[x3d-public] convex field only a hint ?

Andreas Plesch andreasplesch at gmail.com
Mon Nov 23 08:34:20 PST 2015


This is a request for clarification of the purpose of the convex field. The
standard says that it is an indicator. It looks like the intention is to
aid renderers by not requiring them to figure out if a polygon is convex.
The original motivation for such a field may be that it is trivial to
triangulate a convex polygon but relatively expensive to triangulate a
concave polygon.

Does this mean that the value of convex field is irrelevant for how a
polygon is rendered from the standard's perspective ?
Is it up to the x3d browser to decide what is rendered if there is mismatch
between actual and indicated "convexity" ?
Probably, the expectation is that the rendering of a concave polygon in the
convex="true" case is undefined by the standard. Similarly, the rendering
of a convex polygon with convex="false" may also be undefined. If this is
the intention, should such language be added to the standard ?

Given technological advances, it may be possible to deprecate the convex
field altogether, and forfeit potential performance gains.

Here is the current wording at

http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components/rendering.html#CommonGeometryFields
:

The *convex* field indicates whether all polygons in the shape are convex (
TRUE). A polygon is convex if it is planar, does not intersect itself, and
all of the interior angles at its vertices are less than 180 degrees. Non
planar and self intersecting polygons may produce undefined results even if
the *convex* field is FALSE.

-Andreas

-- 
Andreas Plesch
39 Barbara Rd.
Waltham, MA 02453
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://web3d.org/pipermail/x3d-public_web3d.org/attachments/20151123/e92a43f3/attachment.html>


More information about the x3d-public mailing list