The default procedural sky in Unity is a bit drab, and I do think Bob Ross was onto something when he kept painting those happy little clouds. So I set out to make a skybox!
For Unity you create some kind of projection map (cube map, sphere map), make it a material, and set that material under Window > Lighting. The hard part is making that map...
I tried four different methods, and the third one listed below worked best for me. My issues with the other methods might’ve just been user error, so I think if the process for method 3 gets too tedious I’ll give the others another shot.
1. Texture paint directly on a UV’ed cube
This can be done in both Blender and 3D Coat, but it feels pretty awkward.
2. Unwrap a cube in a cross and paint from the UV layout
This is the “normal” approach in that you’re doing exactly what you’d do if you were texturing a cube. If you unwrap in a horizontal cross Unity will convert accept it if you import the texture, select cubemap as the type, and apply “auto” mapping. Here are two of my first attempts.
Note that you really only have a very narrow area in which to paint. I found it easiest to paint clouds on a separate layer in Photoshop and then transform them to be smaller and more squished looking.
IMO the downside to this is that it’s hard to see what you’re doing with these adjustments. You’re adapting the image to the UV (as you’re supposed to when texturing) but the next method lets you adapt a UV to the image, sort of:
3. Set painted texture as an environment then project onto a cube
I read this tutorial for 3DS Max and thought the equivalent for Blender (Cycles) would be baking a reflection onto a cube. Couldn’t get this to work so I switched to Blender Internal and followed this tutorial instead. It worked! You can adjust how the sky looks on the domed cylinder that is your “environment” and then render the map afterwards. The downside here is that AFAIK you have to manually slice up to the resulting environment map into six images for Unity.
4. Use orthographic camera to render in Cycles
Here you create the domed cylinder to get the benefit of adjusting the sky before rendering, except you use the orthographic camera to render onto a cross cubemap layout. I kept getting a curved horizon in the end result, though.
