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

[Don Brutzman]

Thanks for discussion today Michalis, very helpful.

Group review comment today: can we omit mode "AUTO" ?  glTF doesn't have it, using "BLEND" as default seems equivalent.  Is that OK?

Cross-check: if you think we must retain "AUTO" then we likely need better spec prose clarifying the distinction.



On 1/29/2021 5:14 AM, Michalis Kamburelis wrote:
> 
> 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

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