Non-Surface Models
Participating Media 散射介质
Fog
![https://s3-us-west-2.amazonaws.com/secure.notion-static.com/3e261fd4-9b7b-4574-ac02-071c995e4c2b/Untitled.png](https://s3-us-west-2.amazonaws.com/secure.notion-static.com/3e261fd4-9b7b-4574-ac02-071c995e4c2b/Untitled.png)
Cloud
![https://s3-us-west-2.amazonaws.com/secure.notion-static.com/f9f7d6d5-4cd0-4080-83e2-f1df86d688f0/Untitled.png](https://s3-us-west-2.amazonaws.com/secure.notion-static.com/f9f7d6d5-4cd0-4080-83e2-f1df86d688f0/Untitled.png)
- At any point as light travels through a participating medium, it can be (partially) absorbed and scattered.
如果云中间有光源,那么中间会发光。
在光线行进的过程中,云里面有各种晶体,会把光线随机打到其他光线去。
传播的时候也可能接收到其他地方散射过来的光。
有些光传播着能量就没了,例如乌云,穿不过去,就等于被吸收了。
![https://s3-us-west-2.amazonaws.com/secure.notion-static.com/b372c6a3-3d6b-4075-aa0e-90775255dd5b/Untitled.png](https://s3-us-west-2.amazonaws.com/secure.notion-static.com/b372c6a3-3d6b-4075-aa0e-90775255dd5b/Untitled.png)
- Use Phase Function to describe the angular distribution of light scattering at any point x within participating media.
任何一个点都会向各种地方散射,怎么散由一个函数来定义:Phase Function(相位函数),这个函数决定是均匀地散(下图左2),还是主要往背后散(下图左1)或者向前散(下图左3),与 BRDF 很像。
![https://s3-us-west-2.amazonaws.com/secure.notion-static.com/214ac42f-bb4a-473c-9414-2f34b064ee22/Untitled.png](https://s3-us-west-2.amazonaws.com/secure.notion-static.com/214ac42f-bb4a-473c-9414-2f34b064ee22/Untitled.png)
Rendering
- Randomly choose a direction to bounce
- Randomly choose a distance to go straight
- At each ‘shading point’, connect to the light