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I'm trying to apply boolean cut to a plane which turned into a cylinder with simple deform modifier and than turn that cylinder into a plane again (something like this which i saw in a Numberphile video). First i create a plane, give it enough loop cuts than add simple deform, add rotated cube for boolean operation but when i apply boolean modifier, mesh looks like this.I don't want to apply simple deform modifier because i'll animate cylinder to plane transition. What i am doing wrong? Why does applying boolean modifier messes up geometry?

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    $\begingroup$ Hello and welcome. While files, images, and external videos or links may be helpful additions they should not be the only way to obtain information about your issue. Don't make understanding your question rely on downloading a file, watching a video or visiting an external site. Use the builtin tools to upload images or gifs, along with thoroughly explaining the problem in written form so it can be indexed and searched for thus helping future visitors with similar issues. $\endgroup$ Nov 18 '21 at 10:21
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    $\begingroup$ There must be an smart way to do it but if you begin with a plane (object A), give it a Boolean modifier then a Surface Deform modifier with a second plane (object B) as Object, bind. Give object B a Simple Deform/Bend and bend 360° on Z. Here is what it gives when you unbend: zupimages.net/up/21/46/1q9y.gif $\endgroup$
    – moonboots
    Nov 18 '21 at 11:02
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Dynamic Paint

Once you set up your plane with a modifier, and add a cube, go to physics tab and dynamic paint for both:

  • the cube - brush, paint color black
  • the plane - canvas, Image Sequence format, increase resolution (it's just one frame so I increased it to 2048), frame end the same as frame start (again, just one frame), initial color white, set output to a place where you can easily navigate later and bake.

Now select the plane, in Material Properties > Settings change Blend Mode to Alpha Hashed or Alpha Clip. Modify the nodes of the material by adding an Image Texture node and loading the baked canvas. Connect its Color output to the Principled BSDF's Alpha input.

Now animate the modifier:

You can use a single object, by animating the alpha in the material.

As for your question:

Why does applying boolean modifier messes up geometry?

Because you apply it before the Simple Deform modifier, so you apply it on the flat plane.

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..Late to this, but an option would be to create a plane, with a sinusoidal top edge:

  • Enable the shipped Add-On: 'Add Mesh: Extra Objects', if it isn't enabled already
  • Create a Z math-function surface, sin(pi * (x - 0.5)) as shown..

enter image description here

  • Nick the middle edge from it, and extrude down in Z..
  • Scale the bottom edge to 0 in Z

enter image description here

Now you can give it the Simple Deform > Bend as before.

enter image description here

You can scale the curve in Z, or the whole plane in either direction in Edit Mode, while looking at the deformed result. Its top edge will still be a sine wave..

enter image description here

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    $\begingroup$ love your solutions!!! +1 $\endgroup$
    – Chris
    Nov 19 '21 at 7:27
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    $\begingroup$ I was thinking about this - since the animation represents a mathematical relation, you can just use mathematics to compute the end result. :) $\endgroup$ Nov 19 '21 at 8:20
  • $\begingroup$ @MarkusvonBroady I like the ingenuity of your solution, though :) It's almost certainly just me.. but I always find Dynamic Paint a bit painful? I've gotten slightly phobic. $\endgroup$ Nov 19 '21 at 8:37
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    $\begingroup$ I didn't use dynamic paint much, so this was an excuse and went surprisingly smooth. :) $\endgroup$ Nov 19 '21 at 8:51

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