){kind=link}
/// <summary>
/// Decodes a successive approximation refinement block, as specified in section G.1.2.
/// </summary>
/// <param name="decoder">The decoder instance</param>
/// <param name="h">The Huffman tree</param>
/// <param name="delta">The low transform offset</param>
private void Refine(JpegDecoderCore decoder, ref HuffmanTree h, int delta)
{
Block8x8F *b = this.pointers.Block;
// Refining a DC component is trivial.
if (this.zigStart == 0)
{
if (this.zigEnd != 0)
{
throw new ImageFormatException("Invalid state for zig DC component");
}
bool bit = decoder.DecodeBit();
if (bit)
{
int stuff = (int)Block8x8F.GetScalarAt(b, 0);
// int stuff = (int)b[0];
stuff |= delta;
// b[0] = stuff;
Block8x8F.SetScalarAt(b, 0, stuff);
}
return;
}
// Refining AC components is more complicated; see sections G.1.2.2 and G.1.2.3.
int zig = this.zigStart;
if (this.eobRun == 0)
{
for (; zig <= this.zigEnd; zig++)
{
bool done = false;
int z = 0;
byte val = decoder.DecodeHuffman(ref h);
int val0 = val >> 4;
int val1 = val & 0x0f;
switch (val1)
{
case 0:
if (val0 != 0x0f)
{
this.eobRun = (ushort)(1 << val0);
if (val0 != 0)
{
this.eobRun |= (ushort)decoder.DecodeBits(val0);
}
done = true;
}
break;
case 1:
z = delta;
bool bit = decoder.DecodeBit();
if (!bit)
{
z = -z;
}
break;
default:
throw new ImageFormatException("Unexpected Huffman code");
}
if (done)
{
break;
}
zig = this.RefineNonZeroes(decoder, zig, val0, delta);
if (zig > this.zigEnd)
{
throw new ImageFormatException($"Too many coefficients {zig} > {this.zigEnd}");
}
if (z != 0)
{
// b[Unzig[zig]] = z;
Block8x8F.SetScalarAt(b, this.pointers.Unzig[zig], z);
}
}
}
if (this.eobRun > 0)
{
this.eobRun--;
this.RefineNonZeroes(decoder, zig, -1, delta);
}
}
/// <summary>
/// Process the current block at (<see cref="bx"/>, <see cref="by"/>)
/// </summary>
/// <param name="decoder">The decoder</param>
/// <param name="i">The index of the scan</param>
/// <param name="compIndex">The component index</param>
/// <param name="hi">Horizontal sampling factor at the given component index</param>
private void ProcessBlockImpl(JpegDecoderCore decoder, int i, int compIndex, int hi)
{
var b = this.pointers.Block;
int huffmannIdx = (AcTableIndex * HuffmanTree.ThRowSize) + this.pointers.Scan[i].AcTableSelector;
if (this.ah != 0)
{
this.Refine(decoder, ref decoder.HuffmanTrees[huffmannIdx], 1 << this.al);
}
else
{
int zig = this.zigStart;
if (zig == 0)
{
zig++;
// Decode the DC coefficient, as specified in section F.2.2.1.
byte value =
decoder.DecodeHuffman(
ref decoder.HuffmanTrees[(DcTableIndex * HuffmanTree.ThRowSize) + this.pointers.Scan[i].DcTableSelector]);
if (value > 16)
{
throw new ImageFormatException("Excessive DC component");
}
int deltaDC = decoder.Bits.ReceiveExtend(value, decoder);
this.pointers.Dc[compIndex] += deltaDC;
// b[0] = dc[compIndex] << al;
Block8x8F.SetScalarAt(b, 0, this.pointers.Dc[compIndex] << this.al);
}
if (zig <= this.zigEnd && this.eobRun > 0)
{
this.eobRun--;
}
else
{
// Decode the AC coefficients, as specified in section F.2.2.2.
for (; zig <= this.zigEnd; zig++)
{
byte value = decoder.DecodeHuffman(ref decoder.HuffmanTrees[huffmannIdx]);
byte val0 = (byte)(value >> 4);
byte val1 = (byte)(value & 0x0f);
if (val1 != 0)
{
zig += val0;
if (zig > this.zigEnd)
{
break;
}
int ac = decoder.Bits.ReceiveExtend(val1, decoder);
// b[Unzig[zig]] = ac << al;
Block8x8F.SetScalarAt(b, this.pointers.Unzig[zig], ac << this.al);
}
else
{
if (val0 != 0x0f)
{
this.eobRun = (ushort)(1 << val0);
if (val0 != 0)
{
this.eobRun |= (ushort)decoder.DecodeBits(val0);
}
this.eobRun--;
break;
}
zig += 0x0f;
}
}
}
}
if (decoder.IsProgressive)
{
if (this.zigEnd != Block8x8F.ScalarCount - 1 || this.al != 0)
{
// We haven't completely decoded this 8x8 block. Save the coefficients.
// this.ProgCoeffs[compIndex][((@by * XNumberOfMCUs) * hi) + bx] = b.Clone();
decoder.ProgCoeffs[compIndex][((this.by * this.XNumberOfMCUs) * hi) + this.bx] = *b;
// At this point, we could execute the rest of the loop body to dequantize and
// perform the inverse DCT, to save early stages of a progressive image to the
// *image.YCbCr buffers (the whole point of progressive encoding), but in Go,
// the jpeg.Decode function does not return until the entire image is decoded,
// so we "continue" here to avoid wasted computation.
return;
}
}
// Dequantize, perform the inverse DCT and store the block to the image.
Block8x8F.UnZig(b, this.pointers.QuantiazationTable, this.pointers.Unzig);
DCT.TransformIDCT(ref *b, ref *this.pointers.Temp1, ref *this.pointers.Temp2);
var destChannel = decoder.GetDestinationChannel(compIndex);
var destArea = destChannel.GetOffsetedSubAreaForBlock(this.bx, this.by);
destArea.LoadColorsFrom(this.pointers.Temp1, this.pointers.Temp2);
}