[x3d-public] PR with new X3D field: Appearance.alphaMode

[Michalis Kamburelis]

Don Brutzman <brutzman at nps.edu> wrote:
>
> Sounds good - now 9 pacific.  You can call me directly if you were thinking it is earlier.

9 AM Pacific seems to match what I had in my calendar (5 PM Polish
time) :) I'll be there.

>
> Questions please:
>
> a. Wondering if this applies to all of the various texture nodes used in physically based materials?  Any issues in that direction?

No issues.

Note that the formulation of "alphaMode" doesn't talk about specific
textures (and it's not about textures only). The "alphaMode" says what
to do with "final alpha value". And the "final alpha value" is
calculated using lighting equations, that already specify what
textures affect/don't affect this.

In case of PhysicalMaterial, the final alpha depends on
PhysicalMaterial.transparency and the alpha channel of
PhysicalMaterial.baseTexture . The other textures (like
PhysicalMaterial.normalTexture or PhysicalMaterial.emissiveTexture) do
not affect the "final alpha value" following the lighting equations.

>
> b. Shouldn't we add the alphaCutoff field?  Seems like an important parameter for image analysis.
>
>         SFInt32 [in out] alphaCutoff 0.5   [0,1]
>
> alphaCutoff is glTF name, "Alpha Clip (clip threshold)" is terminology used by Blender.

I think yes, good point. This is trivial to add, and it's a good time
to add it now. I'll do it ASAP today.

Note that it's SFFloat, not SFInt32 :) Any float value between 0 and 1
makes sense, the default 0.5 matching both glTF and CGE.

Regards,
Michalis