[Soc-2018-dev] Weekly Report #03 - Many Light Sampling

[Brecht Van Lommel]

Great to see an initial working implementation already!

Regarding how Cycles represents energy for lights, it's defined by shader
nodes which make it a bit tricky. To start I suggest using
light->shader->is_constant_emission(&constant_emission) to get a constant
emission value if it exists.

In general lights can have textures, and we can imagine some ways to
estimate average emission by averaging a few samples, or analyzing the
shader node tree. But I wouldn't worry about that case for now.

On Fri, Jun 1, 2018 at 10:41 PM, Erik Englesson <erikenglesson at gmail.com>
wrote:

> Hi all,
>
> This week I had my final exam so now I can focus on the project full-time
> the entire summer! Looking forward to it.
>
> My project consists of two code parts: the light BVH construction and the
> traversal code to sample a light. Our idea is to do this iteratively by
> first creating a simple BVH construction and traversal code and then extend
> this more and more.
>
> This week I have been working on the following:
>
>    - A simple implementation of the light BVH that is based on the PBRT
>    book
>    - The splitting method to divide a node into two children is the
>       simplest possible right now. It is not using orientations or SAH.
>       - Method to convert the light BVH data representation on the host
>    to a data structure that can be used in the kernel
>       - The data structure of the BVH for the kernel is also the simplest
>       possible right now. It is essentially a single array of structures only
>       that the structure is represented as 4xfloat4.
>       - Kernel code to traverse the light BVH to chose a light
>    - This code calculates the probability of going down the left and
>       right child as described in the paper and then randomly picks one and
>       continues the process until a leaf node(think light) is found.
>
> That is, I have a bare-bones implementation of the full pipeline now. It
> is very much work in progress and there are several things that can be
> improved upon. I pushed all of this to my local branch here
> <https://developer.blender.org/rB2e17c3f3a10bb2f6a62b1e8d5d236c437f7ae4e8>
> .
>
> *Plan for next week*
>
> The main focus of next week will be on implementing the splitting method
> for the light BVH construction that is described in the paper. If I have
> the time I also want to have a look at some smaller details:
>
> 1. Traversal code: Figure out a better way to rescale/stretch a random
> number so I can reuse it
> 2. Traversal code: Talk to the authors of the paper about the "uncertainty
> angle"
> 3. Each node should have a member that represents the "energy" of all
> lights inside it. I need to figure out how Cycles represents
> energy(strength?) for each light and set this member correctly.
> 4. Get a better understanding/overview of the kernel code e.g. the
> kernel_path_surface.h file.
>
> Unfortunately, I do not have any images to show you guys this week. Maybe
> next week!
>
> Have a great weekend!
>
> Thanks,
> Erik
>
>
>
>
> --
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> https://lists.blender.org/mailman/listinfo/soc-2018-dev
>
>
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