RGB channels: total inscattered light along the camera ray to the current sample. A channel: average transmittance across all wavelengths to the current sample.

calling with component = 0.0 will return the atmosphere’s absorption density, while calling with component = 1.0 will return the atmosphere’s scattering density.

samples from the atmosphere scattering LUT. neg_LdotV is the dot product of the light direction and the incoming view vector. Nonlinear phase mapping to mitigate banding in low-resolution LUTs.

evaluates L_scat, equation 3 in the paper, which gives the total single-order scattering towards the view at a single point

Clamp a position to the planet surface (with a small epsilon) to avoid underground artifacts.

Returns the observer’s position in the atmosphere

We assume the up vector at the view position is the y axis, since the world is locally flat/level. t = distance along view ray in atmosphere space NOTE: this means that if your world is actually spherical, this will be wrong.

Given a ray starting at radius r, with mu = cos(zenith angle), and a t = distance along the ray, gives the new radius at point t

Convert uv [0.0 .. 1.0] coordinate to ndc space xy [-1.0 .. 1.0]

Convert ndc space xy coordinate [-1.0 .. 1.0] to uv [0.0 .. 1.0]

Converts a direction in world space to atmosphere space

Converts a direction in atmosphere space to world space

Modified from skybox.wesl. For this pass we don’t need to apply a separate sky transform or consider camera viewport. Returns a normalized ray direction in world space.