/// <summary>
/// Attempts to read 16 bytes of the stream.
/// </summary>
internal static ActlChunk Read(Stream stream)
{
var chunk = new ActlChunk
{
Length = BitHelper.ConvertEndian(stream.ReadUInt32()), //Chunk length, 4 bytes.
ChunkType = Encoding.ASCII.GetString(stream.ReadBytes(4)) //Chunk type, 4 bytes.
};
//If the second chunk is not the animation control (acTL), it means that this is a normal PNG.
if (chunk.ChunkType != "acTL")
{
return(null);
}
//var pos = stream.Position;
//chunk.ChunkData = stream.ReadBytes(chunk.Length);
//stream.Position = pos;
//Chunk details + CRC, 8 bytes + 4 bytes.
chunk.NumFrames = BitHelper.ConvertEndian(stream.ReadUInt32());
chunk.NumPlays = BitHelper.ConvertEndian(stream.ReadUInt32());
chunk.Crc = BitHelper.ConvertEndian(stream.ReadUInt32());
return(chunk);
}
internal bool ReadFrames()
{
//Png header, 8 bytes.
if (!InternalStream.ReadBytes(8).SequenceEqual(new byte[] { 137, 80, 78, 71, 13, 10, 26, 10 }))
{
throw new Exception("Invalid file format, expected PNG signature not found.");
}
//IHDR chunk, 25 bytes.
Ihdr = IhdrChunk.Read(InternalStream);
//aCTl chunk, 16 bytes.
Actl = ActlChunk.Read(InternalStream);
//If there's no animation control chunk, it's a normal Png.
if (Actl == null)
{
return(false);
}
var masterSequence = 0;
var frameGroupId = -1;
//Read frames.
while (InternalStream.CanRead)
{
//Tries to read any chunk, except IEND.
var chunk = Chunk.Read(InternalStream, masterSequence++);
//End reached, prematurely or not.
if (chunk == null || chunk.ChunkType == "IEND")
{
break;
}
//Chunks can be grouped into frames.
if (new[] { "fcTL", "fdAT", "IDAT" }.Contains(chunk.ChunkType))
{
if (chunk.ChunkType == "fcTL")
{
frameGroupId++;
}
chunk.FrameGroupId = frameGroupId;
}
Chunks.Add(chunk);
}
return(true);
}
