Right now, we have gotten our implementation to a good place, however the inherent limitations of the method means that in the future we will move to a different, non-precomputed method which doesn’t suffer from these issues and would allow us greater flexibility.Ītmosphere as LightingRecall that we have the transmittance that we discussed earlier as the part of light that reaches the observer and objects in the atmosphere. This is where most of the engineering effort in implementing precomputed atmospheric scattering is spent.

The original paper offers a nice way to distribute samples, but we found that it works best for physical settings matching those of Earth, but not for some of the settings used at Kerbal scale.įinally, we review all the lossy transformations in the math and try to minimize any loss of precision and guard against various edge cases. The way to deal with this is to first inspect the look-up tables, see if anything is stored in low precision textures or with any lossy compression, and use high precision instead where needed typically (16-bit and 32-bit per channel floating point textures).Īfter that, we can then change the parametrization for how samples are distributed across the look-up table to maximize resolution where it is needed. The aerial perspective method described earlier only makes precision issues worse by taking the difference between 2 samples, especially on high variance areas (typically around the horizon) where any imprecisions are amplified. Recall that we are using look-up tables, these are loaded on the graphics card as textures, and they have limited resolution and precision (bit depth). Hmm that looks really strange around the horizon, so what's happening here? Putting It In-GameSo now that we know the method to render aerial perspective, we can plug it in-game, and see what we get. We also must apply transmittance to the observer to second sample (in red on the diagram) for everything to be correct. However, since the look-up tables allow us to get the colour of the sky from any viewpoint, we can re-express the scattered light up to a point/object as the difference between two samples to the edge of the atmosphere, starting from different positions. This is because the look-up tables would otherwise become impractically big and would eat up our memory budget. The look-up tables only allow us to get the light scattered towards us from the edge of the atmosphere, and assume we are always looking towards the edge of the atmosphere, so we cannot use it to directly to get the colour of the atmosphere up to an object. How Aerial Perspective is RenderedThe look-up tables I’ve described earlier can be used to find the colour of the sky for any given viewpoint inside or outside the atmosphere, as well as how much the atmosphere occludes celestial objects behind it (this is known as transmittance or also extinction, it describes how much of the original object’s light is transmitted and makes it to the observer).

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