Tangents on curves

[alaRHYJ8]

If you have something animated from point A to point B and want to add a key between them, there is a good change this happens. I've seen a demo of maya where it looks like it didn't do that. Can that migrate to max?

In case the picture doesn't make sense, the tangents on the middle key does not follow the line, which it really should.

 

[Casey_H_]

What happens if you set the middle point to linear, then set it back to bezier?

[lauri_barnhart]

Hi @alaRHYJ8,

I wanted to check in and see if you saw @Casey_H_'s ollow up question and if assistance is still needed or if you found a solution to your question already? Please share any available information so the community can assist you further.

All the best,

Lauri | Community Manager

[alaRHYJ8]

Same thing

[alaRHYJ8]

I have attached how I "make" the curve or mistake.

[Casey_H_]

Isn't the red curve X? But you already have the full X movement keyed, so all you need is a key on Z. I believe the Auto-Key is placing an unnecessary key on X, at the mid-point, instead of only a key on the Z curve. When the box moves in both +Z and +X at the same time, the X curve needs to stay smooth, but the extra key is basically telling the box to ease into the middle position, then ease out of it. The X movement doesn't need that key!

[MartinBeh]

The video is very useful, thanks! With that I can reproduce the issue: when you create a new Position keyframe for the Z axis, the X and Y axis also get keys at that frame, but their new tangents are set such that the curve for X and Y does change a little bit around that keyframe, even though the X/Y values at the specific frame have not changed.

To me this feels like a bug in how the new tangents are calculated. Maybe, maybe, it is a limitation in how a Bezier controller with "Auto" tangents works, but the issue also happens if you set the first and last keyframe tangents to "Spline" before inserting a key in between.

In fact you can see the same issue if all you do is to move the timeslider between the first and last keyframe and rt-click the timeslider to create a new key (i.e. without moving the object). Even with that the curves between the first key and this new one do change a bit. Same for the curve between this new key and the last key.

The best suggestion I have is to afterwards delete the new X and Y keyframe and only keep the new Z keyframe. That will restore the original curve for X and Y.

[alaRHYJ8]

I know and assume this is a bug, or at least it feels like something is off. I remember seening a demo a while ago from Maya where this wasn't a problem (or a button fixed it), where i definitely felt jealous...
I have also tested it in Houdini and blender and they don't have the same issue.

[MartinBeh]

@alaRHYJ8 - I just sent you a DM with a link to a script you can try. Maybe that helps?

[alaRHYJ8]

It does create a tangent the way it "should" but workflow wise, it is an extra step and to boil it down it feels like max is doing it wrong. Ideally it should make a tangent like than, just by using the auto key.

[AndyVanDalsem]

This has always bothered me about Max's animation curves. It seemed to me that it's because the tangent is simply "pointing at" the closest key, not taking in to account the curve's actual slope. 
@MartinBeh Any chance you could share your script? I've always wondered what math would need to happen to get the tangents to follow the curve's slope and not just "aim" at the adjacent key. 

[MartinBeh]

@AndyVanDalsem - I just sent you a PM with a download link for a (largely untested) script.

Not sure it will always produce the desired tangents, but it worked for me in a few test cases.