Logo for AMD FidelityFX Parallel Sort

AMD FidelityFX™ Parallel Sort provides an open source header implementation to easily integrate a highly optimized compute-based radix sort into your game.


  • DirectX®12
  • Vulkan®

Download the latest version v1.1:

This release adds the following features:

  • Vulkan® implementation.
  • Upgraded framework to Cauldron v1.4.
  • General code cleanup and readability improvements.

Download the latest version v1.2

This release includes:

Part of the AMD FidelityFX™ SDK

AMD FidelityFX SDK components


State-of-the-art algorithm

Optimized for Shader Model 6.0+

Open source, MIT license

Additional features:

  • Direct and Indirect execution support.
  • AMD RDNA™+ optimized algorithm.
  • 32-bit key and payload sort support
  • Support for DirectX®12 API and Vulkan®.
  • Shaders written in HLSL utilizing Shader Model 6.0 wave-level operations.

A sample application is provided for DirectX®12 and Vulkan®.


Algorithm overview

AMD FidelityFX Parallel Sort is an AMD RDNA™-optimized version of the Radix Sort algorithm.

At a high level, the algorithm works by recursing over a data set to be sorted (key or key/value pairs), and re-arranging it in place by 4-bit increments. Each pass guarantees that the data set is fully sorted up to the number of bits processed. For example, after 4 iterations, we are guaranteed that the first 16 bits of the key is properly sorted.

For each iteration that is executed, 5 actions are taken on the data set:

  1. The 4-bit value range we are currently sorting is summed up into buckets from 0-15, so that we know how many of each value occurs throughout the data set.
  2. The number of occurrences go through a reduction phase in order to pre-increment offsets on a thread group basis later on.
  3. The reduced occurrences go through a scan-prefix to calculate offset values for each value group (0-15) on a thread group basis.
  4. The full occurrences buffer then also goes through a scan-prefix, and adds the reduced scan-prefix values to properly index the data across all thread groups.
  5. The data set is read in one more time, and written to its new sorted offset location. If there is also a payload, it is also copied over at this time.

Once all iterations have run (in the case of 32-bit keys, it runs 8 times), the entire data set is sorted.

Additional resources

FidelityFX Testimonials

Find out what developers are saying about AMD FidelityFX.

Comparison: GPU particle sorting

Unsorted GPU particles Sorted GPU particles

Comparison: image index buffer sorting

Unsorted image index buffer Sorted image index buffer

Version history

  • Vulkan® implementation.
  • Upgraded framework to Cauldron v1.4.
  • General code cleanup and readability improvements.
  • Initial release

Part of the AMD FidelityFX SDK

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