[x3d-public] comments on Projective texture mapping: near/far naming, textureTransform

[Don Brutzman]

Dick and I discussed this today.

On 10/12/2020 10:38 PM, Don Brutzman wrote:
> Comments on
> 
> 42  Projective texture mapping component
> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-WD2/Part01/components/ProjectiveTextureMapping.html
> 
> ---
> 
> 1. the SFFloat nearDistance and farDistance fields are very similar (perhaps identical) to nearClippingPlane and farClippingPlane in
> 
> 23.3.1 X3DViewpointNode
> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-WD2/Part01/components/navigation.html#X3DViewpointNode
> 
> Any reason why we shouldn't use the same name?

Yes we should use the same name throughout.

Interestingly, nearClippingPlane and farClippingPlane in X3DViewpointNode were defined in X3D4.  So an option is that they could be renamed to match.

Originally these were defined in NavigationInfo avatarSize float-array parameters.  Exposing them as fields in Viewpoints added a lot to animation controllability.

Curiously since the fields are SFFloat, they do not define planes per se.  They do define offset distances from the Viewpoint/OrthoViewpoint/GeoViewpoint nodes.

We decided on consistent naming, specifically: nearDistance and farDistance.  Seems like a straightforward refinement.

Am applying these changes immediately so that they can be in next build (later today probably).  Reclama discussion Friday if needed.

> ---
> 
> 2. Why don't the TextureProjector (Parallel/Perspective) nodes include a textureTransform field?  It can be applied to the texture field just as in Appearance textureTransform field
> 
> * 12.4.2 Appearance
>    https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-WD2/Part01/components/shape.html#Appearance
> 
>    SFNode [in,out] texture            NULL [X3DTextureNode]
>    SFNode [in,out] textureTransform   NULL [X3DTextureTransformNode]

Seems logical and straightforward.  Indeed it might even be easier for some implementers since they likely have a close relationship between texture and textureTransform.

We will wait to hear feedback from implementers, but absent objections this seems likely to be added.  (I will test it in forthcoming build to ensure there are no hidden difficulties).

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