Our latest blog post is all about performance improvements in 4.4 made possible through the use of a Signed Distance Field (SDF). Plus, a new 4.4 update is now available, and a reminder about our great collaboration with Dash and their amazing offer you don’t want to miss!

Rendering improvements for 4.4

For trueSKY cloud rendering, we use a compute shader to trace the path of the light as it interacts with the clouds in the scene. This part of the rendering is critical for performance as we take hundreds of steps over hundreds of kilometres per pixel in cubemap.

In that shader, we check at every step whether the grid cell contains any cloud density. Naturally, this is computationally expensive, so with trueSKY 4.3 we added the variable grid rendering system. The variable grid system used the lowest mip of our cloud density volume texture as a pseudo-acceleration structure, allowing us to skip large parts of the scene that contained no clouds. Whilst this did improve performance, there were limitations to the system such as the added memory and sampling issue of having mipmaps on a large volume texture, and lack of detail in that lowest mip for accurate and efficient forward steps in the trace.

trueSKY 4.4 comes with a raft of new features and one of the flagships is our new SDF Cloud Rendering system. SDF stands for Signed Distance Field as we use it as a pseudo-acceleration structure to skip vast swathes of the scene; vastly increasing performance. SDFs are a spin-off of Voronoi Diagrams, and we use Jump Flood algorithms to generate the SDF volume texture. See this blog for a deeper explanation of this technique. 

How SDF works

For each texture cycle, we calculate a new SDF volume texture; with each pixel in that texture container the distance to the nearest cloud and the seed co-ordinate. We actually only need the distance, as we can’t encode any directionality, because we need to trace the volume from any position and in any direction.

Back in our compute shader for tracing the path of the light, we simply look up into the SDF texture, which tells how far we can step to safely reach the next potential cloud. In the diagram below, you can see how the ray speeds through empty space, decelerates and accelerates into and out of clouds respectively.

(Image Source)

Limitations and future ideas

There are some limitations to this system however, such as rays that travel parallel to a wall of cloud. SDF will claim that the nearest cloud is but a few kilometres away. Obviously, this is not the case, but due to the lack of directionality in the SDF texture, the step distance is restricted in its potentiality. Although, with this new data set, there is the potential to upgrade our cloud shadowing technique to have more refined shadows by doing path tracing.

The Numbers

trueSKY – D3D12 Sample – Nvidia RTX 3070 – 1440 x 900

4.3 (Variable): 1.81ms

4.4 (SDF): 1.00ms

That’s a time reduction of 44.75%! We still have many ideas on further improvements for 4.4 and beyond, so I hope you have enjoyed this insight into our new rendering, plus please go ahead and try trueSKY 4.4!

Latest Beta Update

A new Beta update is now available on our downloads page! During our beta we are aiming to release frequent, smaller updates to address any issues found. This means you can expect improvements every 1 to 2 weeks. For this first update, some of the included fixes and updates are shown below:


  • Cloud Shadow improvements
  • Unreal Timeline UI Improvements
  • Removed unused Unreal Actor settings when in 4.4
  • Fix for samples not copying correctly

We are still aware of an Unreal issue regarding precipitation, which will be fixed for the next update.


  • Globe view can now trace solar eclipse paths on the Earth. For a better view check out this link.
  • Added support for basic mesh rendering in our editor (DX11 and DX12 for now)
  • General stability improvements for DX12 and Vulkan

Dash + trueSKY

Don’t miss out on our collaboration with Polygonflow and their Unreal Engine plugin Dash. Dash is a great plugin to help with world building, which makes designing a scene intuitive and simple.

Dash are offering 55% off an annual licence when you use code TRUESKY and follow this link.

Unreal 5.4

Unreal 5.4 has just released, with many new features and improvements. We will be releasing a trueSKY 4.3 and a 4.4 plugin for UE5.4 as soon as we can. Firstly, we need to investigate the changes made to 5.4 and what we need to do to keep support. So look out for our next blogpost where we will have a greater idea of the timeline to plugin release.

Thanks again for reading our latest blog, stay tuned for more exciting new about trueSKY!