel.</param>
/// <param name="width">The width of the image in pixels.</param>
/// <param name="interlaceMethod">The interlace method used.</param>
/// <param name="palette">The palette for images using indexed colors.</param>
/// <param name="colorType">The color type.</param>
public RawPngData(byte[] data, int bytesPerPixel, int width, InterlaceMethod interlaceMethod, Palette palette, ColorType colorType)
{
if (width < 0)
{
throw new ArgumentOutOfRangeException($"Width must be greater than or equal to 0, got {width}.");
}
this.data = data ?? throw new ArgumentNullException(nameof(data));
this.bytesPerPixel = bytesPerPixel;
this.width = width;
this.palette = palette;
this.colorType = colorType;
rowOffset = interlaceMethod == InterlaceMethod.Adam7 ? 0 : 1;
}