Import texture as cubemap: panel vs. source texture resolution?

Unity Engine
1

I am using the new cubed skybox renderer and so am now importing single textures as cubemaps for the skybox instead of individual panels.

My old skyboxes were 1024 on a side for each panel in the skybox cube.

I want my new skyboxes to have a similar resolution. So I expect that my source texture for the skybox would need to be 4096 x 2048 to be wrapped around a cylinder and then projected onto the cube faces, and get a comparable resolution of 1024 per face. However, when I import the main texture and set it to cubemap, if I choose 1024 as the face resolution, that appears to become the maximum resolution of the main texture as well when I select it in the inspector for the cubemap.

Is that really what the main texture is now sized at? Does that mean that the 1024 per face is scaling up the master texture from 1024? Or is that just a mistake/artifact in the reporting for displaying the main texture size, and the face size is taking advantage of the full resolution of the source texture? Or is it the case that with the way the cylindrical cubemap is created, there is actually a different effective resolution compared to using separate panels?

2

It looks like the size you choose when generating a cubemap is in fact the face resolution. So the source texture should be big enough to support total number of pixels on the faces. (The confusion is that the size reported for the source texture is therefore not really accurate).

A greater mystery is that a generated cubemap takes way more VRAM than a comparable 6-sided skybox assembled from 6 separate textures of the same effective size. A 1024 sized cubemap uses 18 MB of VRAM, while the older version uses only 3 MB.

This is reported by the Statistics panel in the Game view.

Is that accurate, or a bug in the accounting done for the Statistics panel? If it’s correct, it’s enough to not allow me to use a generated cubemap for the skybox.