X‑Plane announces Physically Based Rendering

I always won­dered when X‑Plane would jump on the PBR band­wag­on. I like X‑Plane, I think its the best active­ly-devel­oped* flight sim­u­la­tor out there, but I always felt that shad­ing could be bet­ter. For instance, there is this unre­al­is­tic ‘Lam­bert-shad­ed’ world ter­rain tex­ture, which becomes too dark at sun­set; anoth­er is the dread­ed ‘con­stant ambi­ent col­or’ that plagues the shad­ing of objects.

Now in this post on the X‑Plane devel­op­er blog, Ben announces that Phys­i­cal­ly Based Ren­der­ing is a future devel­op­ment goal, yay! Then he goes on to say that, while sur­face shad­ing will be a solved prob­lem™ because of PBR, oth­ers like par­tic­i­pat­ing media (clouds, atmos­phere) would still need mag­ic tricks for the fore­see­able future.

I’m not argu­ing with that. I did many mag­ic tricks in the past all kinds of shad­ing, sur­face, cloud and atmos­phere includ­ed. Many can be found scat­tered around this blog. Here are two mag­ic tricks which are non-dis­rup­tive and easy to imple­ment, which could improve sur­face shad­ing in X‑Plane right now:

  • Replace the con­stant ambi­ent term with some­thing like hemi­sphere light­ing [1]!
    Shad­ing in X‑Plane is most­ly out­door, so two hemi­sphere col­ors based on the sky and ground of the air­craft posi­tion does won­ders to the shad­ing of areas that are not in direct sunlight.
  • Use the Lom­mel-Seel­iger law [2] for the world ter­rain texture!
    This law is still cheap to cal­cu­late and is more appro­pri­ate for the most­ly rough plan­e­tary sur­face, for which it has been devel­oped [3].

(* which elim­i­nates MSFS from the equation)


[1] Shawn Har­g­reaves (2003): “Hemi­sphere Light­ing with Radios­i­ty Maps”

[2] Fair­bairn, M. B. (1999): “Plan­e­tary Pho­tom­e­try: The Lom­mel-Seel­iger law”

[3] Hugo Seel­iger (1887) “Zur The­o­rie der Beleuch­tung der großen Plan­eten, ins­beson­dere des Saturn”
(direct link to the rel­e­vant page in the only online ver­sion that seems to exist)


4 Gedanken zu „X‑Plane announces Physically Based Rendering

    • Hal­lo Max,
      its not entire­ly clear what the lamb­da means because he ref­er­ences an ear­li­er pub­li­ca­tion of him in a quar­ter­ly (“Viertel­jahress­chrift”) on which the for­mu­la is based. How­ev­er, lat­er in the text, lamb­da is set rou­tine­ly to 1 so I think it serves as an empir­i­cal parameter.
      I’ve not seen this para­me­ter in the mod­ern ver­sion of the Lom­mel-Seel­iger BRDF either.

  1. Hel­lo Christian,
    thanks for explanation.
    Glad to report we’ve improved our ter­rain light­ing great­ly with Lom­mel-Seel­iger BRDF, pre­vi­ous­ly we’vve used it only for moon shad­ing. Thanks for point­ing out!

  2. Pingback: Elite Dangerous: Impressions of Deep Space Rendering | The Tenth Planet

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