[x3d-public] Defaults of SpotLight.cutOffAngle, beamWidth changed (maybe by mistake) in X3D 3.3

[Michalis Kamburelis]

Note: I have a hypothesis why this happened.

The drawing presented at SpotLight description (it is the same in all X3D
versions) shows a situation when beamWidth < cutOffAngle. The drawing shows
a situation when these is smooth falloff between beamWidth and cutOffAngle.
Maybe someone thought that defaults do not match this drawing, ans thus
reversed the defaults.

I would say that the drawing just doesn't, and never meant to, show the
default state. It just shows an example state that is possible.

Regards,
Michalis

W dniu pon., 14.02.2022 o 05:10 Michalis Kamburelis <
michalis.kambi at gmail.com> napisał(a):

> Hi,
>
> I just noticed an alarming regression at SpotLight definition across
> X3D versions.
>
> 1. In VRML 97, X3D 3.0, 3.1 and 3.2 the default values are:
>
>   - beamWidth pi/2
>   - cutOffAngle pi/4
>
>   This means that there is no smooth falloff from beamWidth to
> cutOffAngle. Spot light has multiplier = 1 in range 0...pi/4, and then
> it's zero outside of pi/4.
>
>   I think this is the good definition. It makes sense as default.
>
>   See:
>
>   - VRML 97:
> http://tecfa.unige.ch/guides/vrml/vrml97/spec/part1/nodesRef.html#SpotLight
>
>   - X3D 3.0:
> https://www.web3d.org/documents/specifications/19775-1/V3.0/Part01/components/lighting.html#SpotLight
>
>   - X3D 3.1: this version seems to be published only as "diff from X3D
> 3.0", and it has no change regarding SpotLight, see
>
> https://www.web3d.org/documents/specifications/19775-1/V3.1/Part01/components/lighting.html
>
>   - X3D 3.2:
> https://www.web3d.org/documents/specifications/19775-1/V3.2/Part01/components/lighting.html#SpotLight
>
> 2. In X3D 3.3 and 4.0 however, the defaults are reversed:
>
>   - beamWidth pi/4
>   - cutOffAngle pi/2
>
>   This makes a different behavior, and one that is IMHO less expected.
> cutOffAngle pi/2 means that "total angle of spotlight" is pi, 180
> degrees. This is possible, but unexpected as default for a spot light.
> It's a very wide light, effectively shining on half of 3D space.
>
>   See:
>
>   - X3D 3.3:
> https://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components/lighting.html#SpotLight
>
>   - X3D 4.0 draft:
>
> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-CD1/Part01/components/lighting.html#SpotLight
>
> What others do?
>
> - Castle Game Engine and view3dscene always followed AD 1. I didn't
> even know that there was a change to this in X3D 3.3.
>
> - InstantReality (at least docs) also follows AD 1, looking at
> https://doc.instantreality.org/documentation/nodetype/SpotLight/
>
> - X3DOM (at least docs) is confused, judging from
> https://doc.x3dom.org/author/Lighting/SpotLight.html . They say that
> both cutOffAngle and beamWidth are both pi/2 by default, which is not
> consistent with any X3D version.
>
> I didn't test InstantReality or X3DOM in practice, only looked at docs now.
>
> Proposal: let's fix X3D 4.0. Revert the defaults to what was in X3D 3.2:
>
>   - beamWidth pi/2
>   - cutOffAngle pi/4
>
> Unless someone knows a good reason for change in X3D 3.3, I'm tempted
> to call this just a simple human mistake when someone was editing X3D
> 3.3.
>
> Regards,
> Michalis
>
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