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

[Erik Englesson]

Yes, I am happy about that too! :D

Thanks for the suggestion! I will have a look at using
is_constant_emission() for now and will get back to doing something more
advanced in a later iteration.

Thanks!
Erik


On 2 June 2018 at 14:07, Brecht Van Lommel <brechtvanlommel at gmail.com>
wrote:

> 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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>>
>>
>
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