[Xinlai Ni]

sorry, my original expression doesn’t really work, it needs dim-2 array, but you get the idea.
I hope you mean [x,y] at the end, and use scale[1] in both places in the y expression,

Xinlai Ni

[Xinlai Ni]

If I understood you correctly, you need the scale at the inPoint to be 90 and after a while, it’s 100?

startScale = 90;
endScale = 100;
stretchDuration = 5;
linear(time, inPoint, inPoint + stretchDuration, startScale, endScale)

[Xinlai Ni]

I think you can only pickwhipping maskPath property to the same type, not a position type which is a vector of dim 2 or 3.
And by my understanding of AE’s manual, you can’t access any internal properties of maskPath numerically but you can
– pickwhipping to other maskPath, or
– copy your maskPath to a some position property to create a motion path