atmosphere-shader

Atmosphere Shader Skill

Render physically-accurate skies, sunsets, and planetary atmospheres through atmospheric scattering — Rayleigh, Mie, and Ozone models composed via raymarching in GLSL fragment shaders. Four progressive modes from flat backdrop to LUT-optimized planetary pipeline.

Modes

Mode	Output	Complexity
sky-dome	Single-pass fragment shader, flat sky backdrop	Entry point
atmosphere-post	Depth-aware post-processing effect with atmospheric fog	Intermediate
planet	Spherical atmosphere shell around a mesh, logarithmic depth	Advanced
lut	Transmittance + Sky View + Aerial Perspective LUTs, FBO pipeline	Production

Gotchas — What Claude Gets Wrong

These are the highest-signal items in this skill. Every one is a concrete, reproducible failure mode.

1. Wrong scattering coefficients

Claude invents plausible-looking but physically incorrect beta values. Use these exact constants for Earth:

const vec3 BETA_R = vec3(5.8e-3, 13.5e-3, 33.1e-3);   // Rayleigh scattering (1/km)
const float BETA_M_SCATTER = 21e-3;                      // Mie scattering
const float BETA_M_EXT = 21e-3 * 1.1;                    // Mie extinction (scatter + absorb)
const vec3 BETA_OZONE_ABS = vec3(0.65e-3, 1.881e-3, 0.085e-3); // Ozone absorption

const float RAYLEIGH_SCALE_HEIGHT = 8.0;   // km
const float MIE_SCALE_HEIGHT = 1.2;        // km
const float MIE_G = 0.76;                  // Henyey-Greenstein anisotropy
const float ATMOSPHERE_HEIGHT = 100.0;     // km (Karman line)

See references/scattering-coefficients.md for Mars and custom planet parameter sets.

2. Missing nested light march

Claude implements only the view-ray loop, producing a blue gradient but no sunsets. The critical missing piece: at each sample point along the primary ray, a secondary march toward the sun accumulates sunOD (optical depth between sample and sun). Without this, tau only contains view-direction extinction and the sky is uniformly blue regardless of sun angle.