G2D-FFT

A Unity Based GPU-Accelerated Radix-2 2D-FFT Library

Uses

• Frequency Domain Image Processing
• Convolutional Bloom
• Numerical Computations

Usage

1. Initialize an instance of the GFFT class and pass the PD_Radix_2.compute ComputeShader as the parameter
2. Configure the GFFT instance for the size of the image you're processing and the number of color channels in your image
3. Call the relavant methods to perform the fourier transform

• There are 3 types of transforms available
  • Real to Complex Forward Transform
  • Complex to Real Inverse Transform
  • Real to Real Forward Transform (Power Spectrum)

Examples

Basic Use

// Init
// computeShader => Compute Shader provided with this library
GFFT gfft = new GFFT(computeShader);

// size of the input image
int size = 256;
// number of color channels in the input image
GFFT.Mode mode = GFFT.Mode.MultiChannel;

gfft.ConfigureForSize(size, mode);

// Real to Complex
gfft.ForwardFFT2_R2C(input_re, ref output_re, ref output_im);
// Complex to Real
gfft.InverseFFT2_C2R(input_re, input_im, ref output_re);
// Real to Real Forward
gfft.PowerSpectrum_R2R(input_re, ref output_re);

// input_re and input_im are of the type UnityEngine.Texture
// output_re and output_im are of the type UnityEngine.RenderTexture

// You must dispose the GFFT instance after using it
gfft.Dispose();

• If your code is time critical, you can synchronize the FFT with the render pipeline using a CommandBuffer
• For that, pass the command buffer as the first argument

// cmb = CommandBuffer
gfft.ForwardFFT2_R2C(cmb, input_re, ref output_re, ref output_im);
gfft.InverseFFT2_C2R(cmb, input_re, input_im, ref output_re);

Extras

• The provided helper method GFFT.CreateRT(ref RenderTexture rt, GraphicsFormat format, FilterMode filterMode, int size) should be used to create RenderTextures for the output of the Fourier Transforms.

• To create RenderTextures, GFFT provides 4 graphics formats

  • GFFT.SingleChannelHalfPrecision - Single Channel, 16 bits per texel
  • GFFT.MultiChannelHalfPrecision - RGBA Channels, 16 bits per channel, 64 bits per texel
  • GFFT.SingleChannelSinglePrecision - Single Channel, 32 bits per texel
  • GFFT.MultiChannelSinglePrecision - RGBA Channels, 32 bits per channel, 128 bits per texel

• Use of single precision floats has a significantly higher cost than the use of half precision floats

• Use single precision textures, only if it's absolutely required. Otherwise stick with half precision textures

// output rt
RenderTexture output;
// format of the texture
var format = GFFT.MultiChannelHalfPrecision;

GFFT.CreateRT(ref output, format, FilterMode.Point, size);