Zero-padding issue in Y dimension (CUDA backend)

[Clemasteredge]

Hi there,

I'm having trouble getting the zero-padding optimization to work with the CUDA backend.

It seems to be doing what I want when padding only the first dimensions (X).

Input array is 1024x512 complex single precision with random phases.

When padding in X only to 1536x512, I'm getting the expected results (compared with MATLAB using fft2 with padding):

• Padded input phases:

• FFT magnitudes:

When padding in Y only to 1024x768, the input padding looks correct, but the FFT is obviously wrong:

• Padded input phases:

• FFT magnitudes:

Apologies for the wrong MATLAB plot orientation, I was playing with the dimensions to see if that was causing the problem (it wasn't).

The VkFFTConfiguration zero-padding is configured as follows:

// Configure VkFFT and execute
VkFFTConfiguration configuration = VkFFTContext::createConfiguration(fftDims, precision, inputArray.complexity_);
configuration.normalize = 0;
configuration.performZeropadding[0] = padSize.x > 0;
configuration.performZeropadding[1] = padSize.y > 0;
configuration.performZeropadding[2] = padSize.z > 0;
configuration.fft_zeropad_left[0] = inputDims.x;
configuration.fft_zeropad_right[0] = fftDims.x;
configuration.fft_zeropad_left[1] = inputDims.y;
configuration.fft_zeropad_right[1] = fftDims.y;
configuration.fft_zeropad_left[2] = inputDims.z;
configuration.fft_zeropad_right[2] = fftDims.z;

The createConfiguration() method assigns the correct FFT dimensions, precision and complexity.

Is this a known issue? Or am I doing something obviously wrong?

Thanks,
Clement

[Clemasteredge]

Quick update: I tried to use a separate input buffer, which works fine without padding or with X-only padding, but it also doesn't work with Y padding. In fact, it produces mostly 0s when using the separate input buffer, versus using the internal buffer (which produces the streaks like above). Not sure why it would produce different results in the first place?

I also noted that in some configurations, the output is sometimes missing a few rows at the top. That is with the zero-padding disabled.