<p>I have a few questions about setting up a bidirectional path tracer described by Veach <a href="https://graphics.stanford.edu/courses/cs348b-03/papers/veach-chapter10.pdf" rel="nofollow noreferrer">here</a>.</p>

<p>I have created both an eye path and a light path. Both are using BRDF for calculating how much light can pass after bounce and directions are sampled with importance sampling.</p>

<p>My first question is: Can I connect all possible combinations of paths? In the example below, it is a connection of points [1;3], [1;4], [1;light], [2;3], [2;4], [2; light]. It is definitely a bad idea to connect the camera with anything, but I am not sure if it the same with directly connecting with a light source.</p>

<p><a href="https://i.sstatic.net/SUTpD.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/SUTpD.png" alt="enter image description here"></a></p>

<p>And secondly, do I have to average the radiance coming from all the connected paths? I am not implementing a multiple-importance sampling for now. It will be the next step because without it I am adding even more variance.</p>

<p>Last one. Because I am using an importance sampling I am dividing by PDF. But when I am connecting these two paths I am making deterministic connection so I use PDF of 1. Is this right?</p>

CC BY-SA 4.0
2020-05-09T23:50:36.267Z
There aren't many resources for BDPT without MIS. I'd suggest reading the original Lafortune's paper on BDPT where he describes one such naive method.
gallickgunner
CC BY-SA 4.0
2020-05-10T08:15:46.043Z
I suggest directly reading Veach's paper on MIS.
lightxbulb
CC BY-SA 4.0
2020-05-10T08:41:58.333Z
Lafortune paper?? Never heard of it. I will give it a try.
Vít Gardoň
CC BY-SA 4.0
2020-05-10T09:26:50.203Z
But do I have to directly sample the light source??
Vít Gardoň
<pathtracing><sampling>
Birectional path tracing - connection of paths
Vít Gardoň
# Birectional path tracing - connection of paths

(Asked by: username_0 on 2020-05-09)

I have a few questions about setting up a bidirectional path tracer described by Veach [here](https://graphics.stanford.edu/courses/cs348b-03/papers/veach-chapter10.pdf).

I have created both an eye path and a light path. Both are using BRDF for calculating how much light can pass after bounce and directions are sampled with importance sampling.

My first question is: Can I connect all possible combinations of paths? In the example below, it is a connection of points [1;3], [1;4], [1;light], [2;3], [2;4], [2; light]. It is definitely a bad idea to connect the camera with anything, but I am not sure if it the same with directly connecting with a light source.

[![enter image description here](https://i.sstatic.net/SUTpD.png)](https://i.sstatic.net/SUTpD.png)

And secondly, do I have to average the radiance coming from all the connected paths? I am not implementing a multiple-importance sampling for now. It will be the next step because without it I am adding even more variance.

Last one. Because I am using an importance sampling I am dividing by PDF. But when I am connecting these two paths I am making deterministic connection so I use PDF of 1. Is this right?

**Tags:** pathtracing, sampling

> **Comments:**
> **username_1**: There aren't many resources for BDPT without MIS. I'd suggest reading the original Lafortune's paper on BDPT where he describes one such naive method.  
> **username_2**: I suggest directly reading Veach's paper on MIS.  
> **username_0**: Lafortune paper?? Never heard of it. I will give it a try.  
> **username_0**: But do I have to directly sample the light source??  

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## 0 answers

