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--- 01_user_documentation:05_object:02_light:12_shaders:04_ggx [2026/09/22 12:16] – created Tim
+++ 01_user_documentation:05_object:02_light:12_shaders:04_ggx [2026/09/22 12:37] (current) – Tim
@@ Line 1: / Line 1: @@
 ====== GGX ======
+ A GGX (Trowbridge-Reitz) microfacet BRDF shader.
+=====  =====
+The BRDF is:
+$f_r = k_d / π  +  D(h) · F(l,h) · G(l,v) / (4 · cos θ_i · cos θ_o)$
+where:
+D(h) := GGX normal distribution function:
+$D = α² / (π · (cos²θ_h · (α²−1) + 1)²)$
+F(l,h) := Schlick Fresnel approximation:
+$F = F₀ + (1−F₀)(1−cos θ_{lh})⁵$
+, where F₀ = specular
+G(l,v) := Smith height-correlated masking-shadowing:
+$G = G₁(l) · G₁(v),  G₁(v) = 2/(1 + √(1 + α² tan²θ_v))$
+Importance sampling uses GGX NDF half-vector sampling:
+$θ_h = atan(α √(ξ₁/(1−ξ₁))),  φ_h = 2π ξ₂.$
+Transmission is supported via the optional transparency,
+which enables Fresnel-weighted straight-through (delta BTDF) in the
+CPU light model only.