public void defilter(int xOffset, int yOffset,
int xStep, int yStep,
int passWidth, int passHeight, IPngImageOutput output)
{
if (passWidth == 0 || passHeight == 0)
return;
int bytesPerRow = (bitDepth * samples * passWidth + 7) / 8;
bool isShort = bitDepth == 16;
int rowSize = bytesPerRow + bpp;
byte[] prev = new byte[rowSize];
byte[] cur = new byte[rowSize];
for (int srcY = 0, dstY = yOffset; srcY < passHeight; srcY++, dstY += yStep) {
int filterType = stream.ReadByte();
if(filterType == -1)
throw new EndOfStreamException();
fillBuffer(cur, bpp, bytesPerRow);
defilter(cur, prev, bpp, filterType);
output.writeLine(cur, bpp);
byte[] tmp = cur;
cur = prev;
prev = tmp;
}
}
public void read(Stream stream, IPngImageOutput imageOutput)
{
this.imageOutput = imageOutput;
CRCInputStream crcstream = new CRCInputStream(stream);
BigEndianBinaryReader reader = new BigEndianBinaryReader(crcstream);
//check signature
if(!IsPng(stream))
throw new BadImageFormatException("signature invalid");
//sort of an inefficient way to do it, but at 3:30am itll do fine
MemoryStream msIDAT = new MemoryStream();
int state = 0;
for(; ; ) {
bool skipChunk = false;
int chunkLen = reader.ReadInt32();
crcstream.resetCrc();
int chunkType = reader.ReadInt32();
//expect an IHDR
if(state == 0) {
if(chunkType != type_IHDR) throw new BadImageFormatException("did not encounter initial IHDR");
ihdr.read(reader);
//validate ihdr: do we support interlaced images for now?
state = 1;
} else
if(state == 1) {
switch(chunkType) {
case type_IEND:
//actually do the imagedata read now
msIDAT.Position = 0;
readImagedata(new BigEndianBinaryReader(msIDAT), (int)msIDAT.Length);
state = 2;
break;
case type_IHDR:
throw new BadImageFormatException("encountered supernumerary IHDR");
case type_IDAT:
byte[] buf = new byte[chunkLen];
reader.BaseStream.Read(buf, 0, chunkLen);
msIDAT.Write(buf, 0, chunkLen);
break;
case type_PLTE:
readPLTE(reader, chunkLen);
break;
default: {
skipChunk = true;
byte[] bytes = System.BitConverter.GetBytes(chunkType);
//debug: which chunk was skipped?
//Console.WriteLine("{0}{1}{2}{3}", (char)bytes[3], (char)bytes[2], (char)bytes[1], (char)bytes[0]);
}
break;
}
}
//if we skipped the chunk, skip the bytes.
if(skipChunk) {
reader.BaseStream.Position += chunkLen + 4; //+4 for the crc
} else {
//if we didnt skip it, do the crc validation
if(!skipChunk) {
int actualCrc = (int)crcstream.Value;
int targetCrc = reader.ReadInt32();
if(actualCrc != targetCrc)
throw new BadImageFormatException("Crc failure");
}
}
if(state == 2) break;
}
}
