ptracey

P.Shirley's The Rest of Your Life Path Tracer with Assimp and Spectral Rendering Switch

Docs are available in: https://d-k-e.github.io/ptracey/

This is basically what you get in P. Shirley's awesome The Rest of Your Life tracer available in here in book form. For the code checkout here.

with model loading capabilities of assimp, which is available in here

Features

• Very simple multi threaded rendering with c++11 <future>.

• Each mesh and model is loaded as bvh_node.

• Documentation (well automatically generated by doxygen for now, but I am hoping improve it when I have more time)

• Spectral Rendering switch.

• Spectral Power Distribution IO in several formats:

  • Json: Dumps spds to a json file as they come out from rendering function. The structure of the json file is quite simple. x and y denote the placement of image pixel, values is the array whose elements are wave length - power value pairs. The first element is the wave length. The second element is the power value. The structure of the io object is very simple. Checkout spdio.hpp for more details.

  • Csv: Dumps spds to a Comma Separated Value (CSV) file. It should be much more compact than json. The structure of the file is quite simple. First row is x,y values for pixels. From the second row and below, values under the x column are wavelength values, values under y column are power values. The separator for the csv file is ','. When the length of two spds don't match, we pad the shorter spd with zeros, so that both wavelength value and the associated power value would be zero. This should help to distinguish padded rows from actual values.

  • Spb: Spectral Binary Format is an acknowledged format by CIE. Its specification is really simple. The parser I use come from another project of mine. It is a little rough around edges, but it gets the job done. However, in order to support serialization into .spb we need to resample the image spectra into a more homogeneous structure. Since specification of spb requires that each spectrum needs to have the same amount of wave length resolution and same amount of number of channels (number of channels correspond to number of sampled wave lengths, and wave length resolution corresponds to distance between each wave, if I understood the specification correctly), we do an additional resampling of spectra before passing them to its corresponding io object.

In Progress

• Metropolis Light Transport algorithm for rendering

• Refactoring...

• Other bsdfs.

Requirements

• Assimp

• c++17+

• cmake 3+

• rapidcsv for reading csv files (included in headers)

• stb for reading images.

• Json for Modern C++ parser

Building

The only dependency that might be problematic is Assimp. Just set the absolute path to its shared library to AssimpSOPath variable in CMakeLists.txt file and proceed regularly that is, once the value of AssimpSOPath is set:

• mkdir build

• cd build

• cmake ..

Install

Asset paths are hard coded into code, so stable install location would be good for the overall project. I have used bin folder inside the main directory.

• mkdir bin

• Now you can do stuff like make install and arrange your assets with respect to the install location of your executable which in this case is bin folder situated at the same level of the README file.

Small Note on Spectral Rendering Switch

Spectral rendering code has been heavily influenced from pbrt especially during conversion of rgb's to spectrums. It also inherits the idea of having the capacity to compile code with different rendering switches.

If you want to turn on, spectral rendering you should comment out the relative section in spectrum.hpp. Once you rendered the image, if you are unsatisfied with what you have, try changing xyz2rgb__* function under sampled_spectrum.hpp, with something else defined in specutils.hpp. If you are unsatisfied with all of the functions there, try using another matrix for conversion process.

You'll see that besides the function xyz2rgb_pbr which is the exact same function used by the pbr source code, all functions are defined in the same manner. You define a matrix, then multiply it with xyz vector. If you are interested in doing spectral rendering in c++, you should be able to understand what is going on in the other functions so much so that you reproduce them with different values for matrices.

Another side note. Though the code is heavily influenced from pbrt, the spectral power distribution object defined in spd.hpp, has relatively distinct features. I differ a lot from pbrt in that perspective, for the better or the worse.

Screen shots

Here are some eye candy. They are mostly reproductions from P. Shirley's books.

Spectral Rendering Output

A Special Hallmark for #RTKitty

The model is made by EKA: twitter @bakin___

It is traced by PTracey.

• Anger Kitty

• Glass Kitty

• Invisible Kitty

• Metal Kitty

• Night is Yours Kitty

• Glow me Thy Name Kitty