Final Cut Pro bezier interpolation and acceleration scaling
Final Cut Pro bezier interpolation and acceleration scaling
- Subject: Final Cut Pro bezier interpolation and acceleration scaling
- From: Richard <email@hidden>
- Date: Sun, 05 Feb 2012 16:46:07 +1100
Hello,
I'm very confused by the description of bezier interpolation and
acceleration scaling for the 2D case, as mentioned in:
https://developer.apple.com/library/mac/#documentation/appleapplications/Reference/FinalCutPro_XML/Interpolation/Interpolation.html
I've generated the scaling values as per the code listing C-4, and
attempted to apply them as mentioned in the second last paragraph:
"Now that Final Cut Pro has all the information needed about the
Cartesian position of the current line segment along the actual
curve, it can update the Bezier structure representing the curve
with this data. This process involves recording the start and end
position of the segment and calculating the line connecting these
points, while scaling the line segment by the calculated
acceleration factor. Looping around from point to point, the
application calculates the position of all 40 points of the curve."
... but I don't get the curve I'm expecting to get. Surely all points
should lie on the original curve, ie. just their parametric values
are augmented? Modifying actual piecewise linear segment endpoints
doesn't feel like the right thing to do, especially when they're
being scaled by the quite large and small values that listing C-4
produces.
In any case, can someone with an understanding of this algorithm
please describe it in more detail? (pseudocode or code snippet would
be great if possible)
Many thanks,
Richard.
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