Advanced (?) light transport and materials

A lot, but extremely high-level. Mostly FYI.

Advanced Light Transport

• Unbiased light transport methods
  • Bidirectional path tracing (BDPT)
  • Metropolis light transport (MLT)
• Biased light transport methods
  • Photon mapping
  • Vertex connection and merging (VCM)
• Instant radiosity (VPL / many light methods)
  • 间接光表示为很多小光源

Biased vs. Unbiased Monte Carlo Estimators

• 无偏：An unbiased Monte Carlo technique does not have any systematic error
  • 无论取多少样本，期望永远是对的
• 有偏：其他情况
  • One special case, the expected value converges to the correct value as infinite #samples are used — consistent 有偏，但能收敛到无偏

Bidirectional path tracing (BDPT)

• Traces sub-paths from both the camera and the light (半路径)
• Connects the end points from both sub-paths 半路径末端互相连接，形成通路
• 好处：Suitable if the light transport is complex on the light’s side
  • 比如，光源第一跳大多是diffuse
• 缺点：Difficult to implement & quite slow 能做出来基本能自己写渲染器了

Metropolis light transport (MLT)