Simplex started as a branch from Complex. It has combined features from Path To Victory as well as many other mods through a long history of R&D. This mod aims to excavate the full potential of the Homeworld 2 engine and it will simply blow your mind with incredible fun!
This is an amazing background as well. How did you do it?
1. Download a nebula image.
2. Open it in Photoshop, stretch it to 2048x1024
3. Extend the canvas to 2548x1024, duplicate the left border part to the right, and blend them together using all kinds of tools, so that the left and right of the background can stitch together comfortably.
4. Graduating the top and the bottom of the background to pure colour, to minimize artifacts after conversion.
5. Move the duplicated right part back to the left, and crop the image back to 2048x1024.
6. Ctrl+L, reduce the output from 0-255 to 0-127. Save it as 32bit TGA.
7. Use HW2BGBuilder with stripification turned on to build the background hod.
8. Create a new folder in Homeworld2\Data\Background and copy the new hod to there with new file name.
9. Open the background HOD with CFHodEd, make all the lightings right, based on the colour picker in Photoshop and a calculator to convert 0-255 of RGB to the 0-1 scale.
10. Save the new hod. Add lensflares corresponding to the incoming directions of the light sources in a lua file.
That's basically how I did it. Actually, I'm still a noob, because I still don't know how to add the star field based on the new background.