[x3d-public] Negative scale and ccw

Andreas Plesch andreasplesch at gmail.com
Tue Mar 7 04:29:17 PST 2017


On Mar 6, 2017 8:13 PM, "Don Brutzman" <brutzman at nps.edu> wrote:

...
I think it best not to mention negative scale as part of ccw field per se,
or any geometry/normal definitions, because the negative scaling value is
not defined there.  Rather we can define how a Transform negative scale
affects already-defined geometry coordinates and normals.  Spec sayeth:

        10.4.4 Transform
        http://www.web3d.org/documents/specifications/19775-1/V3.3/
Part01/components/group.html#Transform

which says

        "The scale field specifies a non-uniform scale of the coordinate
system. Scale values may have any value: positive, negative (indicating a
reflection), or zero. A value of zero indicates that any child geometry
shall not be displayed."

So perhaps this question reduces to whether a Transform reflection is
sufficiently well defined?


Yes, I think this a good way to pose the question.

I think the problem in the stack overflow question and perhaps in three is
that normals may be generated after the reflection of vertices ?

I would not have anticipated that this could be considered in an
implementation but if this is really the issue then it is probably worth to
tighten the definition of reflection in the spec.

I may ask this question in the three.js issue.

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
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