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to really understand why set matte works or does not - you need to understand Ae's Render Order.
Set Matte is an effect, and is applied to a layer BEFORE transformations. This means that as long as you toggle off the stretch matte to fit (which is on by default) and don't change any transform property of the layer or matte, including animation of course, or add any masks or effects To the matte - set matte works fine for any layer or matte. For other cases - keep reading.
now, this will solve some of the cases but not most. the issue comes from the fact that we usually need a matte for animation purposes - aka travelling matte i.e you are moving the layer or matte to make it hide or show and not just using a still layer and still matte... so we usually need the option to change/animate transform properties for the matte or layer. if you do change any of the transform properties of the matte or the layer - you need to take into consideration the render order. if you add masks/effects to the matte - you need to set the option in the effect to take them into account.
Introducing the Collapse / Sunburst / Continuously Resterize Switch - a way to reverse the render order.
- Shapes and Text have the collapse switch turned on by default
among other things, it reverses the layer's render order so that the effect is applied AFTER transformations. that's why Set Matte works for shapes and text as is - for layer and matte.
- Solids also have this switch, but it's not turned on by default:
turn it on, and you can use solids same as text and shapes with the Set Matte as is for the layer and the matte.
so, to conclude so far, if you change the transform properties of the matte or layer, the collapse switch on the layer you changed them in needs to be turned on for the Set Matte effect to work properly.
- raster layers or videos don't have an option to toggle this switch on
that's why if you change any of the transform properties for the matte or layer that has not reversed the render order - it won't work. for the matte, it simply won't know you changed anything in the layer (because effects are rendered before transformations - including reference layers), and for the layer you applied it to - the effect will transform with the matte (because effects are rendered before transformations)
the workaround for taking into account transform properties for matte or layer of raster images or video is to precompose the layer (leave all attributes) - now you got the switch, turn it on and everything should work. obviously, you don't have to precomp a layer to which you did not change the transform properties...
as for masks/effects applied to the layer - as of CC2017, all compound effects have the option to take into consideration the masks or masks and effects applied to the reference layer
this saves you the need to precompose if you have a mask or effect on the matte layer and can use it as is. as usual, if you changed any transform properties of matte or layer - turn the collapse switch for them.
- Set Matte works for any layer, as is, as long as you don't change the transform properties or add masks/effects (for layers with no collapse switch, you should toggle off the "stretch matte to fit" in the Set Matte effect)
- if you do change the transform properties, the layer on which you changed the properties needs to be with the collapse switch turned on for the effect to work. this happens in Shape and Text layers by default, on Solids you can set it on or off. on raster layers or video - you will need to precomp.
- if you add masks and effects to the matte layer, you can use the option in the effect to take them into account in the effects settings
Have to agree with Roei. It seems you don't really understand AE's render pipeline to begin with, including seeing things like pre-composing as your enemy, when in fact it is an inevitable and powerful tool to do some things. I'm not debating whether or not some things are clunky to do in AE, but every renderer has his specific order and based thereon requires different procedures. This wouldn't be any different in Nuke, Fusion and what have you. As an effect Set Matte will operate at a different step in the rendering processs and by extension even be affected by seemingly unrelated trivial things like preceding effects modifying the Alpha and sub-pixel calculations affecting congruency of channels, aka causing fringes. There's really nothing wrong here, you just need to "think" yourself into it and work with the program's features, not against them.
These replies are all well and good except that normal track mattes work fine and all users want is to be able to apply a track matte to multiple layers. Set matte is obviously a hack in service of this more fundamental goal. And given how much explanation is required about the render order (even though you guys definitely know your stuff, inside and out), most users will always be confused. It's a sorry state of affairs, given it seems pretty straightforward to add something like a pick-whip to the left of the track matte menu (as per parenting), or even allow an expression to apply a track matte to a layer, or god forbid contemplate adding node-based functionality of some description. But life goes on!
1 person found this helpful
I get what you are saying. the explanation was given for deep understanding of the feature, not for instructions how to use it. you could simply say it in one sentence:
for set matte to work properly, both layers need to be with the collapse switch turned on.
and if you are bold enough, another sentence:
text and shapes do this automatically, other layers will require you to switch collapse on (solids or Ai layers) or precomp (all other)
the set matte effect will save you when you have many layers and you want only one matte. your setup will be much more elegant and easy to change.
it does need some work:
1. there is not stopwatch icon for the matte used so you cant rig it with expressions
2. copy pasting any compound effect (like set matte) will reset the matte used and you would need to pick it again. (workaround: use "Duplicate" instead, but this won't save you when moving between comps)
still very useful. when you have many layers using the same matte you will see why when the change comes, you will be happy you used and understood how this feature works.
if you do have an idea to make it better, ask for it in the wishform page.
Thanks for your response Roei, I do see your point.