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I'm having trouble making a plane using the screw modifier transparent, because "the plane" is shining through?

In this video, using an old version of Blender (2.78), it looks as easy as enabling transparency, and adjusting the alpha https://youtu.be/owid9yrq97s?t=2494

However in the "new" version of blender (2.92.0), it seems they've quite reworked the way materials work. I've created a material that uses an Emission and Transparent BDSF shader, through a mix-shader, so I can adjust the transparency, and while it's working great for "solid?" objects, it doesn't work for the object using a screw modifier:

I've tried to create a minimal example below:

Fac ("alpha") 1 is great. There is no transparency.

enter image description here

But when I adjust it down.. I get two different colors.

enter image description here

I'm using the screw modifier for the object, so I imagine that it's being drawn over itself? And that I'm seeing the object over itself. Because if I delete one of the vertices, like in the gif below, suddenly I get the color that I want? But then I don't get the shape that I want anymore.

enter image description here

Furthermore I would really like to keep using the screw modifier, so I can lock different angles to keyframes and do the "radial animation"-thing.

I've tried enabling Backface Culling, it has the same result as deleting the vertice: (I reckon it's probably not "the same," but it looks identical.)

enter image description here

Disabling "Show Backface" and "Backface Culling" gives this really weird color, that I believe is due to some clipping:

enter image description here

It feels like I'm missing something super simple, but I was at it for 4 hours the other day, and since I very recently picked up Blender, I'm simply not aware of what tools I have at my disposal.

I've tried searching online, but I'm just not sure what I should be searching for, "transparent plane screw modifier" isn't giving me anything other than tutorials on the "screw modifier" or "transparent planes."

Thank you.

PS: I am using the Eevee render engine. I don't know if this bears significance.

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  • $\begingroup$ You're using a completely opaque shader on the uppermost rendering, then you use a mix factor. If you used exactly 50% mix the all places of your mesh where the rays go through it twice will actually have full opacity, (0.5 first bounce, 0.5 2. bounce) it's behaving as expected in my eyes. I'm guessing you want something like start and end caps? Try beveling a curve along a bezier circle. $\endgroup$
    – Frederik Steinmetz
    Commented Mar 14, 2021 at 21:05

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Alright, so I'm not entirely happy with this solution, but maybe I should be?

I've managed to work around it by.. enabling Backface Culling on the material:

enter image description here

I've been here before, but I also noticed that you can "flip normals" under the Screw Modifier:

enter image description here

Now I can duplicate the shape and remove the Screw Modifier:

enter image description here

.. and finally set the "plane with the screw modifier" as a parent object:

enter image description here

Setting it as parent isn't strictly necessary for the color part, but it makes it quite nice to scale and manipulate otherwise...

If anyone has a good solution that just uses the single object with the screw modifier, I would like to see that!

This feels quite hacky, but "if it's stupid and it works, it's not stupid" 🙃 😄

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