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Unexpected behavior: Sin(time) seems to be "invisibly" remapped

Hi, there! This is a quick, and maybe pedantic question about the Sin and Time nodes in Unreal, but I'm experiencing some odd behavior that I'd like to better understand.

In this screen recording, I have a simple material set up with sin(time) going into the opacity channel (after being remapped from -1,1 to 0,1) -- and the odd thing is, that produces an oscillation with a period of one second.

In my mind, the expected behavior would be a period of 2π, or 6.28 seconds, because the sin node receives an input in radians and the default period of a sin operation is 2π. Meanwhile, when I try to multiply the Time node output by 2π / PERIOD PARAMETER in the video (which is what I would think to do in order to create a cleanly parameterizable period), I get an oscillation with 2π oscillations per minute.

So, what's going on here? Does the sin node somehow "know" that it's receiving a time input and trigger some special remapping behavior? Is my time input just operating on a 2π-multiplied scale? This isn't necessarily a blocker, but if there's some predetermined behavior I'd like to know how it works and be able to work around it

Much thanks! Brendan

Product Version: UE 4.17
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asked Sep 11 '17 at 10:40 PM in Rendering

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This is definitely an intended behavior.

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answered Sep 11 '17 at 10:59 PM

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avatar image BrendanLoBuglio Sep 15 '17 at 10:58 PM

Hi, Deathrey! I agree that it totally seems intended, but my question is more with regard to the way that this is implemented -- whether this happens only if the Time is directly hooked up to a Sin node or if Time -> arbitrary node -> Sin also works, whether there are other nodes that have custom behavior with Time input or sin output, and other things of that nature.

It's obviously a nice convenience, but invisible behaviors like these can be dangerous if you don't 100% understand them. Ultimately, I wish there was some documentation!

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