Re: LANG: VRML Transforms (fwd)

Patrick Sweeney (pjs@clark.net)
Thu, 5 Oct 1995 21:59:25 -0400 (EDT)


On Thu, 5 Oct 1995, Stephen Chenney wrote:

> > Since I just joined this list I am not sure if this is the best place to
> > post a question, but here goes. I am currently writing a VRML viewer and
> > have run into a problem. What is the order of transformations? I am
> > trying to view office.wrl which places a table (Obj_4) using code
> > such as:
> > TransformSeparator {
> > Translation { translation -0.437 0 -1.7 }
> > Rotation { rotation 0 1 0 1.5708 }
> > USE Obj_4
> > }
> > My viewer moves the object and then rotates it about the Y axis. VRweb
> > apparently rotates the object and then translates it. I hope this is clear.
>
> The transformations are placed on a stack, and then applied from the top
> down. So the most recent transform is applied first.
Well that fixed it. One bug down, infinity minus one to go :-) Thanks.

>
> This highlights something I've meant to gripe about for some time.
>
> The VRML spec as presented assumes knowledge about Inventor. The
> transform example is one case. Another is how the camera is aligned.
> It seems unacceptable for me to expect people to know about Inventor
> in order to use VRML. It is counterproductive to the aim of establishing
> VRML as the standard for web 3D.
I agree. The VRML spec can be interpreted in too many different ways.
Today I got to the point where I went to Border's Bookstore in search of
Open Inventor books to clarify things (end up getting Graphics Gems V
instsad ;-)
>
> Still on the camera example, even now I can't figure out how the f#$% it
> works. I've wasted so many hours on it that I've been forced to give up.
> That results in a modeller that produces strangly behaved scenes, but I
> cannot offer more.
>
> To make matters worse, the open spec means that every browser (and I
> literally mean every) does something differently. We had Guy Steele
> here last week talking about Java, and the current process of tightening
> the Java specs before release. He emphasised that everything must be bolted
> down firmly, because any possibility for variation will lsad to
> incompatability among browsers, and that is enough to kill a standard.
>
> I think that's a vote for a library of test scenes, which is finally coming
> into fruition. It is also a vote for a tight standard. Before the flame wars
> begin, I do realise that one of the aims of VRML is to put it out there
> and see how it evolves. My point is that with insufficient agreement it
> cannot evolve.
>
> Steve.
>
Thanks again for the help.
- pat


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