/// <summary>
/// Returns the offset of the next bit in the range
/// [bitStart..bitEnd] that is different from the
/// specified color. The end, bitEnd, is returned
/// if no such bit exists.
/// Like FindDifference, but also check the
/// starting bit against the end in case start > end.
/// </summary>
/// <param name="reader">The reader.</param>
/// <param name="bitStart">The offset of the start bit.</param>
/// <param name="bitEnd">The offset of the end bit.</param>
/// <param name="searchOne">If set to <c>true</c> searches "one" (i. e. white), otherwise searches black.</param>
/// <returns>The offset of the first non-matching bit.</returns>
private static uint FindDifferenceWithCheck(BitReader reader, uint bitStart, uint bitEnd, bool searchOne)
{
// Translated from LibTiff
return((bitStart < bitEnd) ? FindDifference(reader, bitStart, bitEnd, searchOne) : bitEnd);
}
/// <summary>
/// 2d-encode a row of pixels. Consult the CCITT documentation for the algorithm.
/// </summary>
/// <param name="writer">The writer.</param>
/// <param name="bytesFileOffset">Offset of image data in bitmap file.</param>
/// <param name="imageBits">The bitmap file.</param>
/// <param name="currentRow">Index of the current row.</param>
/// <param name="referenceRow">Index of the reference row (0xffffffff if there is none).</param>
/// <param name="width">The width of the image.</param>
/// <param name="height">The height of the image.</param>
/// <param name="bytesPerLineBmp">The bytes per line in the bitmap file.</param>
static void FaxEncode2DRow(BitWriter writer, uint bytesFileOffset, byte[] imageBits, uint currentRow, uint referenceRow, uint width, uint height, uint bytesPerLineBmp)
{
// Translated from LibTiff
uint bytesOffsetRead = bytesFileOffset + (height - 1 - currentRow) * bytesPerLineBmp;
BitReader reader = new BitReader(imageBits, bytesOffsetRead, width);
BitReader readerReference;
if (referenceRow != 0xffffffff)
{
uint bytesOffsetReadReference = bytesFileOffset + (height - 1 - referenceRow) * bytesPerLineBmp;
readerReference = new BitReader(imageBits, bytesOffsetReadReference, width);
}
else
{
byte[] tmpImageBits = new byte[bytesPerLineBmp];
for (int i = 0; i < bytesPerLineBmp; ++i)
{
tmpImageBits[i] = 255;
}
readerReference = new BitReader(tmpImageBits, 0, width);
}
uint a0 = 0;
uint a1 = !reader.GetBit(0) ? 0 : FindDifference(reader, 0, width, true);
uint b1 = !readerReference.GetBit(0) ? 0 : FindDifference(readerReference, 0, width, true);
// ReSharper disable TooWideLocalVariableScope
uint a2, b2;
// ReSharper restore TooWideLocalVariableScope
for (;;)
{
b2 = FindDifferenceWithCheck(readerReference, b1, width, readerReference.GetBit(b1));
if (b2 >= a1)
{
int d = (int)b1 - (int)a1;
if (!(-3 <= d && d <= 3))
{
/* horizontal mode */
a2 = FindDifferenceWithCheck(reader, a1, width, reader.GetBit(a1));
writer.WriteTableLine(HorizontalCodes, 0);
if (a0 + a1 == 0 || reader.GetBit(a0))
{
WriteSample(writer, a1 - a0, true);
WriteSample(writer, a2 - a1, false);
}
else
{
WriteSample(writer, a1 - a0, false);
WriteSample(writer, a2 - a1, true);
}
a0 = a2;
}
else
{
/* vertical mode */
writer.WriteTableLine(VerticalCodes, (uint)(d + 3));
a0 = a1;
}
}
else
{
/* pass mode */
writer.WriteTableLine(PassCodes, 0);
a0 = b2;
}
if (a0 >= width)
{
break;
}
bool bitA0 = reader.GetBit(a0);
a1 = FindDifference(reader, a0, width, bitA0 /*reader.GetBit(a0)*/);
b1 = FindDifference(readerReference, a0, width, !bitA0 /*reader.GetBit(a0)*/);
b1 = FindDifferenceWithCheck(readerReference, b1, width, bitA0 /*reader.GetBit(a0)*/);
}
}
/// <summary>
/// Returns the offset of the next bit in the range
/// [bitStart..bitEnd] that is different from the
/// specified color. The end, bitEnd, is returned
/// if no such bit exists.
/// </summary>
/// <param name="reader">The reader.</param>
/// <param name="bitStart">The offset of the start bit.</param>
/// <param name="bitEnd">The offset of the end bit.</param>
/// <param name="searchOne">If set to <c>true</c> searches "one" (i. e. white), otherwise searches black.</param>
/// <returns>The offset of the first non-matching bit.</returns>
private static uint FindDifference(BitReader reader, uint bitStart, uint bitEnd, bool searchOne)
{
// Translated from LibTiff
reader.SetPosition(bitStart);
return(bitStart + (searchOne ? CountOneBits(reader, bitEnd - bitStart) : CountZeroBits(reader, bitEnd - bitStart)));
}