/// <summary>
/// Attempts to read 26 bytes of the stream.
/// </summary>
internal static FctlChunk Read(uint length, byte[] array)
{
var chunk = new FctlChunk
{
Length = length, //Chunk length, 4 bytes.
ChunkType = "fcTL" //Chunk type, 4 bytes.
};
using (var stream = new MemoryStream(array))
{
//Chunk details, 26 bytes.
chunk.SequenceNumber = BitHelper.ConvertEndian(stream.ReadUInt32());
chunk.Width = BitHelper.ConvertEndian(stream.ReadUInt32());
chunk.Height = BitHelper.ConvertEndian(stream.ReadUInt32());
chunk.XOffset = BitHelper.ConvertEndian(stream.ReadUInt32());
chunk.YOffset = BitHelper.ConvertEndian(stream.ReadUInt32());
chunk.DelayNum = BitHelper.ConvertEndian(stream.ReadUInt16());
chunk.DelayDen = BitHelper.ConvertEndian(stream.ReadUInt16());
chunk.DisposeOp = (Apng.DisposeOps)stream.ReadByte();
chunk.BlendOp = (Apng.BlendOps)stream.ReadByte();
}
return(chunk);
}
internal ApngFrame GetFrame(int index)
{
//Build each frame using:
//Starting blocks: IHDR, tIME, zTXt, tEXt, iTXt, pHYs, sPLT, (iCCP | sRGB), sBIT, gAMA, cHRM, PLTE, tRNS, hIST, bKGD.
//Image data: IDAT.
//End block: IEND.
var chunks = Chunks.Where(w => w.FrameGroupId == index).ToList();
var otherChunks = Chunks.Where(w => w.FrameGroupId == -1 && w.ChunkType != "IDAT").ToList();
if (!chunks.Any())
{
return(null);
}
var frame = new ApngFrame();
//First frame • Second frame
//Default image is part of the animation: fcTL + IDAT • fcTL + fdAT
//Default image isn't part of the animation: IDAT • fcTL + fdAT
if (chunks[0].ChunkType == "fcTL")
{
var fctl = FctlChunk.Read(chunks[0].Length, chunks[0].ChunkData);
frame.Delay = fctl.DelayNum == 0 ? 10 : (int)(fctl.DelayNum / (fctl.DelayDen == 0 ? 100d : fctl.DelayDen) * 1000d);
frame.Width = fctl.Width;
frame.Height = fctl.Height;
frame.Left = fctl.XOffset;
frame.Top = fctl.YOffset;
frame.ColorType = Ihdr.ColorType;
frame.BitDepth = Ihdr.BitDepth;
frame.DisposeOp = fctl.DisposeOp;
frame.BlendOp = fctl.BlendOp;
using (var stream = new MemoryStream())
{
//Png signature, 8 bytes.
stream.WriteBytes(new byte[] { 137, 80, 78, 71, 13, 10, 26, 10 });
//Image header chunk. 25 bytes.
Ihdr.Write(stream, fctl.Width, fctl.Height);
//Any other auxiliar chunks.
foreach (var other in otherChunks)
{
other.Write(stream);
}
//Frame has multiple chunks.
if (chunks.Count > 2)
{
var datas = new List <byte[]>();
//Data chunks.
for (var i = 1; i < chunks.Count; i++)
{
switch (chunks[i].ChunkType)
{
case "fdAT":
{
var fdat = FdatChunk.Read(chunks[i].Length, chunks[i].ChunkData);
datas.Add(fdat.FrameData);
break;
}
case "IDAT":
{
var idat = IdatChunk.Read(chunks[i].Length, chunks[i].ChunkData);
datas.Add(idat.FrameData);
break;
}
}
}
//Write combined frame data.
var length = datas.Sum(s => s.Length);
stream.WriteUInt32(BitHelper.ConvertEndian((uint)length)); //4 bytes.
stream.WriteBytes(Encoding.ASCII.GetBytes("IDAT")); //4 bytes.
stream.WriteBytes(datas.SelectMany(s => s).ToArray()); //XX bytes.
stream.WriteUInt32(BitHelper.ConvertEndian(CrcHelper.Calculate(stream.PeekBytes(stream.Position - (length + 4), length + 4)))); //CRC, 4 bytes.
}
else
{
switch (chunks[1].ChunkType)
{
case "fdAT":
{
var fdat = FdatChunk.Read(chunks[1].Length, chunks[1].ChunkData);
fdat.Write(stream);
break;
}
case "IDAT":
{
var idat = IdatChunk.Read(chunks[1].Length, chunks[1].ChunkData);
idat.Write(stream);
break;
}
}
}
//End chunk.
stream.WriteUInt32(BitHelper.ConvertEndian(0u)); //Chunk length, 4 bytes.
stream.WriteBytes(Encoding.ASCII.GetBytes("IEND")); //Chunk type, 4 bytes.
stream.WriteUInt32(BitHelper.ConvertEndian(CrcHelper.Calculate(stream.PeekBytes(stream.Position - 4, 4)))); //CRC, 4 bytes.
//Gets the whole Png.
frame.ImageData = stream.ToArray();
}
}
else
{
//This is not supposed to happen.
//All chunks with an FrameGroupId are grouped with a starting fcTL, ending with a IDAT or fdAT chunk.
LogWriter.Log(new Exception("Missing fcTL on frame number " + index), $"It was not possible to read frame number {index}");
return(null);
}
return(frame);
}
