RE: Cubic interpolation in XSI

["Salam Bahnassi" <sinshey_kodou(at)hotmail.com>]

Thanks a lot Andrew.
Only one more question, I've been searching for a period now on how to apply 
the values I have from XSI into this formula...

Now we have the start point A (at t=0), and end point D (at t=1). B and C 
are the control points for the curve (these can be set at any time [0,1]).
So my question is, how do I get all this info into the formula?
What do I pass for A,B,C, and D?

Super thanks!

> -----Original Message-----
> From: Andrew Skowronski [mailto:askowron(at)Softimage.COM]
> Sent: Monday, August 22, 2005 11:03 PM
> To: 3DGames(at)Softimage.COM
> Subject: RE: Cubic interpolation in XSI
>
> In the scripting reference for the FCurve Object it has this comment,
> which I hope answers your question:
>
>
>
> Note: Interpolation (how the value is evaluated between FCurveKeys) can be
> constant, linear, or cubic. 'Cubic' means that a Bezier curve is
> calculated as the interpolation between the keys. XSI uses cubic Bezier
> curves defined as follows:
>
> "Four points A, B, C and D in the plane or in three-dimensional space
> define a cubic Bezier curve. The curve starts at A going toward B and
> arrives at D coming from the direction of C. In general, it will not pass
> through B or C; these points are only there to provide directional
> information. The distance between A and B determines "how long" the curve
> moves into direction B before turning towards D." (from de Casteljau's
> algorithm)
>
> The parametric form of the curve is:
>
> B(t) = A(1-t)^3 + 3Bt(1-t)^2 + 3Ct^2(1-t) + Dt^3
>
> -----Original Message-----
> From: owner-3dgames(at)Softimage.COM [mailto:owner-3dgames(at)Softimage.COM]On
> Behalf Of Salam Bahnassi
> Sent: Monday, August 22, 2005 4:00 PM
> To: 3dgames(at)Softimage.COM
> Subject: Cubic interpolation in XSI
>
>
> Hi people,
>
> This is quite a quiet list I suppose, but I hope I get the answer...
> Because
> I'm really desperate for it...
> Through my adventure to open dotXSI files, I faced the cubic fcurve
> interpolation.. So far, I've managed to get all other types working
> (constant, linear, and hermite), but for this one I can't really find the
> math for doing the interpolation.
>
> I searched for cubic interpolation, but all the forms I found deal with
> the
> curves in a different manner than specifying the tangents through LeftXY
> and
> RightXY...
>
> Would someone (perhaps from softimage) be kind and provide me with the
> math
> or code for dealing with XSI's cubic fcurves?
>
> Thanks a ton!

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