/// <summary>
/// Two dimensional Fast Fourier Transform.
/// </summary>
///
/// <param name="data">Data to transform.</param>
/// <param name="direction">Transformation direction.</param>
///
/// <remarks><para><note>The method accepts <paramref name="data"/> array of 2<sup>n</sup> size
/// only in each dimension, where <b>n</b> may vary in the [1, 14] range. For example, 16x16 array
/// is valid, but 15x15 is not.</note></para></remarks>
///
/// <exception cref="ArgumentException">Incorrect data length.</exception>
///
public static void FFT2(Complex[,] data, Direction direction)
{
int k = data.GetLength(0);
int n = data.GetLength(1);
// check data size
if (
(!Tools.IsPowerOf2(k)) ||
(!Tools.IsPowerOf2(n)) ||
(k < minLength) || (k > maxLength) ||
(n < minLength) || (n > maxLength)
)
{
throw new ArgumentException("Incorrect data length.");
}
// process rows
Complex[] row = new Complex[n];
for (int i = 0; i < k; i++)
{
// copy row
for (int j = 0; j < n; j++)
{
row[j] = data[i, j];
}
// transform it
FourierTransform.FFT(row, direction);
// copy back
for (int j = 0; j < n; j++)
{
data[i, j] = row[j];
}
}
// process columns
Complex[] col = new Complex[k];
for (int j = 0; j < n; j++)
{
// copy column
for (int i = 0; i < k; i++)
{
col[i] = data[i, j];
}
// transform it
FourierTransform.FFT(col, direction);
// copy back
for (int i = 0; i < k; i++)
{
data[i, j] = col[i];
}
}
}
private static void fftpc(ref Complex[,] data, Direction direction, int start, int end, int rows)
{
Complex[] col = new Complex[rows];
for (int j = start; j < end; j++)
{
// copy column
for (int i = 0; i < rows; i++)
{
col[i] = data[i, j];
}
// transform it
FourierTransform.FFT(col, direction);
// copy back
for (int i = 0; i < rows; i++)
{
lock (data)
{
data[i, j] = col[i];
}
}
}
}
private static void fftpr(ref Complex[,] data, Direction direction, int start, int end, int cols)
{
Complex[] row = new Complex[cols];
for (int i = start; i < end; i++)
{
// copy row
for (int j = 0; j < cols; j++)
{
row[j] = data[i, j];
}
// transform it
FourierTransform.FFT(row, direction);
// copy back
for (int j = 0; j < cols; j++)
{
lock (data)
{
data[i, j] = row[j];
}
}
}
}