[Expression Problem] LoopOut not working for one shape layer, behaving like LoopIn

[YuanJAhn]

I was following along a tutorial and this drove me insane. I added an expression to the rotation of the left wing of the bird.

loopOut("pingpong");

 This worked perfectly. Then, following the tutorial, i pasted the expression to the other wing, but it didn't work. After much trouble I found the "Show Post-Expression Graph" and saw that the expression was actually working - just in the opposite direction, as you can see in the screenshot. Changing the expression to

loopIn("pingpong");

solved my problem, the loop was finally happening for the other wing as well. But I need to know why, why is the expression not working like in the tutorial, why can't I just use the same loop expression for both wings? Is something about the shape layer reversed, inverted, buggy? Please help me understand why this is happening, thank you.

[Meng Zhiqun]

H YuanjAhn,

By any chance either of the wings are a duplicate and scaled with a -100 in either axis of the other?

[YuanJAhn]

Hi, thanks for the reply. The layers were probably duplicated in Illustrator, but in After Effects they're just two seperated layers, both parented to the main bird body, both are at standard 100% scale.

[Mylenium · Accepted solution]

What Meng said. Most likely you scaled the layer negatively or time-reversed it, which of course also turns the expression logic on its head.

Mylenium

[YuanJAhn]

Thank you, yes for whatever reason the time stretch was set to -100! Thanks for saving my sanity, have a wonderful day 😄