[x3d-public] Proposal: new field "factor" in Transform node

[Michalis Kamburelis]

On kwi 21 2016, at 1:20 am, Yves Piguet <yves.piguet at gmail.com> wrote:  

> On 21 avr. 2016, at 00:26, Michalis Kamburelis wrote:

>

> > 1\. IMHO, it would be more consistent to specify scale treatment such  
> that factor=0 means identity and factor=1 means "use the original  
> Transform".

>

> It's actually the case.

  

You're absolutely right. Sorry, I didn't look closely enough at your equation.
Looking closer, indeed

  

\- factor=0 means you get sign(s) * exp(0) which is 1 or -1, depending on
original scale sign.

\- factor=1 means you get back the original value.

  

This is cool. Still "factor=0" does not make "identity" in case of negative
original scale (it makes -1). But this seems OK, even an advantage
(interpolating between negative scale and identity seems not much useful,
better to reach -1 in case of a negative scale).

  

> > E.g. set "scale = lerp(factor, 1, scale)". This makes  
> "scale" interaction with "factor" similar to how "factor" affects  
> "translation" and "rotation" in your proposal.

>

> But then, extrapolating is less practical: you get a degenerated zero scale
when factor is -1, and e.g. 2s-1 when factor is 2, which isn't very useful.

>

> I've written the handling of scale as a special case, but actually plain
multiplication of the translation and the rotation can also be seen as a kind
of logarithmic modulation of the transform. In all cases, if factor is 2, it
has the same effect as applying the transform twice; if factor is 0.5,
applying it twice has the same effect as the original transform.  

  

Good point, and it makes me agree with your equations 100%:) I see that the
treatment of translation/rotation/scale is actually consistent. Great!

  

Best regards,

Michalis

  

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