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Phantom key frames.


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Sometimes I run into an issue of things moving in a direction that they should not be. For example; a leg that is not connected to anything nor hip movement that could also cause the leg to move is in place in the first frame and the next  key frame has the leg moving upward. When I press play, instead of the leg going straight up, it dips down, as if there is an invisible key frame there, before going up. What is causing this to happen? I did some animation in flash years ago and never ran into this issue so my only assumption that there is a key frame later in the timeline that is somehow manipulating movement earlier in the timeline somehow.

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Basically the loop is not closed and that's why it does this. It's not really phantom, it's a leftover from some other line.


In most cases, it means, your beginning and your end of the loop are different, you need to copy & paste the entire beginning frame to close the loop, do this for all the loops in case you're using an interactive pose, for an animation pose you only got 1 loop. The beginning frame and ending frame of each loop need to be the same. There's some exceptions to this, but it's way safer to always have the exact same frame at the beginning and ending. 


There's other phantom frames depending on what type of interpolation & tangent (smooth/linear/flat) you use.

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@Drahzar is right, it depends on whether you're using smooth/linear/flat interpolation between keys.  There aren't really any "phantom" keys, just the game engine's interpretation of the movement between keys based on the interpolation you're using.  Your leg moving down first before moving up is a result of using the "smooth" (wavy line) interpolation for that key, it creates some momentum movement prior to moving in the right direction, and it'll do the same when the leg reaches its destination key there will be momentum after.  The amount of momentum depends on how much the limb is asked to move between keys and how little time.  The more movement and less time usually means more pronounced momentum.

Using the "less-wavy" interpolation for that key will reduce or eliminate this in likely both start and end keys.  Using the "jagged-line" interpolation usually produces very linear results making for very jagged movement like stop-frame animation as the limb moves very robotically from one key position to another.  But this jagged interpolation is also useful to try and control a limb in mid-flight and some of its destination movement by putting another key in between, such as a hand moving across a bed and trying to land neatly on a boob.  You might need 1 or 2 keys in between start and destination in the right frame (earlier/later) with different interpolations to arrive at something that looks right.  It takes a bit of practice to figure out what you need gives you what you want to make the movement look natural.

For the above boob example, I would guess it takes about a whole second (24 frames) to naturally complete that move in the real world, so most of my poses rely on 1-second intervals between things happening, and control keys in between if necesssary.  For a body rolling over or standing up, maybe 2 seconds etc.


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What you're experiencing is simply the effect of a bad choice of tangents. Try linear instead of smooth, especially for fast movements/transitions.


Another possible culprit is the "Lock" feature, which I never fully explored.

When you lock a key, new keys are generated automatically on subsequent frames (works similarly to linking, but it's a different thing). When the lock is removed (manually, or by saving/reloading the pose) these generated keys remain in place, as constraints for the animation.


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I'll add my tuppence here: the default interpolation method is 'smooth', which is intended to reduce robotic movements.

However, I think a better term would be 'circular' as movements orbit around points A and B rather than moving directly from one to the other.

So using the smooth method on a limb will mean it will circle around point A, move to point B, then circle that before settling exactly where intended, hence your 'phantom' movements. The effect is greater, I find, the harsher the transition.

The other methods will give you straighter movements ('linear' is point A-B on a straight line - so will look robotic, 'flat' is a hybrid of smooth and linear and probably the best of both worlds).

You can change the methods by clicking on the icons seen below, the first is smooth, the second linear, the third flat.


And this explains the mechanic a little more:  https://sites.google.com/view/tk17documentation/home/pose-edit?authuser=0#h.p_gzBQ_U3eoh7d

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