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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