My little path tracer

A picture is worth a thousand words.
dawelter
Posts: 9
Joined: Sun Oct 29, 2017 3:15 pm

My little path tracer

Postby dawelter » Sat Dec 09, 2017 8:39 am

This came out of my path tracer.
cornelbox3.jpg
cornelbox3.jpg (161.07 KiB) Viewed 1001 times


Unfortunately convergence stagnated after some 10k samples per pixel. Not unexpected since it is a difficult scene. Lit by two point lights through the holes in the ceiling. I haven't implemented area lights. The medium has chromatic collision coefficients with high scattering for blue wavelengths.

Cheers

dawelter
Posts: 9
Joined: Sun Oct 29, 2017 3:15 pm

Re: My little path tracer

Postby dawelter » Mon Dec 11, 2017 12:42 pm

Trying to reproduce results from Peter Kutz's Sky Render.
Using 10 discrete wavelengths, no ozone, purely exponential density decrease. Something is wrong. Much too greenish for my taste.
atmosphere_fisheye1.jpg
atmosphere_fisheye1.jpg (61.03 KiB) Viewed 958 times

atmosphere_fisheye2.jpg
atmosphere_fisheye2.jpg (46.42 KiB) Viewed 958 times

My approximation to the solar emission spectrum might be inadequate in the blue wavelengths :roll:
solarspectrum10bins.png
solarspectrum10bins.png (14.11 KiB) Viewed 958 times


EDIT:
Yeah that looks better!
https://www.dropbox.com/s/0jjsmpi5jvfmi ... 3.jpg?dl=0
https://www.dropbox.com/s/nh80qd93qnbje ... 4.jpg?dl=0

I changed two things at once: 36 bins instead of 10. sRGB output instead of CIE RGB 1931 because if I tell CIMG to write jpg it is probably going to be interpreted as sRGB.

Because I need RGB to spectrum conversions, I implemented the way of Smits (1999) but with more bins (kind of). The code is easily adaptable. I put it up on github: https://github.com/DaWelter/ToyTrace/bl ... sWay.ipynb

dawelter
Posts: 9
Joined: Sun Oct 29, 2017 3:15 pm

Re: My little path tracer

Postby dawelter » Sat Jan 20, 2018 2:05 pm

Been working on my path tracer. Implemented table lookup for the height profile of collision coefficients. After some more work I could reproduce the blueness of the evening sky due to absorption by ozone.
atmosphere_fisheye_ozone_compare.jpg
atmosphere_fisheye_ozone_compare.jpg (473.17 KiB) Viewed 698 times


Now there is support for area lights - in the form of triangles and spheres. Before, it supported only point lights and distant directional lights. Implemented MIS weighting for light vs. BRDF sampling.
arealights.jpg
arealights.jpg (453.05 KiB) Viewed 698 times


Quick test rendering with clouds went super slow. The ground is not a plane but a huge sphere. Thus the geometry is extremely inhomogeneously distributed. And my naive Kd-tree cannot cope with it.
atmosphere_cloudy.jpg
atmosphere_cloudy.jpg (65.41 KiB) Viewed 698 times

koiava
Posts: 46
Joined: Thu Apr 24, 2014 8:18 am
Location: Munich, Germany
Contact:

Re: My little path tracer

Postby koiava » Tue Feb 06, 2018 11:21 am

Really good results :)
Colibri Renderer

dawelter
Posts: 9
Joined: Sun Oct 29, 2017 3:15 pm

Re: My little path tracer

Postby dawelter » Wed Feb 07, 2018 7:56 am

Thank you!

Meanwhile I have a better pic. Something about the clouds strikes me as odd. Still a nice second try if you ask me. :-)
atmosphere_cloudy.jpg
atmosphere_cloudy.jpg (776.3 KiB) Viewed 363 times


To test my algorithms needed a material that has a "delta peak" plus a continuous density, so I implemented a dielectric material with a perfectly specular reflective layer. I followed a publication by Kelemen and Kalos (2001) to obtain a symmetric brdf which goes to fully specular towards grazing angles. The result:
material_test_scene.jpg
material_test_scene.jpg (323.38 KiB) Viewed 363 times

dawelter
Posts: 9
Joined: Sun Oct 29, 2017 3:15 pm

Re: My little path tracer

Postby dawelter » Thu Feb 22, 2018 8:44 am

Bidirectional path tracing! The first correct image! Well, as far as I can tell ;)
cornelbox5.jpg
cornelbox5.jpg (351.36 KiB) Viewed 72 times

High variance at 128 bidirectional random walks per pixel. Paths are weighted by one over the number of techniques that can generate the path. Implementation of MIS pending ...

graphicsMan
Posts: 157
Joined: Mon Nov 28, 2011 7:28 pm

Re: My little path tracer

Postby graphicsMan » Thu Feb 22, 2018 2:55 pm

Nice :)


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