/// <summary>
/// Loads a Portable Network Graphics image.
/// </summary>
/// <param name="stream">The stream containing the image.</param>
/// <param name="rasterImage">The image storage.</param>
/// <exception cref="InvalidOperationException">If the stream represents an invalid or unsupported image format.</exception>
public static void Load(Stream stream, RasterImage rasterImage)
{
var decoder = new BinaryDecoder(stream);
if (decoder.ReadByte() != 137 || decoder.ReadByte() != 80 || decoder.ReadByte() != 78 || decoder.ReadByte() != 71)
{
throw new InvalidOperationException(Resources.FormatMessage(Resources.Key.InvalidFileMarker, "Portable Network Graphics"));
}
decoder.Skip(8);
if (decoder.ReadByte() != 'I' || decoder.ReadByte() != 'H' || decoder.ReadByte() != 'D' || decoder.ReadByte() != 'R')
{
throw new InvalidOperationException(Resources.GetMessage(Resources.Key.InvalidHeader));
}
var width = decoder.ReadInt32BigEndian();
var height = decoder.ReadInt32BigEndian();
rasterImage.Size = (width, height);
var colorDepth = decoder.ReadByte();
var colorType = decoder.ReadByte();
var bitsPerPixel = GetBitsPerPixel(rasterImage, colorDepth, colorType);
if (decoder.ReadByte() != 0 || decoder.ReadByte() != 0)
{
throw new InvalidOperationException(Resources.GetMessage(Resources.Key.InvalidFormat));
}
if (decoder.ReadByte() != 0)
{
throw new InvalidOperationException(Resources.GetMessage(Resources.Key.InterlacedPNGNotSupported));
}
decoder.Skip(4);
using var inflateStream = new DeflateStream(new PortableNetworkGraphicsDataStream(decoder), CompressionMode.Decompress);
var dataLength = (width * height * bitsPerPixel + 7) / 8;
byte[] data;
if (rasterImage.Data.Length >= dataLength)
{
data = rasterImage.Data;
}
else
{
data = new byte[dataLength];
}
var bytesPerPixel = (bitsPerPixel + 7) / 8;
var bytesPerLine = (width * bitsPerPixel + 7) / 8;
var bitPadding = bytesPerLine * 8 - width * bitsPerPixel;
var removePaddings = bitsPerPixel < 8 && bitPadding != 0;
var previousLine = new byte[bytesPerLine];
var currentLine = new byte[bytesPerLine];
for (int y = 0; y < height; y++)
{
var filterType = inflateStream.ReadByte();
var offset = 0;
var count = bytesPerLine;
for (;;)
{
var read = inflateStream.Read(currentLine, offset, count);
if (read == 0)
{
throw new EndOfStreamException();
}
offset += read;
count -= read;
if (count == 0)
{
break;
}
}
switch (filterType)
{
case 0:
break;
case 1:
for (int i = bytesPerPixel; i < bytesPerLine; i++)
{
currentLine[i] += currentLine[i - bytesPerPixel];
}
break;
case 2:
for (int i = 0; i < bytesPerLine; i++)
{
currentLine[i] += previousLine[i];
}
break;
case 3:
for (int i = 0; i < bytesPerPixel; i++)
{
currentLine[i] += (byte)(previousLine[i] >> 1);
}
for (int i = bytesPerPixel; i < bytesPerLine; i++)
{
currentLine[i] += (byte)((currentLine[i - bytesPerPixel] + previousLine[i]) >> 1);
}
break;
case 4:
for (int i = 0; i < bytesPerPixel; i++)
{
currentLine[i] += (byte)ComputePredictor(0, previousLine[i], 0);
}
for (int i = bytesPerPixel; i < bytesPerLine; i++)
{
currentLine[i] += (byte)ComputePredictor(currentLine[i - bytesPerPixel], previousLine[i], previousLine[i - bytesPerPixel]);
}
break;
default:
throw new InvalidOperationException(Resources.GetMessage(Resources.Key.InvalidFormat));
}
if (removePaddings)
{
throw new NotImplementedException();
}
else
{
Array.Copy(currentLine, 0, data, bytesPerLine * y, bytesPerLine);
}
var t = previousLine;
previousLine = currentLine;
currentLine = t;
}
rasterImage.Data = data;
}
