[x3d-public] Defaults of SpotLight.cutOffAngle, beamWidth changed (maybe by mistake) in X3D 3.3
Brutzman, Donald (Don) (CIV)
brutzman at nps.edu
Mon Feb 14 07:14:21 PST 2022
Thanks for continued analysis.
I like the clearer field names in glTF reference that you provided:
Property
Description
Required
innerConeAngle
Angle, in radians, from centre of spotlight where falloff begins. Must be
greater than or equal to 0 and less than outerConeAngle.
No, Default: 0
outerConeAngle
Angle, in radians, from centre of spotlight where falloff ends. Must be
greater than innerConeAngle and less than or equal to PI / 2.0.
No, Default: PI / 4.0
It seems clear to me that innerConeAngle corresponds to beamWidth, and
outerConeAngle corresponds to cutOffAngle.
If you disagree with “cutOffAngle > beamWidth” (perhaps greater than or
equals) relationship, then you think the opposite and thus would need a new
diagram, correct? Similarly, that is a functional change to the (possibly
still incorrect?) X3D Spotlight.
* X3D4 Architecture, Figure 17.1 - SpotLight node
* https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-
CD1/Part01/components/lighting.html#f-SpotLightnode
If these parameters have been forever broken, then we need to unambiguously
define and illustrate the correct approach. I am open to possibility of
alignment with glTF to ensure that no misunderstandings are carried forward.
If a simpler adjustment of default values might work, that is possible… in
general though, defaults are chosen to be somewhat forgiving so that
authors can tell something is going on (directionality is sometimes
difficult) and then tune values accordingly.
Taking a step back: this all seems fundamental yet we are circling…
suggest we get together on Web3D teleconference this week. Hoping that
Friday’s regular X3D weekly meeting might work for you? Several people
can be in attendance then.
all the best, Don
--
Don Brutzman Naval Postgraduate School, Code USW/Br brutzman at nps.edu
Watkins 270, MOVES Institute, Monterey CA 93943-5000 USA +1.831.656.2149
X3D graphics, virtual worlds, Navy robotics https://
faculty.nps.edu/brutzman
-----Original Message-----
From: Michalis Kamburelis <michalis.kambi at gmail.com>
Sent: Monday, February 14, 2022 3:50 AM
To: Brutzman, Donald (Don) (CIV) <brutzman at nps.edu>
Cc: X3D Graphics public mailing list <x3d-public at web3d.org>
Subject: Re: [x3d-public] Defaults of SpotLight.cutOffAngle, beamWidth
changed (maybe by mistake) in X3D 3.3
I have to say
1. I don't agree that "Thus default values need to have cutOffAngle >
beamWidth."
2. And I don't agree that cutOffAngle = pi/2 is good default. It's
surprisingly wide, all other software/formats I checked (see below) have
smaller cutOffAngle (aka outerConeAngle).
AD 1 - The specification explicitly allows "If the beamWidth is greater
than the cutOffAngle, beamWidth is defined to be equal to the cutOffAngle
and the light source emits full intensity within the entire solid angle
defined by cutOffAngle...." And the equations in spec reflect that,
everything works OK when beamWidth > cutOffAngle.
You don't have a smooth falloff in this case, but it looks reasonable.
AD 2 - This is my main pain point. I really think that cutOffAngle =
pi/2 is too wide, it means that whole spot angle is 180 degrees, so
SpotLight is at "maximally wide" state shining on half of 3D space. I
looked at defaults in other formats/application, and noone has so wide
default:
- glTF punctual lights (
<https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.co
m%2FKhronosGroup%2FglTF%2Ftree%2Fmain%2Fextensions%2F2.0%2FKhronos%2FKHR_lig
hts_punctual&data=04%7C01%7Cbrutzman%40nps.edu%7C5493278ab60b46b9951e08d
9efb03649%7C6d936231a51740ea9199f7578963378e%7C0%7C0%7C637804363573077429%7C
Unknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLC
JXVCI6Mn0%3D%7C3000&sdata=d3IA54ENWoYel6mMl6mRHOy9QEdJ7qX%2FERHqNIDVXno%
3D&reserved=0>
https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com
%2FKhronosGroup%2FglTF%2Ftree%2Fmain%2Fextensions%2F2.0%2FKhronos%2FKHR_ligh
ts_punctual&data=04%7C01%7Cbrutzman%40nps.edu%7C5493278ab60b46b9951e08d9
efb03649%7C6d936231a51740ea9199f7578963378e%7C0%7C0%7C637804363573077429%7CU
nknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJ
XVCI6Mn0%3D%7C3000&sdata=d3IA54ENWoYel6mMl6mRHOy9QEdJ7qX%2FERHqNIDVXno%3
D&reserved=0
) have by default outerConeAngle = pi/4
- Blender Spot light has by default size = 45 degrees, but this expresses
2*outerConeAngle. So Blender default is like outerConeAngle = 22.5 degrees
= pi/8, even smaller
- Unity Spot has by default size = 30 degrees, but this is also
2*outerConeAngle. So again it is even smaller, like outerConeAngle =
15 degrees = pi/12
So really noone has so large default cutOffAngle = pi/2, everyone I see has
smaller. I believe that VRML 97 and X3D 3.0, 3.1, 3.2 did it right, no
change was necessary. And we should revert to that. So defaults at
- beamWidth pi/2
- cutOffAngle pi/4
If you really want to make beamWidth by default smaller, then change only
beamWidth. Make beamWidth by default pi/4 or even pi/8. But don't change
the cutOffAngle to pi/2. This is so large (and compatibility-breaking for
no good reason, IMHO) that I'm really reluctant to follow X3D 3.3 defaults
in Castle Game Engine / view3dscene, and I'm tempted to just stay with
older defaults.
Regards,
Michalis
pon., 14 lut 2022 o 09:32 Brutzman, Donald (Don) (CIV) <
<mailto:brutzman at nps.edu> brutzman at nps.edu> napisał(a):
>
> Thanks for looking at this Michalis. Further detail is available at
>
>
>
> Mantis 441: 17.4.3 SpotLight -- Default Values
> <https://www.web3d.org/member-only/mantis/view.php?id=441>
https://www.web3d.org/member-only/mantis/view.php?id=441
>
>
>
> Essential point: beamWidth is the inner angle of full intensity,
cutOffAngle is the outer angle of zero intensity. Thus default values need
to have cutOffAngle > beamWidth.
>
>
>
> So I think that this change, performed in 2009, fixed a prior problem in
the specification. Brightest area needs to be the inside cone, with
intensity gradually fading until reaching the outside cone.
>
>
>
> Hopefully that now looks better to you. Thanks for all scrutiny.
>
>
>
> *
> <https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-CD1/P>
https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-CD1/P
> art01/components/lighting.html#SpotLight
>
> 17.4.4 SpotLight
>
> SpotLight : X3DLightNode {
>
> SFFloat [in,out] ambientIntensity 0 [0,1]
>
> SFVec3f [in,out] attenuation 1 0 0 [0,∞)
>
> SFFloat [in,out] beamWidth π/4 (0,π/2]
>
> SFColor [in,out] color 1 1 1 [0,1]
>
> SFFloat [in,out] cutOffAngle π/2 (0,π/2]
>
> SFVec3f [in,out] direction 0 0 -1 (-∞,∞)
>
> SFBool [in,out] global TRUE
>
> SFFloat [in,out] intensity 1 [0,∞)
>
> SFVec3f [in,out] location 0 0 0 (-∞,∞)
>
> SFNode [in,out] metadata NULL [X3DMetadataObject]
>
> SFBool [in,out] on TRUE
>
> SFFloat [in,out] radius 100 [0,∞)
>
> SFBool [in,out] shadows FALSE
>
> SFFloat [in,out] shadowIntensity 1 [0,1]
>
> }
>
>
>
> p.s. I just confirmed correctly matching values in X3D XML Schema and DTD.
>
>
>
> all the best, Don
>
> --
>
> Don Brutzman Naval Postgraduate School, Code USW/Br
<mailto:brutzman at nps.edu> brutzman at nps.edu
>
> Watkins 270, MOVES Institute, Monterey CA 93943-5000 USA
+1.831.656.2149
>
> X3D graphics, virtual worlds, Navy robotics https://
> faculty.nps.edu/brutzman
>
>
>
> From: x3d-public < <mailto:x3d-public-bounces at web3d.org> x3d-public-
bounces at web3d.org> On Behalf Of Michalis
> Kamburelis
> Sent: Sunday, February 13, 2022 8:42 PM
> To: X3D Graphics public mailing list < <mailto:x3d-public at web3d.org> x3d-
public at web3d.org>
> Subject: Re: [x3d-public] Defaults of SpotLight.cutOffAngle, beamWidth
> changed (maybe by mistake) in X3D 3.3
>
>
>
> 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 <
<mailto:michalis.kambi at gmail.com> 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:
> <https://nam10.safelinks.protection.outlook.com/?url=http%3A%2F%2Ftecfa>
https://nam10.safelinks.protection.outlook.com/?url=http%3A%2F%2Ftecfa
> .unige.ch%2Fguides%2Fvrml%2Fvrml97%2Fspec%2Fpart1%2FnodesRef.html%23Sp
> otLight&data=04%7C01%7Cbrutzman%40nps.edu%7C5493278ab60b46b9951e08
> d9efb03649%7C6d936231a51740ea9199f7578963378e%7C0%7C0%7C63780436357307
> 7429%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBT
> iI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=DR7HBogG27XNmzipDNWEXGHtHw0
> HQyJgaT%2BSPqIcKWY%3D&reserved=0
>
> - X3D 3.0:
> <https://www.web3d.org/documents/specifications/19775-1/V3.0/Part01/com>
https://www.web3d.org/documents/specifications/19775-1/V3.0/Part01/com
> ponents/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/com>
https://www.web3d.org/documents/specifications/19775-1/V3.1/Part01/com
> ponents/lighting.html
>
> - X3D 3.2:
> <https://www.web3d.org/documents/specifications/19775-1/V3.2/Part01/com>
https://www.web3d.org/documents/specifications/19775-1/V3.2/Part01/com
> ponents/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/com>
https://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/com
> ponents/lighting.html#SpotLight
>
> - X3D 4.0 draft:
> <https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-CD1/P>
https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-CD1/P
> art01/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://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoc>
https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoc.
> instantreality.org%2Fdocumentation%2Fnodetype%2FSpotLight%2F&data=
> 04%7C01%7Cbrutzman%40nps.edu%7C5493278ab60b46b9951e08d9efb03649%7C6d93
> 6231a51740ea9199f7578963378e%7C0%7C0%7C637804363573077429%7CUnknown%7C
> TWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVC
> I6Mn0%3D%7C3000&sdata=n1Vnxg6FcwwzV54VjD0hAvPq3X25SCrYvmP%2FFSNtrc
> k%3D&reserved=0
>
> - X3DOM (at least docs) is confused, judging from
> <https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoc>
https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoc.
> x3dom.org%2Fauthor%2FLighting%2FSpotLight.html&data=04%7C01%7Cbrut
>
zman%40nps.edu%7C5493278ab60b46b9951e08d9efb03649%7C6d936231a51740ea9199f757
8963378e%7C0%7C0%7C637804363573077429%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLj
AwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=payjbN
AnAV%2B2lc8N7Ku0EGt7K6sJdWMyV%2FTJtAsds4Q%3D&reserved=0 . 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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://web3d.org/pipermail/x3d-public_web3d.org/attachments/20220214/428ce7d9/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 5353 bytes
Desc: not available
URL: <http://web3d.org/pipermail/x3d-public_web3d.org/attachments/20220214/428ce7d9/attachment-0001.p7s>
More information about the x3d-public
mailing list