Simple animation smoothing algorithm

An easy trick to smooth animation keyframes - 06/2023 - #Jumble

Consider the previous and next keyframe, do a linear interpolation to create an "intermediate" keyframe. Then do a linear interpolation between this newly created keyframe and the existing keyframe in the middle (or replace it altogether) 

t = (pose.secs - prevPose.secs) /
(nextPose.secs - prevPose.secs);

lerpPose = Lerp(prevPose, nextPose, t);
res= Lerp(pose, lerpPose, smoothStrength);

A more detailed version: 



for (int j = 0; j < nb_smoothing_iterarions; ++j)
{

    Animation<SkeletonPose> smoothed = new Animation<SkeletonPose>();
    smoothed.keys.Add(_cooked.keys[0]);
    for (int i = 1; i < _cooked.keys.Count - 1; ++i)
    {
        SkeletonPose previousPose = _cooked.keys[i - 1];
        SkeletonPose current = _cooked.keys[i];
        SkeletonPose nextPose = _cooked.keys[i + 1];
        
        float parameter = (current.seconds - previousPose.seconds) /
                          (nextPose.seconds - previousPose.seconds);

        // Lerp every joint transformations inside the pose 
        // Works best when the skeleton uses quaternions:
        SkeletonPose predictedPose = previousPose.Lerp(nextPose, parameter);
        smoothed.keys.Add(current.Lerp(predictedPose, smoothingAmount));
    }

    smoothed.keys.Add(_cooked.keys[_cooked.keys.Count - 1]);
    _cooked = smoothed;
}

Better smoothing algorithms exists such as Savitsky-Golay filters, however, they are way more involved.

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