private static void ParseInterlaced(byte[] data, PngFileHeader fileHeader, int bytesPerPixel, IColorReader reader, byte[] pixels)
{
const int passes = 7;
var readOffset = 0;
var done = false;
var r = new Span <byte>(data);
for (var i = 0; i < passes; i++)
{
int columns = Adam7.ComputeColumns(fileHeader.Width, i);
if (columns == 0)
{
continue;
}
int rowSize = GetScanlineLength(columns, fileHeader) + 1;
// Read rows.
Span <byte> prevRowData = null;
for (int row = Adam7.FirstRow[i]; row < fileHeader.Height; row += Adam7.RowIncrement[i])
{
// Early out if invalid pass.
if (r.Length - readOffset < rowSize)
{
done = true;
break;
}
var rowData = new Span <byte>(new byte[rowSize]);
r.Slice(readOffset, rowSize).CopyTo(rowData);
int filter = rowData[0];
rowData = rowData.Slice(1);
readOffset += rowSize;
// Apply filter to the whole row.
for (var column = 0; column < rowData.Length; column++)
{
rowData[column] = ApplyFilter(rowData, prevRowData, filter, column, bytesPerPixel);
}
reader.ReadScanlineInterlaced(rowData, pixels, fileHeader, row, i);
prevRowData = rowData;
}
if (done)
{
break;
}
}
}
private static byte[] ParseInterlaced(byte[] pureData, PngFileHeader fileHeader, int bytesPerPixel, int channelsPerColor, ColorReader reader)
{
PerfProfiler.ProfilerEventStart("PNG Parse Interlaced", "Loading");
// Combine interlaced pixels into one image here.
var width = (int)fileHeader.Size.X;
var height = (int)fileHeader.Size.Y;
var combination = new byte[width * height * channelsPerColor];
var pixels = new byte[width * height * 4];
const int passes = 7;
var readOffset = 0;
var done = false;
var data = new Span <byte>(pureData);
for (var i = 0; i < passes; i++)
{
int columns = Adam7.ComputeColumns(width, i);
if (columns == 0)
{
continue;
}
int scanlineLength = GetScanlineLengthInterlaced(columns, fileHeader, channelsPerColor) + 1;
int length = scanlineLength - 1;
int pixelsInLine = Adam7.ComputeBlockWidth(width, i);
// Read scanlines in this pass.
var previousScanline = Span <byte> .Empty;
for (int row = Adam7.FirstRow[i]; row < height; row += Adam7.RowIncrement[i])
{
// Early out if invalid pass.
if (data.Length - readOffset < scanlineLength)
{
done = true;
break;
}
Span <byte> scanLine = data.Slice(readOffset + 1, length);
int filter = data[readOffset];
readOffset += scanlineLength;
ApplyFilter(scanLine, previousScanline, filter, bytesPerPixel);
// Dump the row into the combined image.
Span <byte> convertedLine = ConvertBitArray(scanLine, fileHeader);
for (var pixel = 0; pixel < pixelsInLine; pixel++)
{
int offset = row * bytesPerPixel * width + (Adam7.FirstColumn[i] + pixel * Adam7.ColumnIncrement[i]) * bytesPerPixel;
int offsetSrc = pixel * bytesPerPixel;
for (var p = 0; p < bytesPerPixel; p++)
{
combination[offset + p] = convertedLine[offsetSrc + p];
}
}
previousScanline = scanLine;
}
if (done)
{
break;
}
}
// Read the combined image.
int stride = width * bytesPerPixel;
int scanlineCount = combination.Length / stride;
for (var i = 0; i < scanlineCount; i++)
{
Span <byte> row = new Span <byte>(combination).Slice(stride * i, stride);
reader(width, row, pixels, i);
}
PerfProfiler.ProfilerEventEnd("PNG Parse Interlaced", "Loading");
return(pixels);
}
