[x3d-public] Negative scale and winding order

Thu Sep 21 17:29:33 PDT 2023

See the problem is, I just found a glitch in my email.

motionsEnabled is part of HAnimHumanoids.  (credit to Doug Sanden)

On Thu, Sep 21, 2023 at 7:21 PM John Carlson <yottzumm at gmail.com> wrote:

> I agree, write a good specification, then let the programmers have at it.
> I am a research prototyper and non-professional tester and pretty awesome
> at finding glitches.
>
> And there are several currently outstanding in XML Schema, no
> motionsEnabled in XML Schema. HAnimMotion joints and channels fiields are
> MFStrings in XMLSchema, but SFString in x3d4.
>
> I’ve been trying to get a report out, including diffs.  These are critical
> to generating good XML and VRML code with x3d.py.
>
> WS is a priority.  Can someone recommend a good Maya .ma to .x3d converter
> before I go traipsing around the universe finding one?
>
> John
>
> On Thu, Sep 21, 2023 at 6:56 PM Brutzman, Donald (Don) (CIV) <
> brutzman at nps.edu> wrote:
>
>> Negative scaling is certainly a special case and not something that has
>> historically been supported in VRML or X3D. Thanks for careful
>> consideration of any unexpected variations.
>>
>> Our design goals make it clear that we have no desire to vary from glTF
>> in X3D 4.0. If there are any recommendations needed for authors to maximize
>> and hopefully achieve full interoperability with glTF rendering, they are
>> always welcome.
>>
>> v/r Don
>> ------------------------------
>> *From:* x3d-public <x3d-public-bounces at web3d.org> on behalf of Holger
>> Seelig <holger.seelig at yahoo.de>
>> *Sent:* Thursday, September 21, 2023 2:56:48 PM
>> *To:* Joe D Williams <joedwil at earthlink.net>
>> *Cc:* Andreas Plesch <andreasplesch at gmail.com>; X3D <x3d-public at web3d.org>;
>> holger.seelig at googlemail.com <holger.seelig at googlemail.com>
>> *Subject:* Re: [x3d-public] Negative scale and winding order
>>
>> Unfortunately, I can't just change something that has been implemented
>> this way since the beginning of X_ITE's existence. The way X_ITE handles
>> negative scaling is exactly the way it is specified in glTF, which is not
>> bad and is implemented in CGE under the term Robust Negative Scale. Until
>> everything is thought over, I have to agree with Andreas with his advice to
>> just set the solid field to false, as it is the easiest way to avoid this
>> issue.
>>
>> Best regards,
>> Holger
>>
>> --
>> Holger Seelig
>> Leipzig, Germany
>>
>> holger.seelig at yahoo.de
>> https://create3000.github.io/x_ite/
>>
>> Am 21.09.2023 um 19:24 schrieb Joe D Williams <joedwil at earthlink.net>:
>>
>> So perhaps the question is how to apply negative scale transforms
>> tonormals as intended by the spec.The Leif example has ccw=false and a
>> negative scale (for z). Itappears as outside in on x_ite and outside out on
>> view3dscene andx3dom.
>>
>>
>> Of course I am interested in this because to me the X_ITE rendering is
>> wrong, unless that is, the player is required to reverse the normals for
>> scale z = -1.
>> X_ITE is 'automagically' reversing the normals, so when I do the
>> ccw=FALSE the  thing  is transparent from the front of the polygon. Of
>> course if I use ccw=TRUE then the  other tools look like X_ITE, transparent
>> from the front.
>>
>> Holger, can you please either convince the other players they are wrong,
>> or fix yours to work like the rest. If the spec is not certain what to do
>> about this, then please either fix the spec or X_ITE.
>>
>> I just want the model to show as intended and be correct, even if sort of
>> a practical hack, so please l figure it out because I really need everyone
>> to do the right thing on this, whatever that might be.
>>
>> . Thanks and Best Regards,
>> Joe
>>
>>
>> -----Original Message-----
>> From: Joe D Williams <joedwil at earthlink.net>
>> Sent: Sep 19, 2023 1:26 PM
>> To: Andreas Plesch <andreasplesch at gmail.com>, X3D Graphics public
>> mailing list <x3d-public at web3d.org>, <holger.seelig at googlemail.com>
>> Subject: Re: [x3d-public] Negative scale and winding order
>>
>> While this approach is very practical, I am not sure what the
>> spec.actually requires in this respect.
>>
>>
>> I did not care, it worked and I will look more later. The following is
>> all good. I think the players show it different because the user code is
>> changed from what I sent.
>>
>>
>> Sorry I sort of wrote this off, to both you and Holger.
>> A good, reliable solution to this problem is needed, as learned or not
>> from recent experience.
>>
>> One thing I think happened to me was seeing that common graphics
>> authoring programs use as a 'Native' default or pre-selected +Zin with
>> left-hand rule for axis rotations.
>> For the Humanoid animation, we want to align ourselves in +Zout character
>> space, so the character Front is looking out of the screen with +y up, +x
>> to character left. In the case of x3d +Zout, the character is gaze is
>> toward +z. In the case of +Zin, the character Front gaze is toward -z. Or,
>> we may find the situation where the character is drawn in +Zin with gaze
>> toward +z.
>>
>> For HAnim there are three main issues: skeleton and skin and animations.
>> Well, actually these boil down into just one problem: They all have to work
>> together. So to even consider importing stuffs drawn or animated in a
>> different space a plan is needed. I used standard features to force display
>> of skin because it was drawn in a different space. This almost worked
>> everywhere.
>>
>> I think it should work everywhere, because the -1 for z scaling is going
>> to operate just the same as if I had actually negated the coord points(?).
>> Since the +Zin model with scale 1 1 1 will be seen as facing -z the
>> character's back is toward the x3d default camera. Using scale 1 1-1
>> operates so that the character is now facing the x3d default camera.
>> However, just guessing, since the polygon that was drawn ccw true is now
>> being drawn ccw false and is now transparent from its front. Changing ccw
>> to false seemed to get the normal aimed in the right direction.
>>
>> Thanks for the help,
>> Joe
>>
>>
>>
>>
>>
>>
>>
>> -----Original Message-----
>> From: Joe D Williams
>> Sent: Sep 19, 2023 11:09 AM
>> To: Andreas Plesch , X3D Graphics public mailing list
>> Subject: Re: [x3d-public] Negative scale and winding order
>>
>>
>> -----Original Message-----
>> From: Andreas Plesch
>> Sent: Sep 19, 2023 9:03 AM
>> To: X3D Graphics public mailing list
>> Subject: [x3d-public] Negative scale and winding order
>>
>> Holger made good points on why a negative scale in the parent
>>
>> transform should not affect which side of a geomet is considered
>> facing outward and visible with solid=true.
>>
>> OK, I thought I tried that with no effect.
>>
>> While this approach is very practical, I am not sure what the spec.
>>
>> actually requires in this respect.
>>
>> I did not care, it worked and I will look more later.
>> The following is all good. I think the players show it different because
>> the user code is changed from what I sent.
>>
>> First, it does not explicitly single out the case of a negative scale.
>>
>> Should it ? If so, it would probably have to deal with the effective
>> world transform.
>>
>>
>> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-IS.proof/Part01/components/rendering.html#CommonGeometryFields
>>
>> 'The ccw field defines the ordering of the vertex coordinates of the
>> geometry with respect to user-given or automatically generated normal
>> vectors used in the lighting model equations. If ccw is TRUE, the
>> normals shall follow the right hand rule; the orientation of each
>> normal with respect to the vertices (taken in order) shall be such
>> that the vertices appear to be oriented in a counterclockwise order
>> when the vertices are viewed (in the local coordinate system of the
>> Shape) from the opposite direction as the normal. If ccw is FALSE, the
>> normals shall be oriented in the opposite direction. If normals are
>> not generated but are supplied using a Normal node, and the
>> orientation of the normals does not match the setting of the ccw
>> field, results are undefined.'
>>
>> has the relevant ccw field language.
>>
>> I think the specified process is:
>>
>> - Compute the outward facing normal of a triangle using the ordering
>> of the vertices in such a way that the ordering appears
>> counterclockwise when viewed in the opposite direction of the computed
>> normal. This uses the local, untransformed (raw) coordinates.
>>
>> - invert the normal if ccw=false.
>>
>> - Apply the accumulated transforms to both the vertices and the
>> computed normal. The spec. has a strict definition on how to apply a
>> transform to vertices to transform from the child space to the parent
>> space. For normals transformations there is a computer graphics
>> standard approach and probably opengl based equations but the spec.
>> itself seems to be silent.
>>
>> So perhaps the question is how to apply negative scale transforms to
>> normals as intended by the spec.
>>
>> The Leif example has ccw=false and a negative scale (for z). It
>> appears as outside in on x_ite and outside out on view3dscene and
>> x3dom.
>>
>> A workaround is solid=false but that may not always be possible or
>> desired.
>> Another workaround is to not use negative scales/mirroring, eg.
>> preprocess geometry accordingly which seems like a major limitation.
>>
>> -Andreas
>>
>> On Tue, Sep 19, 2023 at 10:37 AM wrote:
>>
>>
>> Send x3d-public mailing list submissions to
>> x3d-public at web3d.org
>>
>> To subscribe or unsubscribe via the World Wide Web, visit
>> http://web3d.org/mailman/listinfo/x3d-public_web3d.org
>> or, via email, send a message with subject or body 'help' to
>> x3d-public-request at web3d.org
>>
>> You can reach the person managing the list at
>> x3d-public-owner at web3d.org
>>
>> When replying, please edit your Subject line so it is more specific
>> than "Re: Contents of x3d-public digest..."
>>
>>
>> 2. Negative Scale
>>
>> A negative scale will not affect what is front face and what is back
>> face. This means that a Text node with solid true, mirrored with negative
>> scale (0 -1 0), also shows its front face to the camera. This makes it
>> possible to create a text with solid true which has a mirrored counterpart
>> which is a clone of the Text node.
>>
>> A negative scale will not turn the model inside out, it stays as it is.
>> The main advantage is as described above: we can use solid true models in
>> many situations where a negative scale is used without flipping inside out.
>>
>> This effect is achieved by detecting if there is any negative scale,
>> which can be determined if the determinant of the scale-rotation matrix is
>> less than zero. If this is the case, ccw must be exchanged with cw and vice
>> versa.
>>
>>
>> _______________________________________________
>> x3d-public mailing list
>> x3d-public at web3d.org
>> http://web3d.org/mailman/listinfo/x3d-public_web3d.org
>>
>>
>> _______________________________________________
>> x3d-public mailing list
>> x3d-public at web3d.org
>> http://web3d.org/mailman/listinfo/x3d-public_web3d.org
>>
>>
>>
>> _______________________________________________
>> x3d-public mailing list
>> x3d-public at web3d.org
>> http://web3d.org/mailman/listinfo/x3d-public_web3d.org
>>
>>
>>
>> _______________________________________________
>> x3d-public mailing list
>> x3d-public at web3d.org
>> http://web3d.org/mailman/listinfo/x3d-public_web3d.org
>>
>>
>> _______________________________________________
>> x3d-public mailing list
>> x3d-public at web3d.org
>> http://web3d.org/mailman/listinfo/x3d-public_web3d.org
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://web3d.org/pipermail/x3d-public_web3d.org/attachments/20230921/1d2879a2/attachment-0001.html>