Fractolog

For my game, I would like to have a realistic sky in the background. I have a preference for a procedurally-generated sky over a skybox. But then, I need to learn about different ways of modeling the sky.

I first considered reusing the computations in the sky example from Three.js’s documentation, as it is liberally licensed. However, I decided I’d like to understand more of the theory behind it and use my own implementation instead of copying the Three.js’s example’s code.

The Three.js example’s implementation references the Preetham model. Introduced in 1999, the Preetham model seems to have been the baseline standard for a procedural sky for a long time. The original paper does its best to explain the scientific terminology to graphics practitioners, but there is still enough left unsaid that I found the paper hard to interpret in isolation. The most useful reference I found providing necessary background knowledge is Timothy Kol’s technical report. Kol also implements and compares the newer 2012 Hošek–Wilkie model. The remainder of this post mostly distills information from these three papers.

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While working on my little game, I’ve iterated through different ways of displaying game state:

1. Command line
2. Web page
3. 2D canvas
4. 3D canvas

In each port, I preserve some elements and change others out. One of the elements I want to keep from the 2D version in the 3D version is rounded rectangles.

Initially, I used NanoVG to render the 2D elements into 3D. This works, but NanoVG is a lot of code. It’s very general. I don’t need that level of generality. I just want rounded rectangles. So how do we do that?

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