I have a moving solid mask composition, which forms a white line that moves vertically from the middle to the left and back.

I now want to create a copy of that composition, mirror it and link the position. So that the mirrored comp will move from middle to right and back.

How could I achieve this? Setting the width = -100% did not work.


2 Answers 2


Pre comp your layer, then apply the Mirror effect to the comp. If your comps are 1920x1080, set the mirror centre to 960x540, and the reflection angle to 0.enter image description here

I think your scaling to -100% didn't work because it's a masked layer. You might have more luck using a shape layer to create your line, then you should be able to scale it as you suggested.

  • Masks transform with their layers, so that's not the reason it didn't work.
    – stib
    Jan 3, 2015 at 1:21
  • See my comment above on your answer - the mirror is needed to maintain mirrored movement - I should have made it clearer in my answer
    – tomh
    Jan 3, 2015 at 9:19
  • This did not mirror the movement. Dec 6, 2018 at 22:09

Did you unlink the scale x and y before you set it? if you don't the y will be set to -100 too. It's the little chain link next to the value.

linked and unlinked scale

What you described should work, masks are transformed with their layers. mirrored layer

There's a more convenient way of flipping a layer - by going to the Layer menu and choosing Layer>Transform>Flip Horizontal

  • 1
    This doesn't solve the problem of the movement - the original question says the line moves up and to the left, so the mirrored object should move up and right. If you mirror using horizontal scale of -100%, any movement keyframes will still move up and left. Same if you used Transform -> Flip Horizontal. The quickest/simplest way to get mirrored movement was by pre-comping and using a Mirror effect.
    – tomh
    Jan 3, 2015 at 9:18
  • I was assuming that the OP had already precomped - since he said: "I now want to create a copy of that composition".
    – stib
    Jan 3, 2015 at 11:43

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