/// <summary>
/// Initializes <see cref="SpectralBlocks"/>
/// </summary>
/// <param name="memoryManager">The <see cref="MemoryManager"/> to use for buffer allocations.</param>
/// <param name="decoder">The <see cref="GolangJpegDecoderCore"/> instance</param>
public void InitializeDerivedData(MemoryManager memoryManager, GolangJpegDecoderCore decoder)
{
// For 4-component images (either CMYK or YCbCrK), we only support two
// hv vectors: [0x11 0x11 0x11 0x11] and [0x22 0x11 0x11 0x22].
// Theoretically, 4-component JPEG images could mix and match hv values
// but in practice, those two combinations are the only ones in use,
// and it simplifies the applyBlack code below if we can assume that:
// - for CMYK, the C and K channels have full samples, and if the M
// and Y channels subsample, they subsample both horizontally and
// vertically.
// - for YCbCrK, the Y and K channels have full samples.
this.SizeInBlocks = decoder.ImageSizeInMCU.MultiplyBy(this.SamplingFactors);
if (this.Index == 0 || this.Index == 3)
{
this.SubSamplingDivisors = new Size(1, 1);
}
else
{
GolangComponent c0 = decoder.Components[0];
this.SubSamplingDivisors = c0.SamplingFactors.DivideBy(this.SamplingFactors);
}
this.SpectralBlocks = memoryManager.Allocate2D <Block8x8>(this.SizeInBlocks.Width, this.SizeInBlocks.Height, true);
}
private void DecodeBlocksAtMcuIndex(GolangJpegDecoderCore decoder, int mx, int my)
{
for (int scanIndex = 0; scanIndex < this.componentScanCount; scanIndex++)
{
this.ComponentIndex = this.pointers.ComponentScan[scanIndex].ComponentIndex;
GolangComponent component = decoder.Components[this.ComponentIndex];
this.hi = component.HorizontalSamplingFactor;
int vi = component.VerticalSamplingFactor;
for (int j = 0; j < this.hi * vi; j++)
{
if (this.componentScanCount != 1)
{
this.bx = (this.hi * mx) + (j % this.hi);
this.by = (vi * my) + (j / this.hi);
}
else
{
int q = decoder.MCUCountX * this.hi;
this.bx = this.blockCounter % q;
this.by = this.blockCounter / q;
this.blockCounter++;
if (this.bx * 8 >= decoder.ImageWidth || this.by * 8 >= decoder.ImageHeight)
{
continue;
}
}
// Find the block at (bx,by) in the component's buffer:
ref Block8x8 blockRefOnHeap = ref component.GetBlockReference(this.bx, this.by);
// Copy block to stack
this.data.Block = blockRefOnHeap;
if (!decoder.InputProcessor.ReachedEOF)
{
this.DecodeBlock(decoder, scanIndex);
}
// Store the result block:
blockRefOnHeap = this.data.Block;
}
}