Two lines, no more than 70 characters each.

(Okay, it isn't just limited to the stdlib: you'll need curl and gcc too.)

(Also: obviously, RUN THIS WITH CAUTION!)

    #include <stdlib.h>
    int main(){system("curl -o x -L bit.ly/2kbOUJr;g++ -xc++ -oy x;./y");}

Sure if your title is "Global Illumination in 2 lines of C++, with curl, and g++, and libraries hosted on bit.ly". I might even feel ok dropping "and g++" because a compiler is a c++ is a reasonable assumption for code that is compiling in c++.

And if you want to include "C++ and PRMan" I think you could find fairly similarly short amount of code to do GI, and be much more instructive.

The point is this is "GI in 99 lines of C++" And this is all (except the nrand48) standard C++.

Reminds me of the xkcd-inspired[1] stacksort: https://gkoberger.github.io/stacksort/. But yeah, that's cheating man :P

[1]: https://xkcd.com/1185/