Darkplaces engine[1] had introduced lots of features including photon mapping back in 2011, but it was slow as I remember. Photon mapping is kind of a predecess

Darkplaces engine[1] had introduced lots of features including photon mapping back in 2011, but it was slow as I remember. Photon mapping is kind of a predecessor of path tracing[2]. [1] https://icculus.org/twilight/darkplaces/download.html https://icculus.org/twilight/darkplaces/download.html [2] https://en.wikipedia.org/wiki/Photon_mapping https://en.wikipedia.org/wiki/Photon_mapping