ease() vs eased keyframes

Report · Aug 18, 2015

Trying to figure out the difference in values between the standard ease() and eased keyframes with default values of 33% influence. They're very close to being exactly similar, but aren't!

ease(time, 0, 4, 0, 1000) -- this seems to be a perfect cubic bezier curve, with handles of (0.33, 0, 0.66, 1) as defined by cubic-bezier.com‌. Have adapted existing cubic bezier functions to work as expressions, and the match is perfect. However, two keyframes, bezier interpolation, 33% influence out & in (on first and second, respectively) doesn't match above.

Exaggerating & displaying the difference between the values gives this:

However! I have no idea what to do with this information. As you can see, the difference is miniscule, but it's certainly present. Can any light be shed on this?

Report · Aug 21, 2015

A maximum difference of 1e-6 for a value in the range [0-1000] is really nothing, and i think you can concude that the two methods do give the same result.

One possible reason for a non zero difference is that the ease expression uses an exact influence of 1/3 while the keyframe one uses 33.333333% (this is at least what one gets by querying the influence by script).

If that's the case, you cant expect absolute match. (I did some tests, it does create a difference of similar magnitude, very small, but it does not explain the nice nearly sinusoidal shape of the difference though).

Xavier.