Basically, anything you place in a scene around your ‘reflective’ object, will be projected onto the cube map images and then could be used in a game engine that uses that convention for generating a skydome or environment map
But how to generate it, and as you can see the tricky distortion built into each plane, that when viewed from the player’s position appears like the curve of the horizon.
I created a simple squashed sphere or ‘skydome’ in 3D Studio Max, where a long strip of clouds wrapped around the walls of the cylinder, and the bowl of the ocean plane was another. Everything is softly curved and I even added a bit of geo to the islands to add some parallax when I generate the cube map. The sky is separate from the ocean only to show the use of the textures. The ceiling or ‘cap’ of the skydome is just a single pixel of blue stretched across.
Once you have the skydome assembled, place an object in the center of the scene (or wherever you want the cube map to be generated ‘from’) I put a small cube. This cube will have the Standard > Reflect/Refract Material assigned to it.
1> Place the cube where you want the ‘point of view’ of the cube map.
2> Assign an empty material node to it. Click on the ‘diffuse’ channel button and select ‘Reflect/Refract’ from the pop-up menu.
Now the fun part! Once switched to Reflect/Refract, the options dialog panel will appear…
1> Switch the Source from ‘Automatic’ to ‘From File’. Switching to ‘From File’ enables the Render Maps feature below.
2> Enter what resolution you want your cube map images to be. I chose 512 for a nice crisp environment map.
3> Click on the empty ‘To File’ entry field and proceed to save a file. There is nothing to save, but this process is how the tool comes up with what naming convention to use when it generates the maps.
4> Then click ‘Pick Object and Render Maps’ and select the cube object in the center of your scene. A small render window will appear as the tool creates the images and closes them.
5> You will now see your 6 new images in the Material.
FINAL STEPS
You’re pretty much done! You now have six images that can be plunked into a game engine for creating an environment map. Mine looked something like this:
Now, because at the time I created the textures for the skydome, there was no way to actually match the bottom of the long 1024 texture to the round ocean plane, once the images are projected you can open them and paint out the seams, but with help of the curved distortion to guide you. Like so…
So there you go. A nice little way to have your hand-painted imagery be projected onto the 6 separate images needed to create a cube map… with all the proper distortion.
Author: Jude Godin
Bake Skybox using reflection probe Unity: Video01 Video02 (Baked reflection probes only capture game objects that are marked as static) (Import Setting: Convolution to None, Mipmap off, Compress None)