[x3d-public] Spec 9.2.4 Browser options: add PBR shading? X3D3 Inline use cases for X3D4

[Andreas Plesch]

Hi Don,

On Sat, Aug 15, 2020 at 6:53 PM Don Brutzman <brutzman at nps.edu> wrote:
>
> Michalis and Andreas: thanks for close analysis.
>
> 9.2.4 Browser options
> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-WD2/Part01/components/networking.html#BrowserProperties
>
> Am understanding that we ought to change table-row default from Gouraud to Phong:
>
> =======================================================
> Name,    Description,    Type/valid range,    Default
>
> Shading;    Specify shading mode for all objects;    Wireframe, Flat, Gouraud, Phong;    Gouraud
> =======================================================

Yes, I agree with Michalis that the default should be "Phong".

> For updating the X3D4 specification, some questions remain however:
>
> a. Given your interpretation previously, does this break compliance of existing browsers?

As far as I remember, Michalis touched on that. Most browsers should
support "Phong". For those which support it, it should be
straightforward to switch to "Phong" as default if they are
maintained. Some may already have "Phong" as default and would then
move automatically into closer compliance with X3DV4. Browsers which
support "Phong" but cannot switch to it as a default due to resource
constraints would fall out of X3DV4 compliance. Since X3DV4 also will
require other, more expensive changes, to stay in compliance, resource
constraints would have this consequence regardless. Browsers which do
not support "Phong" would require action to stay in compliance: either
start supporting it (a requirement anyways in 2020) or report
"Gouraud" for the current BrowserProperties.Shading value which they
probably do already.

It would be probably helpful to have a simple test scene which renders
obviously different with Gouraud and Phong shading but I cannot think
of any. A cube with a close point light ?

> b. Do we add another value to the list of allowed enumerations, such as "PBR"?  If so, what is accompanying prose.

My understanding is that the answer is no. PBR is not an alternative
to the existing Shading options. A PBR material can be Flat (face
based), Gouraud (vertex based) or Phong (pixel based) shaded.

I cannot think of other values to consider. "Unlit" is a material
choice, not a global shading choice.

Looking at UnlitMaterial, there is a slight question with regards to
the gltf KHR_Unlit_Material extension. UnlitMaterial uses the emissive
color/texture while the gltf Unlit extension uses the base color of a
PBR material. Base color is more similar to the diffuse color of
Material. There would be better alignment with gltf if
PhysicalMaterial had an "unlit" field. I feel there was probably a
discussion why introducing an UnlitMaterial is preferable but at first
glance it seems just adding the "unlit" field to PhysicalMaterial and
in parallel relying on the current way to have unlit shading on
regular Material would be less disruptive in a practical sense. What
this means is also that supporting UnlitMaterial is probably not a
priority for x3dom until there is demand. It is not that critical
since it does not affect Inline support for gltf. Inline gltf already
has unlit support in x3dom.

Hope this helps, Andreas

> 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 http://faculty.nps.edu/brutzman



-- 
Andreas Plesch
Waltham, MA 02453