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I'm not really doing video production as living, just for fun. So my knowledge is very limited.

In the Trapcode Particular I'm creating a particles with simple 3D emitter:

Particles with source emitter

Now, I only want particles to come from the top of the icon, so what I did is using Linear Wipe to cut off the emitter source to hide those bottom particles:

Particles with the Linear Wipe

Now, my question is does After Effects actually render and process those hidden particles ? Or he is smart enough to know it will never be visible and he skips them ?

Edit: Forgot to mention that the Linear Wipe is actually on the Particles Effect. I also have it on the Emitter source, but for some reason it generates particles ignoring the Linear Wipe on the Emitter Source. (The Linear Wipe of the Emiiter Source is on a pre-composed of the icon)

Edit 2: I actually went inside the Pre-composed emitter source, did a Mask Subtract and the I think that it should of solve my rendering issue ? So, to sum up my questions, does the issue I described actually happens ? and does my solution with the mask solved it ?

enter image description here

enter image description here

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I think you have answered your own question, but let me try to answer it from the perspective of a programmer (not one who wrote After Effects, but one who has written a lot of programs and seen a lot of source code).

After Effects (or any other compositing program) operates on layers. Layers can be combined, masked, or used as inputs to transformations or operations.

The layer that contains your icon doesn't know about any processes or effects that come after it. If you apply a particle emitter to that layer, particles will be emitted regardless of whatever masks come later. Some particles may be masked by later layers/operations, but none of that affects what particles may be emitted due to the shape/color of your icon.

When you compose your icon with a mask, and then apply the emitter to that result, then of course the emitter is starting with the masked pattern.

Which is correct? It depends what you want. If you want to show lots of particles being obscured by a mask, the first is what you want. If you want to show an alternative shape emitting particles, the second is what you want.

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  • I think the options I tried and the solution I came with, it is probably also because I'm coming from a programmer background, like the great answer you gave. I was able to guess what could happen from the AE source code. AE is a complex program, and where it comes to effects. Especially Particular it could be very expensive for the AE to try and calculate on each particle if it as a FOV of rendering, if it not being hidden by a different layer/effects, if it not being hidden by a different composition, it includes checking for the alpha channel for each of them to understand if the part of th
    – Ido
    Feb 14, 2017 at 10:24
  • ... if the part of the layer on-top is actually transparent and the particle can be visible, much more complicated where things are 3D rather than just 2D layers. And much much more, and actually. just rendering the particle could be much more effective. So I came with the 2nd solution because I thought it from the computing process rather than what is looks like. Linear wipe on the particles or emitter is the same for us to see or the final results. but it is really different when it comes to performance.
    – Ido
    Feb 14, 2017 at 10:26

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