internal void read(BigEndianBinaryReader reader)
{
width = reader.ReadInt32();
height = reader.ReadInt32();
bitdepth = reader.ReadByte();
colortype = (ColorType)reader.ReadByte();
method = reader.ReadByte();
filter = reader.ReadByte();
interlace = reader.ReadByte();
}
void readImagedata(BigEndianBinaryReader reader, int length)
{
int width = ihdr.width;
int height = ihdr.height;
int bitDepth = ihdr.bitdepth;
int samples = ihdr.getSamples();
bool interlaced = ihdr.isInterlaced();
SubInputStream sis = new SubInputStream(reader.BaseStream, length);
InflaterInputStream iis = new InflaterInputStream(sis);
Defilterer d = new Defilterer(iis, bitDepth, samples, width);
//todo: interlacing
imageOutput.start(this);
d.defilter(0, 0, 1, 1, width, height, imageOutput);
imageOutput.finish();
}
void readPLTE(BigEndianBinaryReader reader, int length)
{
if(length == 0)
throw new BadImageFormatException("PLTE chunk cannot be empty");
if(length % 3 != 0)
throw new BadImageFormatException("PLTE chunk length indivisible by 3: " + length);
int size = length / 3;
if(size > 256)
throw new BadImageFormatException("Too many palette entries: " + size);
switch (ihdr.colortype)
{
case ColorType.PALETTE:
if (size > (1 << ihdr.bitdepth))
throw new BadImageFormatException("Too many palette entries: " + size);
palette = new byte[length];
reader.Read(palette, 0, length);
break;
default:
throw new BadImageFormatException("PLTE chunk found in non-palette colorformat image");
}
}
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;
}
}
