I have a Bezier curve with three shape keys as shown above. All three have the same length. The animation with shape key evaluation time from 0 to 20 (with 'Relative' unchecked) is shown below.
As you can see the curve length changes continuously during the animation. I have tried all the shape key interpolation methods (Bspline, Catmull-Rom etc). But none of them keeps the length intact. Is there a way to ensure the curve length is not modified during the interpolation? In general, it would be great if you could suggest some way to influence the behavior of the shape key interpolation.
There is this question, which I thought had the answer. But it's referring to uniform distribution of points along the curve, so it's not related.