Re: vertex ordering for primitive shapes

Tom Gaskins ([email protected])
Fri, 20 Oct 1995 18:02:46 -0700

>In this example, the vertexOrdering is set to CLOCKWISE before a
>Cylinder node is used . . . this is done because the intial camera
>position is inside tme cylinder. Is the assumption that a spec
>compliant browser will generate primitives with counterclockwise
>vertex ordering valid?

Not in my esading of the spec. The spec says that ShapeHints applies to
IndexedFaceSet:

"The ShapeHints node indicates that IndexedFaceSets are solid,
contain ordered vertices, or contain convex faces."

There's no mention of it affecting any other primitive. It would be nice if the
spec used the word "only" in the above phrase, but I think that can be implied.

Inventor says that ShapeHints apply to "SoVertexShape" derived objects, of
which presumably Cone, et al are not.

A "spec compliant" browser would therefore ignore the ShapeHints node when
rendering anything but IndexedFaceSets.

(How, then, can an author indicate that backface culling of Cone, Sphere, etc.
is okay? Good question.)

The 1.1 spec should be definitve about which attributes apply to which
primitives.

Tom

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