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mmp / pbrt-v4

Source code to pbrt, the ray tracer described in the forthcoming 4th edition of the "Physically Based Rendering: From Theory to Implementation" book.
https://pbrt.org
Apache License 2.0
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InlinedVector sometimes behave differently than std::vector #371

Closed w3ntao closed 1 year ago

w3ntao commented 1 year ago

After replacing InlinedVector<Point3f> with std::vector<Point3f>, I got different result rendering pbrt-v4-scenes/killeroos/killeroo-gold.pbrt. The difference is subtle:

compare left: rendered by official PBRT, mid: diff image, right: after replacing InlinedVector<Point3f> with std::vector<Point3f>

diff diff image: different pixels are highlighted with red dots

Code change can be found at https://github.com/w3ntao/pbrt-v4-inlinedvector/commit/c245fde62d94e7cc39ae3e7fe7d5a962938cb8c3 and it is the only different commit compared with PBRT.

Is this a bug or intended? Does InlinedVector supposed to work exactly like std::vector (when ignoring perfomance issues)?

My guess is InlinedVector might change memory layout.

mmp commented 1 year ago

Sorry for not looking at this sooner...

InlinedVector should give the same results as std::vector. I tried rendering this scene with your change, however, and am not seeing any pixel differences. Can you say more about which OS / CPU/GPU you are using?

w3ntao commented 1 year ago

I was using Debian 11 on ThinkPad L14 Gen 2 (forgot the exact CPU spec but it's i7-X 11 gen) when submitting this issue. That laptop has been gifted to a friend so it will take a while for me to reproduce this bug.

The weird thing is, I couldn't reproduce this bug with either my desktop (Debian 12, i5-13600K) or docker (Debian 11 and Debian 12).

Regarding to the scene killeroo-gold, I think the name was changed to "killeroo-gold.png" and pixelsamples changed to probably one of [16, 32, 64].

It was all CPU rendering, no GPU used. I will come back to this issue when I have access to the original hardware.

w3ntao commented 1 year ago

The bug was originally triggerd on Debian 11 with CPU 11th Gen Intel i7-1165G7 (8) @ 2.800GHz.

Now it can't be reproduced after upgrading to Debian 12. Closing this issue.