public override void ProcessScan(ref JpegReader reader, JpegScanHeader scanHeader)
{
JpegFrameHeader frameHeader = _frameHeader;
JpegBlockOutputWriter?outputWriter = Decoder.GetOutputWriter();
if (frameHeader.Components is null)
{
ThrowInvalidDataException();
}
if (scanHeader.Components is null)
{
ThrowInvalidDataException();
}
if (outputWriter is null)
{
ThrowInvalidDataException();
}
// Resolve each component
Span <JpegArithmeticDecodingComponent> components = _components.AsSpan(0, InitDecodeComponents(frameHeader, scanHeader, _components));
foreach (JpegArithmeticDecodingComponent component in _components)
{
component.DcPredictor = 0;
component.DcContext = 0;
component.DcStatistics?.Reset();
component.AcStatistics?.Reset();
}
Reset();
// Prepare
int maxHorizontalSampling = _maxHorizontalSampling;
int maxVerticalSampling = _maxVerticalSampling;
int mcusBeforeRestart = _restartInterval;
int mcusPerLine = _mcusPerLine;
int mcusPerColumn = _mcusPerColumn;
int levelShift = _levelShift;
JpegBitReader bitReader = new JpegBitReader(reader.RemainingBytes);
// DCT Block
JpegBlock8x8F blockFBuffer = default;
JpegBlock8x8F outputFBuffer = default;
JpegBlock8x8F tempFBuffer = default;
JpegBlock8x8 outputBuffer;
for (int rowMcu = 0; rowMcu < mcusPerColumn; rowMcu++)
{
int offsetY = rowMcu * maxVerticalSampling;
for (int colMcu = 0; colMcu < mcusPerLine; colMcu++)
{
int offsetX = colMcu * maxHorizontalSampling;
// Scan an interleaved mcu... process components in order
foreach (JpegArithmeticDecodingComponent component in components)
{
int index = component.ComponentIndex;
int h = component.HorizontalSamplingFactor;
int v = component.VerticalSamplingFactor;
int hs = component.HorizontalSubsamplingFactor;
int vs = component.VerticalSubsamplingFactor;
for (int y = 0; y < v; y++)
{
int blockOffsetY = (offsetY + y) * 8;
for (int x = 0; x < h; x++)
{
// Read MCU
outputBuffer = default;
ReadBlock(ref bitReader, component, ref outputBuffer);
// Dequantization
DequantizeBlockAndUnZigZag(component.QuantizationTable, ref outputBuffer, ref blockFBuffer);
// IDCT
FastFloatingPointDCT.TransformIDCT(ref blockFBuffer, ref outputFBuffer, ref tempFBuffer);
// Level shift
ShiftDataLevel(ref outputFBuffer, ref outputBuffer, levelShift);
// CopyToOutput
WriteBlock(outputWriter, ref Unsafe.As <JpegBlock8x8, short>(ref outputBuffer), index, (offsetX + x) * 8, blockOffsetY, hs, vs);
}
}
}
// Handle restart
if (_restartInterval > 0 && (--mcusBeforeRestart) == 0)
{
bitReader.AdvanceAlignByte();
JpegMarker marker = bitReader.TryReadMarker();
if (marker == JpegMarker.EndOfImage)
{
int bytesConsumedEoi = reader.RemainingByteCount - bitReader.RemainingBits / 8;
reader.TryAdvance(bytesConsumedEoi - 2);
return;
}
if (!marker.IsRestartMarker())
{
throw new InvalidOperationException("Expect restart marker.");
}
mcusBeforeRestart = _restartInterval;
foreach (JpegArithmeticDecodingComponent component in components)
{
component.DcPredictor = 0;
component.DcContext = 0;
component.DcStatistics?.Reset();
component.AcStatistics?.Reset();
}
Reset();
}
}
}
bitReader.AdvanceAlignByte();
int bytesConsumed = reader.RemainingByteCount - bitReader.RemainingBits / 8;
if (bitReader.TryPeekMarker() != 0)
{
if (!bitReader.TryPeekMarker().IsRestartMarker())
{
bytesConsumed -= 2;
}
}
reader.TryAdvance(bytesConsumed);
}
protected static void DequantizeBlockAndUnZigZag(JpegQuantizationTable quantizationTable, ref JpegBlock8x8 input, ref JpegBlock8x8F output)
{
Debug.Assert(!quantizationTable.IsEmpty);
ref ushort elementRef = ref MemoryMarshal.GetReference(quantizationTable.Elements);
