private int CalculateScanlineStep(PngColorTypeInformation colorTypeInformation)
{
int scanlineStep = 1;
if (header.BitDepth >= 8)
{
scanlineStep = (colorTypeInformation.ChannelsPerColor * header.BitDepth) / 8;
}
return(scanlineStep);
}
private int CalculateScanlineLength(PngColorTypeInformation colorTypeInformation)
{
int scanlineLength = header.Width * header.BitDepth * colorTypeInformation.ChannelsPerColor;
int amount = scanlineLength % 8;
if (amount != 0)
{
scanlineLength += 8 - amount;
}
return(scanlineLength / 8);
}
public void Decode(Image2 image, Stream stream)
{
Image2 currentImage = image;
currentStream = stream;
currentStream.Seek(8, SeekOrigin.Current);
bool isEndChunkReached = false;
byte[] palette = null;
byte[] paletteAlpha = null;
using (MemoryStream dataStream = new MemoryStream()){
PngChunk currentChunk;
while ((currentChunk = ReadChunk()) != null)
{
if (isEndChunkReached)
{
throw new Exception("Image does not end with end chunk.");
}
if (currentChunk.Type == PngChunkTypes.Header)
{
ReadHeaderChunk(currentChunk.Data);
ValidateHeader();
}
else if (currentChunk.Type == PngChunkTypes.Physical)
{
ReadPhysicalChunk(currentImage, currentChunk.Data);
}
else if (currentChunk.Type == PngChunkTypes.Data)
{
dataStream.Write(currentChunk.Data, 0, currentChunk.Data.Length);
}
else if (currentChunk.Type == PngChunkTypes.Palette)
{
palette = currentChunk.Data;
}
else if (currentChunk.Type == PngChunkTypes.PaletteAlpha)
{
paletteAlpha = currentChunk.Data;
}
else if (currentChunk.Type == PngChunkTypes.Text)
{
ReadTextChunk(currentImage, currentChunk.Data);
}
else if (currentChunk.Type == PngChunkTypes.End)
{
isEndChunkReached = true;
}
}
if (header.Width > image.MaxWidth || header.Height > image.MaxHeight)
{
throw new ArgumentOutOfRangeException($"The input png '{header.Width}x{header.Height}' is bigger than the " +
$"max allowed size '{image.MaxWidth}x{image.MaxHeight}'");
}
Color2[] pixels = new Color2[header.Width * header.Height];
PngColorTypeInformation colorTypeInformation = colorTypes[header.ColorType];
if (colorTypeInformation != null)
{
IColorReader colorReader = colorTypeInformation.CreateColorReader(palette, paletteAlpha);
ReadScanlines(dataStream, pixels, colorReader, colorTypeInformation);
}
image.SetPixels(header.Width, header.Height, pixels);
}
}
private void ReadScanlines(MemoryStream dataStream, Color2[] pixels, IColorReader colorReader,
PngColorTypeInformation colorTypeInformation)
{
dataStream.Position = 0;
int scanlineLength = CalculateScanlineLength(colorTypeInformation);
int scanlineStep = CalculateScanlineStep(colorTypeInformation);
byte[] lastScanline = new byte[scanlineLength];
byte[] currentScanline = new byte[scanlineLength];
int filter = 0, column = -1;
using (ZlibInflateStream compressedStream = new ZlibInflateStream(dataStream)){
int readByte;
while ((readByte = compressedStream.ReadByte()) >= 0)
{
if (column == -1)
{
filter = readByte;
column++;
}
else
{
currentScanline[column] = (byte)readByte;
byte a;
byte c;
if (column >= scanlineStep)
{
a = currentScanline[column - scanlineStep];
c = lastScanline[column - scanlineStep];
}
else
{
a = 0;
c = 0;
}
byte b = lastScanline[column];
if (filter == 1)
{
currentScanline[column] = (byte)(currentScanline[column] + a);
}
else if (filter == 2)
{
currentScanline[column] = (byte)(currentScanline[column] + b);
}
else if (filter == 3)
{
currentScanline[column] = (byte)(currentScanline[column] + (byte)((a + b) / 2));
}
else if (filter == 4)
{
currentScanline[column] = (byte)(currentScanline[column] + PaethPredicator(a, b, c));
}
column++;
if (column == scanlineLength)
{
colorReader.ReadScanline(currentScanline, pixels, header);
column = -1;
Swap(ref currentScanline, ref lastScanline);
}
}
}
}
}
