[x3d-public] X3D Working Group meeting minutes, 27 July 2018: ISO, SIGGRAPH, Python, LocalFog, regexes

[GPU Group]

I'm pretty sure freewill follows the Michalis interpretation.
-Doug

On Fri, Jul 27, 2018 at 6:28 PM, Michalis Kamburelis <
michalis.kambi at gmail.com> wrote:

> 2018-07-27 18:49 GMT+02:00 Don Brutzman <brutzman at nps.edu>:
> > 4. LocalFog work.  Sungmin Kwon and I have been considering how to use
> > LocalFog for
> >
> > 24.4.4 LocalFog
> > http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/
> components/enveffects.html#LocalFog
> >
> > states:
> > "The LocalFog node provides a way to simulate atmospheric effects by
> > blending objects with the colour specified by the color field based on
> the
> > distances of the various objects from the viewer."
> >
> > This is incorrect.  LocalFog intensity doesn't consider the viewer
> distance.
> > Rather the next sentence pertains:
> > "The distances are calculated in the coordinate space of the LocalFog
> node."
> >
> > Recommended correction: change "from the viewer" to something like "from
> the
> > local center of the LocalFog node's transformation heirarchy".
>
> The change of LocalFog prose, as you propose, would break the way it
> is implemented in view3dscene / Castle Game Engine. It would also
> break my understanding, and use-cases, of the LocalFog node.
>
> I see in http://www.web3d.org/x3d/content/examples/
> ConformanceNist/Miscellaneous/LocalFog/LocalFogEffectsPresentation.pdf
> that you  made tests (with 2 browsers that support LocalFog). But I
> tested X_ITE at
> http://www.web3d.org/x3d/content/examples/ConformanceNist/Miscellaneous/
> LocalFog/LocalFogEffectsTestIndex.html
> now, and I don't see your conclusions. In X_ITE, the visible intensity
> of fog produced by "LocalFog" depends on the distance from the viewer.
> X_ITE (at least on my browser, Firefox 60.0.1) behaves exactly like
> X3D specification currently says, and exactly like view3dscene/CGE
> already do. The fog amount depends on the distance from the viewer,
> i.e. moving the camera makes the fog appear at objects closer to you.
>
> For me (and for my implementation of view3dscene / Castle Game
> Engine), LocalFog means that the fog is applied based on the distance
> *from the viewer*, not from the "local center of the LocalFog node's
> transformation hierarchy" as you propose to change. Various prose in the
> specification makes it clear IMHO that it's the distance from the
> viewer:
>
> - "...based on the distances of the various objects from the viewer"
>
> - "Objects located outside the visibilityRange from the viewer are
> drawn with a constant colour..."
>
> From http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/
> components/enveffects.html#LocalFog
> .
>
> The LocalFog calculation is much like global Fog calculation in this
> regard.
>
> The only difference (and the reason for "Local" prefix) betwen
> LocalFog and Fog is that LocalFog only affects a subset of the scene
> (following "24.2.2.3 Local fog semantics",
> http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/
> components/enveffects.html#LocalFogSemantics
> ). Only the things within the same parent as LocalFog are affected. In
> contrast, global Fog affects everything, and is a "bindable" node.
>
> While the X3D spec talks about the "local coordinate system" of
> LocalFog, I always understood it to mean that one should apply the
> scaling (from LocalFog parent transformations) to visibilityRange.
> Nothing more. Exactly the same as the global Fog node is also in
> "local coordinate system" (
> http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/
> components/enveffects.html#Fog
> ).
>
> My use-case for LocalFog is when you want to cover only specific nodes
> with fog, while leaving the rest of the world un-fogged (or with
> different fog settings). Like this (in classic encoding):
>
> ```
>   Group { ... stuff that is unaffected by red fog ... }
>   Group {
>     children [
>       LocalFog { color 1 0 0 }
>       Group { ... stuff that is affected by red fog ... }
>     ]
>   }
> ```
>
> That being said, I support the idea of testing this on various X3D
> browsers. If all the other X3D browsers interpret LocalFog as you
> describe (calculating distance from local center, not viewer), then of
> course we should adjust the specification, and I will adjust my
> implementation:)
>
> Maybe I misinterpret something in your mail and PDF, since your own
> test (on X_ITE) contradicts your conclusions, as far as I can see.
> X_ITE seems to measure the distance from the viewer, just like X3D
> spec already says, and as view3dscene/CGE do.
>
> Apologies in advance if this is just a big misunderstanding on my part:)
>
> Best regards,
> Michalis
>
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