/// <summary>
/// Initializes a new instance of the <see cref="ScanDecoder"/> class.
/// </summary>
/// <param name="stream">The input stream.</param>
/// <param name="frame">The image frame.</param>
/// <param name="dcHuffmanTables">The DC Huffman tables.</param>
/// <param name="acHuffmanTables">The AC Huffman tables.</param>
/// <param name="fastACTables">The fast AC decoding tables.</param>
/// <param name="componentIndex">The component index within the array.</param>
/// <param name="componentsLength">The length of the components. Different to the array length.</param>
/// <param name="restartInterval">The reset interval.</param>
/// <param name="spectralStart">The spectral selection start.</param>
/// <param name="spectralEnd">The spectral selection end.</param>
/// <param name="successiveHigh">The successive approximation bit high end.</param>
/// <param name="successiveLow">The successive approximation bit low end.</param>
public ScanDecoder(
DoubleBufferedStreamReader stream,
PdfJsFrame frame,
PdfJsHuffmanTables dcHuffmanTables,
PdfJsHuffmanTables acHuffmanTables,
FastACTables fastACTables,
int componentIndex,
int componentsLength,
int restartInterval,
int spectralStart,
int spectralEnd,
int successiveHigh,
int successiveLow)
{
this.dctZigZag = ZigZag.CreateUnzigTable();
this.stream = stream;
this.frame = frame;
this.dcHuffmanTables = dcHuffmanTables;
this.acHuffmanTables = acHuffmanTables;
this.fastACTables = fastACTables;
this.components = frame.Components;
this.marker = JpegConstants.Markers.XFF;
this.markerPosition = 0;
this.componentIndex = componentIndex;
this.componentsLength = componentsLength;
this.restartInterval = restartInterval;
this.spectralStart = spectralStart;
this.spectralEnd = spectralEnd;
this.successiveHigh = successiveHigh;
this.successiveLow = successiveLow;
}
private void DecodeScanBaseline(
PdfJsHuffmanTables dcHuffmanTables,
PdfJsHuffmanTables acHuffmanTables,
PdfJsFrameComponent[] components,
int componentsLength,
DoubleBufferedStreamReader stream)
{
if (componentsLength == 1)
{
PdfJsFrameComponent component = components[this.compIndex];
ref short blockDataRef = ref MemoryMarshal.GetReference(MemoryMarshal.Cast <Block8x8, short>(component.SpectralBlocks.Span));
ref PdfJsHuffmanTable dcHuffmanTable = ref dcHuffmanTables[component.DCHuffmanTableId];
/// <summary>
/// Decodes the spectral scan
/// </summary>
/// <param name="frame">The image frame</param>
/// <param name="stream">The input stream</param>
/// <param name="dcHuffmanTables">The DC Huffman tables</param>
/// <param name="acHuffmanTables">The AC Huffman tables</param>
/// <param name="components">The scan components</param>
/// <param name="componentIndex">The component index within the array</param>
/// <param name="componentsLength">The length of the components. Different to the array length</param>
/// <param name="resetInterval">The reset interval</param>
/// <param name="spectralStart">The spectral selection start</param>
/// <param name="spectralEnd">The spectral selection end</param>
/// <param name="successivePrev">The successive approximation bit high end</param>
/// <param name="successive">The successive approximation bit low end</param>
public void DecodeScan(
PdfJsFrame frame,
DoubleBufferedStreamReader stream,
PdfJsHuffmanTables dcHuffmanTables,
PdfJsHuffmanTables acHuffmanTables,
PdfJsFrameComponent[] components,
int componentIndex,
int componentsLength,
ushort resetInterval,
int spectralStart,
int spectralEnd,
int successivePrev,
int successive)
{
this.dctZigZag = ZigZag.CreateUnzigTable();
this.markerBuffer = new byte[2];
this.compIndex = componentIndex;
this.specStart = spectralStart;
this.specEnd = spectralEnd;
this.successiveState = successive;
this.endOfStreamReached = false;
this.unexpectedMarkerReached = false;
bool progressive = frame.Progressive;
this.mcusPerLine = frame.McusPerLine;
this.mcu = 0;
int mcuExpected;
if (componentsLength == 1)
{
mcuExpected = components[this.compIndex].WidthInBlocks * components[this.compIndex].HeightInBlocks;
}
else
{
mcuExpected = this.mcusPerLine * frame.McusPerColumn;
}
while (this.mcu < mcuExpected)
{
// Reset interval stuff
this.mcuToRead = resetInterval != 0 ? Math.Min(mcuExpected - this.mcu, resetInterval) : mcuExpected;
for (int i = 0; i < components.Length; i++)
{
PdfJsFrameComponent c = components[i];
c.Pred = 0;
}
this.eobrun = 0;
if (!progressive)
{
this.DecodeScanBaseline(dcHuffmanTables, acHuffmanTables, components, componentsLength, stream);
}
else
{
bool isAc = this.specStart != 0;
bool isFirst = successivePrev == 0;
PdfJsHuffmanTables huffmanTables = isAc ? acHuffmanTables : dcHuffmanTables;
this.DecodeScanProgressive(huffmanTables, isAc, isFirst, components, componentsLength, stream);
}
// Reset
// TODO: I do not understand why these values are reset? We should surely be tracking the bits across mcu's?
this.bitsCount = 0;
this.bitsData = 0;
this.unexpectedMarkerReached = false;
// Some images include more scan blocks than expected, skip past those and
// attempt to find the next valid marker
PdfJsFileMarker fileMarker = PdfJsJpegDecoderCore.FindNextFileMarker(this.markerBuffer, stream);
byte marker = fileMarker.Marker;
// RSTn - We've already read the bytes and altered the position so no need to skip
if (marker >= PdfJsJpegConstants.Markers.RST0 && marker <= PdfJsJpegConstants.Markers.RST7)
{
continue;
}
if (!fileMarker.Invalid)
{
// We've found a valid marker.
// Rewind the stream to the position of the marker and break
stream.Position = fileMarker.Position;
break;
}
#if DEBUG
Debug.WriteLine($"DecodeScan - Unexpected MCU data at {stream.Position}, next marker is: {fileMarker.Marker:X}");
#endif
}
}
