// Perform a single 2D FFT by performing nx+ny 1D FFTs
// fft_2d(complex* x, int nx, int ny, int x_stride, int y_stride)
// 1. Perform 1D FFTs along rows
// Element x[i,j] is located at x[i * x_stride + j * y_stride]
// So each row starts at x + 0 * x_stride + j * y_stride, has length nx, and stride x_stride
// 2. Perform 1D FFTs along columns
// Element x[i,j] is located at x[i * x_stride + j * y_stride]
// So each column starts at x + i * x_stride + 0 * y_stride, has length ny, and stride y_stride
void fft_2d(complex* x, int nx, int ny, int x_stride, int y_stride) {
int i, j;
for(j=0; j<ny; j++)
fft_1d(x + j * y_stride, nx, x_stride, Wkn_fft);
for(i=0; i<nx; i++)
fft_1d(x + i * x_stride, ny, y_stride, Wkn_fft);
}
/*---------------------------------------------------------------------------*/
static void fft_2d(double * data, int nn, int mm, int isign, double * copy)
{
int i, j, index1, index2;
/* Transform by ROWS for forward transform */
if (isign == 1)
{
index1 = 0;
for (i = 0; i < mm; i++)
{
fft_1d(data+index1, nn, isign);
index1 += (nn << 1);
}
}
/* Transform by COLUMNS */
for (j = 0; j < nn; j++)
{
/* Copy pixels into temp array */
index1 = (j << 1);
index2 = 0;
for (i = 0; i < mm; i++)
{
copy[index2++] = data[index1];
copy[index2++] = data[index1 + 1];
index1 += (nn << 1);
}
/* Perform transform */
fft_1d(copy, mm, isign);
/* Copy pixels back into data array */
index1 = (j << 1);
index2 = 0;
for (i = 0; i < mm; i++)
{
data[index1] = copy[index2++];
data[index1 + 1] = copy[index2++];
index1 += (nn << 1);
}
}
/* Transform by ROWS for inverse transform */
if (isign == -1)
{
index1 = 0;
for (i = 0; i < mm; i++)
{
fft_1d(data+index1, nn, isign);
index1 += (nn << 1);
}
}
}
