/// <summary>
/// Writes decoded pixel to buffer at a given position.
/// </summary>
/// <param name="buffer">The buffer to write to.</param>
/// <param name="offset">The position to write to.</param>
/// <returns>The number of bytes written.</returns>
public int WriteTo(Span <byte> buffer, int offset)
{
if (this.Length == 0)
{
return(0);
}
if (this.Length == 1)
{
buffer[offset] = this.value;
return(1);
}
LzwString e = this;
int endIdx = this.Length - 1;
if (endIdx >= buffer.Length)
{
TiffThrowHelper.ThrowImageFormatException("Error reading lzw compressed stream. Either pixel buffer to write to is to small or code length is invalid!");
}
for (int i = endIdx; i >= 0; i--)
{
buffer[offset + i] = e.value;
e = e.previous;
}
return(this.Length);
}
private void AddStringToTable(LzwString lzwString)
{
if (this.tableLength > this.table.Length)
{
TiffThrowHelper.ThrowImageFormatException($"TIFF LZW with more than {MaxBits} bits per code encountered (table overflow)");
}
this.table[this.tableLength++] = lzwString;
if (this.tableLength > this.maxCode)
{
this.bitsPerCode++;
if (this.bitsPerCode > MaxBits)
{
// Continue reading MaxBits (12 bit) length codes.
this.bitsPerCode = MaxBits;
}
this.bitMask = BitmaskFor(this.bitsPerCode);
this.maxCode = this.MaxCode();
}
if (lzwString.Length > this.maxString)
{
this.maxString = lzwString.Length;
}
}
private LzwString(byte value, byte firstChar, int length, LzwString previous)
{
this.value = value;
this.FirstChar = firstChar;
this.Length = length;
this.previous = previous;
}
/// <summary>
/// Decodes and decompresses all pixel indices from the stream.
/// </summary>
/// <param name="pixels">The pixel array to decode to.</param>
public void DecodePixels(Span <byte> pixels)
{
// Adapted from the pseudo-code example found in the TIFF 6.0 Specification, 1992.
// See Section 13: "LZW Compression"/"LZW Decoding", page 61+
int code;
int offset = 0;
while ((code = this.GetNextCode()) != EoiCode)
{
if (code == ClearCode)
{
this.Init();
code = this.GetNextCode();
if (code == EoiCode)
{
break;
}
if (this.table[code] == null)
{
TiffThrowHelper.ThrowImageFormatException($"Corrupted TIFF LZW: code {code} (table size: {this.tableLength})");
}
offset += this.table[code].WriteTo(pixels, offset);
}
else
{
if (this.table[this.oldCode] == null)
{
TiffThrowHelper.ThrowImageFormatException($"Corrupted TIFF LZW: code {this.oldCode} (table size: {this.tableLength})");
}
if (this.IsInTable(code))
{
offset += this.table[code].WriteTo(pixels, offset);
this.AddStringToTable(this.table[this.oldCode].Concatenate(this.table[code].FirstChar));
}
else
{
LzwString outString = this.table[this.oldCode].Concatenate(this.table[this.oldCode].FirstChar);
offset += outString.WriteTo(pixels, offset);
this.AddStringToTable(outString);
}
}
this.oldCode = code;
if (offset >= pixels.Length)
{
break;
}
}
}