I'm working on a game that's going to have some planets and stuff. But we won't be going down to the terrain level, so it'll just be textures for our world map stuff. View from space pretty much. But either way I can post the info I've written down as planning our planetary rendering scheme here, just a copy/pasta from our dev forum.
I don't have a planetary rendering engine ready, but when I've finished it I can send you the shaders and code and that. Not the textures though... I wouldn't mind releasing the assets for the game we're making as open source along with shaders and that, but I need to talk about that with my partner, also finish the game too.
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KyallH
We can definitely have pixelated or nicely rendered planet. I'd go with pretty much what ever is easiest to use.
I want to try and adapt valve's alpha tested magnification algorithm for planetary detail:
http://www.valvesoft...gnification.pdf
Basically we have a small texture map (64x64 probably like what they have on page 2 of that document) that specifies the land/sea areas on a planet. Land/Sea/Ice might be a bit more difficult, we're probably just going to have to live with only 2 textures per planet for the surface. And we can use the same algorithm for cloud layers as well.
KyallH
Planet Types:
Type A (Homoterranean Atmospheric): 1 product texture for surface, No distance texture for surface, 1 library texture for atmosphere, Distance texture for the atmosphere
Type B (Heteroterranean Atmospheric): 2 product textures for surface, Distance texture for surface, 1 library texture for atmosphere, Distance texture for atmosphere
Type C (Homoterranean Anatmospheric): 1 product texture for surface, No distance texture for surface, No texture for atmosphere, No distance texture for atmosphere
Type D (Heteroterranean Anatmospheric): 2 product textures for surface, Distance texture for surface, No texture for atmosphere, No distance texture for atmosphere
Type E (Anterranean Conatmospheric): No texture for surface, No distance texture for surface, 1 library texture for atmosphere, No distance texture for atmosphere
KyallH
So basically we have planets that have a mixture of land/sea or land/ice, for the surface, or have only 1 texture for the surface. The distance texture if you read the valve source article is a pretty good way of discriminating the boundary between the 2 different textures to create land forms or ice caps, that uses a texture that is very small so reduces the download size of the application. We can have clouds that cover completely ( so no surface texture ) or we can have no clouds, or we can have partially obscuring clouds. The partially obscured clouds will use a distance texture as well.
Appendix:
Distance texture: Opacity map that hopefully doesn't contain aliased articles.
Product texture: A combination of blending of two or more library textures
Library texture: A texture from a library
The terrains I think can use the product textures which we combine on the fly because blending those and having a good result would be easy.
The atmospheres I think we'll just have to use a library texture (although we could tint it) because combining library textures may not produce a good enough result for atmospheres.
KyallH
Note on language: I'm debating whether to use the anti meaning pretext Anatmospheric, which means not vapor sphere, or use Vacuuspheric which means empty sphere.... Both sort of fail to describe the situation properly. Maybe subatmospheric? In terms of rendering I think anatmospheric is the best definition. Atmospheric as in visible atmosphere, anatmospheric for invisible atmosphere.. And Conatmospheric for an atmosphere that occludes the surface 100%
Dalfury
To be honest I wouldn't worry so much about the naming scheme, players won't see it.
KyallH
I don't think they'll see this forum either...

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And I hate a chat with a fella a while ago about planetary generation down at the micro-level where you would actually visit. And there's a fair number of rules governing geology. I'd recommend using that algo above for rendering from space, and the distance texture can be generated from whatever geological stuff you generate at the micro level, so the distance textures would be on the fly. Anywho, the rules we came up for geological simulation were:

First create coasts and land masses, first step in that is to determine the ratio of land/sea. distances from the costs and location in the world (tropical regions, cold regions) dictate where you'll see vegetation. As does elevation, a lot of trees only live within certain vegetation bands of elevation. Rivers run to the seas, just make some observations about how geology works and you'll have what you need to generate good realistic terrain.

To be honest I appear to have forgotten 80% of that discussion.