đ¨ PBR (Physically Based Rendering)
Physically Based Rendering (PBR) is a rendering technique that simulates
materials and lighting based on real-world physics laws. It has become the standard
in the game and film industry since the early 2010s.
History: The concept of PBR originated from Jim Kajiya's rendering equation
in the 1980s, and a practical workflow was established with Disney's "Principled BRDF"
announcement in 2012. It is now used as standard in most 3D software including
Unreal Engine, Unity, and Blender.
Core Principles:
- Energy Conservation - Reflected light cannot exceed incident light
- Microfacet Theory - Surface is a collection of microscopic mirrors
- Fresnel Effect - Reflectivity changes with viewing angle
đĄ BRDF (Bidirectional Reflectance Distribution Function)
Bidirectional Reflectance Distribution Function (BRDF) is a function
that mathematically defines how light reflects from a surface. It takes incident
and reflection angles as input to determine the amount and direction of reflected light.
History: The BRDF concept was first defined by Fred Nicodemus in 1965.
Since then, various BRDF models have been developed including Cook-Torrance (1982),
Oren-Nayar (1994), and GGX (2007).
Components:
- Diffuse - Light that scatters uniformly from the surface
- Specular - Light that reflects like a mirror from the surface
- Fresnel - Reflectivity change based on viewing angle
⨠Disney BRDF (Principled BRDF)
Disney BRDF is an "artist-friendly" physically based shading model
presented by Brent Burley of Walt Disney Animation Studios in 2012. It was first
introduced in the paper "Physically Based Shading at Disney".
Features: Complex physical parameters have been simplified into
intuitive 0-1 range parameters that artists can easily understand. It pursues
a balance between physical accuracy and ease of use.
Key Parameters:
- Base Color - Base color (shared for Diffuse/Metal)
- Metallic - Metalness (0=non-metal, 1=metal)
- Roughness - Surface roughness (0=smooth, 1=rough)
- Specular - Reflection intensity for non-metals
- Clearcoat - Transparent coating layer (car paint, etc.)
- Anisotropic - Anisotropic reflection (brushed metal)
- Subsurface - Subsurface scattering (skin, wax)
- Sheen - Edge gloss for cloth materials