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Blending land and sky

Add Comment! By David Rosen on July 22nd, 2009

Since Overgrowth mostly takes place outdoors, we put a lot of effort into making the sky look nice. We've already talked about the sun placement tools and atmospheric haze, but now I would like to talk about how we achieve smooth transitions between the land and the sky. Let's start at the beginning, with the panoramic sky texture:

Cloud sunset sky

Here is how that looks when we wrap it around a scene:

Partial sky

As you can see, the bottom half of the sky looks stretched and unrealistic. It doesn't match the terrain at all, so the edge of the terrain is clearly visible. To make it blend in better, we stretch out the terrain texture onto a large, slightly-indented plane that reaches to the horizon:

Partial sky

Now the scene looks more complete. However, the horizon still has a harsh line between the land and the sky. To cover this, we use what I call a 'horizon band' or 'fog band', a fuzzy strip that is colored by a heavily blurred version of the sky texture. Here is what that looks like by itself.

Partial sky

When we put it all together, it all fits together pretty well, and the process is entirely automated in a fraction of a second! Here is the final result again:

Finished sky

Here are some other skies using the same technique, to show that it works for a variety of sky types:

Finished sky
Finished sky

This technique allows us to render convincing vistas very efficiently -- in terms of both development time and run-time resources. Do you have any ideas about how we could make the land and sky fit together even better?