Sine node in material editor gives unexpected results

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I’m trying to input degree angles in function.
I convert the value to radians ( rad= deg/180 *pi).
It seems to work correctly when the result is used as input for a cosine node, but not for a sine.
As shown in the picture, cosine gives me “expected results” when passing from 0° to 180° ( white, grey, black, well… at 180° I’m expecting -1 as result, so a black color will be right… but I have white) but I can’t say the same things for the sine node…

12517-sine_cosine_problem.jpg
12517-sine_cosine_problem.jpg2000×943 356 KB

In fact, trying to obtain x,y coordinates of a versor I have a wrong vector.
Am I missing something or there is a strange bug in the sine node?

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Ok… I’ve found the answer by myself… :slight_smile:
The sine and cosine nodes have a default period = 1.
To obtain usual “geometric” values it needs to be changed to 2pi…
With this adjustment all the values are correct.
Ah, trigonometry… old friend :slight_smile:

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I just stumbled over this as well.

Wondering what the reason is behind these Sin/Cos Nodes having a different period than the Sin/Cos Functions elsewhere.

Or is this the case in general for the sin/cos functions in HLSL/GLSL etc ?

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The doc says the input is in radians, it is not true.

Imagine if you want a friendly 30 or 45 degrees.

If the input is in radians, the input should be: Pi x 30/180 = Pi / 6 = 0.524 radian.
For 45 degress: Pi x 45/180 = Pi / 4 = 0.785 radian.

But actually you need to input: 30 / 360 = 1 / 12 circle.
For 45 degress: 45 / 360 = 1 / 8 circle.

Conclusion: The input is in a fraction of a circle.

The legacy Rotator is in range: 0 ~ 65535, converting to 0 ~ 1 is easy so the input of sine is 0 ~ 1?

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The documentation is wrong on this (Math Material Expressions in Unreal Engine | Unreal Engine 5.2 Documentation)

It said the input is in radians (as you would expect), but as other have stated before, it seems to be in radians/PI. Meaning an input of 1 is actually an input of PI radians…

Fix documentation, or fix the input type of the sine node please,

Thanks!

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Bump!! How can Epic not have corrected this yet?!

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The issue is that he sin and cosign where not designed as the normal maths functions but rather as outputs to generate waveforms. Hence they go 0-1 to -1 to +1

So you have to map 0-360 => 0-1 so simply divide by 360.
However as the input is -180 to 180 you have to adjust for that first (if -ve add 360)

If dealing in radians one circle = 2pi radians so you have to divide by 2pi

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