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I
IMPNL
Participant
March 23, 2019
Question

Crazy masking problem

  • March 23, 2019
  • 1 reply
  • 1238 views

Hi, I'm pretty new to After Effects and trying to animate an image to make it look like it's burning down. I'm using Saber for this.

I created a transparent solid to put the Saber effect on, drew an 8 point line mask at the top of the image and moved it down every few frames. So far it looks pretty good.

Then I copied the mask onto the image (a pre-comp consisting of 2 images) and added a few extra points to close the loop around the image and have the "burned" part disappear.

Now when I play the animation the mask immediately starts to move around on its own and 'reverse' the mask points (last point moves to the first position and vice versa) until it's completely turned around, after which it plays along just fine.

I tried drawing the mask the other way around (closing the loop at the top and inversing it) and also tried manually readjusting the mask points every frame, which both didn't work.

I'm now trying to draw a new mask and get as close to the original mask points as possible, which is quite a chore with how AE works. There should be an easier way to do this I reckon.

I'm using AE CC 2019.

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    1 reply

    Mylenium
    Mylenium
    Legend
    March 23, 2019

    The flaw is here:

    added a few extra points

    You mustn't do that. It messes up the internal point order. The proper way to proceed would be to draw the mask from the start with as many points as needed and use it on both layers, regardless of whether you may actually need the extra points on your glow layer.

    Mylenium

    I
    IMPNLAuthor
    Participant
    March 23, 2019

    If I added those extra points to close the loop on the top layer, wouldn't I have this whole extra part of glow (or fire in this case) just floating around in the air?

    Would deleting those point give me the same problem, or is this specific to adding mask points?

    R
    Community Expert
    Rick GerardCommunity Expert
    Community Expert
    March 23, 2019

    Set the first vertex using the Layer>Mask and Path>Set first vertex menu

    If you have the pen tool selected (g) and you hold down the Ctrl/Cmnd key you get a white selection arrow. You can drag a selection around the vertex you want to be the first vertex.

    When you animate a mask the vertices always move in a straight line. There is a Mask Interpolation tool that will help you fix some problems but when you closed your mask and added more animation the first vertex probably got changed and the flipping behavior you are experiencing is caused by the change in vertex order. As Mylenium said, don't add extra points, it just causes problems.

    Unfortunately, if setting the first vertex for your mask path to where you originally started drawing the mask does not fix the problem you will have to redo the entire path animation. I would go to the last part of the animation where the path seems to be behaving itself and then delete all previous keyframes and work backward. That might save you some time.

    A screenshot of your comp with the modified properties of the layer giving you problems revealed (select the layer and press uu) will give us a much better idea of exactly what you are dealing with.

    I strongly suggest that you type 'animating paths' or 'animating masks' in the Search Help field in the top right corner of AE and spend some time with the user guide.

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