Mantion specular reflection approximation

Author: virtualzavie

approximation.md.html

@@ -23,6 +23,12 @@
 As mentioned in the Reduction to a mixture of lobes section, the mix and layer operations can approximated as a weighted sum of BSDF lobes.
 
 
+Specular lobes
+-------------------------------------
+
+The specular BRDF described in the specification is the classic GGX-Smith model, which has been common in both offline and real-time rendering for a decade. The so called "split-sum" approximation introduced by [#Karis2013] allows efficient rendering of the isotropic version of this BRDF with image-based lighting.
+
+
 <!-- Markdeep: -->
 <style class="fallback">
     body { visibility:hidden }

index.html

@@ -1542,6 +1542,8 @@
 
 [#Jensen2001]: Henrik Wann Jensen, Stephen R. Marschner, Marc Levoy, and Pat Hanrahan. *A Practical Model for Subsurface Light Transport*, ACM SIGGRAPH (2001).
 
+[#Karis2013]: Brian Karis, *Real Shading in Unreal Engine 4*, ACM SIGGRAPH Courses: Physically Based Shading in Theory and Practice (2013).
+
 [#Kelemen2001]: Csaba Kelemen and Laszlo Szirmay-Kalos. *A Microfacet Based Coupled Specular-Matte BRDF Model with Importance Sampling*, Eurographics (2001).
 
 [#Kettner2015]: Lutz Kettner, Matthias Raab, Daniel Seibert, Jan Jordan, Alexander Keller. *The Material Definition Language*, Eurographics (2015).