[gst-devel] GstController interpolation modes

Sebastian Dröge slomo at circular-chaos.org
Tue May 15 16:33:20 CEST 2007

On Mo, 2007-05-14 at 13:17 -0700, David Schleef wrote:
> On Mon, May 14, 2007 at 09:28:32PM +0200, Sebastian Dröge wrote:
> > For the cubic interpolation there exist many good possibilities to
> > provide good and smooth-looking interpolation.
> > First of all we want all data points to be hit and then the combined
> > spline graph to be twice differentiable everywhere. Additionally we need
> > two other conditions and this could either be a slope of zero at the
> > first and last data point or the second derivate being zero there.
> > Would anybody want something different for this?
> This makes sense.  If someone wants additional splines, they can add
> support for it. :)
> I believe the natural choice is second derivative being zero at the
> endpoints.  In any case, there's going to be someone that disagrees
> with your choice no matter what you choose, so just add whatever you
> want, and tell people to extend it.

The only problem I see with the second derivative being zero at the
endpoints is that we also have to handle values outside of the
endpoints. With the slope being zero one could just continue with the
value at the endpoints, with the second derivative being zero one could
only continue with the same slope...

The linear interpolation currently uses the value at the endpoint for
the values outside of them. Doing this for the cubic interpolation would
yield to a non-continous curve at the endpoints unfortunately.

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