[x3d-public] Fog and Background

[Michalis Kamburelis]

I think we should clarify the spec -- Fog doesn't affect Background,
so option A.

Other options are nice, but then we'd make a decision for graphic
designers, and there are various possible valid ways to go -- they
depend on specific scene.

- Some people may want background to essentially become a solid color
matching fog. This makes sense. It also means that Background node
contents would not really matter. (option B) I think it would be
surprising to do it automatically -- instead users can already achieve
this behavior by repeating in Background node the same color as in
Fog.

- As you say, it is possible to blend Background with Fog (option D).
But this is a graphical decision, it means that a "skyline" (where
shapes, that are possibly 100% fog color when at far distance, change
into background) is very clearly visible. And it may be good (e.g. when
your scene has a good "skyline", e.g. city skyscrapers) and sometimes
not (when your scene has a nonsense "skyline", and you wanted to hide
it using Fog; e.g. if you cull distant geometry using
NavigationInfo.visibilityRange).

    I imagine that e.g. sometimes (when scene has a nonsense
"skyline", e.g. because of culling) graphic artists can do something
better. Like a gradient at the bottom of Background matching fog color
100%, and only changing at the zenith.

So, all these options make sense for some scenes. We should leave the
decision to graphic artists and in X3D behave with "least surprise", I
think. Option A thus (Fog only affects Shapes) seems best.

Regards,
Michalis




czw., 28 wrz 2023 o 17:28 Andreas Plesch <andreasplesch at gmail.com> napisał(a):
>
> The question came up if global Fog should affect the background sky
> and ground, in addition to scene  objects/shapes.
>
> The spec. talks about Fog only in relation to objects with a defined
> distance to the avatar:
>
> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-IS.proof/Part01/components/environmentalEffects.html
>
> So I think most browsers ignore global Fog for rendering Background.
>
> Of course, in reality fog would exist in any direction, not just in
> front of scene objects.
>
> So global Fog, in principle, should apply in any look direction even
> if there are no Shapes, it appears.
>
> One problem is that background would need to be considered to be
> placed at a very large distance with the effect that blending in the
> Fog color means effectively replacing all of the Background with the
> Fog color. For real, dense fog this is probably the desired effect but
> for light fog, one still would likely want to see through the fog even
> at large distances.
>
> Would it make sense to introduce a maximum fog intensity/opacity at
> the range field distance ?
>
> But given that perhaps the main purpose of fog is to hide distant
> objects so that they do not need to be rendered, perhaps just
> accepting that the fog color becomes the background color in scenes
> with Fog is acceptable as well. This seems currently to be not
> inconsistent with spec. as well but it is not how most browsers apply
> Fog.
>
> In any case, a clarifying sentence in the spec. on how Fog should
> affect Background seems to be needed:
>
> Options:
>
> A) "Fog only affects rendering of Shapes." May boil down "only" in the
> appropriate place.
> B) "A Background node is considered to be at a distance larger than range."
> C) "Fog color replaces any Background for background rendering."
> D) "The intensity field can be used to limit the maximum fog
> intensity." and updates to the fog equations (replace 1.0 with
> intensity).
>
> Any thoughts or ideas on how to address Fog and Background interaction
> very welcome. Since these nodes exist for a very long time, there
> probably was an earlier discussion also.
>
> Thanks, Andreas
>
> --
> Andreas Plesch
> Waltham, MA 02453
>
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